Theories of Everything with Curt Jaimungal - Juan Maldacena: Geometry as Entanglement, and the Emergence of Spacetime

Episode Date: May 4, 2026

SPONSORS: - Go to https://shortform.com/toe for a free trial and an exclusive $50 OFF on your annual subscription - I subscribe to The Economist for their science and tech coverage. As a TOE listener, get 35% off! No other podcast has this: https://economist.com/TOE Juan Maldacena wrote the most cited paper in theoretical physics, birthing AdS/CFT and realizing holography — and today, the problem keeping him up at night is wormholes. He suspects space-time isn't fundamental at all, that geometry itself might be what entanglement looks like from the inside. The singularity isn't a place, it's a name for everything we don't yet understand. I hope you enjoy it. FOLLOW: - Spotify: https://open.spotify.com/show/4gL14b92xAErofYQA7bU4e - Substack: https://curtjaimungal.substack.com/subscribe - Twitter: https://twitter.com/TOEwithCurt - Discord Invite: https://discord.com/invite/kBcnfNVwqs - Crypto: https://commerce.coinbase.com/checkout/de803625-87d3-4300-ab6d-85d4258834a9 - PayPal: https://www.paypal.com/donate?hosted_button_id=XUBHNMFXUX5S4 TIMESTAMPS: - 00:00:00 - Emergent Space-Time Geometry - 00:05:28 - GR and QM Incompatibility - 00:11:52 - The Singularity Problem - 00:17:00 - Extremal Black Hole Thermodynamics - 00:22:00 - The Island Formula - 00:27:30 - Spacetime and Quantum Information - 00:34:15 - ER equals EPR - 00:41:51 - Traversable Wormhole Physics - 00:47:24 - Simulating Wormholes with Qubits - 00:52:53 - Celestial Holography and Symmetries - 00:58:00 - dS/CFT and Dark Energy - 01:04:24 - Quantum Error Correction Codes - 01:10:00 - The Physicist’s Mindset - 01:15:19 - Inflationary Gravity Wave Predictions - 01:21:03 - Clocks and Emergent Time - 01:26:44 - Is Space-Time Doomed? - 01:32:00 - AI in Theoretical Physics - 01:38:00 - Overcoming Academic Inadequacy LINKS MENTIONED: - Juan Maldacena's Website: https://www.ias.edu/sns/malda - Large N Limit of Superconformal Field Theories [Paper]: https://arxiv.org/abs/hep-th/9711200 - Eternal Black Holes in AdS [Paper]: https://arxiv.org/abs/hep-th/0106112 - Holographic Derivation of Entanglement Entropy [Paper]: https://arxiv.org/abs/hep-th/0603001 - Real Observers Solving Imaginary Problems [Paper]: https://arxiv.org/abs/2412.14014 - Building Spacetime with Quantum Entanglement [Paper]: https://arxiv.org/abs/1005.3035 - Entropy of Bulk Quantum Fields [Paper]: https://arxiv.org/abs/1905.08762 - Entanglement Wedge Reconstruction [Paper]: https://arxiv.org/abs/1905.08255 - Comments on the Double Cone Wormhole [Paper]: https://arxiv.org/abs/2310.11617 - Traversable Wormholes in Four Dimensions [Paper]: https://arxiv.org/abs/1807.04726 - JT Gravity as a Matrix Integral [Paper]: https://arxiv.org/abs/1903.11115 - Single-Minus Gluon Tree Amplitudes [Paper]: https://arxiv.org/abs/2602.12176 - Bulk Locality and Quantum Error Correction [Paper]: https://arxiv.org/abs/1411.7041 - Black Hole Information Paradox: https://en.wikipedia.org/wiki/Black_hole_information_paradox - Chilloquium 2023 [Lecture]: https://youtu.be/Ow81IJyzmUQ - Erik Verlinde [TOE]: https://youtu.be/ilVImMHcr_g - Leonard Susskind [TOE]: https://youtu.be/2p_Hlm6aCok - Edward Frenkel [TOE]: https://youtu.be/RX1tZv_Nv4Y More links at https://curtjaimungal.substack.com Guests do not pay to appear. #science Learn more about your ad choices. Visit megaphone.fm/adchoices

Visit BetMGM Casino and check out the newest exclusive. The Price is Right Fortune Pick. BetMGM and GameSense remind you to play responsibly. 19 plus to wager. Ontario only. Please play responsibly. If you have questions or concerns about your gambling or someone close to you, please contact connects Ontario at 1-866-531-2,600 to speak to an advisor,

free of charge. BetMGM operates pursuant to an operating agreement with Eye Gaming Ontario. One holes are a bit like leaky pipes. Not everything is fitting together. The singularity is not a place inside the black hole. It's a place in the future. I think it's common. Maybe not to feel good,

or to feel that maybe you're not good enough. But well, eventually you'll make your contributions. Professor Juan Maldesana has spent 30 years probing deeper and deeper into what the heck space time is. In this episode, we explore how it comes down to the claim that geometry in some cases is what entanglement looks like from the inside. Today we discuss what ER equals EPR actually means, and we discuss black hole interiors where...

Singularity is just the name for things we don't understand. Most of us intuitively assume there's a sort of view from nowhere, that you can just do quantum mechanics from the outside, look in, and write down what's there. Professor Juan Maldesana discusses why we can't. On this channel, I interview researchers regarding their theories of reality with rigor and technical depth. My name's Kirchai Mungle. I've included further resources on my substack at Kirchai Mungal.com if you're interested. Stick toward the end for advice for students.

For you, the listener, as we see a strikingly honest, vulnerable, and inspiring perspective from the man who wrote the most cited paper in theoretical physics. During his graduate studies, even Juan Maldesana didn't feel good enough. If you're struggling with something similar, hang in there. Keep studying, keep pushing forward, and don't give up. Professor, it's an honor to meet you. Well, it's great to be with you. What is space time made out of?

Well, space time in the theory of general relativity, it's not made out of anything. It's a primary concept. It's the main dynamical object of the theory. The question about what it is made of is only relevant. for a more fundamental theory, some other theory. And we think, by thinking about the quantum mechanics of space time, that it can be at least convenient sometimes to think of it as made of something else. And something else could be qubits or some other fundamental quantum degrees of freedom

that live in the boundaries of this space time, that live far away. Yeah, that's a relationship that we've been studying quite a bit in the last, maybe 20 years or more. Yeah, so it's a picture where space time is immersion from some other degrees of freedom that live on the boundary space time. So in that picture, there is this boundary, this region far away that serves as a framework

as some overall space where, or space time, where the degrees of freedom that describe the interior of the space time live. So in that description, we at least need that boundary. You said it could be quantum degrees of freedom. Yes. What else could it be? Well, it could be other things.

I mean, in physics, when we say something is made out of something else, right? We think about some more fundamental things. And in different examples, they're made of different things. In general, in all of physics, in most of physics, it's made out of particles, we say. I mean, that's what, let's say, we learn in high school and so on, that matter is made out of particles. In modern physics, we describe things, not as made out of particles, but made out of fields, like the electromagnetic field, electron field, Higgs field, various fields. And that we think is the basic fabric of reality of nature at short distances.

That's the theory we really have experimental confirmation from. Then all those fields live in some space time. The space time is given, is some kind of fixed arena where everything happens. But in general, relativity, space time itself moves and changes. And we think that in some sense it's described as some other field. And whereas the fields of matter, we describe them quantum mechanically. The field that makes the metric or the space time geometry, we describe only classically. We only know how to describe it classically.

And if we try to, we can describe it quantum mechanically in an approximate way. And that approximate theory can give us some answers, but it cannot give us all answers somehow. We know it fails in some cases. The most important place where it fails, it's in the beginning of the universe. And this is the main reason we want to find a better theory, to find out what happened in the beginning of the universe. Another place where it fails is in the interior of black holes,

and that's another reason for trying to understand the better theory. So we know of places in the universe where our current understanding of physics breaks. And the idea is to develop at least some theory that can describe such things and then try to figure out, of course, in some way that that theory is the correct theory. We don't know whether the theories we have right now

of quantum space-time, more complete theories where they are the correct theory or not. And what would you say is the primary reason for the difficulty of combining GR with quantum theory. So the pop-size is that, oh, one is discrete and one is continuous or one is linear or one is non-linear. How do you see the incompatibility between the two? Well, I think the main issue is that in quantum mechanics,

there is usually some time, some order between operators and in order between the measurements we make. in general relativity and in gravity, space time can have different geometries, different topologies. We don't know what the order is. Also another conceptual difficulties is that in quantum mechanics we have some observer who's outside the system,

and in gravity, everything is somehow inside the system. So we cannot have an observer that has no mass, that has no energy that measures things from outside. whatever observer exists inside the universe has its own energy. These are some of the features that make it difficult. I mean, there are some other technical things. People often discuss that are special to, let's say, four space-time dimensions,

which is that there are certain infinities that appear in the calculations. But that, I would say, it's a more technical issue rather than more conceptual issues like the ones we mentioned earlier. Now, what's the difference between a conceptual issue and then a mathematical one? Well, I would say mathematical one is one where the issue is not there, let's say, in two dimensions, but it's there maybe in four dimensions. So from this point of view, it looks like an accident that we live in four dimensions. I mean, yeah, we happen to live in two dimensions. We would still have a bunch of conceptual issues related to quantum gravity, but we would not have perhaps that technical issue we just mentioned.

