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Carlo Rovelli: The Genius Exposing Quantum Gravity
October 15, 2024
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What happens if you fall into a black hole? The results are very interesting. The experimental results is a confirmation of something that the majority of loop quantum gravity community expected on theoretical results. We see the black holes. We see the matter falling in. We see the spiraling
Carlo Rovelli, welcome back. It's been two years and I'm extremely happy to be speaking with you again. Thank you very much, Kurt. It's a great pleasure being here with you again.
So as you know, there are some recent results, I believe from China, that people present as a death blow to loop quantum gravity. What are those results and do you agree with this assessment? The results are very interesting. The experimental results, they have not been presented a death blow to loop quantum gravity by the authors of those results, not at all.
And they're not death brought to loop quantum gravity at all. In fact, the opposite is a confirmation of something that the majority of loop quantum gravity community expected on theoretical reasons, but they do disprove
some suggestions that were done about 15 years ago of something that if happened would have been great, a way to confirm the theory, which unfortunately is not there. Okay, so what is that? So the situation is the following. Some time ago, there was a suggestion by Lee Smolin and some collaborators of him
that perhaps there could be a way of finding a trace of quantum gravity in some signals coming from very far away from the in the universe, some light pulses, some very short pulses of light that we get from from very far away. And the idea was the following was a beautiful idea. In fact, I got very excited when it came out.
The idea is that quantum gravity in general, quantum series of gravity tend to predict that there is a minimal length. There is a structure of space at some length. Now, what's important here is that it's a minimal spatial length and not a minimal space time length or space time volume. Yes, very good. Very good, Kurt. There is a minimal spatial length. So if you measure something,
You can measure a certain length, a shorter length, a shorter length, but there's a minimal one, a minimum non zero one. You can measure zero, of course, but you can measure a minimal non zero one. Now, if you take this naively, you can make a consideration which it's very tempting and the consideration is the following. All right. So this means that space is like a grid with a minimal length.
Now, we know that on grids with a certain spacing, light does not behave like light in vacuum, but behave in a more rich way in the following sense. In vacuum, all the colors of light fly at the same speed, the speed of light. But if there's a grid,
The high-frequency color are sort of slow down. Why? Because they interact with the grid itself. So the equation of at some point light, if it is sufficiently
small wavelength high frequencies of the color it's appropriate light has doesn't move in a in a in a uniform space move in a in a in a granular space and this affect the propagation of light and slows down high frequency more than short frequencies this is well known i mean there's a reason for which light yeah
In water goes a different speed that lies in vacuum, like interact with them with a with a material in which it is. So when we say that light goes always the same speed, we mean if there's nothing interference, if there's no structure, no, no granular, no matter in light goes like cause the speed of light. But in the presence of something light slows down, so to say.
And so the idea was, okay, so quantum gravity says that a very, very teeny, small scale, there's a structure and therefore we should see this dependence of the speed of light from the color. That was the idea. It's a very tempting idea because you can put numbers in, you know, the length at which you expect the space to become granular and therefore you expect
So this was a quantitative prediction. It's not just qualitative in the way that you're explaining it here. No, it was a quantitative. That's what made it interesting. Because if you want, it's easy to do a calculation of how the certain greed, the certain greed with a certain spacing of certain length of the elementary steps, how it can affect light, which frequency would affect. So
We know the size of the granular structure of space, so to say. So people with least one in particular had this great idea. Say wonderful. I mean, perhaps this might affect the speed of light. Now, it is a very, very teeny change of velocity, of course, because the dimension of the grain are very, very small. But that's a key idea. If you have light traveling for very, very long distances,
Teeny difference piles up. Right. Because some race was a little bit faster than the other. So they come up separated. And since there are the universe is nice and gives it gives us some explosive phenomena very, very far away. And we see pulses of light come from this explosive phenomena. Some supernova some some very intense
Explosion they're the corner of the universe the light that gets to us if what I've said is correct Should arrive some some wavelength should some color should arrive before some other color so we should see a Delay in the pulses that arrive to us some frequency right before some frequency right later
And in that case, what's important is not only the distance, but also that what's being sent is a high energy photon, and then also some mixture high energy and low energy. What is important is that what we receive is not a photon of a single energy or a group of photo for single energy, but is a pulse of different energies. So we have energy means frequency for light. So we have some light of different colors, if you want some some more red, some blue.
Some high-frequency some short-frequency and by resolving them Which is easy. That's what optics instrument do If this is correct, we should have seen this pulses to arrive Expanded in color. So first arrived say the red and then to write the blue nice phenomenon namely the arrival of distant signals
I'm of different colors a slightly different time so is what has been disproven by the recent results. And so there is a result basically they observed some signals coming from far away and they checked that at the level of of precision where was expected this phenomenon to happen if it does not happen. So that phenomenon was
Was a hope to see a granularity of space, but it doesn't happen. Now, I haven't yet answered your question, Kurt, why this is not a problem for loop quantum gravity. The answer is that at the time, many years ago, when this phenomenon was suggested by Lee Smalling, a lot of people, including myself, got very excited, so said, OK, so Lee has this
Intuitive picture of what could happen. Does it happen for real in loop quantum gravity? Uh-huh and very soon a number of paper appeared including a paper by mine That convinced the community that no that's not going to happen This this phenomenon that we suggest it's it's it's not predicted by loop quantum gravity and the reason is that
The kind of discreetness is not at all. The idea is not at all that space is like a grid. Space is not like a grid. If it was a grid, it would be a classical grid, not a quantum phenomenon. And it would contradict
A property that it's a property of the theory, uh, which is invariance of the Lawrence transformation, invariance of the, the, the similitude of special activity. Now the theory is invariant under, um, Lawrence transformations and this phenomenal breaks Lawrence invariance. So it cannot be predicted by the theory. Now this is beautiful because, um, uh, it's really a quantum phenomenon. And that's why people get confused about that.
Now quantum mechanics allows precisely symmetry and discreteness to happen together. It would not be possible classically. Let me give you an example because I think, or a couple of examples, because these are, I think that they explain. One is that in quantum mechanics, we all know when we study quantum mechanics, the original thing,
is that if you measure some angular momentum, how things rotate or the angular velocity of something, this is quantized. That's one of the quintessential quantum phenomena. So you only measure certain values, certain discrete values. Now, in classical theory,
If the angular momentum was quantized, it meant that along some variable, some directions, things could turn only at certain velocity and not at other velocity. But of course, imagine that you have a body that turns around this axis at a certain velocity. If you look at it rotated,
With respect to the new axis the component of the angular momentum is just a little bit smaller not much you reduce it okay and therefore from a rotated frame.
You would not see the angular momentum quantized. You could change the value of the angular momentum continuously. Right. If you're allowed to rotate continuously. If you're allowed to rotate continuously. So that seems to say that it is impossible to have angular momentum quantized and rotational invariance. But that's wrong, because in quantum mechanics we have angular momentum quantized and rotational invariance. How come? Well, what happened is that when you measure
Um, the agreement in one direction and in another direction, uh, the two, um, operations do not commute. So if you, if you measure one, when you measure the other one, you don't have a precise value. You have a probability distribution of values. You can have a probability to measure the same or one smaller or one larger, right? So what changes continuous is a probability distribution.
while what you actually measure, it's only those particular values. So one should be very careful because the fact that length is quantized in quantum gravity does not mean that, however, does not mean that you're breaking any invariance of the theory. It only means that you go there and make a measurement. You get a finite result.
If you had it measured from a different Lorentz frame, you would have obtained the same result. Another way of thinking about that is the following. Imagine you take a standard model or any quantum field theory. We know that even in the vacuum, if you measure in a small region, it's a quantum effect, you find particles.
Right. That's a so-called virtual particles. It's a physical fact. If I go in a small region and check if there are particles, I find them, even the vacuum, because it's only if I if I measure in large region that is back. Now, one could reason that would be the mistake. Oh, if light travels in the vacuum, OK, if the frequency is high, it would see a small region. So it would see this
This virtual particles, virtual particles, even without loop quantum gravity, even without loop quantum gravity. And therefore it would slow down because we know that light slows down if there's matter around. OK, so therefore in standard quantum field theory, high energy, high frequency light should go slower.
But it doesn't. It's not true. It's not correct. And he couldn't because the series it's Lawrence invariant and it learns where the theory light vacuum goes at the speed of light. So the mistake is to take to literally.
The granularity of space, particular quantum gravity, and it's beautiful. Quantum gravity doesn't say that space is granular. Quantum gravity says that if you make a small measurement, you see a minimum length. Okay. This is like quantum field theory. Quantum field theory doesn't say that the space is full of particle. The vacuum is full of particle. It says that if you make a measurement in the small,
You see particles. It's very different things. Light can travel in a vacuum of quantum field theory without seeing anything. But if you make a measurement, you see particles. So similarly, light travels at the speed of light in a loop quantum gravity background space or quantum background space. But then if you go there and make a measurement, you cannot go smaller than something. So this is the
This was realized long ago. There was a lot of discussion at the time, many papers, quantum gravity and Lorentz invariance, minimal length and Lorentz invariance, it was clarified and the loop quantum gravity community was disappointed at the time because somehow theoretically the window, the possibility of seeing
A quantum gravity phenomena would have been great i was very excited that that's why i started looking it but the theoretical analysis of the calculation showed okay this effect is not going to happen. Time passes the experimental. Do the experiment the the the observation of the people in astronomy do this measurement they confirm the fact
On which the community agreed that if the theory is correct, this should not happen. So everything is fine. It's if you want is disappointed. It would have been better if we had a but everything is fine for the theory. Now, fortunately, let me put it this way.
The experimental were completely clear in the paper. They said if a theory predicts granularity, there's a problem for that theory, but they never obviously said this is a problem for loop quantum gravity. In fact, if you want even string theory, they were papers that suggested a similar similar phenomena for string theory. But nobody in fact, in the astronomers paper, they
quote various people that had suggested similar phenomena in loop quantum gravity string theory. But right. Never there was a clear result of string theory predict that. And therefore the fact that doesn't happen is not a problem for string theory. Similarly, never there was a clear argument that implied that the phenomena come from loop quantum gravity. Now, unfortunately, not from the scientific community, but from external commentators who like to
Okay, going back to the reason why in quantum field theory, you should not expect a variable speed of light dependent on frequency
You said that it's only when you measure a small distance that you get these virtual particles. But isn't it technically if you measure any distance, you get virtual particles. They're just of different energies like infrared. If you measure any distance, you're right. But when you measure large distances, so to say, the number of virtual particle goes down, down, down, down.
So for a high energy photon, why isn't it acting like it's measuring at any given point? That's a very good question.
That's a very good question. That's a very good question. It just, it isn't, uh, you try, you go into the equation with theory. It isn't, that's a very good question because somehow once we get to the idea of the virtual particle, uh, we use it, uh, uh, we use it intuitively, but we should be careful because the virtual particle are not real particles. Um, we have this idea.
Yes, just like we talked about science commentators, there's also some science communicators and they show those animations of a jittery space time. And it makes people say, wow, that's so cool, bro. It's so cool, but it shouldn't be taken too literally. That's, that's often the problem with quantum mechanics is counterintuitive.
So you try to make it intuitive, which expresses some aspect, but the analogy is not good, so it doesn't express. For instance, the vacuum of quantum field theory, in some sense, it is full of virtual particles. But as a state, it doesn't change with time. It's stationary. Nothing moves.
So this image of everything moving faster is the sense is completely wrong because it's a stationary state is a solution of the Schrodinger equation where nothing changes. In elementary quantum mechanics, we say that an harmonic oscillator has a ground state and this ground state is a Gaussian mathematically. In the ground state, the oscillator is in the minimal of the energy, but with some probability distribution.
The state never changes. It's just that. If you let it untouched, it stays that. Now, if you look where the particle is, if you try to pinpoint the particle, which is a vacuum state, you don't find a zero. There is a probability you find here, you find it there, because that's the spread, the quantum spread of the state. So it's true that if you look, you find it somewhere. Then you look again, you find it somewhere else. Then you look again, you find it somewhere else. Even if you
If you try not to disturb too much, which is hard, you have the spread. Okay. But this doesn't mean that there's a jumping particle there. There is a state which doesn't move. The source of the confusion is that we're not talking about particles. Okay. We're talking about quantum objects, which are not particles. So
A quantum space time is not a discrete space time right is a quantum space time to say that. A quantum space time is a discrete space time is the same misunderstanding saying that a quantum particles a particle of dance dances there there is here there.
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When people talk about quantum fields, they often to the lay public give this idea of a temperature field is usually the first analogy. And then they give this idea that it's something akin to an ocean and then there's ripples. But technically speaking in quantum field theory, it's not a field in the same way that we think of a temperature field. It's an operator valued distribution. So they're operators. Is there something else that's going on with
the discretization of space in loop quantum gravity that is akin to, well, it's actually operator value discretization or something like that. Yeah, to say that something it's an operator, it's some variable, it's given by an operator is precisely to say this variable is a quantum variable, right? It's a mathematical translation of the same thing. And to be a quantum variable, it means that
The system doesn't, there is a science in which the system doesn't have a specific value of that variable, but you could talk about a probability distribution of that variable. Well, there's quantum probability distribution. It doesn't mean that can be either here or there. It means when it interacts, you can find it here and there.
So that's what we call quantum superposition. I mean, when we say a particle is in a quantum superposition can be here or there, it means if you look, you find it here or you find it there. But you shouldn't think that is here and there because the two can interfere. So if you think that is here or there, you make a mistake about your prediction of the future. So in a sense, it's here and there at the same time.
or more precisely, you can always say that if you look, if you interact with the thing, you find it here and there. But if you want to see what's going to happen later, you have to still consider both possibilities. So that's a quantum superposition. Good. So now if you have a field like the electric field, the magnetic field or the electromagnetic field, quantum field has to be thought as a superposition of different field configurations. So sort of
A wave function of cloud in the space of possible fields, in the space of possible configurations of the field. So that field is neither here like that nor like that, nor that black level of that. But there's a little bit of those and the quantum state gives a probability to each one of those. When you go to quantum gravity. Gravity, that's what we learned from Einstein, is a geometry of space.
There's a very visual possibility that gravity is just space bending. Good. Beautiful. So in quantum gravity, the geometry of space is not determined. It is a superposition of different geometries. So here around us, space is roughly flat. Mikowski space is a flat space. But if we keep into account quantum gravity,
In the small, it's a super quantum superposition, all possible fluctuations. And in this quantum superposition, light can still travel at speed of light. But if you go into small and bingo, you want to. So what is the geometry here? You find a geometry which is neither this nor that. You find the geometry which have limitations in length. So there's no structure smaller than a certain length. Yes.
Now, when someone's in high school and they learn about gravity, they learn it's a force. And then some clever undergraduate says, actually, it's the curvature of space time. And then some clever graduate students says, actually, it can be torsion. And then some PhD may say, well, it could be non-matricity or torsion or any combination of that and curvature. Does loop quantum gravity make a definitive statement as to whether
Gravity is curvature, torsion, non-metricity, or some combination of them? Great question, Kurt. Let me ask, let me answer in steps. First step, you go to high school and they tell you that gravity is a force, okay? Sun and the moon, the sun and the earth pull one another with a force which act at a distance.
Maybe careful. Is that false? Or is that right? I believe that's right. That's not false. It's just approximate. It's an approximate description of reality. Okay. If I say, I look there and I see a forest and you come to me and you say, no, Carlo, you're wrong. It's not a forest. It's a lot of trees with leaves and so on and so forth.
Okay, you have a better description, but it's still a forest. Okay. Yeah. So once you learn general activity, you learn that there's a better description. Why better? Because it, the other description doesn't capture some phenomena is approximate. Okay. So there's a better description in terms of curvature, but in the common situation, which you are, you can still talk, talk about force, not wrong to talk about force, just proper,
Names for something that happened in when you don't look to in detail. That's the first point. So could we say that Newton theory is an approximation and generativity is a true story? I know, of course, because we know there is quantum gravity. So Newton theory is some approximation. Einstein
Gravity, it's a much better description of reality. Quantum gravity is going to be a better description of reality. Is that going to be the last ultimate description? No, come on. Your program is titled theory of everything, which is great, but I don't believe we are any close to any theory of everything. Plenty of things we don't know. We don't know what is dark matter. We don't know what is
It better be, otherwise I'm out of a job shortly. Exactly. So I believe that your show can go on for a long time before we could ever think about the theory of everything. If we get there, we'll talk about, but we're not there by very far. So every theory, it's a way of describing the world at some level of precision. Okay. It's not one right, one wrong.
Okay, having clarified all that, which I think is important because it's not often said. And because we used to say, it's wrong that space time is flat. It's not wrong. It's true. It's just not very precise around here. Space time is flat. Okay, to all degree, I can measure it is flat. So I'm saying something very right.
And if you say, well, but if you measure even better, it wouldn't be flat. True. But to the extent I can measure it is flat. So I'm saying something right. There is a force pulling down. If I let my hand fall by force pull down, it's true. Can you say it's false? No, it's true. Okay. So having clarified that, I get back to your question. Okay. In general activity, in the context of general activity,
Spacetime, gravity is due to curvature. No torsion, no no metricity, nothing like that. There are attempts to rewrite generativity, if that is possible, or extensions of generativity with some more geometrical, different geometrical, more reach or different geometrical
Nothing as far as I know that I've given a lot of that has had a lot of success that allows us to understand better. If you go to loop quantum gravity, gravity is not just curvature. It's certainly not no metricity. It's quantum curvature. So gravity is a geometry which is curved, so it's curvature.
But in addition, it can be, as I was saying before, in a superposition of different curvatures. So you don't really change the traumatic language that you use it, but you allow it to be to be quantum, namely your reality to be in a quantum superposition of different geometries. So if loop quantum gravity is correct, if loop quantum gravity is correct, the best way of thinking about gravity is that
If quantum mechanics is correct, the best way of thinking about particles is still a particle, but it can be spread, can be in a superposition of here and there. And that's the wave function. So if loop quantum gravity is correct, you can still think a gravity of geometry, but this geometry is spread. So you have a quantum superposition of geometry, the wave functions of the geometries.
Have any people gotten so far as to do interpretations of loop quantum gravity in the same way they're interpretations of quantum mechanics? So some may say that the wave function is some pilot and then the particle is just riding atop that pilot. Are there any loop quantum gravitas that would say, well, the curvature is somehow riding atop some pilot curvature? Yes, there are exactly papers that do what you just said.
The quantum gravity is still a quantum theory. So all the mysterious aspects of quantum theory are inherited by loop quantum gravity. So if you want to interpret the quantum theory, it makes sense to it, which I think is not a bad idea to go into this exercise.
There are various ways of interpreting quantum. One is the one you just mentioned, the other is many-world, the other is relational quantum mechanics, which have worked a lot, and each one of these can be applied to loop quantum gravity. So if you want, you can be a loop quantum gravity many-world guy, a loop quantum gravity relation quantum mechanics guy. It seems to me that
The relational way comes more naturally in November next month. I'm going to philosophy department to give a series of lectures in which that will be one of the main topics at Princeton. I will be I'm invited one month in prison to give a series of lectures and I'm going to I'm going to talk about how to interpret how to make sense of quantum mechanics, keeping in mind that quantum mechanics should include also
So can you explain, just give a brief outline of what relational quantum mechanics is
And then also explain what it's like to articulate an interpretation of quantum mechanics, because many people as they're showering or they're driving, as they're going about their day, they're like, I have an interpretation of quantum mechanics. But is there something that's more symbolic or more quantitative, more rigorous, more precise or stringent than just surmising on your own about the interpretations of quantum mechanics?
