Sean Carroll: General Relativity, Quantum Mechanics, Black Holes & Aliens | Lex Fridman Podcast #428

the whole point of Relativity is to say there's no such thing as right now when you're far away and that is doubly true for what's inside a black hole and you might think well the Galaxy is very big it's really not it's some tens of thousands of light years across and billions of years old so you don't need to move at a high fraction of the speed of light to fill the Galaxy the number of Worlds is Big very very very big what do those worlds fit where do they go the short answer is the worlds don't exist in space space exists separately in each world the following is a conversation with Shan Carol his third time in this podcast he is a theoretical physicist at John Hopkins host of the mindscape podcast that I personally love and highly recommend and author of many books including the most recent book series called the biggest ideas in the universe the first book of which is titled space time and motion and it's on the topic of general relativity and the second coming out on May 14th so you should definitely pre-order it is titled quanta and Fields and that one is on the topic of quantum mechanics Shawn is a legit active theoretical physicist and at the same time is is one of the greatest communicators of physics ever I highly encourage you listen to his podcast read his books and pre-order the new book to support his work this was as always a big honor and a pleasure for me this is Alex Freedman podcast to support it please check out our sponsors in the description and now dear friends here's Sean Carol in book one of the series the biggest ideas in the universe called space-time motion you take on classical mechanics general relativity uh by taking on the main equation of general relativity and making it uh accessible easy to understand so um maybe at the high level what is general relativity what's a good way to start to try to explain it probably the best way to start to try to explain it is special relativity which came first 1905 uh it was the culmination right of many decades of people putting things together but it was Einstein in 1905 in fact it wasn't even Einstein I should give more credit to manowski in 1907 so Einstein in 1905 figured out that you could get rid of The Ether the idea of a rest frame for the universe and all the equations of physics would make sense with the speed of light being a maximum but then it was manowski who used to be Einstein's professor in 1907 who realized the most elegant way of thinking about this idea of Einstein's was to blend space and time together into space time to really imagine that there is no hard and fast division of the four-dimensional world in which we live into space and time separately Einstein was at first dismissive of this he thought it was just like oh the mathematicians are over formalizing again but then he later realized that if SpaceTime is a thing it can have properties and in particular it can have a geometry it can be curved from place to place and that was what let him solve the problem of gravity he was always been he had previously been trying to fit in what we knew about gravity from Newtonian uh mechanics the inverse Square law of gravity to his new relativistic Theory it didn't work so the final leap was to say gravity is the curvature of SpaceTime and that statement is basically general relativity and uh the tension with Makowski was he was a mathematician yes so it's the tension between physics and and Mathematics in fact in uh your lecture about this equation one of them you uh say that Einstein is a better physicist than he gets credit for yep I know that's hard that's a little bit of a joke there right because we all give Einstein a lot of credit but then we also partly based on fact but partly to make ourselves feel better tell ourselves a story about how later in life Einstein couldn't keep up uh there were younger people doing quantum mechanics and quantum field Theory and particle physics and he was just sort of uh unable to really philosophically get over his objections to that and I think that that story about the latter part is completely wrong like almost 180 degrees wrong I think that Einstein understood quantum mechanics as well as anyone at least up through the 1930s I think that his philosophical objections to it are correct so he should actually have been taken much more seriously about that and what he did what he achieved in trying to think these problems through is to really basically understand the idea of quantum entanglement which is kind of important these days when it comes to understanding quantum mechanics now it's true that in the 40s and 50s uh he placed his efforts in hopes for unifying electricity and magnetism with gravity that didn't really work out very well all of us you know try things that don't work out I don't hold that against him but in terms of IQ points in terms of trump to be a clear thinking physicist he was really really great what does greatness look like for a physicist so how difficult is it to take the leap from special relativity to general relativity how difficult is it to imagine that to consider SpaceTime together and to imagine that uh there's a curvature to this whole thing yeah that's a great question um I think that if you want to make the case for Einstein's greatness which is not hard to do there's two things you point at one is in 1905 his famous miracle year he writes three different papers on three wildly different subjects all of which are would make you famous just for writing that one paper um special relativity is one of them Brownie and motion is another one which is just you know the little vibrations of tiny little dust specs in the air but who cares about that what matters is it proves the existence of atoms he explains browni and motion by imagining there molecules in the air and deriving their properties brilliant and then he basically starts the world on the road to Quantum Mechanics with his paper on which again is given a boring label of the photoelectric effect what it really was is he invented photons he showed that light should be thought of as particles as well as waves and he did all three of those very different things in one year okay but the other thing that gets him genius status is like you said general relativity so this takes 10 years from 1905 to 1915 he wasn't only doing general relativity he was working on other things he wrote he invented a refrigerator he did various interesting things and he wasn't even the only one working on the problem there were other people who suggested relativistic theories of gravity but he really applied himself to it and I think as your question suggests the solution was not a matter of turning a crank it was was something fundamentally creative you know the in his own telling of the story his greatest moment his happiest moment was when he realized that if the way that we would modern in say it in modern terms if you were in a rocket ship accelerating at one g at one uh acceleration due to gravity if the rocket ship were very quiet you wouldn't be able to know the difference between being in a rocket ship and being on the surface of the Earth gravity is sort of not detectable or at least not distinguishable from acceleration so number one that's a pretty clever thing to think but number two if you or I had that thought we would have gone huh we're pretty clever he Reasons from there to say okay if gravity is not detectable then it can't be like an ordinary Force right the electromagnetic force is detectable we can put charged particles around positively charged particles and negatively charged particles respond differently to an electric field or to a magnetic field he realizes that what his thought experiment showed or at least suggested is that gravity isn't like that everything responds in the same way to gravity how could that be the case and then this other leap he makes is oh it's because it's the curvature of SpaceTime right it's a feature of SpaceTime it's not a force on top of it and the feature that it is is curvature and then finally he says okay clearly I'm going to need the mathematical tools necessary to describe curvature I don't know them so I will learn them and they didn't have mukes or AI uh helpers back in those days he had to sit down and read the math papers and he taught himself differential geometry and invented general relativity what about the step of including time as just another dimension so combining space in time is that a simple mathematical leap as Makowski suggested it's certainly not simple actually um it's a it's a profound Insight that's why I said I think we should give mow more credit than we do you know he's the one who really put the finishing touches on special relativity again many people had talked about how things change when you move close to the speed of light uh what Maxwell's equations of electromagnetism predict and so forth what their symmetries are so people like Lorent and Fitzgerald and poner there's a story that goes there and in in the usual telling Einstein sort of puts the Capstone on it he's the one who says all of this makes much more sense there just is no ether it is undetectable we don't know how fast everything is relative thus the name relativity but he didn't take the actual final step which was to realize that the underlying structure that he had invented is best thought of as unifying space and time together I honestly don't know what was going through makowski's mind when he thought that that I'm not sure if he was you know so mathematically Adept that it was just clear to him uh or he was really struggling it and he did trial in err for a while I'm not sure I mean do you for him or for Einstein visualize the four-dimensional space try to play with the idea of time is just another dimension oh yeah all the time I mean we of course make our lives easy By ignoring two of the dimensions of space so instead of four dimensional SpaceTime we just draw pictures of one dimension of space one dimension of time the so-called SpaceTime diagram but you know I mean maybe this is lurking underneath your question but even the best physicists we'll draw you know a hor a vertical axis and a horizontal axis and they'll go space time but deep down that's wrong because you're sort of preferring One Direction of space and One Direction of time and it's really the whole two-dimensional thing that is spacetime the more legitimate thing to draw on that picture are rays of light are light cones from every point there is a fixed Direction at which the speed of light would represent and that is actually inherent in the structure the division into