Or that technical issue would be a little easier. But the other questions are still there. In two dimensions, we still have black holes that are confusing. In finite universes, we have the issue of having to include the observer and exactly how we should do that. Yeah, so those are issues that still remain. Earlier you mentioned observers. Now, Witten, along with Pennington and some other collaborators, helped fix what happens inside a black hole interior with type 3 to type 2 algebras and some technicalities. Is that observer that's talked about in those papers,

the same sort of observer that's talked about in, say, the foundations of quantum mechanics? Yeah, it's related. I mean, their description is perturbative, so starting with a particular background and considering small fluctuations around that background. It's in the context of what we sometimes call semi-classical gravity. So I mentioned previously that quantum gravity makes sense

in a certain approximation, and that's the approximation in which they did their discussion. And so it's an extension of those methods to deal with situations where maybe we have a close to a space, so especially compact universe or a region of the universe where the observer can access only to a portion of the universe, such as the citer space, and let's say it's an improvement relative to what we had before.

So that's what it does. It does not answer the questions of, you know, what happened in the beginning of the Big Bang or have the observer actually immersed in the very beginning and so on. So that does not do. But this is normally in physics, right? So we do some things. We understand some aspects and make progress and there are still important questions. Was it a surprising result to you? Yeah, I think it was a beautiful.

way of improving our understanding of the so-called generalized entropy. So let me mention, let me say a little bit more what that is. So if you have a black hole, the black hole has an entropy

in the leading approximation, which is the area of the horizon in Planckonets. This is a very large number for a microscopic black hole. But this entropy was then supposed to have a quantum correction that comes from hooking radiation. So hooking radiation is some radiation that is, you know, pretty, well, it's some

thermal radiation that comes out of the black hole. And if you're looking at this radiation and you're looking it from the point of view of an observer who states outside the black hole and you approach the boundary of the horizons or the boundary of the region that is accessible, then it looks like it's hotter and hotter and hotter. And naively computed the contribution to the entropy coming from that would be infinite. However, we think that that infinite contribution somehow combines with this area contribution, which is very large and gives really something that should be viewed as finite.

And what these papers did is they understood how to combine, how to derive an expression for the entropy that would be finite or would describe changes in this entropy in a consistent way without ever having to talk about any infinity or cancellations of infinities. So it's a better way to think about black hole entropy in the semi-classical theory. It answers some questions of black hole entropy. Again, it doesn't answer all the questions, but it answers some important questions. It answers the questions that are related to, let's say, the interaction of a black hole with some amount of matter, an amount of matter which is not big enough to change the mass of the black hole in an appreciable way.

but it describes that matter in a completely quantum mechanical way and the entropy of that matter in a completely quantum mechanical way without any infinities or anything. Right. Now, these infinities are some technical issue, which occurred with this paper solved and made the theory more reasonable. You said it solves some problems of black holes,

some important problems. That means that there are some other important problems that may be left unsolved. So what are the greatest unsolved problems about black holes? I would say that the greatest problem is understanding better the black hole interiors. And the black hole interior,

the space-time curvature becomes infinite. That infinite means that something happens that we don't know how to describe. So if you don't know what this means, we don't know either. We don't know what happens at the so-called singularity. So singularity is just the name

for things we don't understand. But so the Einstein equations themselves predict that as you evolve them towards the interior, you hit this singularity. The singularity is not a place sort of inside the black hole. It's a place in the future. You go to the interior of the black hole and you find this singularity in your future. So you can't avoid it. It's a bit like a big crunch singularity, somewhat similar.

So a singularity where the whole, that whole region of the universe collapses. I mean, one way to think about it is that, you know, the universe is generally expanding, right? And so we're all happy when the universe expands. But in some regions where a lot of matter gets concentrated, the universe starts collapsing. And in these regions, you produce a small big crunch,

so a region where the spacetime curvature becomes infinite, the opposite of a big band. And that is not visible from the outside. It's behind the so-called black hole horizon. So we don't directly get any signal from this region. But if you were someone who's falling into the black hole, you would get into this region and you would collapse together with the rest of the matter making the black hole. Now, so the fact that the space-time curvature becomes very large,

suggests that in these regions the quantum effects will become important. And so if a full theory should say, exactly what happens there and should give us a more complete description. And we don't yet have such a thing. What we do have are some theories that can describe aspects of black holes as seen from the outside. So if you remain outside the black hole and ask what we think are very precise questions about the black hole, then we think we know what would happen,

at least conceptually. part of what we were discussing previously about the entropy and the algebras and the work of penitence is related to describing the black hole from the outside. I have a question about Elysio and Tirayche, if I'm pronouncing that correctly. Either way, I'll place a link on screen and in the description. If I recall correctly, they showed that semi-classical near-extremal black holes that their thermodynamics breaks down at the short scenes. scale. Now, does that break holography or is that just specific to JT gravity? Yeah, let me try to describe this general area. So there are black holes and there are

charged black holes. So black holes can carry charge. And if you have a large charge black holes, as it evaporates, the temperature becomes smaller and it emits energy, but it keeps its charge. And so there is some state that it approaches where it has the minimal mass consistent with that charge, and that's a non-zero mass, and its hawking temperature goes to zero. That's so-called an extremal black hole. And the black hole develops a geometry that has a near-horizon geometry with a very long near-horizon region, if you wish. and it develops a kind of scaling symmetry, which becomes self-similar in some way.

So you can get closer and closer and closer to the horizon and the black hole looks the same. Okay, so you can have one of these very big black holes, and if the black hole is very big, then you would expect that the quantum corrections, quantum gravity corrections are very small, you might think. But if you go to very, very, close to zero temperature or very, very close to extremality,

then there is a very particular quantum corrections that becomes important. And that's very interesting because it's an example of a controllable situation in quantum gravity where only one aspect of the geometry becomes quantum mechanical, but the remaining aspects of the geometry are still classical and we don't have to worry about them. So it's a case where you can really quantize gravity.

You can quantize if you wish a particular degree of freedom of gravity. In some sense, it is as if the black hole becomes very long and this length can have fluctuations, quantum fluctuations, and you can treat them precisely. And this exact quantum treatment of the fluctuations is something that was really only understood. This aspect of extremal black holes was only understood in the last maybe decade or so.

And it went through a sequence of developments, starting with some toy models based on condensed matter analysis and so on. So it's a pretty interesting story that I won't give you in detail. And this particular paper that you quoted by Ilyosio and Turechi, they analyzed this for four-dimensional black holes in general activity that carry very big electric charts. and they show that the entropy as your approach extremality

goes to, becomes small. I should say that the important aspect is that these quantum corrections change some qualitative aspects of these black holes. In particular, these black holes seem to violate the third law thermodynamics. So the third law of thermodynamics says that, As you decrease the temperature of the system all the way to zero, its entropy should also go all the way to zero. Now, this black hole, if you just treat them purely classically, ignoring the quantum corrections, at extremality, they have zero temperature, but non-zero entropy.

And once you include the quantum corrections, the entropy sort of decreases essentially all the way to zero. So this correction has the important feature of making this black host also now consistent with the third ortho dynamics, more similar to ordinary quantum systems. That's one aspect. And well, there are other aspects in this highly quantum regime that are also very interesting. I subscribe to the economist. Their science and their AI coverage is among the best I found anywhere. And I say that as someone who reads plenty of it. I'll give you some examples. They just ran an analysis on how attitudes towards science are changing

in American politics and what this means for research and funding in scientific institutions moving forward. This sort of high-quality reporting is fantastic. They even covered how dark energy may be weakening over time. Now, if that holds up, it completely changes our understanding of the universe's fate. If you watch this channel, those are exactly the kinds of questions that we explore every week. I subscribe to the economist because their science and their AI reporting regularly surprises me with how deep it goes. And they're also, of course, known for global affairs, both political and economic reporting. They are top tier. And interestingly, and flatteringly, Toa is one of the only podcasts that the economist partners with. So as a listener,

you get an exclusive 35% off. That's not a deal that they have just anywhere. Head to Economist.com slash T-O-E to subscribe. That's economist.com slash T-O-E for 35% off. Now what about the island formula? Yeah, so this is related to the black hole information paradox. So there is a problem that was pointed out originally by Hawking that after he discovered Hawking radiation,

he thought, well, a black hole can collapse in many different ways. but the radiation in the midst seems to be a featureless thermal radiation that's largely independent of what fell in and that does not seem to be consistent with the unitary to quantum mechanics I mean the black hole might evaporate completely

and you get this featureless thermal radiation and of course something similar happens when you burn a piece of paper and so on but in that particular case if you work hard enough and so on you would be able to

recover the information, at least in principle. The loss of physics are understood to the extent that in principle should allow you to do it. I mean, it might be super expensive, not worth the trouble and so on. But in principle... It's like in detective shows when they try to take the shredded documents and put it together. It's a more complicated version of that. Exactly. It's the same thing.