The point is that if you if you take a shower you come out with an idea and you start telling it around very soon somebody would tell you about look think carefully if you want to say is correct then this and this and this and you say ah yeah you're right it doesn't work so
Most way of thinking either don't work or. Force us to some very. Unexpected consequence so the discussion. About the definition of quantum mechanics is a discussion about this consequences and the strange this.
When I make a measurement, I measure the particle and then I split with a Stengel algorithm. Then I see whether it's here or there. So I've measured the spin of the particle and can be one direction or the other. This is a thing that can be done in a laboratory. A grad student can go in a laboratory of physics and do this measurement. And then something strange happens because
Quantum theory doesn't really tell you what's going on. It tell you only you have a probability of seeing this, a probability of seeing that. Now, the various ways of thinking about that. One way, for instance, is that, well, there is much more than what the theory is telling you. The theory is telling you that this wave, this superposition, but as you were saying,
In addition, there is also true particle that is riding the wave and going here and there, which we didn't know where it was exactly before. So you add a lot of extra equations to the theory, extra variables, which we don't see, but that's supposed to make sense of what is going on. OK, some people say, why do you want to add plenty of things which you never use? Other people say that's a different interpretation of quantum mechanics. Oh, but
It's not really that either one thing happened or the other thing both things happen You see one thing happen because you yourself become two There's one you that sees up once you that sees down There's never a moment in which something strange happened that the particle CO that the particle is still in both places But you also become in both places. So there's one you that sees up when you assist them Okay, that takes away some problems but
Then we have to think, Kurt, that you and I are just one version of zillions of copies of us that doing other things. And so, so whatever you try to do, you have to clash something harder to digest. Is this an empty conversation? No, I don't think so. Because I think through this conversation, we're going to get some clarity how to think about quantum mechanics. When Newton did his
Newton and Galileo and Huygens and Kapler and everybody else got to the Newtonian mechanics. It was a long discussion because people were saying, well, wait a moment. Can I say something is moving or not? In Newtonian mechanics, you cannot. There's no meaning in saying something is moving or not. You can always say something is moving with respect to another thing or not. Okay.
That's incredibly strange. It is strange, but we have digested it. We have digested exactly what we have learned. We have learned that there's no meaning in being still versus moving unless it's referred to some object. And so it was a strange message we have understood about the world. Now it's clear.
We haven't yet understood what is a strange message about the world that has come with quantum mechanics. I believe I have my own way of viewing. I'm convinced of my own, but until it becomes common, it's not an answer. People who are proponents of the many worlds will say that what they're doing is following the math. They'll say this phrase, quote unquote, like we take Schrodinger's equations seriously.
But yet yours is an alternative that doesn't do away with Schrodinger. So are they incorrect in saying that they're just following the math? They're actually following the math plus putting an interpretation on, or is it true that you can from the math in further interpretation of many worlds? I don't think they're exactly correct. They do mean something. They're not stupid.
They have a way of thinking they're very smart people out there. But I think it's not exactly correct that they follow the mark for the following reason. If you if you go to school and follow a good class in in quantum mechanics, at some point you get a clean math. OK. And the math, it's essentially the Schrodinger equation plus the operators
Plus the eigenvalue eigenvector construction that give the probabilities of seeing one thing and the other. So the Mac has various parts. What they do is trying to do the following. Forget this, forget this, just skip this and follow the math and see if you can get the other one.
So they make a choice. They make a choice at the beginning of the of the mathematical book, the so-called postulates of quantum mechanics. They discard the projection postulate. They discard the measurement postulate. They discard the value postulate. They just keep the quantum state and the way it evolves. And they say this is a two month. But I wouldn't say that this is a two month. I would say that the relevant I would say that the relevant math is the rest.
Interesting. Yeah. So what they say is they take away part of the mathematics of the ways it's commonly presented and they try to recover it just from the first bit. To some extent they do but with a very long and complicated story and a lot of, you know,
this complicated idea that implies that in some sense you and I are just one of many copies. So you have to accept something very strange about reality if you go that way. The idea that this part of the math, it's not true
Going back to the Chinese experiment, did they outrule even something like Wolfram's model, which is about space-time atoms, or do they just put a bound? Oh, that's a good question. I actually don't know. I should, I should. They definitely,
rule out certain things. I mean, that many things, any naive idea of that, that, you know, want to make quantum gravity. Most people would agree gives a finite length. OK, the question is how to how this finite length is. It's actually coming in in nature. They rule out the idea that this finite length is actually a finite grid in space.
That's out. It would definitely give this effect and the effect is not there. I would suspect that it could be used to rule out any theory which is non-quantum. Wolfram, through in a sense, want to derive quantum from something else.
And there's a granularity, which is classical. So it might be that gives a problem to that theory, but I'm not sure because I've not looked into the, into the details. And, um, you asked, uh, it's just putting a bound on it. Yeah. I can't see why it wouldn't just put a bound. Look,
Theoretical physics is less clean than the ways usually sold. You can always change parameters and save yourself. Theories are not really ruled out by, it's very rare that theories are ruled out by just an experiment or a group of experiments.
Theory usually come with flexibility. Theoreticians can add flexibility and so new experiments you can just patch up your theory. The point is that
Yes, in the loop quantum gravity case, it's not flexibility that is evading this experiment. Right. That's correct. It's that loop quantum gravity didn't predict what they're saying it predicted to begin with. That's correct. That's correct. Right. So what would commonly happen is that some some measurement are hard to fit into a theory, harder and harder. And at some point you say, no, come on.
Look, take Newton's theory, right? Where did Newton's theory go wrong? Newton's theory go wrong in Mercury. Mercury essentially doesn't do ellipses. The ellipses turn, the periallium ellipses turn in a way that doesn't fit with Newton's theory. That's a fact, we know. And in fact, general relativity account for this shift of the periallium perfectly, this marvelous well. But when it was measured,
Did people say, oh, that kills Newton theory? No. People say, oh, yeah, but maybe the sun is not really a sphere. Maybe there's another little planet inside Vulcan that gives this effect. Or there's another planet. Yeah. Maybe this, maybe that. They were all open options.
So, it didn't kill Newton's theory. It was a trouble for Newton's theory. He had to do funny things to fit it. And when generativity came out and gave bingo, exactly the right number in such a beautiful, marvelous, clean way, people say, oh no, that has to be a better explanation. So why do you think these polemical commentators, as you put it, are so eager to say there's a death blow to loop quantum gravity?
I think the polemic between loop quantum gravity string theory sells a lot. People get excited, look, this is winning, this is losing. And of course, if you can say something strong like that, it looks
It looks raising a polemic and it looks, uh, science is, it's slow. It's a lot of debates. Things are not clear. It takes time. Um, it's not about big, uh, big emotion. I mean, sometimes they're big emotions. I mean, the fact that, uh, everybody expected super symmetry was not found was, was a big shock for the community. I mean, there were articles written by scientists in the, in the, in some Le Monde.
The French journal saying, Oh, it's a big crisis for the physics. Uh, but even there that does this rule out string theory? No, of course it doesn't. Um, it's not that because there were no, uh, because string theory doesn't really uniquely predict low energy supersymmetry. Um, as I said, right. I think commenting about science, it's not.
It's really commenting about clear cut things. And in this case, I don't know. I mean, I don't know exactly what what has happened, but in that there have been a little bit of acrimony between strings and loops, which is stupid. I think we just don't know. I mean, we should each each one of us. And in the discussion is good to say, look, you're wrong here, you're wrong here. That's that's how the discussion
Um, but, uh, but, uh, definitely nobody's dead. No theory is dead. And, uh, um, the, we all wish things went faster, but science has never been fast. Fundamental science has never been fast. It takes decades. You wish things went faster except the high energy photons.
That's correct. Absolutely. Then the counter argument that I've read in the comments from some of the commentators and some of the comments themselves say, OK, well, then that either means that loop quantum gravity was disproven or that it's untestable. But it sounds to me like what you're saying is that it's either disproven or this wasn't a test for it, not that this is untestable. Absolutely correct. That was not a test for it since the very beginning. I mean, there have been a discussion within a theoretical discussion within the community
And the outcome was clear. No, this is not a test of the theory. People are working hard for finding tests of the theory or at least measurement that could help support the theory or help take away credibility in the theory. So there's a lot of that's what many people look at gravity doing right now.
I have a quote from Sabine Hassenfelder from the video that I sent you and she said that the smallest possible area which we talked about is not compatible with Einstein's theory and you need to modify Einstein's theory to do that and if you do you'll find that the speed of light is not constant. So that was the argument of Smolin back then and then she said the opposite was
vocally represented by Carlo Rovelli who said, no, no, no, we can recover the symmetries of Einstein by averaging over all possible ways to take space apart into areas. Right. And yes, I think you can do that. This is her now. But in this case, you effectively get back areas of zero size because there will always be some observer for whom area is arbitrarily small. And you go back to the problem with singularities that loop quantum gravity was trying to avoid.
So basically, you can't have your cake and eat it too. And I'm curious what your response is to that. Areas of zero size are part of the theory and are not the, there's nothing to do with the singularity. The spectrum of the area operator includes a minimal area, which is sort of roughly the plank area, the square of the plank length, but also zero, of course.
The question is the area of what, right? So if I take two, let's say, let's let's speak in terms of length, which is easier. If I pick two points, I can ask what is the length between the two? OK, if I if I say, is there a greed with some length space, I can ask what is the space of that hypothetical greed?
If I make a measurement of a diffusion of particle by something, the diffusion number is measured in terms of area. So that's another. So loop quantum gravity says that when you measure something, you get an eigenvalue which could be zero or could be one plank area or two plank areas or whatever.
This is perfectly compatible with the fact that, let me put it in this way, from the point of view of a photon, it's a very imaginative language, who's traveling a distance from a different galaxy to us, it is like the minimal area was zero. True. Okay. It's in a regime of curvature, which is very small.
And that particular sort of measurement, so to say, done by the proton is like the minimal area was zero. It's not, it's the minimal area of its own evolution, so to say. That's nothing to do with the singularity. Singularity, it's what happens at high curvature. For instance, the central black hole or early universe near the Big Bang, where the
The curvature space-time is very high and what loop quantum gravity says is that there's a maximum curvature because somehow you imagine you have the little sphere, curvature is maximum because the sphere cannot be smaller than a blank area.
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So the way
The bound on the size of things come in to help with the singularities. It has nothing to do with what happened near flat space with this light traveling. Carlo, you know that Sabine just had a rebuttal or retort about this exact issue and she said, and I quote,
If you quantize the angular momentum operator, the spectrum of the eigenvalues is discrete and that doesn't violate rotational invariance. Carlo claims that it works similarly in loop quantum gravity with Lorentz invariance, but it doesn't. If you calculate the expectation value of the angular momentum operator, it will respect rotational symmetry, yes. However, that's because its eigenvalues are both positive and negative, allowing it to average to zero.
In contrast, the eigenvalues of the area operator in loop quantum gravity are all positive and have a lower bound. Consequently, the expectation value for the area in loop quantum gravity is bounded from below and it can't transform under the Lorentz group.
This is a mathematical fact. Of course, Carlo knows this. Everyone who works on this stuff knows it. They just repeat this angular momentum story because it sounds superficially plausible if you don't know anything about quantum physics. Now you might say, all right, the area can't transform under Lorentz transformation. Maybe there's some quantum stuff going on. Some weird things happen. Yes, actually Carlo and Simone mentioned that in their paper.
That's also why some people in loop quantum gravity suggested there ought to be deviations from Lorentz invariance. I tried to tell them this but they didn't want to hear that. So what should we hear? It's a technical misunderstanding. Sabine has an argument and I think I understand where is the misunderstanding here.
She heard many times there is a minimal again value of the area and is a sort of plank area squared the plank area the length length plank length square a plank area this is what is said usually it's it's not said correctly for obviously i mean the minimum value zero.
It's a minimal non-zero eigenvalue, which is a Planck area. So in other words, what loop quantum gravity predicts is that there's a zero value and then the next one, it's a finite distance. Yes. So you cannot get any eigenvalues smaller than the minimal and non-zero. Sure, there's a gap. There is a gap. But somehow,
Sabina misunderstood that for some reason, maybe because in some popularization articles or books was not said precisely. So she thought that there is no zero eigenvalue. And therefore she, if there was no zero eigenvalue, she will be correct and sort of complaining, wait a minute, you cannot, Lawrence transformed the mean value of the arbitrary small, which is what is needed for Lawrence invariance.
If there wasn't a zero value, but there is a zero value. So I think maybe she never read the actual papers with the quantization of the area. What makes the loop quantum gravity finite, no ultraviolet divergences is not that any possible area, it's always bigger.
Then the plank area, it's that any possible known zero area, it's bigger for that is there a gap. So once this is clarified, her argument disappear and she was very nervous. I think she she couldn't she had a wrong idea in her mind that it was no zero gain value. That's made him made her she should have perhaps
So this argument of a non-zero expectation value, does it not still apply if you have zero and then positive values and you average that, wouldn't it still be non-zero? No, no. The average can be as small as you want. That's the point. You can continuously make the average as small as you want, including zero.
It's a possibility. If you, uh, in area, uh, becomes arbitrarily small. If you look from a arbitrary boosted, uh, uh, frame. So that's required by law. It's invariant. So can we make it arbitrarily small? Of course we can make it zero. Okay. In other words, the quantum state can rotate.
from maximum probability for finite eigenvalue to increasing probability to zero eigenvalue. And that's exactly what happened in the Lorentz transformation of an eigenstate of the area. It transformed in a linear combination of the other. If you go all the way through to the end, you get just to zero. So you can Lorentz boost it below the Planck length squared?
Oh yeah, yeah. The difference here is the difference between expectation value and eigenvalue, right? So quantum mechanics says if you make one measurement of one quantity, just one, you can only get an eigenvalue.
That's what quantum mechanics is. The expectation value is the average between them. So electron has spin up and spin down, but technically its expectation value is zero then, but there's no spin zero electron. It depends on the state. I mean, a single atom, if I give you an atom, it can be in a configuration such that the
You see necessarily with, suppose it's a spin one thing. There are three possibilities. Spin can be up, down or zero. So now suppose you see it with spin up. So now you rotate your head. Classically, the component of the spin in that direction will be zero. So you continuously rotate the component
In zero from from from one to zero. Now, if you measure various types, you rotate the atom, you don't get something in between. OK, suppose you rotate by by half of 45 degrees, you make a measurement. Then quantum mechanics says you have a half probability of measuring still one and half probability of measuring zero. So the average transform continuously, but what do you measure in one shot?
It depends on the probabilities and the expectation value. So for consistency, you want the expectation values to be able to change continuously when you make continuous rotation or continuous boost and sublimation. That's okay, because there are probabilities. There's nothing really mysterious. It's just quantum mechanics 101. It's not a deep, profoundly quantum stuff. I see.
Sabin somehow was confused because she will say but you cannot go smaller than the minimal area if there's nothing else you can go to okay because she forgot that there is a the error operator has also the the zero eigenvalue in fact the eigenvalues of the error operator given by the square root of j j plus one with j is a half integer so it can be zero one half one sort of this discrete spectrum
times 8 h bar g pi. And j can be zero. If j is zero, the area is zero. It's in the formula for the value of the area, which is in all the papers or the books. Does this whole brouhaha about loop quantum gravity being either testable or the expectation is not zero, et cetera, does this frustrate you?
No, I mean, it's not look quite so testable. It's my last paper, which was published on physical review letter a couple of weeks ago by myself, Alejandro Pérez and Mario Cristodulo, who are respected in Vienna and in Marseille. It's an idea for a possible test of loop quantum gravity.
Uh, that is published. So it's not because one particular proposal of testing it, um, did not materialize and then therefore the theory and untestable. No, I mean, this is, it will be silly. Um, if you, if you cannot test the theory in a certain manner, it doesn't mean that there is untestable. And in fact, there are many other ideas of how to test it. Unfortunately, as we all know, uh,
No theory of quantum gravities for the moment has obtained a positive confirmation, a collaboration. Otherwise we would, you know, claim Nobel prizes and be happy and celebrate. And we hope so. These theories are tentative theories. Loop quantum gravity, string theories, the others are ideas of how the world could be. And that's what science should do. I mean, should should should try to
find possible theories. I think it's remarkable that after many years, we have at least some candidate theory of quantum gravity. It's not true anymore that, oh, we know nothing about, we don't know how the world could be compatible with generativity of quantum mechanics. The world could be like global quantum gravity, as far as we know. Is it, oh, before believing it, we need a corroboration. We haven't got it. They're working.
This Lawrence transformation stuff was one attempt 15 years or 20 years ago. There have been others with cosmological observations now with dark matter, measuring Planck scale things. We hope that at some point, some of these possibilities will be confirmed. What's the reaction been like in the community about this recent fuss over the Chinese experiment and then the subsequent
popular science articles about it, or not articles, but sometimes videos about in the community in the in the with respect to the experiment. No, I think it was not even discussed because the large majority of the community, I would almost all the community was already convinced that that effect should not happen. So it was not a surprise. In fact, I didn't
I don't remember a colleague of my pointing to this experimental thing. The tension was not at all on those Lorentz violations. The tension was on cosmology, on dark matter, on black holes, on other stuff. As you say, in the popularization things,
Look, I got some people writing to me saying, oh, come on, look what these people are writing. Why don't they actually read the papers instead of instead of commenting? I don't I don't I definitely don't want to be negative. I think it's great that this popularization is great. But I think there are different styles of doing popularization. There is a style in which you, you know, you give opportunity to talk, you listen, you make comment, you try to simplify.
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Head over to their website www.economist.com slash totoe to get started. Thanks for tuning in. And now back to our explorations of the mysteries of the universe. We super-popularizes want to put themselves for judges of what is going on. And that's, I don't think it's very useful. Okay. Speaking of black holes, what is the firewall? What is the information paradox? And what does loop quantum gravity say about those two?
Okay, so we know that black holes are there and we are all convinced also it is.
uh... almost all convinced that uh... this is strange phenomena which is hooking evaporation hooking evaporation is a phenomena for which if you take a black hole and you let it stay there isolated on touch for a long time it becomes smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and
Both sides of a disagreement, which I'm going to tell you in a moment, agree that the whole evaporation happens. Now, what we don't know and what people have different opinions about is what happened at the end of the operation.
There is a a part of the community to which i belong which is mostly made by relativists or loop quantum gravity people or this kind of that thinks that.
At the end of the operation, you're in a deep quantum gravity regime because the black hole is very small at this point. And a small black hole doesn't mean you're close to no quantum. It means you're very quantum because you have a very high curvature. That was what I was saying before. The horizon is super curved. And just around it, the curvature is blank. So you're in a deep quantum gravity regime. So what people expect in my community
is that something quantum happens at that point. The other part of the community, which is mostly in the string world, that's another case in which there is a string loop or sort of a stringy world or loopy world, because it's much larger than the people do the actual theories, expect is that when the black hole is very small, poof, disappears. There's nothing, nothing at all there.
Now, why I consider that implausible? Because if you look at the geometry, when the horizon becomes very small, inside is still very big. There's huge stuff inside. That's gravity, right? In a small sphere, you can fit a big volume because space-time is good. So you can imagine a flat thing with a small throat and then a huge bottle inside or a huge pit inside.
So that's black hole. It's very small, but this long thing inside. So what I expect to happen is that there's a quantum transition that allows this internal part to come out. So all the information inside slowly can come out. And so what I expect to happen is that the small black hole, its remaining is becoming a remnant.