space and time is something that's easy for us human beings what is the difference between space and time from the perspective of general relativity it's the difference between X and Y when you draw xes on a piece of paper so there really no difference there is almost no difference there's one difference that is kind of important which is the following if you have a curve in space I'm going to draw it horizontally because that's usually what we do in SpaceTime diagrams if you have a curve in space you've heard the motto before that the shortest distance between two points is a straight line if you have a curve in time which is by the way literally all of our lives right we all evolve in time so you can start with one event in SpaceTime and another event in SpaceTime what manowski points out is that the time you measure along your trajectory in the universe is precisely analogous to the distance you travel on a curve through space and by precisely I mean it is also true that the actual distance you travel through depends on your path right you go a straight line shortest distance and curvy line would be longer the time you measure in SpaceTime the literal time that takes off on your clock also depends on your path but it depends on it the other way so that the longest time between two points is a straight line and if you Zig back and forth in space time you take less and less time to go from point A to point B how do I make sense of that the uh difference between the observed reality and the objective reality underneath it or is objective reality a silly notion given general relativity I'm a huge believer in objective reality I think that objective reality objective is real um but I do think that people kind of are a little overly casual about the relationship between what we observe and objective reality in the following sense of course in order to explain the world our starting point and our ending point is our observations our experimental input the phenomena we experience and see around us in the world but in between there's a theory there's a mathematical formalization of our ideas about what is going on and if a theory fits the data and is very simple and makes sense in its own terms then we say that the theory is right and that means that we should attribute some reality to the entities that play an important role in that theory at least provisionally until we come up with a better Theory down the road I think a nice way to test the difference between objective reality and The observed reality is what happens at the uh at the edge of the Horizon of a black hole so technically as you get closer to that Horizon time stands still yes and no it depends on exactly how careful we're being so here's a a bunch of things I think are correct if you imagine there is a black hole SpaceTime so like the whole solution Einstein's equation and and you treat you and me as what we call test particles so we don't have any gravitational fields ourselves we just move around in the gravitational field that's obviously an approximation okay but let's let's imagine that and you stand outside the black hole and I Fall In And as I'm falling in I'm waving to you you know because I'm going into the black hole you will see me move more and more slowly and also the light from me is red shifted so I kind of look embarrassed because I'm falling into a black hole and there is a limit there is a last moment that light will be emitted from me from your perspective forever okay now you don't literally see it because I'm emitting photons more and more slowly right because from your point of view so it's not like I'm equally bright I basically fade from view in that picture Okay so that's one approximation the other approximation is I do have a gravitational field of my own and therefore as I approach the black hole the black hole doesn't just sit there and let me pass through it kind of moves out to eat me up because its net energy mass is going to mine plus its but roughly speaking yes I think so I don't like to go to the dramatic extremes because that's where the approximations break down but if you see something falling into a black hole you see its clock ticking more and more slowly how do we know it fell in we don't I mean how would we because it's always possible that right at the last minute it had a change of heart and starts accelerating away right if you don't see it pass in you don't know and let's point out that as smart as Einstein was he never figured out black holes and he could have it's kind of embarrassing it took decades for people thinking about general relativity to understand that there are such thing as black holes because basically Einstein comes up with general relativity 1915 two years later Schwarz Shield uh Carl schwar Shield derives the solution to Einstein's equation that represents a black hole the short Shield solution no one recognized it for what it was until the 50s David finlin and other people and that's just you know one of these examples of physicists not being as clever as they should have been well that's the singularity that's the kind of the edge of the theory the limit so it's understandable that it's difficult to imagine the limit of things it is absolutely hard to imagine and a black hole is very different in many ways from what we're used to on the other hand I mean I mean the real reason of course is that between 1915 and 1955 there's a bunch of other things that are really interesting going on in physics all of particle physics and Quantum field Theory so many of the greatest Minds were focused on that but still if the universe hands you a solution to general relativity in terms of curved SpaceTime and it's kind of mysterious certain features of it I would put some effort into trying to figure it out so how does a black hole work put yourself in the shoes of Einstein and take general relativity to its natural conclusion about these massive things it's best to think of a black hole as not an object so much as a region of space SpaceTime okay it's a region with the property at least in classical general relativity quantum mechanics makes everything harder but let's imagine we're being classical for the moment it's a region of SpaceTime with the property that if you enter you can't leave literally the equivalent of escaping a black hole would be moving faster than the speed of light they're both precisely equally difficult you would have to move faster than speed of light to escape from the black hole so once you're in that's fine you know in principle uh you don't even know notice when you cross the Event Horizon as we call it the Event Horizon is that point of no return where once you're inside you can't leave but meanwhile the SpaceTime is sort of collapsing around you uh to ultimately a singularity in your future which means that the gravitational forces are so strong they tear your body apart um and you will die in a finite amount of time the time it takes if the if the black hole is about the mass of the Sun to go from The Event Horizon to the singular ity takes about one millionth of a second and what happens to you if you fall into the black hole like if we think of an object as uh information that information gets destroyed well you've raised a crucially difficult point so that's why I keep needing to distinguish between black holes according to Einstein's theory of general relativity which is book one of SpaceTime and geometry which is perfectly classical and then come the 1970s we start asking about quantum mechanics and what happens in quantum mechanics according to classical general relativity the information that makes up you when you fall into the black hole is lost to the outside world it's there it's inside the black hole but we can't get it anymore in the 1970s Stephen Hawkin comes along and points out that black holes radiate they give off photons and other particles to the universe around them and as they radiate they lose mass and eventually they evaporate they disappear so once that happens I can no longer say the information about you or a book that I threw in the black hole or whatever is still there as hidden behind the black hole because the black hole has gone away so either that information is destroyed like you said or it is somehow transferred to the radiation that is coming out to the Hawking radiation the large majority of people who think about this believe that the information is somehow transferred to the radiation and information is conserved that is the a feature both of general relativity by itself and of quantum mechanics by itself so when you put them together that should still be a feature we don't know that for sure there are people who have doubted it including Steph Hawking for a long time but that's what most people think and so what we're trying to do now in uh a topic which has generated many many hundreds of papers called the black hole information loss puzzle is figure out how to get the information from you or the book into the radiation that is escaping the black hole is there any way to observe Hawking radiation to a degree where you can start getting Insight or is this all just in the space of theory right now right now we are nowhere close to observing Hawking radiation here's the sad fact the larger the black hole is the lower its temperature is so a small black hole like a microscopically small black hole might be very visible it's given off light but something like the black hole the center of our galaxy 3 million times the mass of the Sun or something like that Sagittarius A star uh that is so cold and low temperature that its radiation will never be observable um black holes are hard to make we don't have any nearby the ones we have out there in the universe are very very faint so there's no immediate hope for detecting Hawking radiation allegedly we don't have any nearby as far as we know we don't have any nearby could tiny ones be hard to detect somewhere at the edges the solar system maybe so you don't want them to be too tiny or they're exploding right they're they're very bright and then they would be visible but there's an absolutely regime where black holes are large enough not to be visible because the larger ones are fainter right not giving off radiation but small enough to not been detected through their gravitational effect yeah psychologically just emotionally how do you feel about black holes they scare you I love them I love black holes but the universe weirdly makes it hard to make a black hole right because we really need to squeeze an enormous amount of matter and energy into a very very small region of space so we know how to make Stellar black holes a super massive star can collapse to make a