I mean, when you shred the document in principle and information, instead of if you're patient enough, you can put it back together. But, yeah, if you throw the document into a black hole, can you do that and the loss of physics? And so we think that the loss of physics are such that they would allow you to do that.

And that is true according to some conjectures that use string theory and so on. Now, the question was how to see that more directly from the gravity point of view. So what Hawking said is where I can calculate something called the

amount of quantum information that you get in the radiation. This is sometimes called the phoenotropies. It's a measure of quantum information. And if you calculate it, it looks like it is increasing. So you send

something in and then you get something bigger. And it was a mystery of how you would see this from the gravity point of view. So the island formula, well, it came after developments by I'm Harry, Engelhardt,

Marofan, Maxfee, and a separate paper by Pennington. So this formula is a way to compute the entropy of the outgoing radiation. So there is a way to compute the entropy of the outgoing radiation, which is similar to the entropy of the black hole that we saw before, the area formula. So it's a new type of area formula that allows us to compute the entropy of the radiation. And it gives us an entropy which is consistent with the idea

that you are preserving information. So as the black hole evaporates and when it's close to operating completely, then the entropy becomes smaller. So in the sense that all the information, and that is interpreted as saying that all the information is coming out. So it makes, it's something that closes a bit, the development of black hole entropy from the 70s. So in the 70s, there were people noticed that,

Black holes as seen from the outside, they behave very much like thermodynamic systems. They have a temperature, they have a hocking radiation. All of these are theoretical discoveries. They are not things that have been checked in experiments. We can discuss experiments later. And the area of the black hole also classically always increases. And iron wall also show that even if you include quantum corrections,

the area of black holes increases. The area of black holes are together with the radiation that is outside, the total entropy increases. So that's the so-called second law. So the second law of thermodynamics applied to black holes. And what happened in,

starting around 2006 or so, was that a new formula was discovered for black hole entropy. It was discovered by Rio and Takayanagi. two Japanese physicists, one of them working here in the US. And they found a new formula that calculates a slightly different type of entropy. So in thermodynamics, there are two types of entropy. One is the one that appears in the second law.

It's sometimes called the Boltzmann entropy. But then there is a second kind of entropy, which measures the amount of fine-grained information, so quantum information it measures the amount of information that you have about the system if you are able to measure things precisely

as much as you can. So if you had infinite resources so let's go back to your example of shredding a piece of paper. So if you shred a piece of paper, you naively lose the information that is in the piece of paper. But it's someone with a lot of resources

and the resources of the FBI, etc. it can in principle recover the information, right? So for someone with enough resources, the information is not lost, right? But there are ways of scrambling something enough so that the information is lost if you really take that information away and store it somewhere else.

You take out all the little letters and you just leave the shredded paper and you took out all the letters. Yes. You make sure that. the information is not there. And so the, the, the, this other new form of entropy, what this new, this form of entropy,

well it's a standard form of entropy that people use to describe quantum systems, measures that second kind of information. The information available to someone who has infinite resources. And that's what this new formula gives us. It gives us another, the formula for the entrap in terms of an area. It's not the area of the horizon, it's the area of some other surface, that depends on the geometry of the interior.

So you are supposed to look at the interior of the black hole and find the area, the surface with some extreme alleged area. So the area, which, let's say it's a minimum, just informally speaking, so some vision where the area is a minimum and that minimum value of the area is that entropy. So it's a formula that is surprisingly simple, very similar to the formulas of black hole entropy, and it represents an animal

extension of those ideas of Blackhol thermodynamics to to and it represents a connection between spacetime geometry and quantum information because this this notion of entropy I should say this notion of entropy is intimately connected to it with the Shannon entropy the the notion of classical information actually as a side comment Shannon entropy was invented after for Noiman entropy and after this quantum version of the entropy that we're discussing right now. Anyway, so this concepts of entropy, this is a concept of entropy that is very important for both classical and quantum information theory.

And now we have a connection between black, well, through black holes between quantum information and space-time geometry. And these developments that you mentioned of the alien formula and so are all in this general area. Yes, it's a beautiful formula. I'll place it on screen

and put links in the description. Now, I haven't kept up with the literature, but my understanding is that it's in a Euclidean path integral, or lives in a Euclidean path integral, but I don't know if there's a Lerencian derivation. And if not, is there some reason for the impediment? Why is it so tricky?

Well, the derivation involves path integral techniques and the reason there is some Euclidean evolution is because it's usually necessary to prepare a state. So it's usually convenient to prepare a state by doing so-called Euclidean evolution. That's very common for the thermal state where a thermal state can be viewed by evolving over a Euclidean time in a circle. But we don't think that this is fundamental to the derivation,

and some researchers have suggested more natively, let's say, Laurentian derivations of the formula. For example, Dom Maril, Sik Chidong, and other collaborators from UC Santa Barbara have emphasized this more purely Laurentian derivation of this formula. There is always a little bit of Euclidean evolution because you need to get an answer for the entropy, which is a real answer for the entropy,

and Euclidean path integrals give you phases. Lorentzian path integrals, you mean? Sorry, Lorentzian path integrals give you phases, interference of waves and so. on. So, but, but so recently there's been an understanding of, uh, of this formula from a mostly Laurentian point of view, which is quite useful and makes, well, it's very useful and makes it, makes the derivation more general, more general than what was done previously. Yeah, so this formula is and is being better and better understood, I should say, and apply to new, new

situations. And this island formula is one of the breakthroughs. There are a couple breakthroughs of the past 15 years or so. One is the page curve, and this island formula has a relationship to the page curve, and that helps derive it. So can you please outline that? Well, the formula is interesting because

it connects black holes with quantum information. It gives us the amount of true fine-grained information that the black hole has. That's what makes it interesting. Now, a great breakthrough of the last few years was that the realization

that you could apply this very same formula for computing the entropy of hawking radiation. And this involved also some conceptual breakthrough in how to apply this formula. But fundamentally, it's the same formula. The page curve is a curve that a person called Donpage proposed as how the information of hawking radiation

as it comes out of the black hole, you have the hawking radiation coming out of the black hole. then you can calculate the information that comes out as a function of time or the entropy containing that radiation as a function of time. And what you find is that if the black hole evolves in a unitary way according to the rules of quantum mechanics, then that information should grow and then decrease again and decrease back to something small

when the black hole evaporates completely. That's what's called the page curve. And it was always a challenge to calculate this page curve. And using this new formula, we can calculate the page curve, and it gives that type of qualitative behavior. Now, speaking of constructing something, your dad helped fix elevators. And when you were 12, if my understanding is correct, that you built a working model with rasty blocks. Is that correct? Yeah, that's correct.

Yeah, my dad was a very hands-on person, and he liked to fix the car, fix the washing machine, everything, and then I always loved to watch it. It was a family activity, I guess. Yes, now that led you to going into engineering, but was there anything there that you now still carry over with you into physics? Well, I guess I view physics as a bunch of things that need to be fixed and formulas that maybe we're not fixing wires. you know, mechanical parts, but we're trying to build formulas and make all the formulas work together and fix a kind of conceptual architecture that tries to, you know, extend the conceptual architectures that we have right now, right? That's what theoretical physics, I think, it's about. So, expanding the conceptual tools that we have to describe nature.

Which of your results over the years do you think your dad would understand on site if, well, they're quite abstract, obviously, but if you were to explain it to him, which one do you think he would like the most? Well, maybe, yeah, maybe something more concrete, like how, you know, how energy flows after in particle collisions. So with Diego Hoffman, we did some calculations of that. And, you know, now thanks to the efforts of researchers

like Ian Malt and others, that they are being measured in the great detail, collider. So that's, I think, something that can be understood. Now, my understanding is Leonard Susskin's dad was a hands-on person as well, I believe, a plumber. You and Lenny have a great relationship, and you sent an email to him many years ago. ER equals EPR, just a single word or equation, and he understood it. What did he understand? Well, he understood it because we had been discussing that for quite a while.

So the connection between entanglement and space-time geometry is part of the developments spurred by this new formula of black olentropy, the right by Rui and Takayanagi, that as I said suggested the connection between quantum information and the geometry of space-time. This is the type of information that we sometimes want to measure when we want to quantify entanglement. So this information measure is also useful for that purpose.

So entanglement is a subtle form of correlation we can have in quantum systems. And of course, entanglement was discovered originally by Einstein, Podolsky and Rosen, and is usually known by the acronym of EPR. Now, surprisingly in the same year, Einstein and Rosen wrote another paper, which was the first paper noticing that the original shrashide solution doesn't describe one black holes but essentially two black holes that there are two regions, two outside regions.