It's remaining such, remaining small from outside for a very long period then becomes what is called a white hole, which is a hole from which the inside can come out. So the information inside can come out. Now, if you instead believe that the black hole is disappearing, you're led to believe that the information inside is lost.
or has to come out somehow before. And a lot of people in the string world got convinced that the information has to come out before a certain number of arguments. And so I've devised all sorts of hypothetical phenomena that bring information out before. So you have black hole things fall inside, information inside. It should come out before the end of the evaporation, they think.
If you believe that things come out outside, you also believe that when the black hole is small, the information inside, it cannot be large. Okay. So I think that you can have a small black hole with a huge information inside. Okay. And people say, no, no, no, because a small thing cannot hold a lot of information, which is true of flat space, but it's not true of curved space. Okay. So they have this, uh,
Strong holographic hypothesis as they call them or the central dogma as Maldacena, Juan Maldacena calls it correctly. So because the dogma is not something we know about nature. It's something we think they think could be add to nature that the small black hole doesn't have information anymore. So when it disappeared, there's no information there. Everything has come out before. So they have
A puzzle. How does information come out? And that's the so-called black hole information puzzle. And there are ways to describe it and to solve it, which basically amounts to not believing quantum field theory, to thinking that quantum field theory goes wrong in some strange, mysterious way.
The firewall that you mentioned is related to that.
It's like there is a super high energy so you get sort of burned if you go if you go there. My part of the community, which include myself and many people who look at gravity and many people also for classical turn activity, do not buy this story and think that information comes in, stays in all the way through the evaporation and then comes out slowly from remnants and
I colleagues are trying to use this idea to see if this remnant can be observed. And my last physical regulator is exactly an attempt to describe a device that could measure in principle this remnants. Now, when I speak to people on this channel, often when they propose some new particle or something akin to a remnant, they'll say, and that could be dark matter. In your case, do you also think it could be dark matter?
Yes, of course, because that one is the biggest, I would even say almost the only concrete mysterious thing that doesn't fit with our
With our basic equations, right? Are the remnants so small that they're like neutrinos and could be going through us millions or trillions of times a second and we wouldn't feel them? Are they akin to that or no? We would definitely feel them if they went through us. No, no, it's a first. We would not feel them, not because they're small. Well, they are small. They are super small, but because they only interact gravitationally. So it would not interact a little magnetically, would not interact with a strong force, would not interact with a weak force. So they could go through you.
And the effect to you would be just like the Newtonian attraction of a hair moving next to you, which is absolutely minimal. I thought that they're also exporting something like radiation, but extremely slowly from the information content on the inside. Yeah, they're they're also losing the information outside, but that's extremely slowly, extremely low energy, very, very long wavelength.
So we looked into that. We have some paper about that. I don't think that would be measurable at present. I couldn't come out with any, um, any way of measuring that radiation at present while the passage of this thing. So if dark matter is these things and it could because dark matter, as far as we know, interact only gravitationally and these things interact only gravitation. So they're good. They're good candidate of dark matter. Of course, you know,
They're one of the 10, as you say, they're one of the 20 candidates on dark matter around, but we don't know what's dark matter. So, and I like these candidates because they only, they only, they don't require extra physics in the sense. It's not a new particle. It's not a new field. It's a new, it's just, just general activity and quantum mechanics together. Right. So generative quantum mechanics who make a black hole.
weight becomes very small because one of these ram in the so you have plenty of this so if in the history of the universe and that has to be understood uh somehow many of these things would produce the we could have a lot of these things around that they could be behave they would behave like dogmatic so neil tarak believes that they're right-handed neutrinos that's another of the hypothesis um
The last time when we spoke over email, I told you about the Yoni Dilemma in category theory.
because I saw it as relating to relational quantum mechanics, because in the Unidolk Lemma, it says that an object in category theory is fully understood in terms of its relationships, so its morphisms, with all other objects, as long as you're in something called a locally small category. In other words, some people use this to say that an object is completely defined by its relations to other objects.
that you can either define the relations to objects or you can define the object itself. It's dual. It's exactly the same. And then that had me thinking, hmm, I wonder if that has implications for relational quantum mechanics. Yeah, the answer is I don't know. I mean, what you characterize as the main idea behind this theorem is exactly the idea of traditional quantum mechanics. Right. So, um,
an object is defined by all the relation that has around it. So if you want to think as an object by itself, there's no meaning to the object by itself. And category theory, it's certainly a natural mathematical language for talking about these things, because in a sense, it's a
It's born with this idea that it's a structure, the largest structure that determines what we're talking about. But I am not competent enough to use category theory. Maybe I should. And in fact, people have been telling me, why don't you? People get in love with it when they study it.
Um, oh yeah. And, uh, because obviously there's a great beauty there. Uh, but this complicated to, to get into that, uh, because it's a, it's not just a mathematical theory. It's a mind frame. I would say, um, and I'm not sure, uh, the extent in which it could be useful or could just, uh, um, or is necessary.
For for articulating the idea, uh, underpinning relational quantum mechanics, but also much more trivially and, and, and simply, um, uh, I'm afraid it would, uh, make people, um, uh, stay away from quantum mechanics articulated that way. I think there's been some, some people in French that France that looked into that, but I don't remember right now.
I wish I could be smarter and know more things and add this to the things I'm doing.
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What else is exciting is consciousness. And many physicists don't talk about consciousness. You think plenty about it. You have relational quantum mechanics which says something about consciousness if I'm not mistaken. But either way,
I want to know, in your view, what observes the observer? The mechanics says something about consciousness very indirectly. So it's not a theory that leads to consciousness. I don't think that consciousness has anything to do with quantum theory. But indirectly, yes, because
What's the problem of consciousness? The problem of consciousness is that we think there are two things.
What is matter, atoms, molecules, stones? And one is my spirit, my thinking brain. Okay. And if you start from that, it's very hard to think that the two are of the same kind. But I think that both ideas are very naive. There's no my spirit, my soul,
My thinking might my observing thing. I am just a piece of nature like anything else. Uh huh. And, uh, I, I, I follow laws of physics and says, my brain is very complicated and the complication of my ideas is the complication of the neurons of my brains. Just another way of describing things matter also, um, is not so naive like a sort of a very naive materialism.
Would suggest that matter is not just little stones or molecules bouncing around because we know quantum mechanics quantum mechanics tell us that it's more complicated. Nature is more complicated nature is about how things affect one another. An electron is not a is not a stone it's it's it's something it's real but it's only real as far as interact with something else so if you think matter in that way.
My brain interacting with the rest, it's doing the same thing that the rest of the universe does, species interacting with species. Now this doesn't mean that the universe is mental because my way of being or your way of being, it depends on the specific of the brain. We are very special pieces of nature.
But we're special just because we're complicated and all these things happening. So I think that if we start from a fundamental sort of philosophy where we describe the universe in the way as a collection of things, each one of that can be described in terms of the others and
How things have information about one another, how things attract one another with a unified way. And if you find language in which both, um, the, uh, just changing behavior that we call consciousness, nobody knows what they mean by consciousness. It's just the, how we are, um, and the way, uh, stones and planets and plants and, uh,
In the same manner in which
Some decades ago people thought living beings is completely different than non-living being. The biosphere is something totally different. It's not totally different. It's just a special set of processes, but just physical process, chemical process. We call biological process a peculiar kind of chemical process. So I think our thinking is just
One of the many things of the universe, which is very complicated, we understand it very little. And in your view, because from the surface, it sounds like it's suggesting consciousness is fundamental, if the relations are fundamental, somehow consciousness is related to the relations. It sounds like that. How can it be that there's an experience attached to something that's not conscious? I think relations are fundamental, but what we call consciousness is not at all.
The difference is that I need the notion of relation to describe everything. But when I think about consciousness, I mean, I'm describing you, you have memories, you have language, you have anticipation of the future. You have a brain that does a lot of very peculiar things like keep remembering and yes, exactly. And some of this one by one, some of these things are
Comprehensible, right? It's, uh, for instance, uh, how you take decisions. Well, you have information and you elaborate, you do things and my computer take decision when it plays chess with me in a similar way. So that part is in common. Um, how you look around. Well, the experience part though, the part that it feels like something. Yeah. The point is that when, uh, when, uh, you try to pinpoint what exactly do we mean?
uh by by that thing which is different when we try to say precisely we can't we use vague words and these vague words uh uh just saying that we don't know what you're talking about um so i don't think there is anything special in um
Inexperience by itself is just one of the aspects of the world Which is not very different, which is a much more complicated version of That stone which is falling on the other stone and affecting it much more complicated and this complication is additional complication Is what makes it So rich that we
I don't think there's anything different in me explaining how that stone is affected by another stone and me trying to understand how you Kurt are affected by talking with me. It's just in one case, it's easy in one case is super complicated. The difference is just the level of complications and what we call consciousness is extra complication. So you believe that a stone is feeling something when it's hitting another stone? No.
No, because feel is the I believe that it's a it's behavior is affected by the other one. And what the right language for describing what is going on is a relation between the two. And feeling is related to emotion to to things that you have when you have a
If you had 10 graduate students and you could delegate them to the most tractable promising direction for either relational quantum mechanics or loop quantum gravity, what task would you set them on?
I'm doing sitting down and trying seriously to compute the position amplitude of a black hole at the end of the operation. So the remnant black hole when it finishes being a remnant? Yeah. Yeah. You see, my understanding of loop quantum gravity is that
More or less, it's a theory. It's a good theory. It's a consistent, coherent theory. We don't understand it well. It's hard to do calculation. We're not sure how to define it. I mean, we are fighting about us in loop quantum gravity. This version is a bit better than yours, of course. And there are things which have not been proven yet. So, all sorts of troubles. But it's a theory.
It's a consistent theory of quantum gravity. What we don't know is whether it is correct theory for describe the world or not. So I would tell the students, look, work on the application, try to apply the theory to concrete phenomena. There are many concrete phenomena, early universe. I mean, but the the end of the evaporation seems to me, which is the same problem as the singularity is about the singularity is connected to the end of evaporation.
and uh the number of papers who try to do this calculation but they're very very primitive little it has not been explored yet there is a mathematics which is available it's a beautiful physical problem is out there we see the black holes okay what's going to happen to them in the future uh most likely i mean unless there's people you hinted to before
Right. Most likely they are going to evaporate. Then what? So we're asking some concrete problem. And if it happened to be connected to dark matter, we fabulous because we could then there will be a lot of this remnants that we could check them. So it seems to me that that's a possible opportunity for doing a concrete for using quantum gravity, not just for
Have you thought much about how it came to be that loop quantum gravity is the second place in terms of theoretical physics? What I mean to say is that it's seen from the outside and sometimes from the inside that string theory is the big dog and that its competitor is loop quantum gravity. Whenever people are talking about what is the theory of everything or the theory of quantum gravity, if they say it's string or loop.
Have you thought much about how did loop get to be on that stage and not something like asymptotic safety or Rogers twister program or something else? Yeah. How did that come to be? There's plenty of thought about how string theory rose to prominence. Lee Smolin has at least one book about that. And I'm curious about the sociology of player A and player B.
First of all, I think that the scripture gave us, it's true that people think in these terms, in the science community as well. And what they actually are talking about, it's a scientific judgment, but it's also much more simply a number of people working, right? I mean, it's in total safety, there is a few people working in the other attempt at a possible direction to
There are dozens of groups around the world, there are conferences, hundreds of people. Some do cosmology, some do black holes, some do mathematical physics, some do the covariant version of quantum gravity, some do canonical version of quantum gravity, and so on and so forth. So there's a world around that.
And string theory, people who say they're doing string theory are more. And they're actually much more variety of things they're doing because people try to say this. Some people say they're doing string theory even if it's vaguely related to string theory, what they're doing. There's a lot of development. And this is sort of
A little bit self-sustaining because it's good to be part of a larger community if you can connect to them. So the description you gave does reflect the actual situation. The majority of the people interested in quantum gravity are in these two communities, strings and loops. How come? Historically,
There is a clear track to that, which is the history of general relativity as a scientific research field. General relativity, of course, started with Einstein, who wrote the theory of general relativity more than 100 years ago. And it was a very isolated group of people who were doing that for a long time, very few.
Because there was not much to do. The theory had this three little successes, the pre-early of Mercury, the deflection of light by the sun, and somehow the redshift. And that's it. Nobody knew how to use it to do anything useful. And that was for very long. And then at some point, it started becoming more and more useful. Application, technology, the GPS, astrophysics, cosmology started moving.
And black holes, gravitational waves. So suddenly, generativity became larger and larger and larger. But the people who come from generativity were different people than those who were schooled in the particle physics. So those who did the standard model, who, I mean, Weinberg, all the
And so there were two different communities and when both communities started to be interested in the quantum gravity problem, which of course interest both, they took very different, they had different philosophies, different way of thinking, different mathematical tools that were used. And so this gave a big cultural difference. And then something happened in the eighties, which was
This is just astrology history. Uh, both theories got great results in the eighties. It was a moment of, uh, surprise. Uh, but yeah, uh, theoretical results in, in the eighties. That's the moment in which people got excited, but precisely because it was a great moment of excitement in both parts. Few people looked at the other one. Right. So why?
No, because you see, oh, I'm in a theory that seemed to be working and then you just focus on it. Why you want to look at the others? It seemed to be working. You just go ahead. That's for instance, when, you know, when, when, when string theory, uh, sort of realized that there is an almost unique string theory, um, uh, it was great result with the anomaly, um,
and then look into gravity, there was solution with the weight equations. Wow, incredible solution with the weight equations. So the two communities ignored one another for a while and they had so different mathematical methods, assumptions that every attempt to communicate except few people. I mean, there are some people, at least one is one.
Who try to learn both things. I try to learn string theory, but somehow always as a mature, not as professionals doing theories. Um, and it's, it's, it's really, you see, if you're string theory, if you're string theories, you think that, uh, energy, it's a major thing, momentum, energy, momentum is, it's, it's a fundamental thing in terms of thing to, to think.
If you come from generating the energy momentum is just not defined in general is kind of be fundamental because in general there is no energy momentum of gravity itself which can be defined in any in any decent way there is only a moment of matter but not of gravity itself except.
In specific cases. So what you consider your basic conceptual tool for think about reality in one camp would not in the other camp. So there was this long, long separation and this a little bit is still there. Um, it's okay. I think the debate is still going on and, uh, uh, we do have, uh, hopes of fights. They were both directions. Of course there were hopes of finding something
That could help not much or almost nothing directly observational so far has come in some very disappointing thing has happened i mean super semitic was very disappointing if it had happened.
I suppose many people would say those people have a point to me this they seem to be was it disappointing to you. Supersymmetry is not in loop quantum gravity. I don't know the non non the non discovery of supersymmetry was great for us because.
Because, you know, disappointment to your competitors just by that. You looked personally disappointed. I was not personally disappointed. I was just happy, happy, happy, going around happy and smiling. Yeah, you see, you were all waiting for it. I told you that there was story. So I didn't find this point. But then there's also another difference. And that has to do with the name of your of your shortcut.
Sorry. No, no. Keep it, keep it, keep it. Of course you should keep it because it's a great idea. The hope of finding a theory of everything, but loop quantum gravity never considered it its own problem. Loop quantum gravity in a sense, that's a big difference.
Look at it in a sense it's much more ambitious okay we are going to understand how to do physics without space without time really space is quite not like you who have to go observable to infinity where you know is space and time because we're smarter because we face the big problem directly i mean quantum space and quantum time but on the other hand um look when to gravity is super humble
compared to the ambition of string theory. Zoom quantum gravity is not a final theory of everything. It's not a unification of all the forces. It's not something which pretend to be an arrival point for theoretical physics. It's a very humble enterprise, which is we know the gravitation interaction. What happens when you cannot disregard quantum mechanics?
In this gravitational interaction. So what happened inside the black holes? That's the only or what happened at Big Bang?
I see it two ways when it comes to the humility argument because it could be that we just need to take one step forward but it could be there's some chasm and you actually need to jump and anytime you're taking a step you're just gonna fall you're like well look I'm super humble you all are just jumping into the void yeah well you need to jump further yeah no no of course we don't know I was
You see i i grew up in the seventh i went to school to university physics in the seventies at the time the big problem was a strong interactions i think it was a was a mystery some of the week interaction that was already the attempt to find the salam what we call today the theory of weak interaction.
Um, but the strong interaction were very mysterious and, uh, there was a large number of particles, uh, uh, that were found the zoo of, uh, I was very confused, uh, and the strong interaction was strong, uh, namely you expect the perturbation theory to full and
what i got from my teachers at the time the mantra that everybody was saying my teachers were all wrong they were saying look um quantum field theory has a problem because of the infinities the renormalization uh quantum field theory is shit because you know what is this renormalization business is not clear which is and
The renormalization problem comes because of perturbation theory and the strong interaction. You cannot do perturbation theory. So obviously there were people were saying the problem of understanding the strong interaction and the problem understanding of renormalization, getting rid of renormalization must be the same problem. And therefore the solution must be forget quantum field theory, find an alternative to quantum field theory. And this alternative quantum field theory will not have renormalization problems.
And will make sense of the strong interaction this is ideas go back to heisenberg yes matrix people were working bootstrap and all of them so in other words with two problems clearly we should solve the two together and what happened historically is that that was wrong.
Because gross and will check and everybody else. Gelman solved the strong interactions beautifully with the theory, which is QCD. It's marvelous. One of the best theory we have, which still have all the problem with normalization, infinities and is a quantum field theory. And they were a minority at the time. We'll check and company and gross and, and, and, uh,
And gilbert where minority who is looking for a quantum feels ready to solution for the strong interaction with most people looking for a. No one to feel theoretical solution strong interaction so. Of course i mean i said same trick doesn't work twice but.
I grew up with the idea that you can very well have two problems on the table and think, of course they're connected. That's not true. You can solve one and the other tomorrow. So speaking of David Gross, that conversation that you had with him two years ago or so, that's something that every aspiring physicist and every existing physicist should watch because it shows
String theory is the big boy and it demonstrates that they don't even listen to their competitors. There was a part in the conversation where David was saying, you in loop quantum gravity, though you're the representative at that point, you can't even explain so-and-so. What was it? Fermions, putting fermions in loop quantum gravity. And you said, David, that's something that we solved 20 years ago, something like that.
Do you see this in the same way that I see it? Yeah. Yeah. Yeah. It's a it's a it's it's yes. And it's a double problem. One problem is in communication. So a lot of people theory criticize loop one to gravity, but criticize what loop one was. It was 20 years ago. Oh, this probably is open, but that was open 20 years ago. That's not the problem today. There are problems today.
But also the second, it's more serious as well. I think we don't need to be experts of each other theories, of course, because one cannot be expert of everything. But it's very useful for science, as I said, should go ahead by knowing what are at least the claims on both sides.
I guess one thing to have great results in your theory is another thing to say you're the only game in town. And it's another thing to say you're the only game in town while not looking exactly at what other people are doing. Yeah, that's I think you put it very clearly. We'll end with what are your hopes? What are you working toward other than this Princeton conference coming up for relational quantum mechanics? What are you working on? What do you hope to solve in the short run?