black hole we know we also have these super massive black holes at the center of the galaxies were a little unclear where they came from I mean maybe Stellar black holes that got together uh and combined but that's you know one of the exciting things about new data from the jamesb Space Telescope is that quite large black holes seem to exist relatively early in the history of the universe so it was already difficult to figure out where they came from now it's an even tougher puzzle so these super massive black holes are formed somewhere early on in the universe I mean that's a feature not a bug right that we don't have too many of them otherwise we wouldn't have a uh the time or the space to form the the little pockets of complexity that we call humans I think that's yeah it's always interesting when something is difficult but happens anyway right I mean the probability making a black hole could have been zero it could have been one but it's this interesting number in between which is kind of fun are there more intelligent alien civilization than there are super massive black holes yeah I have no idea but I think your intuition is right that it would have been easy for there to be lots of civilizations and then we would have noticed them already and we haven't so absolutely the simplest explanation for why we haven't is that they're not there yeah I just think it's so easy to make them though so there must be I understand that's the simplest explanation but also how easy is it to make life or UK carotic life or multicellular life it seems like life finds a way intelligent alien civilizations sure maybe there is somewhere along that chain a really really hard leap but once once you start life once you get the origin of life it seems like life just finds a way everywhere in every condition it just figures it out I mean I get it I get exactly what you're thinking I think it's a perfectly reasonable attitude to have before you confront the data I would not have expected Earth to be special in any way I would have expected there to be plenty of very noticeable extraterrestrial civilizations out there um but even if life finds a way even if we buy everything you say how long does it take for life to find a way what if it typically takes 100 billion years then we'd be alone so it's a time thing so to you really there's most likely there's no alien civilizations out there I just I can't see it I believe there's a ton of them and there's another explanation why we can't see them I don't believe that very strongly look I'm not going to uh place a lot of bets here I would not I'm both pretty up in the air about whether or not life itself is all over the place it's possible we know when we visit other worlds other solar systems there's very tiny microscopic life ubiquitous but none of it has reached some complex form it's also possible there's just there isn't any it's also possible that there are intelligent civilizations that have better things to do than knock on our doors so I think you know we should be very humbled about these things we know so little about and it's also possible there's a great filter where there's something fundamental about uh once the civilization develops complex enough technology that technology is more statistically likely to to destroy everybody versus to continue being creative that is absolutely possible I'm actually putting less Credence on that one just because you need to happen every single time right if even one I mean this goes back to F noyman pointing John F noyman pointed out that you don't need to send the aliens around the Galaxy you can build self-reproducing probe and send them around the Galaxy and you might think well the Galaxy is very big it's really not it's some tens of thousands of light years across and billions of years old so you don't need to move at a high fraction of the speed of light to fill the Galaxy so if you were an Al uh intelligent alien civilization the dictator of one you would just send out a lot of probes self-replicating probes 100% And just spread out yes and what you should do this is so if you want the optimistic spin here's the optimistic spin people looking for intelligent life elsewhere often tune in with their radio telescopes right at least we did before aroso was decommissioned that's not a very promising way to find intelligent life elsewhere because why in the world would a super intelligent alien civilization waste all of its energy by beaming it in random directions into the sky for one thing it just passes You by right so if if we're here on Earth we've only been listening to radio waves for aund or a couple hundred years okay so if a intelligent alien civilization exists for a billion years they have to pinpoint exactly the right time to send us this signal it is much much more efficient to send probes and to park to go to the other solar systems just sit there and wait for an intelligent civilization to arise in that solar system this is kind of the 2001 monolith hypothesis right I would I would be less surprised to find uh sort of quient alien artifact in our solar system than I would to catch a radio signal from an intelligent civilization so you're a sucker for in-person conversations versus remote I just want to integrate over time uh a probe can just sit there and wait whereas a radio wave goes right by you how hard is it for for an alien civilization again you're the dictator of one to figure out a probe that is most likely to find a Common Language with whatever it finds couldn't I be like the elected leader ofed leader Democratic leader uh de elected leader of a democratic alien civilization yes I think we would figure out that language thing pretty quickly I mean maybe not as quickly as we do when different human tribes find each other because obviously there's a lot of commonalities in Humanity but there is logic and math and there is the physical world you can point to a rock and go rock right I don't think it would take that long um I know that arrival uh the movie uh based on a Ted Chang story uh suggested that the way that aliens communicate is going to be fundamentally different uh but also they had recognition in other things I don't believe in so I think that if we actually find aliens uh that will not be our long-term problem so there's a folks one one of the places you're affiliated with is Santa Fe and they approach the question of complexity in many different ways and ask the question in many different ways of what is life think thinking broadly so do would be able to find it you'll think you show up a probe shows up to a planet we'll see a thing and be like yeah that's a that's that's a living thing well again if it's intelligent and technologically advanced the the more shortterm term question of if we get you know some spectroscopic data from an exoplanet so we know a little bit about what is in its atmosphere how can we judge whether or not that atmosphere is giving us a signature of Life existing that's a very hard question that people are debating about I mean one very simple-minded but perhaps um interesting approach is to say small molecules don't tell you anything because even if life could make them something else could also make them but long molecules that's the kind of thing that life would produce so signs of complexity mhm I don't know I just have this nervous feeling that we won't be able to detect we'll show up to a planet there a bunch of liquid on it we like dip we take a swim in the liquid and we won't be able to see the intelligence in it whe whether whether that intelligence looks like something like you know ants or we'll see movement perhap strange movement but we won't be able to um see the intelligence in it or communicate with it I guess if we have nearly infinite amount of time to play with different ideas we might be able to you know I think I mean I'm I'm in favor of this kind of humility this intellectual humility that we won't know because we should be prepared for surprises but I do always keep coming back to the idea that we all live in the same physical universe and if well let's put it this way the development of our intelligence has certainly been connected to our ability to manipulate the physical world around us and so I would guess without 100% Credence by any means but my guess would be that any advanced kind of life would also have that capability you know both dolphins and octopuses are potential counter examples to that but uh I I think in the details there would be enough similarities that we would recognize it I don't know how we got on this topic but I think it was from super massive black holes so if we return to black holes uh and talk about the the holographic principle more broadly you have a recent paper on the topic been thinking about the topic in terms of rigorous research perspective and just the as a popular book writer so what is the holographic principle well it goes back to this question that we were talking about with the information and how it gets out in quantum mechanics certainly arguably even before quantum mechanics comes along in classical statistical mechanics there's a relationship between information and entropy entropy is my favorite thing to talk about that I've written books about and we'll continue to write books about so Hawking tells us that black holes have entropy and it's a finite amount of entropy it's not an infinite amount but the belief is is and now we're already getting quite speculative the belief is that the entropy of a black hole is the largest amount of entropy that you can have in a region of SpaceTime it's sort of the most densely packed that entropy can be and what that means is there's sort of a maximum amount of information that you can fit into that region of space and you call it a black hole and interestingly you might expect if I have a box and I'm going to put information in it and I don't tell you how I'm going to put the information in but I ask how does the information I can put in scale with the size of the Box you might think well it goes as the volume of the Box because the information takes up some volume and I can only fit in a certain amount and that is what you might guess for the black hole but it's not what the answer is the answer is that the maximum information as reflected in the black hole entropy scales as the area of the black holes Event Horizon not the volume inside so people thought about that in both deep and superficial ways for a long time and they proposed what we now call the holographic principle that the way that SpaceTime and quantum gravity convey information or hold information is not different bits or cuits for Quantum information at every point in SpaceTime