And they didn't understand everything, but they understood this part about the black hole. And it was later understood more completely. It was later understood completely by Kruskal, you know, about 30 years later. But yeah, and that is sometimes called the Einstein-Rosan bridge. So the idea that there are two regions that look like flat space and they are connected through a black hole horizon

and the two asymptotic regions share a single interior. And if you look at that region at the moment of time, then it looks like a bridge between the joints two separate spatial geometries. So this also sometimes called the wormhole. And so ER stands for Einsteinian and Rosen. So some people read that as saying that the wormhole is entanglement. Would you be so bold or would you say that more like entanglement gives rise to some sort of geometric connection?

How do you see it? Well, so the I think, so the idea is that if, so we were talking about before about black holes and we're saying that if we're looking at, at the black hole from the outside, we can view it as a quantum system. Now when we look at the Schwarzial solution, we really have two black holes. So what's the connection between the two black holes? The idea is that these two black holes are two separate quantum systems that are entangled with each other in a very particular entangled state. It's called the Thermophil Douvel, if you want to know the name of this particular entangle state.

So but if they're entangled in this particular entangled state, then the idea is that they give rise to a geometry, connected geometry, which is that of the full shrashard solution or the Einstein-Rosan bridge. So in this particular example, I think the arguments that the entanglement creates the space-time geometry, or this space-time connection,

is fairly clear and quite convincing, I would say. Now, then the question is whether this is true in any case that we have entanglement. That's a wilder claim and I would say that we cannot make this claim in a meaningful way, in the sense that we don't know a description of geometry that is. I mean, if it is true, it should be true in some generalized sense of geometry. So it's definitely not true if our notion of geometry is the usual geometry

that appears in Einstein's equations. Because if we have just a spin-a-half particle, that two spin-a-half particles which are entangled with, each other there's no connected geometry of any kind, of the conventional kind. But perhaps, so ER equal to PR is a bit like an aspiration. So it's like a slogan or a principle that perhaps a more complete theory of gravity should have. So there might be a new notion of geometry that would generalize Einstein's notion of geometry

and in which this property would be true even for a spin-a-half particle. Earlier you said that you like to view physics problems as something that needs fixing. What are you fixing right now? I'm trying to understand the wormholes. So, wormholes are a bit like leaky pipes in the sense that the logic that surrounds them is not everything is fitting together. So we think we know a bunch of things about the theory of quantum gravity in the presence of wormholes. we like the effects of wormholes in some cases. They produce very interesting effects.

For example, they are important for justifying this island formula that you just mentioned. The derivation of that formula involves a certain kind of wormhole. On the other, they seem to give rise to the idea that the constants of nature are not quite fixed, but they maybe are arbitrary and we should average over them. And in some of our models of string theory and so on, the constants of nature are really fixed. So we don't know how to make everything compatible. Perhaps didn't explain clearly what the problem is.

The problem is a bit subtle. Perhaps a short way to say it is that there are many ideas that surround wormholes and they're not all compatible. with each other. The question is we probably need to modify some ideas or we need to, maybe they have some subtleties that we haven't understood. And this is, I mean, not only what I'm working on, but many other people are also working on this area. It's one of the hot topics in our field at the time. This video is sponsored by Shortform. If you want a free trial and an exclusive $50 off their annual plan, then go to the link in my description, shortform.

If you're like me, you've encountered books that are so dense, finishing them is actually just the beginning. Short form helps with that. Their book guides go far beyond pastiche summaries. They critique, they add context, they include interactive exercises, and connect ideas across authors. Take Gertell-Easher-Bach, or the master and his emissary, two of the most demanding reads in consciousness studies on the popular market. My method is I read the guide first, then the book, then I read the guide again. So it's a triptych of engagement that cements understanding, better understanding for me. The GEB guide maps recursive structures in a way that exhibits intellectual pliotropy where one insight branches into consciousness, computation, and self-reference simultaneously. Short form covers philosophy, science, and

psychology, ipso facto, the intellectual core of this channel. They publish new guides weekly and subscribers vote on what books get covered next. Their browser extension, Shortform AI, summarizes articles and YouTube videos with a single click. Go to shortform.com slash T-O-E for a free trial and an exclusive $50 off your annual subscription. That's shortform.com slash T-O-E. What about traversable wormholes? Ah, okay, so that's, those are fun.

Do you also view those, like, toy models, or do you think that in our universe, they may already be realized or they may be realized, I don't think they exist in our universe. Well, I think it's highly unlikely that they exist in our universe. Maybe that would be a more polite way to say or more cautious way to say. So, well, it's connected to what we discussed before, that if you entangle systems in certain black holes in a certain way,

you could get a connection. And that connection gives you a wormhole, but it's not a traversable warm hole. And you cannot send signals and you cannot travel through this wormhole. And that's consistent with the idea that can be interpreted as entangle states because using entangle states you cannot send signals. However, if you bring this black holes closer together and you let them interact, you let them exchange a bit of information and so on,

then they could develop this Einstein-Rosan bridge can change a little bit. the hole's geometry of the black hole could change, and it could form a warm-hole. So a wormhole would be a traversable warm-hole. It could form a traversable warm-hole, and traversable warm-hole is not quite a black hole, so it will not have a black hole horizon. And it would be some structure where you enter

through one of the mouths of the warm-hole and you exit through the other mouth of the warm-hole. In the warm-holes that are constructed this way, they don't allow you to travel faster in the speed of light in the space where the wormholes are sitting. So they are not like the science fiction wormholes that you might have heard in science fiction stories. And everyone gets excited about wormholes because you might, you think, oh, they will allow us to travel, you know, to the next galaxy and back in a short time. Those type of wormholes we don't think are compatible with the loss of physics.

So that the ones that allow you to violate causality or causality in the ambient space. But these are not. These are a bit more like long detours, but it's a long detour that you take using a wormhole. And let me make an analogy for this kind of traversable wormholes that are the ones that we think exist. Please. Yeah.

Well, before I make the analogy, I should say that they are classically forbidden. So classically, they cannot exist according to the classical equations, but they can exist thanks to quantum corrections because in quantum physics, energies can be negative and then they can exist. But now to the analogy.

So, you know, in the... There is this fine way to travel between two points on the surface of the earth, which is to dig a tunnel and then go down and then go up to the other point. And then if you have a tunnel with no friction, then just...

And you go with a little cart with no friction, then you would slide down this tunnel and come back out in the other side. And in maybe half an hour, 40 minutes, you could be in any place on the surface of the world. Now there are some small reasons why this would not work in practice or might be hard to realize in practice. You know, the interior of the earth is very hot.

There are no frictionless things. Just tiny reasons, yeah. Yeah, there are a few technical incompatessen. conveniences, okay? Yes. In principle, it is possible. So this traversal wormholes are a bit like this, but

imagine the surface of the earth as a structure of space time, and the traversal wormholes as this tunnel that you build through the earth. And, well, the earth is nothing. There is no nothing that exists there. That's roughly something somewhat similar.

And they will allow you to go between these two points, and they will allow you to go from your point of view very fast. So because there is a large gravitational field, you would not experience a very long time in going through these warm holes. So someone from the outside would see that it takes you, I don't know, 10,000 years to go through the warm hole. But if you go and you travel yourself,

it will take you maybe one second. Again, these are not things that will exist in nature. They would require lots of physics, which are new particles that we haven't seen and stuff like this. I'm not these are some solutions that are compatible with the general principles

of nature but not the particular loss of nature that we have in our universe speaking of wormholes there was a hubbub about how there was a publicity campaign about quantum computers creating literally creating wormholes in the lab

those were some of the pop side headlines so what's the actual truth behind the headline Yeah, so that is in this context of entangling quantum. So there is the idea that if you have a quantum system that is complex enough, it could create an immersion space time. Now, this is an interesting point and what is a subject that we've been investigating. And I guess with the promise of quantum computers is that they can make all kinds of new materials and new quantum states of matter.

And this would be a very fun and interesting quantum state of matter that might allow us to test some of these ideas that we have about quantum gravity. Now, this also in particular tells you that if you create two pieces of matter in this way that have an immersion geometry and that then they are entangled with each other, then they would create a wormhole that connects them. And now, what this authors did, they created a quantum simulation that had what they said was the symptom version of this wormhole. So they took the simplest model that displays some phenomenon similar to this wormhole

and they pair down to the model to this bare, very, very, very essentials and they found some features that were a little bit like the features of this wormhole. So it's a correlated quantum system. They had a small number of qubits, maybe I think maybe seven qubits on each side. And so people

have, some people say, well, no, you you don't have enough qubits. This is not the system that is complex enough. But I think it's, I would say it's a first step in this direction. And I think as, you know, quantum computers will become more and more powerful. They will make better and better versions of this type of thing. And at some point, people will say, well, this really is looking like a wormhole, right? I mean, it's a bit like this question of when a sandpile becomes a sandpile, right?