We talked about the black hole, what happened at the black hole at the end of the operation. Before talking to you Kurt, this morning I was on Zoom with a colleague in Marseille, a brilliant young professor, just got a five minute position. We spent three hours this morning getting confused about how to think about this. This is a sort of tunneling
Process so we're thinking trying to understand which sense is a tunneling process. What's how do you a tunneling process? Not in time but of space-time some sense I would love to get some clarity there. Yes, and in fact I Wish I could Concentrate more on there rather than doing all the value things that I'm doing present. That's for me. The what are the various things you're doing? I
Well, I've, you know, I've written popular books and I'm pressure that I get invitation. I do. I do this philosophy thing. I am a bit too dispersive and I when I'm I want to focus more. You asked what would you like to focus on? I would like to focus on understanding that particular it's a it's a well
It's a well-posed physical problem. That's the beauty of it. Black hole. They are there. They are out there. In fact, there is another way of putting this problem. We see the black holes. We see the matter falling in. We see the spiraling, the crescion disk as they call it. And we know, because we know generativity, that matter is spiraling and then going into the horizon. And we know generativity, so it goes into what we call the singularity.
What happened next to that matter? We have no idea. So it's a very concrete thing. A kid could come in and say, oh, there are all these holes in the sky and things falling in. Where does it go? The answer is we don't know. So, I mean, come on. We are scientists. Pretend to understand so well the universe. We should be able to answer this question. We have quantum mechanics. We have generativity. We have all these ideas. We have the tools. That's what I would like to
What happens if you fall into a black hole, like an observer, you want to know what happens to that person? What happened to two is the same question for me. And what happened to the matter that falls into the black hole, which is very much connected to what happened to the black hole at the end of the operation? I see.
The magic of general activity, the classical general activity, the time is very flexible, right? Time can go, you can go from here to here, a very long time, a very short time. Two people can separate and meet and for one is a long time. So if you go into black hole, assuming that you're not squeezed, and if you go through the tunneling and you come out of the white hole, outside is a huge amount of time, but inside is a very short time.
So the information that falls into black hole very fast goes to the singularity or the non singularity, this tunneling and then very fast come out. But from the outside is a very, very long process in which you see the black hole evaporate and then stays and then things come out. So the problem what happened to the matter inside is the same problem as what happened to the end of evaporation. Okay. And that's a problem we would like to get some better understanding.
So in traditional general relativity, when something falls in, if you're an observer on the outside watching something fall in, you don't actually see a cross inside. You see it accumulate at the boundary. And then you're saying, but at some point it does need to evaporate if we're to make it consistent with quantum mechanics. Then what happens? So speaking of boundary, Neemar Khani Hamad said any quantum gravity needs to tell us what happens at the boundary of space-time. What's meant by that? Do you agree?
Yeah, yeah, yeah. I know, I know, I know what they think. And I mean, last time I was in prison physics, I talked with him about that. I agree to some version of this statement, but not to the version that he means. The way we do quantum gravity in loop quantum gravity demands to know
What happened boundary but the boundary can be at a finite in a finite region Okay, so I can do I can do the following experiment suppose where we had a super technology I can take some matter I squeeze it to make a black hole I waited I see what comes out. Okay, all this happens in my room From some initial time to some final time. So I need to know what was the beginning what happened on the walls what at the end and
In a finite time, that's true. I need to know the boundary of the process to see the probability of giving the initial what what? Okay So that's correct. But Nima and with him the Princeton people, I'm not sure the West Coast people string theorists agree They think that the boundary has to be at infinity that I can only go at infinite distance
and look at the boundary there. And that's, I'm not convinced. So they have argument to say that they cannot be in the middle of space time and make measure quantum gravity measurement there. And those are augmented on by, um, I think mathematically they get in trouble if they try to see what happened, if I make measurement that find a distance, but they are in trouble because they assume a continuous space time.
Which is one of the assumption, one of the well, well, there's no continuous space time. That's the point. Uh, the, the, they, they have some infinities that they are struggling with, but there's infinities are the infinities that come from forgetting that there is this quantum discreteness in space time. What's meant by infinity if the universe is infinite, but how do you take the border of infinity?
Well, that's how they think about it. Do you mean infinitely away from some region, like you're defining some region, then you say infinitely away from that? Yes, yes, that's the way they they think about it and me in particular. So they think there's some process here, but the only way to describe it is that I have to go to very large distance and it's very large distance. I see. Because technically speaking, you're at the infinite boundary of something else. If the universe is infinite. You're right. You're right. No, yeah.
What I think is that the way of describing a quantum gravity phenomena is to be at infinite distance from it. And sort of for a very long time, see what happened. And I think this strong requirement for them is easier because at infinite distance, you assume the space time is flat. Right. So you're. They put observable what they call a synthetic
If the boundary is itself in a region where it's curved geometry or strong gravity, you don't have those tools. So no surprise that they have difficulties of working.
at finite distance. I think that it's work to find a distance simplifies the problem. So I want to understand what happened to black hole in a sense by by surrounding the black hole small box and see that's my problem is just a small box, not the entire universe. Carlo, I appreciate that of the 20 different items you can focus on that you're dispersed. And I appreciate that you've spent two hours or so
focused on myself in this conversation that's incredibly flattering and the audience appreciates it as well. Thank you so much. Thank you, Kurt. Again, it was wonderful this conversation. I very much appreciate it.
New update! Started a substack. Writings on there are currently about language and ill-defined concepts as well as some other mathematical details. Much more being written there. This is content that isn't anywhere else. It's not on Theories of Everything. It's not on Patreon. Also, full transcripts will be placed there at some point in the future. Several people ask me, hey Kurt, you've spoken to so many people in the fields of theoretical physics, philosophy, and consciousness. What are your thoughts?
Also, thank you to our partner, The Economist. Firstly, thank you for watching. Thank you for listening. There's now a website, curtjymongle.org, and that has a mailing list. The reason being that large platforms like YouTube, like Patreon, they can disable you for whatever reason, whenever they like.
That's just part of the terms of service. Now, a direct mailing list ensures that I have an untrammeled communication with you. Plus, soon I'll be releasing a one-page PDF of my top 10 toes. It's not as Quentin Tarantino as it sounds like. Secondly, if you haven't subscribed or clicked that like button, now is the time to do so. Why? Because each subscribe, each like helps YouTube push this content to more people like yourself
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"text": " What happens if you fall into a black hole? The results are very interesting. The experimental results is a confirmation of something that the majority of loop quantum gravity community expected on theoretical results. We see the black holes. We see the matter falling in. We see the spiraling"
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"text": " Carlo Rovelli, welcome back. It's been two years and I'm extremely happy to be speaking with you again. Thank you very much, Kurt. It's a great pleasure being here with you again."
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"text": " So as you know, there are some recent results, I believe from China, that people present as a death blow to loop quantum gravity. What are those results and do you agree with this assessment? The results are very interesting. The experimental results, they have not been presented a death blow to loop quantum gravity by the authors of those results, not at all."
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"text": " And they're not death brought to loop quantum gravity at all. In fact, the opposite is a confirmation of something that the majority of loop quantum gravity community expected on theoretical reasons, but they do disprove"
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"text": " some suggestions that were done about 15 years ago of something that if happened would have been great, a way to confirm the theory, which unfortunately is not there. Okay, so what is that? So the situation is the following. Some time ago, there was a suggestion by Lee Smolin and some collaborators of him"
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"text": " that perhaps there could be a way of finding a trace of quantum gravity in some signals coming from very far away from the in the universe, some light pulses, some very short pulses of light that we get from from very far away. And the idea was the following was a beautiful idea. In fact, I got very excited when it came out."
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"text": " The idea is that quantum gravity in general, quantum series of gravity tend to predict that there is a minimal length. There is a structure of space at some length. Now, what's important here is that it's a minimal spatial length and not a minimal space time length or space time volume. Yes, very good. Very good, Kurt. There is a minimal spatial length. So if you measure something,"
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"text": " You can measure a certain length, a shorter length, a shorter length, but there's a minimal one, a minimum non zero one. You can measure zero, of course, but you can measure a minimal non zero one. Now, if you take this naively, you can make a consideration which it's very tempting and the consideration is the following. All right. So this means that space is like a grid with a minimal length."
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"text": " Now, we know that on grids with a certain spacing, light does not behave like light in vacuum, but behave in a more rich way in the following sense. In vacuum, all the colors of light fly at the same speed, the speed of light. But if there's a grid,"
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"text": " The high-frequency color are sort of slow down. Why? Because they interact with the grid itself. So the equation of at some point light, if it is sufficiently"
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"text": " small wavelength high frequencies of the color it's appropriate light has doesn't move in a in a in a uniform space move in a in a in a granular space and this affect the propagation of light and slows down high frequency more than short frequencies this is well known i mean there's a reason for which light yeah"
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"text": " In water goes a different speed that lies in vacuum, like interact with them with a with a material in which it is. So when we say that light goes always the same speed, we mean if there's nothing interference, if there's no structure, no, no granular, no matter in light goes like cause the speed of light. But in the presence of something light slows down, so to say."
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"text": " And so the idea was, okay, so quantum gravity says that a very, very teeny, small scale, there's a structure and therefore we should see this dependence of the speed of light from the color. That was the idea. It's a very tempting idea because you can put numbers in, you know, the length at which you expect the space to become granular and therefore you expect"
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"text": " So this was a quantitative prediction. It's not just qualitative in the way that you're explaining it here. No, it was a quantitative. That's what made it interesting. Because if you want, it's easy to do a calculation of how the certain greed, the certain greed with a certain spacing of certain length of the elementary steps, how it can affect light, which frequency would affect. So"
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"text": " We know the size of the granular structure of space, so to say. So people with least one in particular had this great idea. Say wonderful. I mean, perhaps this might affect the speed of light. Now, it is a very, very teeny change of velocity, of course, because the dimension of the grain are very, very small. But that's a key idea. If you have light traveling for very, very long distances,"
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"text": " Teeny difference piles up. Right. Because some race was a little bit faster than the other. So they come up separated. And since there are the universe is nice and gives it gives us some explosive phenomena very, very far away. And we see pulses of light come from this explosive phenomena. Some supernova some some very intense"
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"text": " Explosion they're the corner of the universe the light that gets to us if what I've said is correct Should arrive some some wavelength should some color should arrive before some other color so we should see a Delay in the pulses that arrive to us some frequency right before some frequency right later"
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"text": " And in that case, what's important is not only the distance, but also that what's being sent is a high energy photon, and then also some mixture high energy and low energy. What is important is that what we receive is not a photon of a single energy or a group of photo for single energy, but is a pulse of different energies. So we have energy means frequency for light. So we have some light of different colors, if you want some some more red, some blue."
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"text": " Some high-frequency some short-frequency and by resolving them Which is easy. That's what optics instrument do If this is correct, we should have seen this pulses to arrive Expanded in color. So first arrived say the red and then to write the blue nice phenomenon namely the arrival of distant signals"
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"text": " I'm of different colors a slightly different time so is what has been disproven by the recent results. And so there is a result basically they observed some signals coming from far away and they checked that at the level of of precision where was expected this phenomenon to happen if it does not happen. So that phenomenon was"
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"text": " Was a hope to see a granularity of space, but it doesn't happen. Now, I haven't yet answered your question, Kurt, why this is not a problem for loop quantum gravity. The answer is that at the time, many years ago, when this phenomenon was suggested by Lee Smalling, a lot of people, including myself, got very excited, so said, OK, so Lee has this"
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"text": " Intuitive picture of what could happen. Does it happen for real in loop quantum gravity? Uh-huh and very soon a number of paper appeared including a paper by mine That convinced the community that no that's not going to happen This this phenomenon that we suggest it's it's it's not predicted by loop quantum gravity and the reason is that"
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"text": " The kind of discreetness is not at all. The idea is not at all that space is like a grid. Space is not like a grid. If it was a grid, it would be a classical grid, not a quantum phenomenon. And it would contradict"
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"text": " A property that it's a property of the theory, uh, which is invariance of the Lawrence transformation, invariance of the, the, the similitude of special activity. Now the theory is invariant under, um, Lawrence transformations and this phenomenal breaks Lawrence invariance. So it cannot be predicted by the theory. Now this is beautiful because, um, uh, it's really a quantum phenomenon. And that's why people get confused about that."
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"text": " Now quantum mechanics allows precisely symmetry and discreteness to happen together. It would not be possible classically. Let me give you an example because I think, or a couple of examples, because these are, I think that they explain. One is that in quantum mechanics, we all know when we study quantum mechanics, the original thing,"
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"text": " is that if you measure some angular momentum, how things rotate or the angular velocity of something, this is quantized. That's one of the quintessential quantum phenomena. So you only measure certain values, certain discrete values. Now, in classical theory,"
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"text": " If the angular momentum was quantized, it meant that along some variable, some directions, things could turn only at certain velocity and not at other velocity. But of course, imagine that you have a body that turns around this axis at a certain velocity. If you look at it rotated,"
},
{
"end_time": 790.06,
"index": 29,
"start_time": 773.251,
"text": " With respect to the new axis the component of the angular momentum is just a little bit smaller not much you reduce it okay and therefore from a rotated frame."
},
{
"end_time": 820.52,
"index": 30,
"start_time": 790.555,
"text": " You would not see the angular momentum quantized. You could change the value of the angular momentum continuously. Right. If you're allowed to rotate continuously. If you're allowed to rotate continuously. So that seems to say that it is impossible to have angular momentum quantized and rotational invariance. But that's wrong, because in quantum mechanics we have angular momentum quantized and rotational invariance. How come? Well, what happened is that when you measure"
},
{
"end_time": 848.012,
"index": 31,
"start_time": 821.323,
"text": " Um, the agreement in one direction and in another direction, uh, the two, um, operations do not commute. So if you, if you measure one, when you measure the other one, you don't have a precise value. You have a probability distribution of values. You can have a probability to measure the same or one smaller or one larger, right? So what changes continuous is a probability distribution."
},
{
"end_time": 877.005,
"index": 32,
"start_time": 849.019,
"text": " while what you actually measure, it's only those particular values. So one should be very careful because the fact that length is quantized in quantum gravity does not mean that, however, does not mean that you're breaking any invariance of the theory. It only means that you go there and make a measurement. You get a finite result."
},
{
"end_time": 906.971,
"index": 33,
"start_time": 877.466,
"text": " If you had it measured from a different Lorentz frame, you would have obtained the same result. Another way of thinking about that is the following. Imagine you take a standard model or any quantum field theory. We know that even in the vacuum, if you measure in a small region, it's a quantum effect, you find particles."
},
{
"end_time": 936.63,
"index": 34,
"start_time": 907.722,
"text": " Right. That's a so-called virtual particles. It's a physical fact. If I go in a small region and check if there are particles, I find them, even the vacuum, because it's only if I if I measure in large region that is back. Now, one could reason that would be the mistake. Oh, if light travels in the vacuum, OK, if the frequency is high, it would see a small region. So it would see this"
},
{
"end_time": 962.244,
"index": 35,
"start_time": 937.21,
"text": " This virtual particles, virtual particles, even without loop quantum gravity, even without loop quantum gravity. And therefore it would slow down because we know that light slows down if there's matter around. OK, so therefore in standard quantum field theory, high energy, high frequency light should go slower."
},
{
"end_time": 981.203,
"index": 36,
"start_time": 962.602,
"text": " But it doesn't. It's not true. It's not correct. And he couldn't because the series it's Lawrence invariant and it learns where the theory light vacuum goes at the speed of light. So the mistake is to take to literally."
},
{
"end_time": 1009.121,
"index": 37,
"start_time": 981.647,
"text": " The granularity of space, particular quantum gravity, and it's beautiful. Quantum gravity doesn't say that space is granular. Quantum gravity says that if you make a small measurement, you see a minimum length. Okay. This is like quantum field theory. Quantum field theory doesn't say that the space is full of particle. The vacuum is full of particle. It says that if you make a measurement in the small,"
},
{
"end_time": 1039.667,
"index": 38,
"start_time": 1009.701,
"text": " You see particles. It's very different things. Light can travel in a vacuum of quantum field theory without seeing anything. But if you make a measurement, you see particles. So similarly, light travels at the speed of light in a loop quantum gravity background space or quantum background space. But then if you go there and make a measurement, you cannot go smaller than something. So this is the"
},
{
"end_time": 1068.302,
"index": 39,
"start_time": 1040.811,
"text": " This was realized long ago. There was a lot of discussion at the time, many papers, quantum gravity and Lorentz invariance, minimal length and Lorentz invariance, it was clarified and the loop quantum gravity community was disappointed at the time because somehow theoretically the window, the possibility of seeing"
},
{
"end_time": 1095.435,
"index": 40,
"start_time": 1069.019,
"text": " A quantum gravity phenomena would have been great i was very excited that that's why i started looking it but the theoretical analysis of the calculation showed okay this effect is not going to happen. Time passes the experimental. Do the experiment the the the observation of the people in astronomy do this measurement they confirm the fact"
},
{
"end_time": 1116.783,
"index": 41,
"start_time": 1095.998,
"text": " On which the community agreed that if the theory is correct, this should not happen. So everything is fine. It's if you want is disappointed. It would have been better if we had a but everything is fine for the theory. Now, fortunately, let me put it this way."
},
{
"end_time": 1142.295,
"index": 42,
"start_time": 1117.125,
"text": " The experimental were completely clear in the paper. They said if a theory predicts granularity, there's a problem for that theory, but they never obviously said this is a problem for loop quantum gravity. In fact, if you want even string theory, they were papers that suggested a similar similar phenomena for string theory. But nobody in fact, in the astronomers paper, they"
},
{
"end_time": 1171.971,
"index": 43,
"start_time": 1142.756,
"text": " quote various people that had suggested similar phenomena in loop quantum gravity string theory. But right. Never there was a clear result of string theory predict that. And therefore the fact that doesn't happen is not a problem for string theory. Similarly, never there was a clear argument that implied that the phenomena come from loop quantum gravity. Now, unfortunately, not from the scientific community, but from external commentators who like to"
},
{
"end_time": 1200.947,
"index": 44,
"start_time": 1172.483,
"text": " Okay, going back to the reason why in quantum field theory, you should not expect a variable speed of light dependent on frequency"
},
{
"end_time": 1226.8,
"index": 45,
"start_time": 1201.34,
"text": " You said that it's only when you measure a small distance that you get these virtual particles. But isn't it technically if you measure any distance, you get virtual particles. They're just of different energies like infrared. If you measure any distance, you're right. But when you measure large distances, so to say, the number of virtual particle goes down, down, down, down."
},
{
"end_time": 1248.968,
"index": 46,
"start_time": 1227.517,
"text": " So for a high energy photon, why isn't it acting like it's measuring at any given point? That's a very good question."
},
{
"end_time": 1277.927,
"index": 47,
"start_time": 1249.667,
"text": " That's a very good question. That's a very good question. It just, it isn't, uh, you try, you go into the equation with theory. It isn't, that's a very good question because somehow once we get to the idea of the virtual particle, uh, we use it, uh, uh, we use it intuitively, but we should be careful because the virtual particle are not real particles. Um, we have this idea."
},
{
"end_time": 1306.237,
"index": 48,
"start_time": 1279.224,
"text": " Yes, just like we talked about science commentators, there's also some science communicators and they show those animations of a jittery space time. And it makes people say, wow, that's so cool, bro. It's so cool, but it shouldn't be taken too literally. That's, that's often the problem with quantum mechanics is counterintuitive."
},
{
"end_time": 1333.66,
"index": 49,
"start_time": 1306.783,
"text": " So you try to make it intuitive, which expresses some aspect, but the analogy is not good, so it doesn't express. For instance, the vacuum of quantum field theory, in some sense, it is full of virtual particles. But as a state, it doesn't change with time. It's stationary. Nothing moves."