it is something holographic which means it's sort of embedded in or located in or can be thought of as as pertaining to one dimension less of the three dimensions of space that we live in so in the case of the black hole The Event Horizon is two dimensional embedded in a three-dimensional universe and the holographic principle would say all of the information contained in the black hole can be thought of as living on the Event Horizon rather than in the interior of the black hole I need to say one more thing about that which is that this was an idea what the idea I just told you was the original holographic principle put forward by people like Gerard and Leonard huskin Super Famous um physicist Leonard huskin was on my podcast and gave a great uh talk he's very very good at explaining these things mindscape podcast every listen that's right yes and you don't just have physicist on I I don't I love mscape oh thank you very much curiosity driven yeah ideas exporation of ideas from smart people yeah but anyway what I was trying to get at was susin and also a Ted were a little vague they were a little handwavy about holography and what it meant where H graphy the idea that information is sort of encoded on a boundary uh really came into its own was with Juan Mala in the 1990s uh and the ads cftd correspondence which we don't have to get into that into any detail but it's a whole full-blown theory of it's two different theories one theory in N dimensions of SpaceTime without gravity and another theory in N plus1 dimensions of SpaceTime with gravity and the the idea is that this n dimensional theory is you know casting a hologram into the N plus one dimensional Universe to make it look like it has gravity and that's holography with a Vengeance and that's the that's an enormous source of interest for theoretical physicist these days how should we picture what impact that has uh the fact that you could store all the information you could think of as all the information that goes into a black hole can be stored at the Event Horizon yeah I mean it's a good question um one of the things that Quantum field Theory indirectly suggests is that there's not that much information in you and me compared to the volume of space time we take up as far as Quantum field theories concerned you and I are mostly empty space and so we are not information dense right the density of information in us or in a book or a CD or whatever computer RAM is in speed uh encoded by volume like there's different bits located different points in space but that density of information is super duper low so we are just like the speed of light or just like the big bang for the information in a black hole we are far away in our everyday experience from the regime where these questions become relevant so it's very far away from our intuition we don't really know how to think about these things we can do the math but we don't feel it in our bones so you can just write off that weird stuff happens in a black to do better but we're trying I mean that's why we have a information loss puzzle because we haven't completely solved it so here just one thing to keep in mind once SpaceTime becomes flexible which it does according to general relativity and you have quantum mechanics which has fluctuations and virtual particles and things like that the very idea of a location in SpaceTime becomes a little bit fuzzy right because it's flexible and quantum mechanics says you can't even Pin It Down so information can propagate in ways that you might not have expected and that's easy to say and it's true but we haven't yet come up with the right way to talk about it that is perfectly rigorous it's crazy how dense with information of black hole is and then plus like quantum mechanics starts to come into play so you know you almost want to romanticize the kind of an interesting computation type things that are going on inside the black hole you do you do but I will I'll point out one other thing um it's information dense but it's also very very high entropy so a black hole is kind of like a very very very specific random number right it takes a lot of digits to specify it but the digits don't tell you anything they don't give you anything useful to work on so it takes a lot of information but it's not of a form that we can uh learn a lot from but hypothetically I guess as you mentioned the information might be preserved the information that goes into a black hole it doesn't get destroyed so what what does that mean when the entropy is really high well the black hole I said that the black hole is the highest density of information but it's not the highest amount of information because the black hole can evaporate and when it evaporates and people have done the equations for this when it evaporates the entropy that it turns into is actually higher than the entropy of the black hole was which is good because entropy is supposed to go up but it's much more dilute right it's spread across a huge volume of SpaceTime so in principle all that you made the black hole out of the information that it took is still there we think in that information but it scattered to the Four Winds we just talked about the event horizon of black hole what's on the inside what's at the center of it no one's been there so it came back to this is a theoretical prediction but you know I I'll say one super crucial feature of the black holes that we know in love that you know the kind that short shield first invented there's a singularity but it's not at the middle of the black hole remember space and time were parts of two different two uh parts of one unified SpaceTime the location of the singularity in the black hole is not the middle of space but our future it is a moment of time it is like a big crunch you know the Big Bang was an expansion from a singularity in the past big crunch probably doesn't exist but if it did it would be a collapse to a singularity in the future that's what the Interiors of black holes are like you can be fine in the interior but things are becoming more and more crowded SpaceTime is becoming more and more warped and eventually you hit a limit and that's the singularity in your future I wonder what time is like on the inside of a black hole time always Ticks by at 1 second per second that's all it can ever do time can tick by differently for different people and so you have things like the twin paradox where two people initially are the same age one goes off near the speed of light and comes back now they're not you can even work out that the one who goes out and comes back will be younger because they did not take the shortest distance path but locally as far as you and your wristwatch are concerned time is not funny time the your your neuro neurological signals in your brain and your heartbeat and your wristatch whatever is happening to them is happening to all of them at the same time so time always seems to be scking along at the same rate but if you fall into a black hole and then I'm an observer just watching it and then you come out once it evaporates a million years later I guess you be exactly the same age have you aged at all you would be converted into photons you would not be you anymore right so it's it's not at all possible that information is preserved exactly as it went in it depends on what you might preserved um it's there in the microscopic configuration of the universe it's exactly as if I took a regular book made of paper and I burned it the laws of physics say that all the information in the book is still there in the heat and light and Ashes you're never going to get it yeah it's a matter of practice but in principle it's still there but what about the age of things from The Observer perspective from outside the black hole from outside the black hole doesn't matter CU they're inside the black hole no so but is there okay there's no way to escape the black hole except to let it evaporate to let it evaporate but also you know by the way just in relativity special relativity forget about general relativity it's enormously tempting to say okay here's what's happening to me right now I want to know what's happening far away right now the whole point of Relativity is to say there's no such thing as right now when you're far away and that is doubly true for what's inside a black hole so you're tempted to say well how fast is their clock ticking or how old are they now not allowed to say that according to relativity cuz space and time is treated the same and so it doesn't even make sense what what happens to time and the holographic Principle as far as we know nothing dramatic happens um we're not anywhere close to being confident that we know what's going on here yet so there are good unanswered questions about whether time is fundamental whether time is emergent whether it has something to do with quantum entanglement whether time really exists at all uh different theories different proponents of different things um but there's nothing specifically about holography that would make us change our opinions about time whatever they happen to be but holography is fundamentally about it's it's a question of space it really is yeah okay so time is just a like an time just goes along for the ride as far as we know yeah so all the questions about time is just almost like separate questions whether it's emergent and all that kind of yeah I mean that might be a reflection of our ignorance right now but yes if we figure out a lot you know millions of years from the about black holes how surprised would you be if they travel back in time and tell told you everything you want to know about black holes how much do you think there is still to know and how mindblowing would it be it does depend on what they would say you know I think that there are colleagues of mine who think that we're pretty close to figuring out how information gets out of black holes how to quantize gravity things like that I'm more skeptical that we are pretty close I think that there's room for a bunch of surprises to come so in that sense I suspect I would be surprised the biggest and most interesting surprise to me would be if quantum mechanics itself Were Somehow superseded by something better as far as I know there's no empirical evidence-based reason to think that quantum mechanics is not 100% correct but it might not be that's always possible so and there are again respectable friends of mine who speculate about it so that's something I would that's the first thing I would want to know oh so like the black hole would be the most clear illustration yeah that's where it if there's something it would it would show up there I mean maybe the point is that black holes are mysterious