So, yeah, you have seven grains of sand, okay, maybe it's not a sandpile. But once you have enough grains, it will become more universally recognized as a sandpile. So they simulated a wormhole but didn't actually create a wormhole or what? Well, yeah, it's debatable of whether in this type of setups you either simul or create. So this is a bit of a language question. So if you have a condensed, if you create a quantum simulator, a quantum state of matter that has a certain property, let's say superfluid or whatever, are you creating it or simulating it? You know, once you, once the quantum computer allows you a level of control that

you can do many things. You can create a quantum state that has various properties. And the question is whether you're simulating them or creating them, I think it's a bit philosophical. When I'm wrestling with a guest's argument about, say, the hard problem of consciousness or quantum foundations, I refuse to let even a scintilla of confusion remain unexamined. Claude is my thinking partner here.

Actually, they just released something major, which is Claude Opus 4.6, a state-of-the-art model. Claude is the AI for minds that don't stop at good enough. It's the collaborator that actually understands your entire workflow thinks with you, not for you, whether you're debugging code at midnight or strategizing your next business move, Claude extends your thinking to tackle problems that matter to you.

I use Claude, actually live right here during this interview with Eva Miranda. That's actually a feature called Artifacts and none of the other LLM providers have something that even comes close to rivaling it. Claude handles, Interalia, technical philosophy, mathematical rigor, and deep research synthesis, all without producing slovenly reasoning. The responses are decorous, precise, well-structured, never sycophantic, unlike some other models. And it doesn't just hand me the answers.

The way that I've prompted it is that it helps me think through problems. Ready to tackle bigger problems? Get started with Claude today at Claude. That's clod.a.ai slash theories of everything. That's clod.a.i slash theories of everything and check out Claude Pro, which includes access to all of the features mentioned in today's episode. And why are you working on these leaky pipe wormholes right now? What is it about them that excites you?

Well, it's that there is a conceptual problem. So there is a, they are interesting because they give interesting effects. And they also raise questions and we are trying to, and there is something not completely understood around them. That's what is interesting. That by understanding them better, we'll understand quantum gravity in a deeper way. I think, so this one holds very mystery

since, let's say, the 80s when people started thinking about this. I mean, soon after this hooking information, that is related to the hooking information problem. and researchers discussed them at the time, Coleman and Giedenstein Strominger discussed them. And the situation was confusing at the time. It wasn't clear what the rules were for quantum gravity. And they didn't seem to be present in strength theory

in any way we understood. But now there are many effects that these wormholes have been, well, have proven useful for deriving, for example, these formulas, for driving properties about the black hole or the energy spectrum of black holes. There is a series of beautiful works by papers by Sad Schenker and Stanford where they show that certain aspects of quantum chaos are reflected in a warm hole closely associated

to the Schwarzschild solution. And, yeah, so WarnPOS are doing wonderful things for us, and we should understand how to fit those wonderful things with the confusing aspects. Speaking of Strominger, he treats the BMS group as a physical symmetry, and that's what undergirds Celestial Holography. I haven't heard you comment on celestial holography on that program. What do you make of it?

Yeah, so, So this program's been recently understanding subtle properties of gravity in flat space. So instead of trying to understand gravity at very short distances, they look at gravity at long distances, but they try to understand deeply the symmetries of flat space and what happens when you emit some waves of radiation at very long distances and so on. And they've uncovered lots of interesting symmetries. I mean, the BMS group is something that was recognized in the 60s, but they found a interesting connection between this BMS group and some other features of scattering amplitudes

and other gravitational phenomena such as the so-called gravitational memory effect and things like that that involve scattering of gravity waves. Now, yeah, so this is a very interesting aspect. aspect. And so in the past, in this symmetries were important for deriving, let's say, dualities between gravity systems and quantum field theories. So there was a beautiful paper of Brown and Hennon, who found that three-dimensional antitheter space, a particular three-dimensional negative-dicklequare space, has a two-dimensional boundary. and on this boundary it has a certain symmetry, which is the same type of symmetry you have in quantum critical systems in, in one-plus-one dimensions.

And then it was then used to propose the duality between these two systems. And well, Strominger himself used this to argue for this duality in general ways. So yeah, so this is something that has proven to be important in the past, and now we don't know whether flat space, gravitational physics in flat space has some alternative description in terms of some quantum system. Of course, if we had that alternative description, we could describe black holes and so on in flat space in a more complete way. And that's one reason for trying to find it.

is somehow also viewed as a stepping stone towards trying to understand the more realistic cosmology. So the cases where we understand a fully quantum mechanical description, more precisely are cases with negative curvature, so cases like hyperbolic space. And then flat space is intermediate, and then, let's say a sphere or an expanding universe

are the more interesting ones. Now, I know that you're also working on DS-CFT correspondences, why is that so tricky? Well, ADSCFT is this relationship between negatively curspaces and field theories or quantum systems at the boundary. D.S. means the CTER, so the CETER was a Dutch astronomers who proposed this expanding universe

and that is a good description of our universe at late times or also at very early times. and the structure of these two space times is fairly similar and they both have a kind of boundary. In the case of an expanding universe, that boundary is what happens very far into the future. So very far into the future, there is a kind of surface that looks spatially flat

and has the structure of three-dimensional space with no time. And it's natural to think that perhaps there is some statistical theory that describes such universes. So it would be a universe where it would be a description where the time would be a merchant. And the main difficulty is that we don't have nice guesses. So we don't.

In the case of the anti-deciter case, we had the help that in those cases, we can have additional symmetry. such as symmetry called supersymmetry, which is very technically useful and useful for generating examples of this relationship. But in the CITER case, it's more complicated to generate examples. Now, maybe we don't generate the examples

because this relationship is not true, maybe the relationship would be intrinsically approximate, so we don't know exactly why we haven't managed find an example. It might be that we just don't have the right techniques to find it. And supposing that DESE's results are correct and that there may be time-varying dark energy, does that put a monkey wrench in DSCFT or does that help DSCFT or it would just be some small mere technicality? Well, I mean, of course it would be a very interesting feature of the universe that the dark energy is changing.

It's not logically connected with the SCFT in any obvious way. So we could have varying dark energy or not varying dark inertia. Of course, if we have a barring dark energy, the structure of the universe in the far future will not be the sitter. I mean, it might still be the sitter because the dark inertia might eventually stop varying. Right. Now, something that is more worrisome is that some of the DESIFITs have suggested that the value of the Arcanache could be, of the equation of state could go below minus 1.

That would be a more severe blows of our understanding of physics. So I suspect that that probably will not be true. Why, though? Well, because there are deep principles, the principles of, you know, no negative null energy. So these principles that enforce causality, that enforce, you know, traversability of lark or traversability of wormholes and so on. So I suspect that these principles are more important than, well, are very important and I find them very sacred. Of course, if it was true that they're violated, it would be super interesting,

and it would be the biggest news in the last, you know, hundred years. But I very much doubt that that's what will happen. I suspect that once they fit the data in a different way. And so I don't think that there is enough evidence to claim that this equation of state parameter, which is called W is less than minus one. Another pillar is unitarity.

and I've heard many physicists say that they'd rather sacrifice locality for unitarity, that unitary is sacred. So can you please give a taste as to why? Why is unitarity so important? Well, unitarity is related to the conservation of probability. So if it wasn't true, then we would have trouble with probabilities. So probabilities might be not possible. or bigger than one and we would have some bigger problems.

So we wouldn't know how to interpret the theory where that's not true. Yeah, so it might be that we might need to give up some other principle of quantum mechanics or some other aspect of the structure of quantum mechanics. That might be possible. Like these discussions of including the observer or some of the problems we face in quantum gravity with the emergence of time, maybe we'll require us. eventually to give up some of the structure of quantum mechanics. But I wouldn't necessarily say that we give up locality.

I would say that we give up some manifest locality in some of our current descriptions. It's not completely obvious we are giving up locality. I think we're just not manifest in the ways that we describe it. What's a manifest locality versus an actual locality? Well, the problem is that locality is hard to define when you don't have a space time, right? When you don't have a background space, a fixed space time, right? So when we are thinking about quantum gravity, first of all, when we're thinking about quantum mechanics, let's say just for a single particle, the particle doesn't have a well-defined position on momentum everywhere.

It can have various possibilities for its momentum and its velocity. Right? Similarly, when we do quantum field theory, a field does not have to have a definite form in everywhere in space-time, but it could have probabilities of having various different possible forms. Now, when we talk about gravity, then what we are saying is that we have a metric or a space-time geometry, and it's not fixed. We can have various probabilities of having different space-time geometries. So, you know, two points that are on man's surface

may be far on that surface, but on some other surface, they are smaller, and both have some probability, right? So they're there. And so when you say that, you cannot say a priori where two points are far away or not. There is always the probability of having some surface where they are close by. And that's why localities sometimes a little harder to define.