},
{
"end_time": 1364.753,
"index": 50,
"start_time": 1334.889,
"text": " So this image of everything moving faster is the sense is completely wrong because it's a stationary state is a solution of the Schrodinger equation where nothing changes. In elementary quantum mechanics, we say that an harmonic oscillator has a ground state and this ground state is a Gaussian mathematically. In the ground state, the oscillator is in the minimal of the energy, but with some probability distribution."
},
{
"end_time": 1392.773,
"index": 51,
"start_time": 1365.384,
"text": " The state never changes. It's just that. If you let it untouched, it stays that. Now, if you look where the particle is, if you try to pinpoint the particle, which is a vacuum state, you don't find a zero. There is a probability you find here, you find it there, because that's the spread, the quantum spread of the state. So it's true that if you look, you find it somewhere. Then you look again, you find it somewhere else. Then you look again, you find it somewhere else. Even if you"
},
{
"end_time": 1417.261,
"index": 52,
"start_time": 1393.251,
"text": " If you try not to disturb too much, which is hard, you have the spread. Okay. But this doesn't mean that there's a jumping particle there. There is a state which doesn't move. The source of the confusion is that we're not talking about particles. Okay. We're talking about quantum objects, which are not particles. So"
},
{
"end_time": 1435.811,
"index": 53,
"start_time": 1417.978,
"text": " A quantum space time is not a discrete space time right is a quantum space time to say that. A quantum space time is a discrete space time is the same misunderstanding saying that a quantum particles a particle of dance dances there there is here there."
},
{
"end_time": 1466.152,
"index": 54,
"start_time": 1436.8,
"text": " Close your eyes, exhale, feel your body relax, and let go of whatever you're carrying today. Well, I'm letting go of the worry that I wouldn't get my new contacts in time for this class. I got them delivered free from 1-800-CONTACTS. Oh my gosh, they're so fast. And breathe. Oh, sorry. I almost couldn't breathe when I saw the discount they gave me on my first order. Oh, sorry. Namaste. Visit 1-800-CONTACTS.COM today to save on your first order."
},
{
"end_time": 1496.169,
"index": 55,
"start_time": 1467.176,
"text": " Hi, I'm here to pick up my son Milo. There's no Milo here. Who picked up my son from school? Streaming only on Peacock. I'm gonna need the name of everyone that could have a connection. You don't understand. It was just the five of us. So this was all planned? What are you gonna do? I will do whatever it takes to get my son back. I honestly didn't see this coming. These nice people killing each other. All Her Fault, a new series streaming now only on Peacock."
},
{
"end_time": 1524.189,
"index": 56,
"start_time": 1497.432,
"text": " When people talk about quantum fields, they often to the lay public give this idea of a temperature field is usually the first analogy. And then they give this idea that it's something akin to an ocean and then there's ripples. But technically speaking in quantum field theory, it's not a field in the same way that we think of a temperature field. It's an operator valued distribution. So they're operators. Is there something else that's going on with"
},
{
"end_time": 1553.968,
"index": 57,
"start_time": 1524.531,
"text": " the discretization of space in loop quantum gravity that is akin to, well, it's actually operator value discretization or something like that. Yeah, to say that something it's an operator, it's some variable, it's given by an operator is precisely to say this variable is a quantum variable, right? It's a mathematical translation of the same thing. And to be a quantum variable, it means that"
},
{
"end_time": 1578.746,
"index": 58,
"start_time": 1555.162,
"text": " The system doesn't, there is a science in which the system doesn't have a specific value of that variable, but you could talk about a probability distribution of that variable. Well, there's quantum probability distribution. It doesn't mean that can be either here or there. It means when it interacts, you can find it here and there."
},
{
"end_time": 1608.302,
"index": 59,
"start_time": 1579.65,
"text": " So that's what we call quantum superposition. I mean, when we say a particle is in a quantum superposition can be here or there, it means if you look, you find it here or you find it there. But you shouldn't think that is here and there because the two can interfere. So if you think that is here or there, you make a mistake about your prediction of the future. So in a sense, it's here and there at the same time."
},
{
"end_time": 1638.643,
"index": 60,
"start_time": 1608.677,
"text": " or more precisely, you can always say that if you look, if you interact with the thing, you find it here and there. But if you want to see what's going to happen later, you have to still consider both possibilities. So that's a quantum superposition. Good. So now if you have a field like the electric field, the magnetic field or the electromagnetic field, quantum field has to be thought as a superposition of different field configurations. So sort of"
},
{
"end_time": 1666.954,
"index": 61,
"start_time": 1639.189,
"text": " A wave function of cloud in the space of possible fields, in the space of possible configurations of the field. So that field is neither here like that nor like that, nor that black level of that. But there's a little bit of those and the quantum state gives a probability to each one of those. When you go to quantum gravity. Gravity, that's what we learned from Einstein, is a geometry of space."
},
{
"end_time": 1696.664,
"index": 62,
"start_time": 1667.346,
"text": " There's a very visual possibility that gravity is just space bending. Good. Beautiful. So in quantum gravity, the geometry of space is not determined. It is a superposition of different geometries. So here around us, space is roughly flat. Mikowski space is a flat space. But if we keep into account quantum gravity,"
},
{
"end_time": 1726.186,
"index": 63,
"start_time": 1697.159,
"text": " In the small, it's a super quantum superposition, all possible fluctuations. And in this quantum superposition, light can still travel at speed of light. But if you go into small and bingo, you want to. So what is the geometry here? You find a geometry which is neither this nor that. You find the geometry which have limitations in length. So there's no structure smaller than a certain length. Yes."
},
{
"end_time": 1752.432,
"index": 64,
"start_time": 1726.493,
"text": " Now, when someone's in high school and they learn about gravity, they learn it's a force. And then some clever undergraduate says, actually, it's the curvature of space time. And then some clever graduate students says, actually, it can be torsion. And then some PhD may say, well, it could be non-matricity or torsion or any combination of that and curvature. Does loop quantum gravity make a definitive statement as to whether"
},
{
"end_time": 1782.671,
"index": 65,
"start_time": 1753.063,
"text": " Gravity is curvature, torsion, non-metricity, or some combination of them? Great question, Kurt. Let me ask, let me answer in steps. First step, you go to high school and they tell you that gravity is a force, okay? Sun and the moon, the sun and the earth pull one another with a force which act at a distance."
},
{
"end_time": 1811.783,
"index": 66,
"start_time": 1784.275,
"text": " Maybe careful. Is that false? Or is that right? I believe that's right. That's not false. It's just approximate. It's an approximate description of reality. Okay. If I say, I look there and I see a forest and you come to me and you say, no, Carlo, you're wrong. It's not a forest. It's a lot of trees with leaves and so on and so forth."
},
{
"end_time": 1840.282,
"index": 67,
"start_time": 1812.415,
"text": " Okay, you have a better description, but it's still a forest. Okay. Yeah. So once you learn general activity, you learn that there's a better description. Why better? Because it, the other description doesn't capture some phenomena is approximate. Okay. So there's a better description in terms of curvature, but in the common situation, which you are, you can still talk, talk about force, not wrong to talk about force, just proper,"
},
{
"end_time": 1869.821,
"index": 68,
"start_time": 1840.759,
"text": " Names for something that happened in when you don't look to in detail. That's the first point. So could we say that Newton theory is an approximation and generativity is a true story? I know, of course, because we know there is quantum gravity. So Newton theory is some approximation. Einstein"
},
{
"end_time": 1899.172,
"index": 69,
"start_time": 1870.128,
"text": " Gravity, it's a much better description of reality. Quantum gravity is going to be a better description of reality. Is that going to be the last ultimate description? No, come on. Your program is titled theory of everything, which is great, but I don't believe we are any close to any theory of everything. Plenty of things we don't know. We don't know what is dark matter. We don't know what is"
},
{
"end_time": 1926.408,
"index": 70,
"start_time": 1899.701,
"text": " It better be, otherwise I'm out of a job shortly. Exactly. So I believe that your show can go on for a long time before we could ever think about the theory of everything. If we get there, we'll talk about, but we're not there by very far. So every theory, it's a way of describing the world at some level of precision. Okay. It's not one right, one wrong."
},
{
"end_time": 1951.937,
"index": 71,
"start_time": 1927.244,
"text": " Okay, having clarified all that, which I think is important because it's not often said. And because we used to say, it's wrong that space time is flat. It's not wrong. It's true. It's just not very precise around here. Space time is flat. Okay, to all degree, I can measure it is flat. So I'm saying something very right."
},
{
"end_time": 1981.51,
"index": 72,
"start_time": 1952.415,
"text": " And if you say, well, but if you measure even better, it wouldn't be flat. True. But to the extent I can measure it is flat. So I'm saying something right. There is a force pulling down. If I let my hand fall by force pull down, it's true. Can you say it's false? No, it's true. Okay. So having clarified that, I get back to your question. Okay. In general activity, in the context of general activity,"
},
{
"end_time": 2012.159,
"index": 73,
"start_time": 1982.568,
"text": " Spacetime, gravity is due to curvature. No torsion, no no metricity, nothing like that. There are attempts to rewrite generativity, if that is possible, or extensions of generativity with some more geometrical, different geometrical, more reach or different geometrical"
},
{
"end_time": 2042.022,
"index": 74,
"start_time": 2012.978,
"text": " Nothing as far as I know that I've given a lot of that has had a lot of success that allows us to understand better. If you go to loop quantum gravity, gravity is not just curvature. It's certainly not no metricity. It's quantum curvature. So gravity is a geometry which is curved, so it's curvature."
},
{
"end_time": 2071.988,
"index": 75,
"start_time": 2042.415,
"text": " But in addition, it can be, as I was saying before, in a superposition of different curvatures. So you don't really change the traumatic language that you use it, but you allow it to be to be quantum, namely your reality to be in a quantum superposition of different geometries. So if loop quantum gravity is correct, if loop quantum gravity is correct, the best way of thinking about gravity is that"
},
{
"end_time": 2098.541,
"index": 76,
"start_time": 2072.722,
"text": " If quantum mechanics is correct, the best way of thinking about particles is still a particle, but it can be spread, can be in a superposition of here and there. And that's the wave function. So if loop quantum gravity is correct, you can still think a gravity of geometry, but this geometry is spread. So you have a quantum superposition of geometry, the wave functions of the geometries."
},
{
"end_time": 2128.046,
"index": 77,
"start_time": 2099.411,
"text": " Have any people gotten so far as to do interpretations of loop quantum gravity in the same way they're interpretations of quantum mechanics? So some may say that the wave function is some pilot and then the particle is just riding atop that pilot. Are there any loop quantum gravitas that would say, well, the curvature is somehow riding atop some pilot curvature? Yes, there are exactly papers that do what you just said."
},
{
"end_time": 2154.65,
"index": 78,
"start_time": 2129.138,
"text": " The quantum gravity is still a quantum theory. So all the mysterious aspects of quantum theory are inherited by loop quantum gravity. So if you want to interpret the quantum theory, it makes sense to it, which I think is not a bad idea to go into this exercise."
},
{
"end_time": 2180.111,
"index": 79,
"start_time": 2155.094,
"text": " There are various ways of interpreting quantum. One is the one you just mentioned, the other is many-world, the other is relational quantum mechanics, which have worked a lot, and each one of these can be applied to loop quantum gravity. So if you want, you can be a loop quantum gravity many-world guy, a loop quantum gravity relation quantum mechanics guy. It seems to me that"
},
{
"end_time": 2209.633,
"index": 80,
"start_time": 2180.538,
"text": " The relational way comes more naturally in November next month. I'm going to philosophy department to give a series of lectures in which that will be one of the main topics at Princeton. I will be I'm invited one month in prison to give a series of lectures and I'm going to I'm going to talk about how to interpret how to make sense of quantum mechanics, keeping in mind that quantum mechanics should include also"
},
{
"end_time": 2228.609,
"index": 81,
"start_time": 2210.094,
"text": " So can you explain, just give a brief outline of what relational quantum mechanics is"
},
{
"end_time": 2253.524,
"index": 82,
"start_time": 2229.019,
"text": " And then also explain what it's like to articulate an interpretation of quantum mechanics, because many people as they're showering or they're driving, as they're going about their day, they're like, I have an interpretation of quantum mechanics. But is there something that's more symbolic or more quantitative, more rigorous, more precise or stringent than just surmising on your own about the interpretations of quantum mechanics?"
},
{
"end_time": 2283.217,
"index": 83,
"start_time": 2254.735,
"text": " The point is that if you if you take a shower you come out with an idea and you start telling it around very soon somebody would tell you about look think carefully if you want to say is correct then this and this and this and you say ah yeah you're right it doesn't work so"
},
{
"end_time": 2305.282,
"index": 84,
"start_time": 2284.138,
"text": " Most way of thinking either don't work or. Force us to some very. Unexpected consequence so the discussion. About the definition of quantum mechanics is a discussion about this consequences and the strange this."
},
{
"end_time": 2330.213,
"index": 85,
"start_time": 2306.476,
"text": " When I make a measurement, I measure the particle and then I split with a Stengel algorithm. Then I see whether it's here or there. So I've measured the spin of the particle and can be one direction or the other. This is a thing that can be done in a laboratory. A grad student can go in a laboratory of physics and do this measurement. And then something strange happens because"
},
{
"end_time": 2355.776,
"index": 86,
"start_time": 2330.623,
"text": " Quantum theory doesn't really tell you what's going on. It tell you only you have a probability of seeing this, a probability of seeing that. Now, the various ways of thinking about that. One way, for instance, is that, well, there is much more than what the theory is telling you. The theory is telling you that this wave, this superposition, but as you were saying,"
},
{
"end_time": 2383.865,
"index": 87,
"start_time": 2356.391,
"text": " In addition, there is also true particle that is riding the wave and going here and there, which we didn't know where it was exactly before. So you add a lot of extra equations to the theory, extra variables, which we don't see, but that's supposed to make sense of what is going on. OK, some people say, why do you want to add plenty of things which you never use? Other people say that's a different interpretation of quantum mechanics. Oh, but"
},
{
"end_time": 2414.445,
"index": 88,
"start_time": 2384.497,
"text": " It's not really that either one thing happened or the other thing both things happen You see one thing happen because you yourself become two There's one you that sees up once you that sees down There's never a moment in which something strange happened that the particle CO that the particle is still in both places But you also become in both places. So there's one you that sees up when you assist them Okay, that takes away some problems but"
},
{
"end_time": 2441.715,
"index": 89,
"start_time": 2415.111,
"text": " Then we have to think, Kurt, that you and I are just one version of zillions of copies of us that doing other things. And so, so whatever you try to do, you have to clash something harder to digest. Is this an empty conversation? No, I don't think so. Because I think through this conversation, we're going to get some clarity how to think about quantum mechanics. When Newton did his"
},
{
"end_time": 2470.35,
"index": 90,
"start_time": 2442.415,
"text": " Newton and Galileo and Huygens and Kapler and everybody else got to the Newtonian mechanics. It was a long discussion because people were saying, well, wait a moment. Can I say something is moving or not? In Newtonian mechanics, you cannot. There's no meaning in saying something is moving or not. You can always say something is moving with respect to another thing or not. Okay."
},
{
"end_time": 2492.637,
"index": 91,
"start_time": 2471.22,
"text": " That's incredibly strange. It is strange, but we have digested it. We have digested exactly what we have learned. We have learned that there's no meaning in being still versus moving unless it's referred to some object. And so it was a strange message we have understood about the world. Now it's clear."
},
{
"end_time": 2520.009,
"index": 92,
"start_time": 2493.422,
"text": " We haven't yet understood what is a strange message about the world that has come with quantum mechanics. I believe I have my own way of viewing. I'm convinced of my own, but until it becomes common, it's not an answer. People who are proponents of the many worlds will say that what they're doing is following the math. They'll say this phrase, quote unquote, like we take Schrodinger's equations seriously."
},
{
"end_time": 2548.336,
"index": 93,
"start_time": 2520.674,
"text": " But yet yours is an alternative that doesn't do away with Schrodinger. So are they incorrect in saying that they're just following the math? They're actually following the math plus putting an interpretation on, or is it true that you can from the math in further interpretation of many worlds? I don't think they're exactly correct. They do mean something. They're not stupid."
},
{
"end_time": 2578.933,
"index": 94,
"start_time": 2549.121,
"text": " They have a way of thinking they're very smart people out there. But I think it's not exactly correct that they follow the mark for the following reason. If you if you go to school and follow a good class in in quantum mechanics, at some point you get a clean math. OK. And the math, it's essentially the Schrodinger equation plus the operators"
},
{
"end_time": 2605.555,
"index": 95,
"start_time": 2579.514,
"text": " Plus the eigenvalue eigenvector construction that give the probabilities of seeing one thing and the other. So the Mac has various parts. What they do is trying to do the following. Forget this, forget this, just skip this and follow the math and see if you can get the other one."
},
{
"end_time": 2636.237,
"index": 96,
"start_time": 2607.193,
"text": " So they make a choice. They make a choice at the beginning of the of the mathematical book, the so-called postulates of quantum mechanics. They discard the projection postulate. They discard the measurement postulate. They discard the value postulate. They just keep the quantum state and the way it evolves. And they say this is a two month. But I wouldn't say that this is a two month. I would say that the relevant I would say that the relevant math is the rest."
},
{
"end_time": 2662.654,
"index": 97,
"start_time": 2636.852,
"text": " Interesting. Yeah. So what they say is they take away part of the mathematics of the ways it's commonly presented and they try to recover it just from the first bit. To some extent they do but with a very long and complicated story and a lot of, you know,"
},
{
"end_time": 2689.241,
"index": 98,
"start_time": 2663.541,
"text": " this complicated idea that implies that in some sense you and I are just one of many copies. So you have to accept something very strange about reality if you go that way. The idea that this part of the math, it's not true"
},
{
"end_time": 2716.015,
"index": 99,
"start_time": 2689.684,
"text": " Going back to the Chinese experiment, did they outrule even something like Wolfram's model, which is about space-time atoms, or do they just put a bound? Oh, that's a good question. I actually don't know. I should, I should. They definitely,"
},
{
"end_time": 2744.599,
"index": 100,
"start_time": 2716.476,
"text": " rule out certain things. I mean, that many things, any naive idea of that, that, you know, want to make quantum gravity. Most people would agree gives a finite length. OK, the question is how to how this finite length is. It's actually coming in in nature. They rule out the idea that this finite length is actually a finite grid in space."
},
{
"end_time": 2772.125,
"index": 101,
"start_time": 2745.333,
"text": " That's out. It would definitely give this effect and the effect is not there. I would suspect that it could be used to rule out any theory which is non-quantum. Wolfram, through in a sense, want to derive quantum from something else."
},
{
"end_time": 2796.971,
"index": 102,
"start_time": 2772.841,
"text": " And there's a granularity, which is classical. So it might be that gives a problem to that theory, but I'm not sure because I've not looked into the, into the details. And, um, you asked, uh, it's just putting a bound on it. Yeah. I can't see why it wouldn't just put a bound. Look,"
},
{
"end_time": 2823.063,
"index": 103,
"start_time": 2798.422,
"text": " Theoretical physics is less clean than the ways usually sold. You can always change parameters and save yourself. Theories are not really ruled out by, it's very rare that theories are ruled out by just an experiment or a group of experiments."
},
{
"end_time": 2838.831,
"index": 104,
"start_time": 2823.592,
"text": " Theory usually come with flexibility. Theoreticians can add flexibility and so new experiments you can just patch up your theory. The point is that"
},
{
"end_time": 2867.637,
"index": 105,
"start_time": 2839.428,
"text": " Yes, in the loop quantum gravity case, it's not flexibility that is evading this experiment. Right. That's correct. It's that loop quantum gravity didn't predict what they're saying it predicted to begin with. That's correct. That's correct. Right. So what would commonly happen is that some some measurement are hard to fit into a theory, harder and harder. And at some point you say, no, come on."