for various reasons so yeah if our best theory of the universe is wrong that might help explain why but do you think it's possible we'll find something interesting like black holes sometimes create new universes or black holes are a kind of portal through SpaceTime to another place or something like this like and then our whole conception of what is the fa fabric of SpaceTime changes completely because black holes it's like swiss cheese type of situation yeah you know um that would be less surprising to me cuz I've already written papers about that we don't have again strong reason to think that the interior of black hole leads to another universe but it is possible and it's also very possible that that's true for some black holes and not others um this is stuff we don't know it's easy to ask questions we don't know the answer to the problem is the questions that are easy to ask that we don't know the answer to are super hard to answer because these objects are very difficult to test and to explore for us the regimes are just very far away so either literally far away in space but also so in energy or mass or time or whatever uh you've uh published a paper on the holographic principle or that involves the holographic princi what can you explain the details of that yeah you know I'm always interested in since my first published paper taking these wild speculative ideas and trying to test them against data and the problem is when you're dealing with wild speculative ideas they're usually not well defined enough to make a prediction right like it's kind of a I know it's going to happen in some cases I don't know what's going to happen in other cases so we did the following thing as I've already mentioned um the holographic principle which is meant to reflect the information contained in black holes seems to be telling us that information there's less information less stuff that can go on than you might naively expect so let's upgrade naively expect to predict using Quantum field Theory Quantum field theory is our best theory ofun Al physics right now unlike this holographic black hole stuff Quantum field theory is entirely local in every point of space something can go on and then you add up all the different points in space okay not holographic at all so there's a mismatch between the expectation for what is happening even in empty space in Quantum field Theory versus what the holographic principle would predict how do you reconcile these two things so there's one way of doing it uh that had been suggested pre previously which is to say that in the quantum field Theory way of talking it implies there's a whole bunch more States a whole bunch more ways the system could be than they really are and the answer and just I'll I'll do a little bit of math just because there might be some people in the audience who like the math if I draw two axes on a two-dimensional geometry like the surface of the table right you know that the whole point of it being two- dimensional is I can draw two vectors that are perpendicular to each other other I can't draw three vectors that are all perpendicular to each other right they need to overlap a little bit that's true for any numbers of Dimensions but I can ask okay how much do they have to overlap if I try to put more vectors into a vector space than the dimensionality of the vector space can I make them almost perpendicular to each other and the mathematical answer is as the number of Dimensions gets very very large you can fit a huge extra number of vectors in that are almost perpendicular to each other so in this case what we're suggesting is the number of things that can happen in a region of space is correctly described by holography it is somewhat overcounted by Quantum field Theory but that's because the quantum field theory states are not exactly perpendicular to each other I should have mentioned that in quantum mechanics states are given by vectors in some huge dimensional vector space very very very very large dimensional Vector space so maybe the quantum field theory states are not quite perpendicular to each other if that is true that's a speculation already but if that's true how would you know what is the experimental deviation and it would have been completely respectable if we had gone through and made some guesses and found that there is no noticeable experimental difference because again these things are in regimes very very far away we stuck our neck necks out we made some very very specific guesses as to how this weird overlap of States would show up in the equations of motion for particles like neutrinos and then we made predictions on how the neutrinos would behave on the basis of those wild guesses and then we compared them with data and what we found is we're pretty close but haven't yet reached the detectability of the effect that we are predicting in other words well basically one way of saying what we predict is if a nutrino and there's reasons why it's neutrinos we can go to it into if you want but it's not that interesting if a nutrino comes to us from Across the Universe from some Galaxy very very far away there is a probability as it's traveling that it will dissolve into other nutrino because they're not really perpendicular to each other as vectors as they would ordinarily be in Quantum field Theory and that means that if you look at neutrinos coming from far enough away with high enough energies they should disappear like if you see if you if you see a whole bunch of nearby neutrinos but then further away you should see fewer and there is an experiment called Ice Cube which is this amazing Testament to the Ingenuity of human beings where they go to Antarctica and they drill holes and they put photo detectors on a string a mile deep in these holes and they basically use all of the ice in a cube you know I don't know whether it's a mile or not but it's like a kilometer or something like that some big region that much ice is their detector and they're looking for flashes when a cosmic ray or nutrino or whatever hits uh ice molecule water molecule in the ice flashes in the ice they're looking for they're looking for flashes in some crazy I mean what what do the detector of that look like it it's a bunch of strings many many many strings with 360° photo detectors yeah and you will that's really cool it's extremely cool and they've um done amazing work and they find neutrinos they're looking for neutrinos yeah so the whole point is most cosmic rays are protons because why because protons exist and they're massive enough that you can accelerate them to very high energies so high energy cosmic rays tend to be protons they also tend to hit the Earth's atmosphere and Decay into other particles so neutrinos on the other hand punch right through at least usually right to a great extent so not just Antarctica but the whole earth occasionally a neutrino will interact with a particle here on Earth and his nutral is going through your body all the time from the Sun from the universe Etc and so if you're patient enough and you have a big enough part of the Antarctic ice sheet to look at it's the nice thing about ice is it's transparent so you built yourself Nature has built you a nutrino detector so I Cube does why why ice so is it is it just because the low noise and you get to watch this thing and it's it's much more dense than air but it's transparent so yeah much more dense so higher probability and then it's transparency and then it's also in the middle of nowhere so you can hum that's you need there's not that much ice right yeah so there's more ice in anartica than anywhere else right so anyway you can go and you can get a plot from the Ice Cube experiment how many nutrino there are that they've detected with very high energies and we predict in our weird little holographic guessing game that there should be a cutoff you should see neutrinos as you get to higher and higher energies and then they should disappear if you look at the data their data gives out exactly where our cut off is that doesn't mean that our cut off is right it means they lose the ability to do the experiment exact where we predict the cut off should be oh boy okay um but why is there a limit oh just because there are fewer or fewer high energy neutrinos so there's a spectrum and it goes down but that what we're plotting here is number of nutrino versus energy it's fading away and they just get very very few and you need the high energy neutrinos for the your our effect is a little bit bigger for higher energies yeah and that that effect has to do with this almost perpendicular thing and let me just mention the name of Oliver Friedrich who was a postdoc who led this he deserves the credit for doing this I was a a co-author and a collaborator I did some work but he really gets the Lions here thank you Oliver thank you for pushing this wild science forward uh just to speak to that the The Meta process of it how do you approach asking these big questions and trying to uh formulate as a paper as an experiment to that could make a prediction all that kind of stuff what's your process there's a very interesting things that happens once you're a theoretical physicist once you become trained you're a graduate student you've written some papers and whatever suddenly you are the world's expert in a really infin asmbly tiny area of knowledge right and you know not that much about other areas there's an overwhelming temptation to just drill deep right just keep doing basically the thing that you started doing but maybe the thing you started doing is not the most interesting thing to the world or to you or whatever so you need to to separately develop the capability of stepping back and going okay now that I can write papers in that area now that I'm sort of trained enough in the general procedure what is the best match between my interests my abilities and what is actually interesting and honestly I I've not been very good at that over my career um you know I have my my process traditionally was I was working in this general area of particle physics field Theory general relativity cosmology and I would sort of try to take things other people were talking about and ask myself whether or not it really fit together like my my two so I guess I have three papers that I've ever written that uh have done super well in terms of getting cited and things like that one was my first ever paper that I get very little credit for that was my adviser and his collaborator you know set that up the other two were basically my idea one was um right after we discovered that the Universe was accelerating so in 1998 observations showed that not only is universe expanding but it's expanding