But maybe it is local in the sense that maybe for each each of the particular surfaces that appears the theory is local in that sense. And there is some notion of causality that you cannot, if you have a space that is some, let's say asymptotically flat, which is flat far away or this negative space is far away, then far away you have a structure, a causal structure that you define. By causal structure, what I mean is that, you know, two point. points might be reachable by an observer who travels at less than the speed of light. And that's usually, well, that we think will be preserved by the bulk space time, even though

it's fluctuating and so on, even though there can be fluctuations where the points are closer and so on. In the end of the day, if you want to send the signal, you cannot send it faster than light. So causality continues to be preserved in that sense. for the entanglement wedge reconstruction there's a objection from Harlow so please explain what's being presupposed explain this whole situation

well I think we can discuss this a little bit so yeah Almeri Don and Harlow wrote a very interesting paper where they propose some analysis between quantum error correction and the way

that holograph is supposed to work So basically quantum error correction and the map between the bulk degrees of freedom and the boundary. Or some analogies between the way that the bulk is embedded in the boundary theory and the way that the quantum information is embedded in a quantum error correcting code. Yeah, and this was very nice. And then was a wonderful paper. And then there were a series of developments involving other techniques that people used to describe quantum systems that involve something called tensor networks. So tensor networks are roughly like neural networks, but to describe quantum systems there is something analogous to neural networks, but it's a mathematical or a physical procedure if you wish to encode a quantum systems.

a series of qubits in a complex quantum system. Yeah, and this shed some light on, you know, how perhaps the Black Hole could be embedded into the boundary theory and other aspects of the holographic dictionary. Now, in this ADS-CFT correspondence or in holography generally, when there's a duality between the boundary and the bulk, is there a reason to privilege one ontologically than the other? so for instance some will say that the bulk emerges from the boundary.

Yeah, yeah. That's a popular thing to say now because we think we understand better the boundary theory. But I think it might be that at some point we'll understand the bulk theory also well enough that we will view it as a true duality between the two things and that both would be ontologically similar. When I was speaking to Eric Verlinde, he said, no he said the boundary is real and then I said why why if they're a dual he said well they're not exactly dual yeah I mean there is a sense in which the the geometrical concepts of general relativity are have some limitation right I mean the general relativity itself is what we call an

effective field theory so it's some theory that it's well defined at long distances but that shorter distances has some problems. It's not quite well defined. So we already know it should be replaced by something else. However, we think that we can replace it by string theory, for example. And then if you take that point of view, then, okay, the bulk theory in principle is also well defined, except that string theory is a work in progress. It's not a theory that has been completely understood.

It's many aspects of being understood, but some remain mysterious. and it is possible that in the future we'll understand that this bulk theory well enough so that will be equivalent to the understanding we have of the boundary theory. But for now, that's a speculation. Are many people working on M theory currently? Well, M theory, I think, is viewed as a kind of phase

or a region of some consistent theory, which also sometimes is called strength theory, and it's a phase where it's 11-dimensional. And yeah, some people are working on some aspects of this. I mean, I personally with Aidan Herdershey wrote a paper a few years ago, a couple of years ago, talking about a very interesting proposal for M-theory that is based on a certain matrix model. So the idea is that you can discuss scattering amplitudes in that theory,

using a simple quantum mechanical matrix model. Yeah, so people continue to work on this subject. It's part of the whole area of quantum gravity, and some questions might be interesting to ask in that 11-dimensional context, some might be interested in a different context. Your office at the IAS is infamously fairly empty on the walls. Why? Well, maybe I never bothered too much to put something on the walls.

It has a few pictures, but not too much. Is that a reflection of your mind? You like to keep it clean or who cares? Yeah, yeah, I like to keep it clean, keep people focused on the blackboard and keep us focused on the blackboard when we come and discuss to my office. What is it like to live in your mind?

I don't know anything else. What does your wife say? Well, she, I guess she finds sometimes a little strange our obsessions with certain things and that same with my wife. Maybe I'm a little obsessive, I guess she says.

Yeah, yeah, same. Yeah. you able to turn off your mind or do you just keep churning on problems? No, I'm not able to turn it off too easily. Yeah, that's right. That's one of the things she complains about. Yeah, same. Yeah, and I constantly have ideas.

I constantly have to pause what we're doing and then have to jot it down and interrupt. I don't know, are you the same? Yeah, yeah. No, I disconnect, but it takes me a while. So, yeah. What's your average day like? Do you have a routine where you set work from, say, 8 a.m. to 5 p.m. or what have you, and you say, I'm not going to work outside of that.

Yeah, I have something like that. So, yeah, usually I'm in my office from 9 a.m. to 7 p.m. And, yeah, I like to do exercise in the morning and, you know, go to the office. And in the office we discussed with various people, with other researchers, with postdocs, visitors. And that's a big part of the day. I mean, that's a big part, I think, of scientist's life, is to talk to other people and, you know, interchange ideas,

make progress together. What exercises? I usually just go jogging. Oh, okay. Sorry, I'm super curious about your work schedule. So do you fix that you're going to be alone closed door from 12 to 3 p.m.? And you can take meetings before that, or is it just varied? No, I usually allow myself to be interrupted.

So I like to be available. Well, usually I arrange meetings with students or post dogs. It is sort of a bit more chaotic. And well, usually there are fixed times for seminars. things of that kind. What's the difference between a good PhD student and a great PhD student? Well, I guess a great PhD student has new ideas

and, you know, comes up with great problems and comes up with things that blow your mind away. So things that are unexpected, things that you think are wrong when you first hear them. And then eventually you realize that, oh, no, that's right. That's a great idea. Many times I've told my students that what they said were wrong, and they ended up being great ideas.

Why don't you give us a flavor of that? Well, for example, a person called Ather Lakeowicz came with an interesting generalization of this formula for the, of Ruehantakian. that we were talking about. And I said, well, I thought it was probably wrong and not justified. But in the end, it was correct. And, yeah, unfortunately, he didn't publish it. The other people published it.

So that was one of my failures as an advisor. Many people may not know this, but your breakthrough paper from 97, it was assigned essentially or inspired by a boring project that was given to you by Callan, your advisor. Well, why don't you tell that story? And then I want to know if you're working on a boring project right now that you think may lead to something. Well, I think, of course, Kurt Callan is one of the greatest founding fathers of the standard model of particle physics and all that. And he had a great intuition for great problems. And, one of the problems he gave me was to work on some statistical models in or field theories in hyperbolic space.

And yeah, so I thought that was a boring problem. But I did it because he was my advisor, he told me. But it gave me some tools that then were useful later. Have you assigned a boring problem to one of your PhD students that turned out to be? Well, no one can match your British. and breakthroughs, but you understand. Well, I don't know whether my problems were as good as Kurt Callan's problems. Yeah, maybe, well, I guess I think they are somewhat interesting, but yeah, maybe my students thought they were boring.

You said that you are a perpetual student. So who are you learning from right now? Well, I guess we, I learned from other people. I learned from my students. I learned from, you know, I were postdocs. I learned from other researchers. And we were constantly learning new things. Okay, let's be concrete.

What's something in recent memory that they taught you? Well, for example, we were talking about this new formulas for blackhol entropy that within Pennington derived. I mean, I had no idea of those techniques, those mathematical techniques. I had to learn them. They taught me these techniques to me. A new way to think about it. Ah, now Cyberg, another colleague of yours,

mentioned that you go after problems that most people stay away from. So is that just his characterization of you? It's a mischaracterization, or would you say that's correct? Like, what is it about you? No, I don't think, well, I think many people work on the same problems

that I work on. I feel, I mean, people are interested in black holes, people are interested in quantum mechanics and black holes. And I feel I've always been in a community of people who have been interested in similar things. What's a result then that you hope is true, but let's say you have. So the ADS CFT has plenty of evidence, and there's no proof. So I was about to say, what's something you hope is true,

but you have no proof of, but proof is quite strong. So I'll be even weaker and say, what's something you hope is true that you have even little evidence of? Okay, I'm going to mention something that I hope is true. Some people think it's not true. And so, is that when you have the theory of inflation,

the field range is as finite. And the field can, in other words, the field cannot move much during the inflationary time. Now, the reason for, thinking that this might be true as well various things about wormhole, so it's not very clear.

And some people most notably, Eva Silverstein, think that this is not true, and we've always debated this. But if it were true, it would be interesting because it would be a falsifiable prediction, so from ideas of quantum gravity.

Unfortunately, we cannot argue whether it's true or not. If it were true, it would predict that the experiments in the near future would not see gravity waves. I mean, the experiments that look for gravity waves in the CMB would not see gravity waves. One part of me hopes that this is true so that we could have a prediction.

The other part of me hopes that we will see gravity waves from inflation. I think that would be more exciting because it would tell us, you know, quantum gravity is real, and inflation probably happened. And, yeah, that would be real. That's one of the most, I think, exciting prospects to see this gravity waves. That was a long and somewhat technical answer to your question. You were probably hoping for a more flashy answer. Well, just so you know, this podcast, it skews quite technical.