},
{
"end_time": 2896.954,
"index": 106,
"start_time": 2868.336,
"text": " Look, take Newton's theory, right? Where did Newton's theory go wrong? Newton's theory go wrong in Mercury. Mercury essentially doesn't do ellipses. The ellipses turn, the periallium ellipses turn in a way that doesn't fit with Newton's theory. That's a fact, we know. And in fact, general relativity account for this shift of the periallium perfectly, this marvelous well. But when it was measured,"
},
{
"end_time": 2916.903,
"index": 107,
"start_time": 2897.312,
"text": " Did people say, oh, that kills Newton theory? No. People say, oh, yeah, but maybe the sun is not really a sphere. Maybe there's another little planet inside Vulcan that gives this effect. Or there's another planet. Yeah. Maybe this, maybe that. They were all open options."
},
{
"end_time": 2946.442,
"index": 108,
"start_time": 2917.875,
"text": " So, it didn't kill Newton's theory. It was a trouble for Newton's theory. He had to do funny things to fit it. And when generativity came out and gave bingo, exactly the right number in such a beautiful, marvelous, clean way, people say, oh no, that has to be a better explanation. So why do you think these polemical commentators, as you put it, are so eager to say there's a death blow to loop quantum gravity?"
},
{
"end_time": 2974.957,
"index": 109,
"start_time": 2947.858,
"text": " I think the polemic between loop quantum gravity string theory sells a lot. People get excited, look, this is winning, this is losing. And of course, if you can say something strong like that, it looks"
},
{
"end_time": 3002.756,
"index": 110,
"start_time": 2975.589,
"text": " It looks raising a polemic and it looks, uh, science is, it's slow. It's a lot of debates. Things are not clear. It takes time. Um, it's not about big, uh, big emotion. I mean, sometimes they're big emotions. I mean, the fact that, uh, everybody expected super symmetry was not found was, was a big shock for the community. I mean, there were articles written by scientists in the, in the, in some Le Monde."
},
{
"end_time": 3032.722,
"index": 111,
"start_time": 3003.37,
"text": " The French journal saying, Oh, it's a big crisis for the physics. Uh, but even there that does this rule out string theory? No, of course it doesn't. Um, it's not that because there were no, uh, because string theory doesn't really uniquely predict low energy supersymmetry. Um, as I said, right. I think commenting about science, it's not."
},
{
"end_time": 3060.538,
"index": 112,
"start_time": 3033.422,
"text": " It's really commenting about clear cut things. And in this case, I don't know. I mean, I don't know exactly what what has happened, but in that there have been a little bit of acrimony between strings and loops, which is stupid. I think we just don't know. I mean, we should each each one of us. And in the discussion is good to say, look, you're wrong here, you're wrong here. That's that's how the discussion"
},
{
"end_time": 3085.794,
"index": 113,
"start_time": 3061.084,
"text": " Um, but, uh, but, uh, definitely nobody's dead. No theory is dead. And, uh, um, the, we all wish things went faster, but science has never been fast. Fundamental science has never been fast. It takes decades. You wish things went faster except the high energy photons."
},
{
"end_time": 3117.5,
"index": 114,
"start_time": 3087.807,
"text": " That's correct. Absolutely. Then the counter argument that I've read in the comments from some of the commentators and some of the comments themselves say, OK, well, then that either means that loop quantum gravity was disproven or that it's untestable. But it sounds to me like what you're saying is that it's either disproven or this wasn't a test for it, not that this is untestable. Absolutely correct. That was not a test for it since the very beginning. I mean, there have been a discussion within a theoretical discussion within the community"
},
{
"end_time": 3144.48,
"index": 115,
"start_time": 3118.319,
"text": " And the outcome was clear. No, this is not a test of the theory. People are working hard for finding tests of the theory or at least measurement that could help support the theory or help take away credibility in the theory. So there's a lot of that's what many people look at gravity doing right now."
},
{
"end_time": 3168.234,
"index": 116,
"start_time": 3145.299,
"text": " I have a quote from Sabine Hassenfelder from the video that I sent you and she said that the smallest possible area which we talked about is not compatible with Einstein's theory and you need to modify Einstein's theory to do that and if you do you'll find that the speed of light is not constant. So that was the argument of Smolin back then and then she said the opposite was"
},
{
"end_time": 3196.578,
"index": 117,
"start_time": 3168.592,
"text": " vocally represented by Carlo Rovelli who said, no, no, no, we can recover the symmetries of Einstein by averaging over all possible ways to take space apart into areas. Right. And yes, I think you can do that. This is her now. But in this case, you effectively get back areas of zero size because there will always be some observer for whom area is arbitrarily small. And you go back to the problem with singularities that loop quantum gravity was trying to avoid."
},
{
"end_time": 3226.869,
"index": 118,
"start_time": 3197.159,
"text": " So basically, you can't have your cake and eat it too. And I'm curious what your response is to that. Areas of zero size are part of the theory and are not the, there's nothing to do with the singularity. The spectrum of the area operator includes a minimal area, which is sort of roughly the plank area, the square of the plank length, but also zero, of course."
},
{
"end_time": 3254.121,
"index": 119,
"start_time": 3227.637,
"text": " The question is the area of what, right? So if I take two, let's say, let's let's speak in terms of length, which is easier. If I pick two points, I can ask what is the length between the two? OK, if I if I say, is there a greed with some length space, I can ask what is the space of that hypothetical greed?"
},
{
"end_time": 3283.063,
"index": 120,
"start_time": 3254.906,
"text": " If I make a measurement of a diffusion of particle by something, the diffusion number is measured in terms of area. So that's another. So loop quantum gravity says that when you measure something, you get an eigenvalue which could be zero or could be one plank area or two plank areas or whatever."
},
{
"end_time": 3315.299,
"index": 121,
"start_time": 3285.572,
"text": " This is perfectly compatible with the fact that, let me put it in this way, from the point of view of a photon, it's a very imaginative language, who's traveling a distance from a different galaxy to us, it is like the minimal area was zero. True. Okay. It's in a regime of curvature, which is very small."
},
{
"end_time": 3342.654,
"index": 122,
"start_time": 3316.323,
"text": " And that particular sort of measurement, so to say, done by the proton is like the minimal area was zero. It's not, it's the minimal area of its own evolution, so to say. That's nothing to do with the singularity. Singularity, it's what happens at high curvature. For instance, the central black hole or early universe near the Big Bang, where the"
},
{
"end_time": 3370.435,
"index": 123,
"start_time": 3343.217,
"text": " The curvature space-time is very high and what loop quantum gravity says is that there's a maximum curvature because somehow you imagine you have the little sphere, curvature is maximum because the sphere cannot be smaller than a blank area."
},
{
"end_time": 3385.606,
"index": 124,
"start_time": 3371.323,
"text": " Think Verizon, the best 5G network is expensive? Think again. Bring in your AT&T or T-Mobile bill to a Verizon store."
},
{
"end_time": 3412.329,
"index": 125,
"start_time": 3390.077,
"text": " Your planet is now marked for death."
},
{
"end_time": 3441.869,
"index": 126,
"start_time": 3413.37,
"text": " So the way"
},
{
"end_time": 3464.445,
"index": 127,
"start_time": 3442.688,
"text": " The bound on the size of things come in to help with the singularities. It has nothing to do with what happened near flat space with this light traveling. Carlo, you know that Sabine just had a rebuttal or retort about this exact issue and she said, and I quote,"
},
{
"end_time": 3493.148,
"index": 128,
"start_time": 3465.811,
"text": " If you quantize the angular momentum operator, the spectrum of the eigenvalues is discrete and that doesn't violate rotational invariance. Carlo claims that it works similarly in loop quantum gravity with Lorentz invariance, but it doesn't. If you calculate the expectation value of the angular momentum operator, it will respect rotational symmetry, yes. However, that's because its eigenvalues are both positive and negative, allowing it to average to zero."
},
{
"end_time": 3510.469,
"index": 129,
"start_time": 3493.695,
"text": " In contrast, the eigenvalues of the area operator in loop quantum gravity are all positive and have a lower bound. Consequently, the expectation value for the area in loop quantum gravity is bounded from below and it can't transform under the Lorentz group."
},
{
"end_time": 3537.056,
"index": 130,
"start_time": 3510.811,
"text": " This is a mathematical fact. Of course, Carlo knows this. Everyone who works on this stuff knows it. They just repeat this angular momentum story because it sounds superficially plausible if you don't know anything about quantum physics. Now you might say, all right, the area can't transform under Lorentz transformation. Maybe there's some quantum stuff going on. Some weird things happen. Yes, actually Carlo and Simone mentioned that in their paper."
},
{
"end_time": 3563.882,
"index": 131,
"start_time": 3537.483,
"text": " That's also why some people in loop quantum gravity suggested there ought to be deviations from Lorentz invariance. I tried to tell them this but they didn't want to hear that. So what should we hear? It's a technical misunderstanding. Sabine has an argument and I think I understand where is the misunderstanding here."
},
{
"end_time": 3585.35,
"index": 132,
"start_time": 3564.377,
"text": " She heard many times there is a minimal again value of the area and is a sort of plank area squared the plank area the length length plank length square a plank area this is what is said usually it's it's not said correctly for obviously i mean the minimum value zero."
},
{
"end_time": 3610.674,
"index": 133,
"start_time": 3586.271,
"text": " It's a minimal non-zero eigenvalue, which is a Planck area. So in other words, what loop quantum gravity predicts is that there's a zero value and then the next one, it's a finite distance. Yes. So you cannot get any eigenvalues smaller than the minimal and non-zero. Sure, there's a gap. There is a gap. But somehow,"
},
{
"end_time": 3640.998,
"index": 134,
"start_time": 3611.169,
"text": " Sabina misunderstood that for some reason, maybe because in some popularization articles or books was not said precisely. So she thought that there is no zero eigenvalue. And therefore she, if there was no zero eigenvalue, she will be correct and sort of complaining, wait a minute, you cannot, Lawrence transformed the mean value of the arbitrary small, which is what is needed for Lawrence invariance."
},
{
"end_time": 3665.128,
"index": 135,
"start_time": 3641.51,
"text": " If there wasn't a zero value, but there is a zero value. So I think maybe she never read the actual papers with the quantization of the area. What makes the loop quantum gravity finite, no ultraviolet divergences is not that any possible area, it's always bigger."
},
{
"end_time": 3690.162,
"index": 136,
"start_time": 3665.589,
"text": " Then the plank area, it's that any possible known zero area, it's bigger for that is there a gap. So once this is clarified, her argument disappear and she was very nervous. I think she she couldn't she had a wrong idea in her mind that it was no zero gain value. That's made him made her she should have perhaps"
},
{
"end_time": 3720.384,
"index": 137,
"start_time": 3690.708,
"text": " So this argument of a non-zero expectation value, does it not still apply if you have zero and then positive values and you average that, wouldn't it still be non-zero? No, no. The average can be as small as you want. That's the point. You can continuously make the average as small as you want, including zero."
},
{
"end_time": 3749.104,
"index": 138,
"start_time": 3720.828,
"text": " It's a possibility. If you, uh, in area, uh, becomes arbitrarily small. If you look from a arbitrary boosted, uh, uh, frame. So that's required by law. It's invariant. So can we make it arbitrarily small? Of course we can make it zero. Okay. In other words, the quantum state can rotate."
},
{
"end_time": 3776.374,
"index": 139,
"start_time": 3749.855,
"text": " from maximum probability for finite eigenvalue to increasing probability to zero eigenvalue. And that's exactly what happened in the Lorentz transformation of an eigenstate of the area. It transformed in a linear combination of the other. If you go all the way through to the end, you get just to zero. So you can Lorentz boost it below the Planck length squared?"
},
{
"end_time": 3790.606,
"index": 140,
"start_time": 3776.903,
"text": " Oh yeah, yeah. The difference here is the difference between expectation value and eigenvalue, right? So quantum mechanics says if you make one measurement of one quantity, just one, you can only get an eigenvalue."
},
{
"end_time": 3816.63,
"index": 141,
"start_time": 3792.483,
"text": " That's what quantum mechanics is. The expectation value is the average between them. So electron has spin up and spin down, but technically its expectation value is zero then, but there's no spin zero electron. It depends on the state. I mean, a single atom, if I give you an atom, it can be in a configuration such that the"
},
{
"end_time": 3846.988,
"index": 142,
"start_time": 3817.551,
"text": " You see necessarily with, suppose it's a spin one thing. There are three possibilities. Spin can be up, down or zero. So now suppose you see it with spin up. So now you rotate your head. Classically, the component of the spin in that direction will be zero. So you continuously rotate the component"
},
{
"end_time": 3876.51,
"index": 143,
"start_time": 3847.466,
"text": " In zero from from from one to zero. Now, if you measure various types, you rotate the atom, you don't get something in between. OK, suppose you rotate by by half of 45 degrees, you make a measurement. Then quantum mechanics says you have a half probability of measuring still one and half probability of measuring zero. So the average transform continuously, but what do you measure in one shot?"
},
{
"end_time": 3904.531,
"index": 144,
"start_time": 3877.961,
"text": " It depends on the probabilities and the expectation value. So for consistency, you want the expectation values to be able to change continuously when you make continuous rotation or continuous boost and sublimation. That's okay, because there are probabilities. There's nothing really mysterious. It's just quantum mechanics 101. It's not a deep, profoundly quantum stuff. I see."
},
{
"end_time": 3935.469,
"index": 145,
"start_time": 3905.52,
"text": " Sabin somehow was confused because she will say but you cannot go smaller than the minimal area if there's nothing else you can go to okay because she forgot that there is a the error operator has also the the zero eigenvalue in fact the eigenvalues of the error operator given by the square root of j j plus one with j is a half integer so it can be zero one half one sort of this discrete spectrum"
},
{
"end_time": 3961.954,
"index": 146,
"start_time": 3935.828,
"text": " times 8 h bar g pi. And j can be zero. If j is zero, the area is zero. It's in the formula for the value of the area, which is in all the papers or the books. Does this whole brouhaha about loop quantum gravity being either testable or the expectation is not zero, et cetera, does this frustrate you?"
},
{
"end_time": 3987.449,
"index": 147,
"start_time": 3962.961,
"text": " No, I mean, it's not look quite so testable. It's my last paper, which was published on physical review letter a couple of weeks ago by myself, Alejandro Pérez and Mario Cristodulo, who are respected in Vienna and in Marseille. It's an idea for a possible test of loop quantum gravity."
},
{
"end_time": 4014.65,
"index": 148,
"start_time": 3987.79,
"text": " Uh, that is published. So it's not because one particular proposal of testing it, um, did not materialize and then therefore the theory and untestable. No, I mean, this is, it will be silly. Um, if you, if you cannot test the theory in a certain manner, it doesn't mean that there is untestable. And in fact, there are many other ideas of how to test it. Unfortunately, as we all know, uh,"
},
{
"end_time": 4045.043,
"index": 149,
"start_time": 4015.862,
"text": " No theory of quantum gravities for the moment has obtained a positive confirmation, a collaboration. Otherwise we would, you know, claim Nobel prizes and be happy and celebrate. And we hope so. These theories are tentative theories. Loop quantum gravity, string theories, the others are ideas of how the world could be. And that's what science should do. I mean, should should should try to"
},
{
"end_time": 4072.602,
"index": 150,
"start_time": 4045.93,
"text": " find possible theories. I think it's remarkable that after many years, we have at least some candidate theory of quantum gravity. It's not true anymore that, oh, we know nothing about, we don't know how the world could be compatible with generativity of quantum mechanics. The world could be like global quantum gravity, as far as we know. Is it, oh, before believing it, we need a corroboration. We haven't got it. They're working."
},
{
"end_time": 4100.606,
"index": 151,
"start_time": 4073.336,
"text": " This Lawrence transformation stuff was one attempt 15 years or 20 years ago. There have been others with cosmological observations now with dark matter, measuring Planck scale things. We hope that at some point, some of these possibilities will be confirmed. What's the reaction been like in the community about this recent fuss over the Chinese experiment and then the subsequent"
},
{
"end_time": 4126.664,
"index": 152,
"start_time": 4100.913,
"text": " popular science articles about it, or not articles, but sometimes videos about in the community in the in the with respect to the experiment. No, I think it was not even discussed because the large majority of the community, I would almost all the community was already convinced that that effect should not happen. So it was not a surprise. In fact, I didn't"
},
{
"end_time": 4154.053,
"index": 153,
"start_time": 4127.295,
"text": " I don't remember a colleague of my pointing to this experimental thing. The tension was not at all on those Lorentz violations. The tension was on cosmology, on dark matter, on black holes, on other stuff. As you say, in the popularization things,"
},
{
"end_time": 4186.8,
"index": 154,
"start_time": 4157.534,
"text": " Look, I got some people writing to me saying, oh, come on, look what these people are writing. Why don't they actually read the papers instead of instead of commenting? I don't I don't I definitely don't want to be negative. I think it's great that this popularization is great. But I think there are different styles of doing popularization. There is a style in which you, you know, you give opportunity to talk, you listen, you make comment, you try to simplify."
},
{
"end_time": 4209.548,
"index": 155,
"start_time": 4187.927,
"text": " As you know, on theories of everything, we delve into some of the most reality spiraling concepts from theoretical physics and consciousness to AI and emerging technologies to stay informed"
},
{
"end_time": 4237.944,
"index": 156,
"start_time": 4209.616,
"text": " in an ever-evolving landscape, I see The Economist as a well-spring of insightful analysis and in-depth reporting on the exact topics explored here and even more. The Economist's commitment to rigorous journalism means you get a clear picture of the world's most significant developments. Whether it's the latest in scientific innovation or the shifting tectonic plates of global politics, The Economist provides comprehensive coverage that goes beyond the headlines."
},
{
"end_time": 4267.773,
"index": 157,
"start_time": 4237.944,
"text": " What sets the economist apart is their ability to make complex issues accessible and engaging, much like we strive to do in this podcast. If you're passionate about expanding your knowledge and gaining a deeper understanding of the forces that shape our world, then I highly recommend subscribing to The Economist. It's an investment into intellectual growth, one that you won't regret. As a listener of Toe, you get a special 20% off discount. Now you can enjoy The Economist and all it has to offer for less."
},
{
"end_time": 4296.852,
"index": 158,
"start_time": 4267.773,
"text": " Head over to their website www.economist.com slash totoe to get started. Thanks for tuning in. And now back to our explorations of the mysteries of the universe. We super-popularizes want to put themselves for judges of what is going on. And that's, I don't think it's very useful. Okay. Speaking of black holes, what is the firewall? What is the information paradox? And what does loop quantum gravity say about those two?"
},
{
"end_time": 4306.954,
"index": 159,
"start_time": 4297.671,
"text": " Okay, so we know that black holes are there and we are all convinced also it is."
},
{
"end_time": 4335.742,
"index": 160,
"start_time": 4307.619,
"text": " uh... almost all convinced that uh... this is strange phenomena which is hooking evaporation hooking evaporation is a phenomena for which if you take a black hole and you let it stay there isolated on touch for a long time it becomes smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and smaller and"
},
{
"end_time": 4356.186,
"index": 161,
"start_time": 4336.067,
"text": " Both sides of a disagreement, which I'm going to tell you in a moment, agree that the whole evaporation happens. Now, what we don't know and what people have different opinions about is what happened at the end of the operation."