faster and faster so that's attributed to either Einstein's cosmological constant or some more complicated form of dark energy some mysterious thing that fills the universe and people were throwing around ideas about this dark energy stuff what could it be and so forth most of the people throwing around these ideas were cosmologists they work on cosmology they think about the universe all at once I you know since I like to talk to people in different areas I was sort of more familiar than average with what a respectable working particle physicist would think about these things and what I immediately thought was you know you guys are throwing around these theories these theories are wildly unnatural they're super finely tuned like any particle physicist would just be embarrassed to be talking about this but rather than just offing at them I sat down and asked myself okay is there a respectable version is there a way to keep the particle physicist happy but also make the universe accelerate and I realized that there is some very specific set of models that is that is relatively natural and guess what you can make a new experimental prediction on the basis of those and so I did that people were very happy about that what was the thing that would make physicists happy that would make sense of this uh fragile thing that people call Dark Energy so the fact that dark energy pervades the whole universe and is slowly changing that should immediately set off alarm Bells because particle physics is a story of length scales and time scales that are generally guess what small right particles are small they vibrate quickly and you're telling me now I have a new field and its typical rate of change is once every billion years right like that's just not natural and indeed you can formalize that and say you know look even if you wrote down a particle that evolved slowly over billions of years if you let it interact with other particles at all that would make it uh move faster it Dynamics would be faster it Mass would be higher etc etc so there a whole story things need to be robust and they all talk to each other in Quantum field Theory so how do you stop that from happening and the answer is symmetry you can impose a symmetry that protects your new field from talking to any other fields okay and this is good for two reasons number one it can keep the dynamic slow so if you just you can't tell me why it's slow you just made that up but at least it can protect it from speeding up because it's not talking to any other particles and the other is it makes it harder to detect um naively experiments looking for fifth forces or time changes of fundamental constants of nature like the charge of the electron these experiments should have been able to detect these dark energy fields and I was able to propose a way to stop that from happening the detection the detection yeah to sort because a symmetry could stop it from interacting with all these other fields and therefore makes it harder to detect and just by luck I realized because it was actually based on my first ever paper there's one loophole if you impose these symmetries so you protect the dark energy field from interacting with any other fields there's one interaction that is still allowed that you can't rule out and it is a very specific interaction between your dark energy field and photons which are very common and it has the following effect as a photon travels through the dark energy the photon has a polarization up down left right whatever it happens to be and as it travels through the dark energy that Photon will rotate its polarization this is called by fringant and you can kind of run the numbers and say you know you can't make a very precise prediction because we're just making up this model but if you want to roughly fit the data You can predict how much polarization rotation there should be couple of degrees okay not that much so that's very hard to detect people have been trying to do it right now literally we're on the edge of either being able to detect it or rule it out using the cosmic microwave background and there is just you know truth in advertising there is a claim on the market that it's been detected that it's there uh it's not very statistically significant if I were to bet I think it would probably go away it's very hard thing to observe but maybe as you get better and better data cleaner and cleaner analysis it will persist and we will have directly detected the dark energy so if we just take this tangent of dark energy people will sometimes breing bring up dark energy and dark matter as an example why physicists have lost it lost their mind we're just going to say that there's this field that permeates everything is unlike any other field and it's invisible uh and it uh helps us work out some of the math uh how do you respond to that kind a suggestion well two ways one way is those people would have had to say the same thing when we discovered the planet Neptune yeah CU it's exactly analogous where we have a very good theory in that case Newtonian gravity in the solar system we made predictions the predictions were slightly off for the motion of the outer planets you found that you could explain that motion by positing something very simple one more planet in a very very particular place and you went and looked for it and there it was right it's that was the first successful example of finding dark matter in the universe it's a matter though we can't see nepe was dark yeah there's a difference between dark matter and dark energy right dark matter as far as we are hypothesizing it um is a particle of some sort it's just a particle that interacts with us very weakly so we know how much of it there is we know more or less where it is we know some of its properties we don't know specifically what it is but it you know it's it's not anything fundamentally mysterious it's a particle dark energy is a different story so dark energy is indeed uniformly spread throughout space and has this very weird property that it doesn't seem to evolve as far as we can tell it's the same amount of energy in every cubic centimeter of space from moment to moment in time that's why Far and Away the leading candidate for dark energy is Einstein's cosmological constant the cosmological constant is strictly constant 100% constant the data say it had better be 98% constant or better so 100% constant where works right and it's also very robust it's just there it's not doing anything it doesn't interact with any other particles it makes perfect sense probably the dark energy is the cosmological constant the Dark Matter super important to emphasize here you know it was hypothesized at first in the 70s and 80s mostly to explain the rotation of galaxies today the evidence for dark matter is both much better than was in the 1980s and from different sources it is mostly from observations of the cosmic background radiation or of large scale structure so we have multiple independent lines of evidence also gravitational lensing and things like that many many pieces of evidence that say that dark matter is there um and and also that say that the effects of dark matter are different than if we modified gravity so that was my first answer your to question is dark matter we have a lot of evidence for but the other one is of course we would love it if it weren't Dark Matter our vested interest is 100% aligned with it being something more cool and interesting than dark matter because dark matter is just a particle that's the most boring thing in the world and it's uh non-uniformly distributed through space Dark Matter absolutely yeah so this you can even see maps of it that we've constructed from gravitational lensing so verifiable sort of clumps of dark matter in the Galaxy that explains stuff bigger than the Galaxy sadly like we think that in the Galaxy dark matter is Lumpy but it's it's just it's weaker it's effects are weaker but of the scale of large scale structure and clusters of galaxies and things like that yes we can show you where the dark matter is could there be a super cool explanation for dark matter that would be interesting as opposed to just another particle that that sits there in clumps the super cool explanation would be modifying gravity rather than inventing a new particle sadly that doesn't really work we've tried I've tried uh that's my third paper that was very successful I tried to unify dark matter and dark energy together that was my idea that was my aspiration not even idea I tried to do it it failed even before we wrote the paper I realized that my idea did not help it helps it could possibly explain Away the Dark Energy but it would not explain Away the Dark Matter and so I thought it was not that interesting actually and then two different collaborators of mine said has anyone thought of this idea like they thought of exactly the same idea completely independently of me I said well if three different people found the same idea maybe it is interesting and so we wrote the paper and yeah it was very interesting people are very interested can you describe this this paper a little bit like it just it's it's fascinating how much of a thing there is dark energy and dark matter and we don't quite understand it so what what was your dive into the exploring how to unify the two so here is what we know about dark matter and dark energy um they become important in regimes where gravity is very very very weak that's kind of the opposite from what you would expect if you actually were modifying gravity like there's a rule of thumb in Quantum field Theory Etc that new effects show up when the effects are strong right we we understand weak fields we don't understand strong Fields but okay maybe this is different right so what do I mean by when gravity is weak the dark energy shows up late in the history of the universe early in the history of the universe the dark energy is irrelevant but remember the density of dark energy stays constant the density of matter and radiation go down so at Early times the dark energy was completely irrelevant compared to matter and radiation at late times it becomes important that's also when the univers is dilute and gravity is relatively weak now think about galaxies okay a galaxy is more dense in the middle less dense on theend outside and there is a phenomenological fact about galaxies that in the interior of galaxies you don't need Dark Matter that's not so surprising because the density of stars and gas is very high there and the dark matter is just subdominant but then there's generally a uh a radius inside of which you don't need Dark Matter to fit the data outside of which you do need Dark Matter to fit the data so