So now, obviously, it can't just be with this many subscribers and watchers, just technical, but there are many artists and truck drivers and so forth. But we skew it toward academics and researchers and physics, philosophy, math. So speaking of flashy, you have a paper from two years ago or so. See, on YouTube, you can be flashy with your titles, with your thumbnails, and so forth. But there's not many paper titles that are grabbing. And so when I find one, I always find it fun. you have one called

oh gosh let me recall this correctly real observers solve imaginary problems yeah so well this was a bit of a play on words

so there are some calculations that you can do in the citter space which is this cosmology there is a Euclidean version of the cedar space and as I

as we mentioned before sometimes the Euclidean versions of certain space times can be useful for calculating thermal properties of those spaces. And in this case, the Euclidean version of the Cedar space is a sphere, and it is supposed to calculate the space as seen from an observer who's in the center of that space and the thermodynamic observations of that observer. This is something that was discussed originally by Gibbons and Hawking in the 70s, it's closely connected to their work on black hole thermodynamics.

Now, when you compute, so that's a leading classical effect, and then if you compute the quantum corrections, you find the funny feature that the quantity that is supposed to be the number of states or counting the total number of states of this thermodynamics system is not positive. So it can have an I, so the I, the imaginary unit, to some power that depends on the dimensions. In different dimensions, you get different answers.

Sometimes it's positive, sometimes there is an eye, sometimes it's negative and so on. And so the idea is that if you consider a slightly more complicated discussion where you include an observer that is moving in this space, So you don't just do the empty space, but you do the space with the observer. As you mentioned this paper, Chandra Sakeran, Longo, Pennington and Witten. They found from the Laurentian point of view, so from the real-time point of view that it was useful to put an observer,

but also from this Euclidean point of view, if you put an observer, then now the number becomes positive. So in that sense, putting an observer, a real observer observer, that is there in the system solves this problem with the imaginary numbers that were appearing. So that's what that title is about.

And as I was going through it, does it mean that there is no view from nowhere in quantum gravity that you require an observer? Yeah, yeah. That's what happens here. Even in perturbation theory around a fixed background?

Well, in perturbation theory, It depends on the background. So it has a bit to do with the choice of time. So in internal relativity, there is no a priori notion of what time is. So you can redefine your times and so on. But if there is something going on in your space time, like, you know, for example, in inflation or in cosmology where the universe is expanding, then in our universe we can think of time as the mean density of the universe.

the universe dilutes, then time progresses, right? And we can use that to measure the passage of time. Or we can have a clock that, I mean, if we have an actual clock, then the clock also measures the passage of time, but well, it's a physical system that has some parts and it's moving and so on, and that measures. So, of course, somehow the physics definition of what time is, the more practical definition is what clock measures. the question is, can you measure time without the clock?

And the idea is that you can't. Interesting. You would need a clock of some kind to be able to talk about time. And that's what these observers are doing. They're providing some type of clock. And also some location in the universe to say where you are. So we are where the earth is and that's our location. So you say we can't measure time without a clock or you can't measure duration without a clock?

Or are those two the same to you? I would say the same view, yeah. So then would you also say that we can't measure length without a ruler? Yeah. Or is that somehow different in this? No, no, it's the same, yeah. When people talk about general relativity, even in Einstein thinking of general relativity, when he was imagining a system of rulers, of observers that were moving in space

and they were exchanging information, synchronizing their clocks and, you know, comparing the rulers and so on. And in the classical theory, you can consider those observers as having no mass and no energy and not doing anything.

But once you consider the quantum theory, you cannot do that. And you have to take them into account as physical systems. And so, well, it's part of what makes the quantum theory a little more complicated. What's the justification for having a single minus sign?

So in other words, a single time direction. Why not have two time directions or three or what have you? I don't have a good answer. So with a single minus, we understand what the theory is like and we are used to that. And I don't know if it is possible to have more minus signs. I mean, it gets very confusing and so on, but just that it is confusing doesn't mean it's impossible. but so I don't know if you can it's not what we seem to have in nature but

yeah I mean I know there are two times theories like bars I believe well it's true that sometimes you can introduce more than one time and this is an idea that goes back to the act for in his treatment of scaling variant theories like electromagnetism and so on But usually if you do that, then you also have the second time,

together with some spatial coordinates form what's sometimes called projective coordinates, which where you eventually end up removing again the time that you introduced. So you somehow introduce one extra time and then you end up removing it again. But it's useful to introduce it to make manifest some of the symmetries of the theory. And it's true. I mean, I don't view this as a fundamentally new introduction of time. I mean, that is something we understand. And, you know, I've used it myself in some of the papers.

But I guess the question is whether really we have more than one physical time that I don't know. Hi, everyone. Hope you're enjoying today's episode. If you're hungry for deeper dives into physics, AI, consciousness, philosophy, along with my personal reflections, you'll find it all on my substack. Subscribers get first access to new episodes, new posts as well, behind-the-scenes insights, and the chance to be a part of a thriving community of like-minded pilgrimers. By joining, you'll directly be supporting my work and helping keep these conversations at the cutting edge.

So click the link on screen here. Hit subscribe, and let's keep pushing the boundaries of knowledge together. Thank you and enjoy the show, just so you know. if you're listening, it's C-U-R-T-J-A-I-M-G-A-L.org. Kirt-Jimungal.org. Space time is doomed. Well, I think that tries to echo the Minkowski's dictum that space is doomed. I mean, we won't have space again.

We won't have time. We'll have now space time. And now you say, well, space time is doomed. What that means is that, the new theory of quantum space time will have to use a different concept that there will be a new concept and we don't really know what the new concept is

so that's what this quotation tries to emphasize. And what do you make of it? It's a challenge for us to find a new concept. There should be a new fundamental concept and I would say that we don't know what the new fundamental concept of quantum gravity is. So the basic concept in the same way that space-time is the basic concept for general relativity. We don't know what the fundamental concept for quantum gravity is.

Two approaches come to mind. So one is Verlindes, entropic gravity. And then another is Nima's positive geometries. So have you looked deeply into them enough to talk about what interests you about them and potentially what disinterests you about them? Well, I think this idea of entropic gravity seems to be very useful and relevant when we think about what happens near a black hole horizon. And it's related to this interesting connections between gravitational and thermodynamics in the context of near black hole horizons. It's not clear how this extends beyond, you know, black hole horizons. And also more recently, as we were saying, there is a deeper connection between quantum information and gravity. So it's not just thermodynamics or entropy, it's just this more fine-grained concept.

That's probably what Eric Berlinde thinks has in mind. But yeah, so maybe some version of that might be true. I mean, all these are ideas for some ways to get at the correct structure. And Nima's discussion is connected a bit to the, well, it's the idea that you study scattering amplitudes and from far away and try to reconstruct the space time where that scattering is occurring and determine the scattering amplitudes through some other alternative theory or other alternative principles where, and then the usual space time will come out. yeah, out of something else. But we haven't yet found it. So there are, it's certainly something people are, I mean, it's a challenge, as we said,

and people are trying to meet this challenge in different ways. Yeah, and those are, well, you know, interesting ideas. And in particular, this idea of looking at the deep mathematical structures in scattering amplitudes is very promising because, you know, you might or might not find space time, but you'll definitely understand. And people have definitely understood the scattering. in amplitudes in ways that are very useful and powerful for colliders.

So, I mean, these methods that they've developed are now used in particle accelerators and are useful for computing other things like cosmological observations and many other applications. What is it about NEMA that you admire? Like, what's different about it? Well, he has unbounded energy. He has an amount of energy. that is pretty amazing and he can go from some mathematical

discussions about the structure of Rasmannians or whatever they are and to aspects of phenomenology in particle physics and he is able to follow many different subjects

he's very amazing actually my brother who is at the University of Toronto is a professor in math finance, was also at the University of Toronto as an undergrad with Nima and said that I've always remembered Nima's energy. Yeah. So what about Witten? What is it about Witten that you admire? What is it like to collaborate with Witten? Well, it's wonderful. I mean, he's very fast and yeah, very deep as I was saying. Yeah, it's really great. He has a depth of understanding that is, you know, light years ahead from mine.

Yeah. Again, he has both a knowledge of math and physics that is amazingly broad and amazingly deep, you know. Many people, you can be deep, but not very broad, but you can be very broad and not very deep. But he's both things in an amazing way, you know. He knows things better than the specialist in those fields. And this in many, many different fields. So Strominger had a paper recently, February of this year, I believe, where he used GPT, one of the models of GPT to find glue-on amplitudes.

Now, do you use AI? Do you hope to use AI? Yeah, I hope to use AI. I use it in a simple way. I haven't written a paper with it. I used it to help me with some calculations, formulas, as probably you and many of our listeners are using AI. Yeah, I think I found a really interesting way to use it, and they found an interesting formula,

and I'm actually discussing this formula with the collaborator of Andy, who's a postdoc at our institute, Alfredo Guevara so we are yeah we're analyzing some other we're doing some follow-up work on this paper and studying some of the consequences

of this formula when I was speaking to Edward Frankel he said that who also collaborated with Witten he said Witten speaks in fully formed sentences that are like an essay where each word matters

yeah it's true I mean he understands it completely and then then you sometimes say, oh, no, but it's better to think about it this other way, and then you realize, no, no, really the way that Edward said in the beginning, that was the best way to say. Yeah. So going back to AI, so for LLMs, like what do you personally use them for, do you use them for idea generation, or do you just, you use them to learn about some topic, or just something mundane, like, hey, make this, make this recipe for me for different amounts of people.