},
{
"end_time": 4372.5,
"index": 162,
"start_time": 4357.619,
"text": " There is a a part of the community to which i belong which is mostly made by relativists or loop quantum gravity people or this kind of that thinks that."
},
{
"end_time": 4402.671,
"index": 163,
"start_time": 4373.285,
"text": " At the end of the operation, you're in a deep quantum gravity regime because the black hole is very small at this point. And a small black hole doesn't mean you're close to no quantum. It means you're very quantum because you have a very high curvature. That was what I was saying before. The horizon is super curved. And just around it, the curvature is blank. So you're in a deep quantum gravity regime. So what people expect in my community"
},
{
"end_time": 4429.821,
"index": 164,
"start_time": 4403.2,
"text": " is that something quantum happens at that point. The other part of the community, which is mostly in the string world, that's another case in which there is a string loop or sort of a stringy world or loopy world, because it's much larger than the people do the actual theories, expect is that when the black hole is very small, poof, disappears. There's nothing, nothing at all there."
},
{
"end_time": 4460.555,
"index": 165,
"start_time": 4431.476,
"text": " Now, why I consider that implausible? Because if you look at the geometry, when the horizon becomes very small, inside is still very big. There's huge stuff inside. That's gravity, right? In a small sphere, you can fit a big volume because space-time is good. So you can imagine a flat thing with a small throat and then a huge bottle inside or a huge pit inside."
},
{
"end_time": 4488.183,
"index": 166,
"start_time": 4461.118,
"text": " So that's black hole. It's very small, but this long thing inside. So what I expect to happen is that there's a quantum transition that allows this internal part to come out. So all the information inside slowly can come out. And so what I expect to happen is that the small black hole, its remaining is becoming a remnant."
},
{
"end_time": 4515.981,
"index": 167,
"start_time": 4488.558,
"text": " It's remaining such, remaining small from outside for a very long period then becomes what is called a white hole, which is a hole from which the inside can come out. So the information inside can come out. Now, if you instead believe that the black hole is disappearing, you're led to believe that the information inside is lost."
},
{
"end_time": 4544.804,
"index": 168,
"start_time": 4517.193,
"text": " or has to come out somehow before. And a lot of people in the string world got convinced that the information has to come out before a certain number of arguments. And so I've devised all sorts of hypothetical phenomena that bring information out before. So you have black hole things fall inside, information inside. It should come out before the end of the evaporation, they think."
},
{
"end_time": 4575.111,
"index": 169,
"start_time": 4546.954,
"text": " If you believe that things come out outside, you also believe that when the black hole is small, the information inside, it cannot be large. Okay. So I think that you can have a small black hole with a huge information inside. Okay. And people say, no, no, no, because a small thing cannot hold a lot of information, which is true of flat space, but it's not true of curved space. Okay. So they have this, uh,"
},
{
"end_time": 4602.5,
"index": 170,
"start_time": 4575.691,
"text": " Strong holographic hypothesis as they call them or the central dogma as Maldacena, Juan Maldacena calls it correctly. So because the dogma is not something we know about nature. It's something we think they think could be add to nature that the small black hole doesn't have information anymore. So when it disappeared, there's no information there. Everything has come out before. So they have"
},
{
"end_time": 4632.824,
"index": 171,
"start_time": 4603.029,
"text": " A puzzle. How does information come out? And that's the so-called black hole information puzzle. And there are ways to describe it and to solve it, which basically amounts to not believing quantum field theory, to thinking that quantum field theory goes wrong in some strange, mysterious way."
},
{
"end_time": 4643.985,
"index": 172,
"start_time": 4633.609,
"text": " The firewall that you mentioned is related to that."
},
{
"end_time": 4669.957,
"index": 173,
"start_time": 4644.514,
"text": " It's like there is a super high energy so you get sort of burned if you go if you go there. My part of the community, which include myself and many people who look at gravity and many people also for classical turn activity, do not buy this story and think that information comes in, stays in all the way through the evaporation and then comes out slowly from remnants and"
},
{
"end_time": 4700.094,
"index": 174,
"start_time": 4671.169,
"text": " I colleagues are trying to use this idea to see if this remnant can be observed. And my last physical regulator is exactly an attempt to describe a device that could measure in principle this remnants. Now, when I speak to people on this channel, often when they propose some new particle or something akin to a remnant, they'll say, and that could be dark matter. In your case, do you also think it could be dark matter?"
},
{
"end_time": 4714.497,
"index": 175,
"start_time": 4700.572,
"text": " Yes, of course, because that one is the biggest, I would even say almost the only concrete mysterious thing that doesn't fit with our"
},
{
"end_time": 4745.316,
"index": 176,
"start_time": 4715.384,
"text": " With our basic equations, right? Are the remnants so small that they're like neutrinos and could be going through us millions or trillions of times a second and we wouldn't feel them? Are they akin to that or no? We would definitely feel them if they went through us. No, no, it's a first. We would not feel them, not because they're small. Well, they are small. They are super small, but because they only interact gravitationally. So it would not interact a little magnetically, would not interact with a strong force, would not interact with a weak force. So they could go through you."
},
{
"end_time": 4774.667,
"index": 177,
"start_time": 4745.998,
"text": " And the effect to you would be just like the Newtonian attraction of a hair moving next to you, which is absolutely minimal. I thought that they're also exporting something like radiation, but extremely slowly from the information content on the inside. Yeah, they're they're also losing the information outside, but that's extremely slowly, extremely low energy, very, very long wavelength."
},
{
"end_time": 4802.466,
"index": 178,
"start_time": 4775.179,
"text": " So we looked into that. We have some paper about that. I don't think that would be measurable at present. I couldn't come out with any, um, any way of measuring that radiation at present while the passage of this thing. So if dark matter is these things and it could because dark matter, as far as we know, interact only gravitationally and these things interact only gravitation. So they're good. They're good candidate of dark matter. Of course, you know,"
},
{
"end_time": 4826.357,
"index": 179,
"start_time": 4803.097,
"text": " They're one of the 10, as you say, they're one of the 20 candidates on dark matter around, but we don't know what's dark matter. So, and I like these candidates because they only, they only, they don't require extra physics in the sense. It's not a new particle. It's not a new field. It's a new, it's just, just general activity and quantum mechanics together. Right. So generative quantum mechanics who make a black hole."
},
{
"end_time": 4852.039,
"index": 180,
"start_time": 4827.056,
"text": " weight becomes very small because one of these ram in the so you have plenty of this so if in the history of the universe and that has to be understood uh somehow many of these things would produce the we could have a lot of these things around that they could be behave they would behave like dogmatic so neil tarak believes that they're right-handed neutrinos that's another of the hypothesis um"
},
{
"end_time": 4881.664,
"index": 181,
"start_time": 4852.5,
"text": " The last time when we spoke over email, I told you about the Yoni Dilemma in category theory."
},
{
"end_time": 4908.899,
"index": 182,
"start_time": 4882.108,
"text": " because I saw it as relating to relational quantum mechanics, because in the Unidolk Lemma, it says that an object in category theory is fully understood in terms of its relationships, so its morphisms, with all other objects, as long as you're in something called a locally small category. In other words, some people use this to say that an object is completely defined by its relations to other objects."
},
{
"end_time": 4937.5,
"index": 183,
"start_time": 4909.838,
"text": " that you can either define the relations to objects or you can define the object itself. It's dual. It's exactly the same. And then that had me thinking, hmm, I wonder if that has implications for relational quantum mechanics. Yeah, the answer is I don't know. I mean, what you characterize as the main idea behind this theorem is exactly the idea of traditional quantum mechanics. Right. So, um,"
},
{
"end_time": 4967.073,
"index": 184,
"start_time": 4938.507,
"text": " an object is defined by all the relation that has around it. So if you want to think as an object by itself, there's no meaning to the object by itself. And category theory, it's certainly a natural mathematical language for talking about these things, because in a sense, it's a"
},
{
"end_time": 4994.821,
"index": 185,
"start_time": 4967.346,
"text": " It's born with this idea that it's a structure, the largest structure that determines what we're talking about. But I am not competent enough to use category theory. Maybe I should. And in fact, people have been telling me, why don't you? People get in love with it when they study it."
},
{
"end_time": 5023.814,
"index": 186,
"start_time": 4995.469,
"text": " Um, oh yeah. And, uh, because obviously there's a great beauty there. Uh, but this complicated to, to get into that, uh, because it's a, it's not just a mathematical theory. It's a mind frame. I would say, um, and I'm not sure, uh, the extent in which it could be useful or could just, uh, um, or is necessary."
},
{
"end_time": 5053.234,
"index": 187,
"start_time": 5024.377,
"text": " For for articulating the idea, uh, underpinning relational quantum mechanics, but also much more trivially and, and, and simply, um, uh, I'm afraid it would, uh, make people, um, uh, stay away from quantum mechanics articulated that way. I think there's been some, some people in French that France that looked into that, but I don't remember right now."
},
{
"end_time": 5059.735,
"index": 188,
"start_time": 5054.804,
"text": " I wish I could be smarter and know more things and add this to the things I'm doing."
},
{
"end_time": 5087.841,
"index": 189,
"start_time": 5061.271,
"text": " Hola, Miami! When's the last time you've been in Burlington? We've updated, organized and added fresh fashion. See for yourself Friday, November 14th to Sunday, November 16th at our Big Deal event. You can enter for a chance to win free wawa gas for a year, plus more surprises in your Burlington. Miami, that means so many ways and days to save. Burlington. Deals. Brands. Wow! No purchase necessary. Visit BigDealEvent.com for more details."
},
{
"end_time": 5117.961,
"index": 190,
"start_time": 5088.882,
"text": " What else is exciting is consciousness. And many physicists don't talk about consciousness. You think plenty about it. You have relational quantum mechanics which says something about consciousness if I'm not mistaken. But either way,"
},
{
"end_time": 5147.688,
"index": 191,
"start_time": 5118.268,
"text": " I want to know, in your view, what observes the observer? The mechanics says something about consciousness very indirectly. So it's not a theory that leads to consciousness. I don't think that consciousness has anything to do with quantum theory. But indirectly, yes, because"
},
{
"end_time": 5177.619,
"index": 192,
"start_time": 5149.155,
"text": " What's the problem of consciousness? The problem of consciousness is that we think there are two things."
},
{
"end_time": 5204.548,
"index": 193,
"start_time": 5178.353,
"text": " What is matter, atoms, molecules, stones? And one is my spirit, my thinking brain. Okay. And if you start from that, it's very hard to think that the two are of the same kind. But I think that both ideas are very naive. There's no my spirit, my soul,"
},
{
"end_time": 5233.729,
"index": 194,
"start_time": 5205.06,
"text": " My thinking might my observing thing. I am just a piece of nature like anything else. Uh huh. And, uh, I, I, I follow laws of physics and says, my brain is very complicated and the complication of my ideas is the complication of the neurons of my brains. Just another way of describing things matter also, um, is not so naive like a sort of a very naive materialism."
},
{
"end_time": 5258.49,
"index": 195,
"start_time": 5234.172,
"text": " Would suggest that matter is not just little stones or molecules bouncing around because we know quantum mechanics quantum mechanics tell us that it's more complicated. Nature is more complicated nature is about how things affect one another. An electron is not a is not a stone it's it's it's something it's real but it's only real as far as interact with something else so if you think matter in that way."
},
{
"end_time": 5287.312,
"index": 196,
"start_time": 5259.053,
"text": " My brain interacting with the rest, it's doing the same thing that the rest of the universe does, species interacting with species. Now this doesn't mean that the universe is mental because my way of being or your way of being, it depends on the specific of the brain. We are very special pieces of nature."
},
{
"end_time": 5309.855,
"index": 197,
"start_time": 5287.722,
"text": " But we're special just because we're complicated and all these things happening. So I think that if we start from a fundamental sort of philosophy where we describe the universe in the way as a collection of things, each one of that can be described in terms of the others and"
},
{
"end_time": 5337.09,
"index": 198,
"start_time": 5310.128,
"text": " How things have information about one another, how things attract one another with a unified way. And if you find language in which both, um, the, uh, just changing behavior that we call consciousness, nobody knows what they mean by consciousness. It's just the, how we are, um, and the way, uh, stones and planets and plants and, uh,"
},
{
"end_time": 5351.015,
"index": 199,
"start_time": 5337.551,
"text": " In the same manner in which"
},
{
"end_time": 5375.589,
"index": 200,
"start_time": 5351.34,
"text": " Some decades ago people thought living beings is completely different than non-living being. The biosphere is something totally different. It's not totally different. It's just a special set of processes, but just physical process, chemical process. We call biological process a peculiar kind of chemical process. So I think our thinking is just"
},
{
"end_time": 5406.101,
"index": 201,
"start_time": 5376.63,
"text": " One of the many things of the universe, which is very complicated, we understand it very little. And in your view, because from the surface, it sounds like it's suggesting consciousness is fundamental, if the relations are fundamental, somehow consciousness is related to the relations. It sounds like that. How can it be that there's an experience attached to something that's not conscious? I think relations are fundamental, but what we call consciousness is not at all."
},
{
"end_time": 5436.323,
"index": 202,
"start_time": 5408.336,
"text": " The difference is that I need the notion of relation to describe everything. But when I think about consciousness, I mean, I'm describing you, you have memories, you have language, you have anticipation of the future. You have a brain that does a lot of very peculiar things like keep remembering and yes, exactly. And some of this one by one, some of these things are"
},
{
"end_time": 5466.8,
"index": 203,
"start_time": 5437.108,
"text": " Comprehensible, right? It's, uh, for instance, uh, how you take decisions. Well, you have information and you elaborate, you do things and my computer take decision when it plays chess with me in a similar way. So that part is in common. Um, how you look around. Well, the experience part though, the part that it feels like something. Yeah. The point is that when, uh, when, uh, you try to pinpoint what exactly do we mean?"
},
{
"end_time": 5494.445,
"index": 204,
"start_time": 5467.295,
"text": " uh by by that thing which is different when we try to say precisely we can't we use vague words and these vague words uh uh just saying that we don't know what you're talking about um so i don't think there is anything special in um"
},
{
"end_time": 5526.749,
"index": 205,
"start_time": 5497.363,
"text": " Inexperience by itself is just one of the aspects of the world Which is not very different, which is a much more complicated version of That stone which is falling on the other stone and affecting it much more complicated and this complication is additional complication Is what makes it So rich that we"
},
{
"end_time": 5557.022,
"index": 206,
"start_time": 5528.524,
"text": " I don't think there's anything different in me explaining how that stone is affected by another stone and me trying to understand how you Kurt are affected by talking with me. It's just in one case, it's easy in one case is super complicated. The difference is just the level of complications and what we call consciousness is extra complication. So you believe that a stone is feeling something when it's hitting another stone? No."
},
{
"end_time": 5584.718,
"index": 207,
"start_time": 5557.244,
"text": " No, because feel is the I believe that it's a it's behavior is affected by the other one. And what the right language for describing what is going on is a relation between the two. And feeling is related to emotion to to things that you have when you have a"
},
{
"end_time": 5616.152,
"index": 208,
"start_time": 5586.271,
"text": " If you had 10 graduate students and you could delegate them to the most tractable promising direction for either relational quantum mechanics or loop quantum gravity, what task would you set them on?"
},
{
"end_time": 5638.148,
"index": 209,
"start_time": 5617.244,
"text": " I'm doing sitting down and trying seriously to compute the position amplitude of a black hole at the end of the operation. So the remnant black hole when it finishes being a remnant? Yeah. Yeah. You see, my understanding of loop quantum gravity is that"
},
{
"end_time": 5660.896,
"index": 210,
"start_time": 5638.763,
"text": " More or less, it's a theory. It's a good theory. It's a consistent, coherent theory. We don't understand it well. It's hard to do calculation. We're not sure how to define it. I mean, we are fighting about us in loop quantum gravity. This version is a bit better than yours, of course. And there are things which have not been proven yet. So, all sorts of troubles. But it's a theory."
},
{
"end_time": 5687.602,
"index": 211,
"start_time": 5661.305,
"text": " It's a consistent theory of quantum gravity. What we don't know is whether it is correct theory for describe the world or not. So I would tell the students, look, work on the application, try to apply the theory to concrete phenomena. There are many concrete phenomena, early universe. I mean, but the the end of the evaporation seems to me, which is the same problem as the singularity is about the singularity is connected to the end of evaporation."
},
{
"end_time": 5709.957,
"index": 212,
"start_time": 5688.387,
"text": " and uh the number of papers who try to do this calculation but they're very very primitive little it has not been explored yet there is a mathematics which is available it's a beautiful physical problem is out there we see the black holes okay what's going to happen to them in the future uh most likely i mean unless there's people you hinted to before"
},
{
"end_time": 5739.565,
"index": 213,
"start_time": 5710.299,
"text": " Right. Most likely they are going to evaporate. Then what? So we're asking some concrete problem. And if it happened to be connected to dark matter, we fabulous because we could then there will be a lot of this remnants that we could check them. So it seems to me that that's a possible opportunity for doing a concrete for using quantum gravity, not just for"
},
{
"end_time": 5769.48,
"index": 214,
"start_time": 5739.821,
"text": " Have you thought much about how it came to be that loop quantum gravity is the second place in terms of theoretical physics? What I mean to say is that it's seen from the outside and sometimes from the inside that string theory is the big dog and that its competitor is loop quantum gravity. Whenever people are talking about what is the theory of everything or the theory of quantum gravity, if they say it's string or loop."
},
{
"end_time": 5795.452,
"index": 215,
"start_time": 5770.128,
"text": " Have you thought much about how did loop get to be on that stage and not something like asymptotic safety or Rogers twister program or something else? Yeah. How did that come to be? There's plenty of thought about how string theory rose to prominence. Lee Smolin has at least one book about that. And I'm curious about the sociology of player A and player B."
},
{
"end_time": 5823.933,
"index": 216,
"start_time": 5795.862,
"text": " First of all, I think that the scripture gave us, it's true that people think in these terms, in the science community as well. And what they actually are talking about, it's a scientific judgment, but it's also much more simply a number of people working, right? I mean, it's in total safety, there is a few people working in the other attempt at a possible direction to"
},
{
"end_time": 5854.394,
"index": 217,
"start_time": 5824.616,
"text": " There are dozens of groups around the world, there are conferences, hundreds of people. Some do cosmology, some do black holes, some do mathematical physics, some do the covariant version of quantum gravity, some do canonical version of quantum gravity, and so on and so forth. So there's a world around that."
},
{
"end_time": 5880.23,
"index": 218,
"start_time": 5855.162,
"text": " And string theory, people who say they're doing string theory are more. And they're actually much more variety of things they're doing because people try to say this. Some people say they're doing string theory even if it's vaguely related to string theory, what they're doing. There's a lot of development. And this is sort of"
},
{
"end_time": 5907.551,
"index": 219,
"start_time": 5880.572,
"text": " A little bit self-sustaining because it's good to be part of a larger community if you can connect to them. So the description you gave does reflect the actual situation. The majority of the people interested in quantum gravity are in these two communities, strings and loops. How come? Historically,"
},
{
"end_time": 5937.705,
"index": 220,
"start_time": 5908.251,
"text": " There is a clear track to that, which is the history of general relativity as a scientific research field. General relativity, of course, started with Einstein, who wrote the theory of general relativity more than 100 years ago. And it was a very isolated group of people who were doing that for a long time, very few."
},
{
"end_time": 5968.507,
"index": 221,
"start_time": 5938.541,
"text": " Because there was not much to do. The theory had this three little successes, the pre-early of Mercury, the deflection of light by the sun, and somehow the redshift. And that's it. Nobody knew how to use it to do anything useful. And that was for very long. And then at some point, it started becoming more and more useful. Application, technology, the GPS, astrophysics, cosmology started moving."