that's again when gravity is weak right so I asked myself um of course we know in field Theory new effects should show up when fields are strong not weak but let's throw that out of the window can I write down a theory where gravity alters when it is weak and we've already said what gravity is what is gravity it's the curvature of SpaceTime so there are mathematical quantities that measure the curvature of SpaceTime and generally you would say like I have an understanding Einstein's equation which I explained to the readers in the book um relates the curvature of SpaceTime to matter and energy the more matter and energy the more curvature so I'm saying what if you add a new term in there that says the less matter and energy the more curvature no reason to do that except to fit the data right so I try to unify the need for dark matter and the need for dark eny that would be really cool if that was the case like super cool right it'd be the best it' be great it work it' be really interesting if gravity did something funky when uh when there's not much of it like almost like at the edges of it it gets noisy that was exactly the Hope right but the great thing about physics is there are equations right I mean you can come up with the words and you can wave your hands but then you got to write down the equations and I did and I figured out that it could help with the dark energy the acceleration of the universe it doesn't help with dark matter at all yeah it just sucks at the scale of galaxies and scale of solar systems uh the physics is kind of boring yeah it does I agree again that's why it is a little bit I tear my hair out when people who are not physicists think you know accuse physicists like you say of sort of losing the plot because they need dark matter and dark energy I don't want dark matter and dark energy I want something much cooler than that I've tried but you got to listen to the equations and to the data you mentioned three papers your first ever your first awesome paper ever and your second awesome paper ever of course you wrote many papers so it's you're you're you're being very harsh on the others but well by the way this is not awesomeness this is impact impact right there's no correlation between awesomeness and impact some of my best papers fell without a stone yeah um the first paper was called limits on Loren and parody violating modification of electromagnetism or electrodynamics so we figured out how to violate Loren and variance which is the Symmetry underlying relativity and the important thing is we figured out a way to do it that didn't violate anything else and was experimentally testable so people love that uh the second paper was called quintessence and the rest of the world so quintessence is this dynamical dark energy field the rest of the world was because I was talking about how the quintessence field would interact with other particles and Fields and how to avoid the interactions you don't want and the third paper was called um is Cosmic speed up due to gravitational physics something like that so you see the common theme I'm taking you know what we know the standard model of particle physics general relativity tweaking them in some way and then trying to fit the data and try to make it so it's experimentally validated ideally yes that's right that's the goal you wrote the book something deeply hidden on the mysteries of quantum mechanics and a new book coming out soon part of that biggest ideas in the universe series we mentioned called quanta and Fields so that's focusing on quantum mechanics big question first biggest ideas in the universe uh what to you is most beautiful or perhaps most mysterious about quantum mechanics quantum mechanics is a harder one you know I wrote a textbook on general relativity and I started it by saying general relativity is most beautiful physical Theory ever invented and I I will stand by that it is less fundamental than quantum mechanics but quantum mechanics is a little more mysterious so we it's it's a little bit cluggy right now you know if you think about how we teach quantum mechanics to our students the Copenhagen interpretation it's a god- awful mess like no one's going to accuse that of being very beautiful I'm a fan of the many worlds interpretation quantum mechanics and that is very beautiful in the sense that fewer ingredients just one equation and it could cover everything in the world um it depends what you mean by Beauty but I think that the answer to your question is quantum mechanics can start with extraordinarily austere tiny ingredients and in principle lead to the world right uh that boggles my mind it's a much more comprehensive general relativity is about gravity and that's great Quantum mechanic is about everything and seems to be up to the task and so I don't know what is that beauty or not but it's certainly impressive so both for the theory the predictive power of the theory and the fact that the theory describes tiny things creating everything we see around us it's am monist theory in classical mechanics I have a particle here particle there I describe them separately I can tell you what this particle's doing what that particle is doing in quantum mechanics we have entanglement right as I Einstein pointed out to us in 1935 and what that means is there is a single state for these two particles there's not one state for this particle one state for the other particle and indeed there's a single state for the whole universe called the wave function of the universe if you want to call it that and it obeys one equation and it is our job then to sort of chop it up to carve it up to figure out how to get tables and chairs and things like that out of it you mentioned the many worlds interpretation and it is in fact beautiful but uh it's one of your more controversial things you stand behind yeah you've probably gotten a bunch of flak for it I'm a big boy I can take it well can you first explain it and then maybe speak to the Flack you may have got short you know the classic experiment to explain quantum mechanics to people is called the stern gerlock experiment you're measuring the spin of a particle okay and in quantum mechanics the spin is you know it's just a spin it's a rate at which something is rotating around in a in a very down toe sense the difference being is that it's quantized so for something like a single electron or a single Neutron it's either spinning clockwise or counterclockwise those are the only two let's put it this way those are the only two measurement outcomes you will ever get there's no it's spinning faster or slower it's either spinning One Direction or the other that's it two choices okay according to the rules of quantum mechanics I can set up an electron let's say in a state where it is neither purely clockwise or counterclockwise but a superposition of both and that's not just because we don't know the answer it's because it truly is both until we measure it and then when we measure it we see one or the other so this is the fundamental mystery of quantum mechanics is that how we describe the system when we're not looking at it is different from what we see when we look at it so we teach our students in the Copenhagen way of thinking is that the Act of measuring the spin of the electron causes a radical change in the physical state it spontaneously collapses from being a superp position of clockwise and counterclockwise to being one or the other and you can tell me the probability that that happens but that's all you can tell me and I can't be very specific about when it happens what caused it to happen why it's happening none of that that's all called the measurement problem of quantum mechanics so many worlds just says look I just told you a minute ago that there's only one way function for the whole universe and that means that you can't take too seriously just describing the electron you have to include everything else in the universe in particular you clearly have to interact with the electron in order to measure it so whatever is interacting with the electron should be included in the wave function that you're describing and look maybe it's just you maybe your eyeballs are able to perceive it but okay I'm going to include you in the wave function and if you do that let's be you know since you have a very sophisticated listenership I'll be a little bit more careful than average what does it mean to measure the spin of the electron we don't need to go into details but we want the following thing to be true if the electron were in a state that was 100% spinning clockwise then we want the measurement to tell us it was spinning clockwise we want your brain to go yes the electron was spinning clockwise right likewise if it was 100% counterclockwise we want to to see that to measure that the rules of quantum mechanics the Schrodinger equation of quantum mechanics is 100% clear that if you want to measure it clockwise when it's clockwise and measure it counterclockwise when it's counterclockwise then when it starts out in a superp position what will happen is that you and the electron will entangle with each other and by that I mean that the state of the universe evolves into part saying the electron was spinning clockwise and I saw it clockwise and part of the state is it's in a superp position with the part that says the electron was spinning counterclockwise and I saw it counterclockwise everyone agrees with this entirely uncontroversial straightforward consequence of the shinger equation and then Neil Spore would say and then part of that wave function disappears and we're in the other part and you can't predict which part it will be only the probability Hugh Everett who was a graduate student in the 1950s was thinking about this says I have a better idea part of the wave function does not magically disappear it stays there the reason why that idea Everett's idea that the whole wave function always sticks around and just obeys the Sher equation was not thought of years before is because naively you look at it you go okay this is predicting that I will be in a super position that I will be in a super position of having seen the electron be clockwise and and having seen it be counterclockwise no experimentor has ever felt like they were in a super position you always see an outcome okay Everett's move which was kind of Genius was to say the problem is not the schinger equation the problem is you have misidentified yourself in the schinger equation you have said oh look there's a person who saw counter clockwise there's a person who's saw clockwise I should be that superposition of both and ever says no no no you're not because the part of the wave function in which the