Well, maybe learning about topics I don't know that are well known so that, you know, as a better Google search. I do some formulas with it. I ask it to check some formulas. I mean, for doing integrals, it can be better than Mathematica sometimes. Then you check it with Mathematica. So Mathematica is this computer program of symbolic manipulation that we use it. So it's good for discovering new formulas and proposing new formulas.

No, it's not always right and can make mistake as the warning sign tells you. It's true. Yes. But it's useful. It's very useful. I have no doubt that it would be more useful in the future. Yes, yeah. The progress in the past few years is remarkable.

Yes. So, as you know, the podcast is watched by many researchers, many PhD students, many blah, blah, blah. so many of them will like to know how the heck do those in the top of their fields use AI? So you just mentioned that you use it to teach yourself and potentially to generate new formulas and so forth. Can you be more specific? Because there are some ways of using it that are poor and there's some ways, I'm sure, that are better than others. I would advise people not to imitate what I do in AI. I think maybe I feel already like a dinosaur

that I'm not learning it fast enough. And you should try it and you should explore yourselves and find new ways, yourselves to do it. I don't have a good answer. Myself, I haven't found myself a really good way to use it. I'm sure that there are wonderful ways to use it. It's a very powerful technology. and I really encourage you to experiment.

I tell this to my students. They come and say, well, I tried this calculation. Did you try it with AI? Yeah. Sir, what's a piece of advice that you've received? Could be from your advisor, could be from anyone that you keep coming back to or that you pass on to your students?

Well, it sounds tried, but just be open-manded and try to learn, question things. understand things deeply, don't go too fast, just, you know, don't repeat what everyone says,

just understand things, your own way. I think those are, those are very important things to do. Can you tell me about some way of understanding that was someone else's way didn't work for you and then you

reformulated it to your own way? It's hard to give an example, but it often happens that people, sometimes there is something called lore, right? That, you know, people in the field maybe repeat, but they haven't really thought

about through very much. And then if you, you know, works with something and do the calculations from the beginning, go to basics, and you really understand it. It's just that people were repeating things without having done the calculation without really having understood.

without having understood it. Now, examples, well, I remember when I started working on cosmological perturbation theory, I found lots of confusing things and I was very confused about how these calculations were done in a curve space, in an expanding universe and so on. I had to go back to basics, you know, how to do it with a harmonic oscillator, a time-dependent harmonic oscillator, and so on, and that was useful to me. And I feel sometimes in some pieces in some pieces, the literature, people were, you know, inventing some grand general schemes that were not

respecting the, we're not working for the simplest case, so for the harmonic oscillator. Yeah, and that was useful for me to go through this just to understand and develop things yourself. And then once you understand things by yourself, you understand what other people are saying, right? You say, oh, this is what this paper was saying. And you, you can then read the other papers and understand what they are saying. there's a lecture that you gave at Harvard called the Chiloquium, if I'm not mistaken. And in it, you said that you didn't feel good enough as a graduate student. And many graduate students feel like that.

So what changed for you? Well, I, yeah, I think it's common. Maybe not to feel good, to feel that maybe you are not good enough. You know, there are the people from the past that did some, great things, but this is not, you know, your time. Now things are more difficult. And, yeah, many people go perhaps to graduate school thinking that they would go in and do all kinds of, you know, amazing discoveries from day one. And the, you know, the reality is that you need to learn many things, you need to know what's known.

You need to, and well, it takes some time. But, well, eventually you'll make your contributions. field first there will be small contributions then maybe a slightly bigger contributions you'll become a specialist in your field then maybe you'll have a great idea at some point you'll make an important contribution

and I think if you if you are in your career in science you'll make some of these contributions along the way and sometimes you'll make them in the beginning of the career sometimes you'll wait long you make but eventually you'll make big contributions and sometimes maybe you make contributions which you didn't realize they were big

and then they become bigger later. Yes. Yeah. And yeah, maybe some things that were thought to be big than they are not big, so we'll see. But it's all part of contributing to science and I think, yeah, that's what's important. Of course there is the issue of careers

and finding a job and so on. That's always challenging. Did you once tell Lisa Randall that you'd like to write a science fiction paper? It is possible. Oh, yes, yes, I did. So, yeah, yeah, I wrote the kind of science fiction paper on these traversable wormholes.

So the stuff we were talking about before is related to traversable wormholes was using one of her ideas. So something called the Randall syndrome model. Yes, yeah. And to be clear to people who didn't read it, it's not science fiction in the sense that it has a hero

and then an antagonist, an evil villain. No, there's no villain. It's just the discussion of this traversable wormholes assuming, you know, this... Okay, so the Randall-Srum model is a possibility for physics beyond the standard model, and there are various versions of it, and there's one particular version

which allows for the construction of transversible wormhole solutions. And, I mean, part of the work that Randall's and Zrum did was that to notice that those particular models for physics beyond the standard model were compatible with all current measurements. Well, of course, they make some new predictions for the future,

but they're at least compatible with all the current things we know. So they're not ruled out. And so one of those versions which are not ruled out could allow for traversal wormholes. Of course, that they are not ruled out doesn't mean that they are likely to exist. And also it doesn't mean that constructing these wormholes, I mean, we constructed mathematically the wormholes as solutions. We didn't give a physical procedure for making them.

So it's a mathematical curiosity, if you wish. But it kind of shows, it gives an interesting scenario where traversable worms or warmth could exist and could be relatively big. Professor, I just wanted to thank you for spending so much time with me, and I appreciate it. Sure, it's been a pleasure, and good luck to everyone. Hi there, Kurt here. If you'd like more content from theories of everything and the very best listening experience,

then be sure to check out my substack at kurtjymongle.org. Some of the top perks are that every week you get brand new episodes ahead of time. You also get bonus written content exclusively for our members. That's C-U-R-T-J-A-I-M-U-N-G-A-L.org. You can also just search my name and the word substack on Google. Since I started that substack, it somehow already became number two in the science category. Now, substack for those who are unfamiliar is like a newsletter, one that's beautifully formatted, there's zero spam.

This is the best place to follow the content of this channel that isn't anywhere else. It's not on YouTube, it's not on Patreon. It's exclusive to the substack. It's free. there are ways for you to support me on substack if you want, and you'll get special bonuses if you do. Several people ask me like, hey, Kurt, you've spoken to so many people in the fields of theoretical physics, of philosophy, of consciousness. What are your thoughts, man? Well, while I remain impartial in interviews, this substack is a way to peer into my present deliberations on these topics.

and it's the perfect way to support me directly. Kurtjymongle.org or search Kurtjimungle substack on Google. Oh, and I've received several messages, emails, and comments from professors and researchers saying that they recommend theories of everything to their students. That's fantastic. If you're a professor or a lecturer or what have you, and there's a particular standout episode that students can benefit from or your friends, Please do share.

And of course, a huge thank you to our advertising sponsor, The Economist. Visit Economist.com slash Toe, T-O-E to get a massive discount on their annual subscription. I subscribe to The Economist, and you'll love it as well. Toe is actually the only podcast that they currently partner with, so it's a huge honor for me, and for you, you're getting an exclusive discount. That's economist.com slash tow, T-O-E. And finally, you should know this podcast is on iTunes. It's on Spotify.

It's on all the audio platforms. All you have to do is type in theories of everything and you'll find it. I know my last name is complicated, so maybe you don't want to type in Jymongle, but you can type in theories of everything and you'll find it. Personally, I gain from rewatching lectures and podcasts. I also read in the comment that Toll listeners also gain from replaying. So how about instead you relisten on one of those platforms, like iTunes, Spotify, Google Podcasts,

whatever podcast catcher you use, I'm there with you. Thank you for listening. The Economist covers math, physics, philosophy, and AI in a manner that shows how different countries perceive developments and how the impact markets. They recently published a piece on China's new neutrino detector. They cover extending life via mitochondrial transplants,

creating an entirely new field of medicine. But it's also not just science. They analyze culture. They analyze finance, economics, business, international affairs across every region. I'm particularly liking their new insider feature. It was just launched this month. It gives you, it gives me, a front row access to the economist's internal editorial debates, where senior editors argue through the news with world leaders and policy makers

and twice-weekly long format shows. Basically, an extremely high-quality podcast. Something else you should know about is that if you go to their app, they not only have daily articles, but they also have long-form podcasts with their editors and writers. This is also available online. Whether it's scientific innovation

or shifting global politics, the Economist provides comprehensive coverage beyond headlines. As a toll listener, you get a special discount. Head over to economist.com slash T-O-E to subscribe. That's economist.com slash T-O-E for your discount.