},
{
"end_time": 5993.609,
"index": 222,
"start_time": 5968.763,
"text": " And black holes, gravitational waves. So suddenly, generativity became larger and larger and larger. But the people who come from generativity were different people than those who were schooled in the particle physics. So those who did the standard model, who, I mean, Weinberg, all the"
},
{
"end_time": 6021.869,
"index": 223,
"start_time": 5994.206,
"text": " And so there were two different communities and when both communities started to be interested in the quantum gravity problem, which of course interest both, they took very different, they had different philosophies, different way of thinking, different mathematical tools that were used. And so this gave a big cultural difference. And then something happened in the eighties, which was"
},
{
"end_time": 6049.838,
"index": 224,
"start_time": 6023.49,
"text": " This is just astrology history. Uh, both theories got great results in the eighties. It was a moment of, uh, surprise. Uh, but yeah, uh, theoretical results in, in the eighties. That's the moment in which people got excited, but precisely because it was a great moment of excitement in both parts. Few people looked at the other one. Right. So why?"
},
{
"end_time": 6074.821,
"index": 225,
"start_time": 6050.435,
"text": " No, because you see, oh, I'm in a theory that seemed to be working and then you just focus on it. Why you want to look at the others? It seemed to be working. You just go ahead. That's for instance, when, you know, when, when, when string theory, uh, sort of realized that there is an almost unique string theory, um, uh, it was great result with the anomaly, um,"
},
{
"end_time": 6101.613,
"index": 226,
"start_time": 6075.555,
"text": " and then look into gravity, there was solution with the weight equations. Wow, incredible solution with the weight equations. So the two communities ignored one another for a while and they had so different mathematical methods, assumptions that every attempt to communicate except few people. I mean, there are some people, at least one is one."
},
{
"end_time": 6129.258,
"index": 227,
"start_time": 6101.971,
"text": " Who try to learn both things. I try to learn string theory, but somehow always as a mature, not as professionals doing theories. Um, and it's, it's, it's really, you see, if you're string theory, if you're string theories, you think that, uh, energy, it's a major thing, momentum, energy, momentum is, it's, it's a fundamental thing in terms of thing to, to think."
},
{
"end_time": 6148.046,
"index": 228,
"start_time": 6129.684,
"text": " If you come from generating the energy momentum is just not defined in general is kind of be fundamental because in general there is no energy momentum of gravity itself which can be defined in any in any decent way there is only a moment of matter but not of gravity itself except."
},
{
"end_time": 6177.056,
"index": 229,
"start_time": 6148.422,
"text": " In specific cases. So what you consider your basic conceptual tool for think about reality in one camp would not in the other camp. So there was this long, long separation and this a little bit is still there. Um, it's okay. I think the debate is still going on and, uh, uh, we do have, uh, hopes of fights. They were both directions. Of course there were hopes of finding something"
},
{
"end_time": 6192.841,
"index": 230,
"start_time": 6177.415,
"text": " That could help not much or almost nothing directly observational so far has come in some very disappointing thing has happened i mean super semitic was very disappointing if it had happened."
},
{
"end_time": 6212.79,
"index": 231,
"start_time": 6193.729,
"text": " I suppose many people would say those people have a point to me this they seem to be was it disappointing to you. Supersymmetry is not in loop quantum gravity. I don't know the non non the non discovery of supersymmetry was great for us because."
},
{
"end_time": 6243.319,
"index": 232,
"start_time": 6213.404,
"text": " Because, you know, disappointment to your competitors just by that. You looked personally disappointed. I was not personally disappointed. I was just happy, happy, happy, going around happy and smiling. Yeah, you see, you were all waiting for it. I told you that there was story. So I didn't find this point. But then there's also another difference. And that has to do with the name of your of your shortcut."
},
{
"end_time": 6269.957,
"index": 233,
"start_time": 6244.138,
"text": " Sorry. No, no. Keep it, keep it, keep it. Of course you should keep it because it's a great idea. The hope of finding a theory of everything, but loop quantum gravity never considered it its own problem. Loop quantum gravity in a sense, that's a big difference."
},
{
"end_time": 6297.927,
"index": 234,
"start_time": 6271.732,
"text": " Look at it in a sense it's much more ambitious okay we are going to understand how to do physics without space without time really space is quite not like you who have to go observable to infinity where you know is space and time because we're smarter because we face the big problem directly i mean quantum space and quantum time but on the other hand um look when to gravity is super humble"
},
{
"end_time": 6326.613,
"index": 235,
"start_time": 6298.456,
"text": " compared to the ambition of string theory. Zoom quantum gravity is not a final theory of everything. It's not a unification of all the forces. It's not something which pretend to be an arrival point for theoretical physics. It's a very humble enterprise, which is we know the gravitation interaction. What happens when you cannot disregard quantum mechanics?"
},
{
"end_time": 6333.695,
"index": 236,
"start_time": 6327.398,
"text": " In this gravitational interaction. So what happened inside the black holes? That's the only or what happened at Big Bang?"
},
{
"end_time": 6363.677,
"index": 237,
"start_time": 6334.343,
"text": " I see it two ways when it comes to the humility argument because it could be that we just need to take one step forward but it could be there's some chasm and you actually need to jump and anytime you're taking a step you're just gonna fall you're like well look I'm super humble you all are just jumping into the void yeah well you need to jump further yeah no no of course we don't know I was"
},
{
"end_time": 6384.428,
"index": 238,
"start_time": 6364.633,
"text": " You see i i grew up in the seventh i went to school to university physics in the seventies at the time the big problem was a strong interactions i think it was a was a mystery some of the week interaction that was already the attempt to find the salam what we call today the theory of weak interaction."
},
{
"end_time": 6406.698,
"index": 239,
"start_time": 6385.145,
"text": " Um, but the strong interaction were very mysterious and, uh, there was a large number of particles, uh, uh, that were found the zoo of, uh, I was very confused, uh, and the strong interaction was strong, uh, namely you expect the perturbation theory to full and"
},
{
"end_time": 6430.333,
"index": 240,
"start_time": 6407.449,
"text": " what i got from my teachers at the time the mantra that everybody was saying my teachers were all wrong they were saying look um quantum field theory has a problem because of the infinities the renormalization uh quantum field theory is shit because you know what is this renormalization business is not clear which is and"
},
{
"end_time": 6457.824,
"index": 241,
"start_time": 6430.64,
"text": " The renormalization problem comes because of perturbation theory and the strong interaction. You cannot do perturbation theory. So obviously there were people were saying the problem of understanding the strong interaction and the problem understanding of renormalization, getting rid of renormalization must be the same problem. And therefore the solution must be forget quantum field theory, find an alternative to quantum field theory. And this alternative quantum field theory will not have renormalization problems."
},
{
"end_time": 6473.882,
"index": 242,
"start_time": 6458.166,
"text": " And will make sense of the strong interaction this is ideas go back to heisenberg yes matrix people were working bootstrap and all of them so in other words with two problems clearly we should solve the two together and what happened historically is that that was wrong."
},
{
"end_time": 6497.807,
"index": 243,
"start_time": 6474.394,
"text": " Because gross and will check and everybody else. Gelman solved the strong interactions beautifully with the theory, which is QCD. It's marvelous. One of the best theory we have, which still have all the problem with normalization, infinities and is a quantum field theory. And they were a minority at the time. We'll check and company and gross and, and, and, uh,"
},
{
"end_time": 6519.735,
"index": 244,
"start_time": 6497.807,
"text": " And gilbert where minority who is looking for a quantum feels ready to solution for the strong interaction with most people looking for a. No one to feel theoretical solution strong interaction so. Of course i mean i said same trick doesn't work twice but."
},
{
"end_time": 6549.957,
"index": 245,
"start_time": 6520.657,
"text": " I grew up with the idea that you can very well have two problems on the table and think, of course they're connected. That's not true. You can solve one and the other tomorrow. So speaking of David Gross, that conversation that you had with him two years ago or so, that's something that every aspiring physicist and every existing physicist should watch because it shows"
},
{
"end_time": 6577.585,
"index": 246,
"start_time": 6550.265,
"text": " String theory is the big boy and it demonstrates that they don't even listen to their competitors. There was a part in the conversation where David was saying, you in loop quantum gravity, though you're the representative at that point, you can't even explain so-and-so. What was it? Fermions, putting fermions in loop quantum gravity. And you said, David, that's something that we solved 20 years ago, something like that."
},
{
"end_time": 6606.408,
"index": 247,
"start_time": 6578.131,
"text": " Do you see this in the same way that I see it? Yeah. Yeah. Yeah. It's a it's a it's it's yes. And it's a double problem. One problem is in communication. So a lot of people theory criticize loop one to gravity, but criticize what loop one was. It was 20 years ago. Oh, this probably is open, but that was open 20 years ago. That's not the problem today. There are problems today."
},
{
"end_time": 6637.159,
"index": 248,
"start_time": 6607.312,
"text": " But also the second, it's more serious as well. I think we don't need to be experts of each other theories, of course, because one cannot be expert of everything. But it's very useful for science, as I said, should go ahead by knowing what are at least the claims on both sides."
},
{
"end_time": 6666.032,
"index": 249,
"start_time": 6637.551,
"text": " I guess one thing to have great results in your theory is another thing to say you're the only game in town. And it's another thing to say you're the only game in town while not looking exactly at what other people are doing. Yeah, that's I think you put it very clearly. We'll end with what are your hopes? What are you working toward other than this Princeton conference coming up for relational quantum mechanics? What are you working on? What do you hope to solve in the short run?"
},
{
"end_time": 6696.237,
"index": 250,
"start_time": 6666.578,
"text": " We talked about the black hole, what happened at the black hole at the end of the operation. Before talking to you Kurt, this morning I was on Zoom with a colleague in Marseille, a brilliant young professor, just got a five minute position. We spent three hours this morning getting confused about how to think about this. This is a sort of tunneling"
},
{
"end_time": 6723.643,
"index": 251,
"start_time": 6696.476,
"text": " Process so we're thinking trying to understand which sense is a tunneling process. What's how do you a tunneling process? Not in time but of space-time some sense I would love to get some clarity there. Yes, and in fact I Wish I could Concentrate more on there rather than doing all the value things that I'm doing present. That's for me. The what are the various things you're doing? I"
},
{
"end_time": 6746.51,
"index": 252,
"start_time": 6724.002,
"text": " Well, I've, you know, I've written popular books and I'm pressure that I get invitation. I do. I do this philosophy thing. I am a bit too dispersive and I when I'm I want to focus more. You asked what would you like to focus on? I would like to focus on understanding that particular it's a it's a well"
},
{
"end_time": 6775.35,
"index": 253,
"start_time": 6747.022,
"text": " It's a well-posed physical problem. That's the beauty of it. Black hole. They are there. They are out there. In fact, there is another way of putting this problem. We see the black holes. We see the matter falling in. We see the spiraling, the crescion disk as they call it. And we know, because we know generativity, that matter is spiraling and then going into the horizon. And we know generativity, so it goes into what we call the singularity."
},
{
"end_time": 6804.667,
"index": 254,
"start_time": 6776.51,
"text": " What happened next to that matter? We have no idea. So it's a very concrete thing. A kid could come in and say, oh, there are all these holes in the sky and things falling in. Where does it go? The answer is we don't know. So, I mean, come on. We are scientists. Pretend to understand so well the universe. We should be able to answer this question. We have quantum mechanics. We have generativity. We have all these ideas. We have the tools. That's what I would like to"
},
{
"end_time": 6830.23,
"index": 255,
"start_time": 6805.862,
"text": " What happens if you fall into a black hole, like an observer, you want to know what happens to that person? What happened to two is the same question for me. And what happened to the matter that falls into the black hole, which is very much connected to what happened to the black hole at the end of the operation? I see."
},
{
"end_time": 6860.282,
"index": 256,
"start_time": 6831.271,
"text": " The magic of general activity, the classical general activity, the time is very flexible, right? Time can go, you can go from here to here, a very long time, a very short time. Two people can separate and meet and for one is a long time. So if you go into black hole, assuming that you're not squeezed, and if you go through the tunneling and you come out of the white hole, outside is a huge amount of time, but inside is a very short time."
},
{
"end_time": 6889.002,
"index": 257,
"start_time": 6861.681,
"text": " So the information that falls into black hole very fast goes to the singularity or the non singularity, this tunneling and then very fast come out. But from the outside is a very, very long process in which you see the black hole evaporate and then stays and then things come out. So the problem what happened to the matter inside is the same problem as what happened to the end of evaporation. Okay. And that's a problem we would like to get some better understanding."
},
{
"end_time": 6917.142,
"index": 258,
"start_time": 6889.548,
"text": " So in traditional general relativity, when something falls in, if you're an observer on the outside watching something fall in, you don't actually see a cross inside. You see it accumulate at the boundary. And then you're saying, but at some point it does need to evaporate if we're to make it consistent with quantum mechanics. Then what happens? So speaking of boundary, Neemar Khani Hamad said any quantum gravity needs to tell us what happens at the boundary of space-time. What's meant by that? Do you agree?"
},
{
"end_time": 6947.585,
"index": 259,
"start_time": 6918.37,
"text": " Yeah, yeah, yeah. I know, I know, I know what they think. And I mean, last time I was in prison physics, I talked with him about that. I agree to some version of this statement, but not to the version that he means. The way we do quantum gravity in loop quantum gravity demands to know"
},
{
"end_time": 6977.944,
"index": 260,
"start_time": 6948.046,
"text": " What happened boundary but the boundary can be at a finite in a finite region Okay, so I can do I can do the following experiment suppose where we had a super technology I can take some matter I squeeze it to make a black hole I waited I see what comes out. Okay, all this happens in my room From some initial time to some final time. So I need to know what was the beginning what happened on the walls what at the end and"
},
{
"end_time": 7007.466,
"index": 261,
"start_time": 6978.592,
"text": " In a finite time, that's true. I need to know the boundary of the process to see the probability of giving the initial what what? Okay So that's correct. But Nima and with him the Princeton people, I'm not sure the West Coast people string theorists agree They think that the boundary has to be at infinity that I can only go at infinite distance"
},
{
"end_time": 7037.807,
"index": 262,
"start_time": 7008.353,
"text": " and look at the boundary there. And that's, I'm not convinced. So they have argument to say that they cannot be in the middle of space time and make measure quantum gravity measurement there. And those are augmented on by, um, I think mathematically they get in trouble if they try to see what happened, if I make measurement that find a distance, but they are in trouble because they assume a continuous space time."
},
{
"end_time": 7068.302,
"index": 263,
"start_time": 7038.968,
"text": " Which is one of the assumption, one of the well, well, there's no continuous space time. That's the point. Uh, the, the, they, they have some infinities that they are struggling with, but there's infinities are the infinities that come from forgetting that there is this quantum discreteness in space time. What's meant by infinity if the universe is infinite, but how do you take the border of infinity?"
},
{
"end_time": 7096.834,
"index": 264,
"start_time": 7068.746,
"text": " Well, that's how they think about it. Do you mean infinitely away from some region, like you're defining some region, then you say infinitely away from that? Yes, yes, that's the way they they think about it and me in particular. So they think there's some process here, but the only way to describe it is that I have to go to very large distance and it's very large distance. I see. Because technically speaking, you're at the infinite boundary of something else. If the universe is infinite. You're right. You're right. No, yeah."
},
{
"end_time": 7126.647,
"index": 265,
"start_time": 7097.329,
"text": " What I think is that the way of describing a quantum gravity phenomena is to be at infinite distance from it. And sort of for a very long time, see what happened. And I think this strong requirement for them is easier because at infinite distance, you assume the space time is flat. Right. So you're. They put observable what they call a synthetic"
},
{
"end_time": 7157.381,
"index": 266,
"start_time": 7127.5,
"text": " If the boundary is itself in a region where it's curved geometry or strong gravity, you don't have those tools. So no surprise that they have difficulties of working."
},
{
"end_time": 7186.254,
"index": 267,
"start_time": 7158.319,
"text": " at finite distance. I think that it's work to find a distance simplifies the problem. So I want to understand what happened to black hole in a sense by by surrounding the black hole small box and see that's my problem is just a small box, not the entire universe. Carlo, I appreciate that of the 20 different items you can focus on that you're dispersed. And I appreciate that you've spent two hours or so"
},
{
"end_time": 7198.268,
"index": 268,
"start_time": 7186.578,
"text": " focused on myself in this conversation that's incredibly flattering and the audience appreciates it as well. Thank you so much. Thank you, Kurt. Again, it was wonderful this conversation. I very much appreciate it."
},
{
"end_time": 7226.852,
"index": 269,
"start_time": 7199.497,
"text": " New update! Started a substack. Writings on there are currently about language and ill-defined concepts as well as some other mathematical details. Much more being written there. This is content that isn't anywhere else. It's not on Theories of Everything. It's not on Patreon. Also, full transcripts will be placed there at some point in the future. Several people ask me, hey Kurt, you've spoken to so many people in the fields of theoretical physics, philosophy, and consciousness. What are your thoughts?"
},
{
"end_time": 7256.783,
"index": 270,
"start_time": 7226.852,
"text": " Also, thank you to our partner, The Economist. Firstly, thank you for watching. Thank you for listening. There's now a website, curtjymongle.org, and that has a mailing list. The reason being that large platforms like YouTube, like Patreon, they can disable you for whatever reason, whenever they like."
},
{
"end_time": 7283.114,
"index": 271,
"start_time": 7256.783,
"text": " That's just part of the terms of service. Now, a direct mailing list ensures that I have an untrammeled communication with you. Plus, soon I'll be releasing a one-page PDF of my top 10 toes. It's not as Quentin Tarantino as it sounds like. Secondly, if you haven't subscribed or clicked that like button, now is the time to do so. Why? Because each subscribe, each like helps YouTube push this content to more people like yourself"
},
{
"end_time": 7301.766,
"index": 272,
"start_time": 7283.114,
"text": " Plus, it helps out Kurt directly, aka me. I also found out last year that external links count plenty toward the algorithm, which means that whenever you share on Twitter, say on Facebook or even on Reddit, etc., it shows YouTube, hey, people are talking about this content outside of YouTube, which in turn"
},
{
"end_time": 7329.838,
"index": 273,
"start_time": 7301.766,
"text": " Greatly aids the distribution on YouTube. Thirdly, there's a remarkably active Discord and subreddit for theories of everything where people explicate toes, they disagree respectfully about theories and build as a community our own toe. Links to both are in the description. Fourthly, you should know this podcast is on iTunes. It's on Spotify. It's on all of the audio platforms. All you have to do is type in theories of everything and you'll find it. Personally, I gained from rewatching lectures and podcasts."
},
{
"end_time": 7349.821,
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"start_time": 7329.838,
"text": " I also read in the comments"
},
{
"end_time": 7373.251,
"index": 275,
"start_time": 7349.821,
"text": " and donating with whatever you like. There's also PayPal. There's also crypto. There's also just joining on YouTube. Again, keep in mind it's support from the sponsors and you that allow me to work on toe full time. You also get early access to ad free episodes, whether it's audio or video. It's audio in the case of Patreon video in the case of YouTube. For instance, this episode that you're listening to right now was released a few days earlier."
},
{
"end_time": 7379.838,
"index": 276,
"start_time": 7373.404,
"text": " Every dollar helps far more than you think. Either way, your viewership is generosity enough. Thank you so much."
}
]
}No transcript available.