spin was clockwise once that exists it is completely unaffected by the part of the wave function that sends says the spin was counterclockwise they are apart from each other they are uninteractive they have no influence what happens in one part has no influence in the the other part so Everett says the simple resolution is to identify yourself as either the one who saw spin clockwise or the one who saw spin counterclockwise there are now two people once you've done that experiment the shinger equation doesn't have to be messed with all you have to do is locate yourself correctly in the wave function that's many worlds the number of Worlds is Big very very very big what do those worlds fit where they go the short answer is the worlds don't exist in space space exists separately in each world so I mean there's a technical answer to your question which is Hilbert space the space of all possible quantum mechanical States but physically you know we we want to put these worlds somewhere that's just a wrong intuition that we have there is no such thing as the physical spatial location of the worlds cuz space is inside the worlds one of the properties of this interpretation is that you can't travel from one world to the other that's right which kind of makes you feel that they're existing separately they are existing separately and simultaneously and simultaneously without locations in space without locations in space how is it possible to visualize them existing without a location in space the real answer to that the honest answer is the equations predicted yeah yeah if you can't visualize it so much worse for you the equations are crystal clear about what they're predicting is there a way to get to the closer to understanding and visualizing the weirdness of the implications of this you know I don't think it's that hard wasn't it wasn't that hard for me you know I don't mind the idea that when I make a quantum mechanical measure there is later on in the universe multiple descendants of my present self who got different answers for that measurement I can't interact with them um Hilbert space the space ball Quantum wave functions was always big enough to include all of them I'm going to worry about the parts of the Universe I can observe so let's put it this way many worlds comes about by taking the schinger equation seriously the schinger equation was was invented to fit the data to fit the spectrum of different atoms and different you know emission and absorption experiments and it's perfectly legitimate to say well okay you're taking this rodinger equation you're extrapolating it you're trusting it believing it beyond what we can observe I don't want to do that right that's perfectly legit except okay then what do you believe come up with a better Theory you're saying you don't believe the schroer equation tell me the equation that you believe in turns out and people have done that turns out it's super hard to do that in a legitimate way that fits the data and many worlds is a really clean absolutely most austere clean no extra baggage theory of quantum mechanics but if it in fact is correct isn't this the weird the weirdest thing of anything we know yes in fact let let me put it this way the single best reason in my mind to be skeptical about many worlds is not because it doesn't make sense or it doesn't fit the data or I don't know where the worlds are going or whatever it's because to make that extrapolation to take seriously the equation that we know is correct in other regimes requires New Philosophy requires a new way of thinking about identity about probability about prediction a whole bunch of things I and I it's work to do that philosophy and I've been doing it and others have done it and I think it's very very doable but it's not straightforward it's not a simple extrapolation from what we already know it's a grand extrapolation very far away and if you just wanted to be sort of methodologically conservative and say that's a step too far I don't want to buy it I'm sympathetic to that I I think that you're just wimping out I think that you should have more courage but I I get the impulse and there is under many worlds an era of time where if you rewind it back uh there's going to be one initial State that's right all of quantum mechanics all different versions require a kind of Arrow of time it might be different in every kind but the quantum measurement process is irreversal you can measure something it collapses you can't go backwards if someone tells you the outcome if I say I've measured an electron it spin is clockwise and they say what was it before I measured it you know there was some part of it that was clockwise but you don't know how much right and many worlds is no different but the nice thing is that the kind of Arrow of time you need in many worlds is exactly the kind of Arrow of time you need anyway for entropy in thermodynamics and so forth you need a simple low entropy initial state that's what you need in both cases so if you actually look at under many worlds into the entire history of the universe correct me if I'm wrong but it looks very deterministic yes in each moment does the moment contain the memory of the entire history of the universe to you does the moment contain the memory of everything that preceded it as far as we know so according to many worlds the wave function of the universe all the branches of the universe at once all the worlds does contain all the information calling it a memory is a little bit um dangerous because it's not the same kind of memory that you and I have in our brains because our memories rely on the Arrow of time and the whole point of the schinger equation or Newton's Laws is they don't have an arrow of time built in they're reversible the state of the universe not only remembers where it came from but also determines is going to go in a way that our memories don't do that but our memories we can do replay can you do this we can but the active forming a memory increases the entropy of the universe it is an irreversible process also right you can walk on a beach and leave your Footprints there that's a record of your passing uh it will eventually be erased by the ever increasing entropy of the universe well but you can imperfectly replay it I guess can we return travel back time imperfectly oh um it depends on the level of precision you're trying to ask that question you know the universe contains the information about where the universe was but you and I don't we're nowhere close and it's what computationally very costly to try to consult the universe well it depends on again exactly what you're asking like there are some simple questions like what was the temperature of the universe 30 seconds after for the Big Bang we can answer that right that's kind of amazing that we can answer that to pretty high Precision but if you want to know where every adom was then no what do you is the Big Bang why why did it why why did it happen we have no idea I I I think that that's that's a super important question that I can imagine making progress on but right now I'm more or less maximally uncertain about what the answer is you think black holes will help no potentially not not that much um quantum gravity will help and maybe black holes will help us figure out quantum gravity so indirectly yes but we have the situation where general relativity Einstein's theory unambiguously predicts there was a singularity in the past there was a moment of time when the universe had infinite curvature Infinite Energy infinite expansion rate the whole bit that's just a fancy way of saying the theory has broken down and classical general relativity is not up to the task of what's saying what really happened at that moment so it is completely possible there was in some sense a moment of time before which there were no other moments and that would be the big bang even if it's not a classical general relativity kind of thing even if quantum mechanics is involved maybe that's what happened it's also completely possible there was time before that space and time and they evolved into our hot big bang by some procedure that we don't really understand and if time and space are emergent then the before even starts getting H getting real weird well I think that if there is a first moment of time that would be very good evidence or that would fit handin glove with the idea that time is emerging if time is fundamental then it tends to go forever because it's fundamental well yeah I mean the the general formulation of this question is what's outside of it what's outside of our universe so in time and in space I know it's a pothead question question Sean I understand I apologize that's my life my life is asking pothead questions some of them the answer is that's not the right way to think about it okay but is it possible to think at all about what's outside our universe it's absolutely legit to ask questions but you have to be comfortable with the possibility that the answer is there's no such thing as outside our universe that's absolutely on the table in fact that is the simplest most likely to be correct answer that we know of but it's the only thing in the universe that wouldn't have an outside if yeah if the universe is the totality of everything it would not have an outside it's so weird to think that there's not an outside we we want there to be we want there to be sort of a Creator a creative force that led to this and outside like this is our town and then there's a bigger world and there's always a bigger world and the because that is our experience that's the world we grew up in right the universe doesn't need to obey those rules such a weird thing when I was a kid that used to keep me up at night like what if the universe had not existed right and and it feels like a lot of pressure that this is the if this is the only universe and uh we're here one of the few intelligent civilizations maybe the only one it's the old theories that were the center of everything it just feels suspicious that's why many worlds is kind of exciting to me because it like is is humbling in all the right kinds of ways it feels like Infinity is the way this whole thing runs there's one Pitfall that I'll just mention because there's a move that is made in these theoretical edges of cosmology that I think is a little bit mistaken which is to say I'm going to think about the Universe on the basis of imagining that I am a typical Observer I this is called the principle of typicality or the principle of mediocrity or even the cernic principle nothing special about me I'm just typical in the universe but then you draw some conclusions from this and what you end up realizing is you've been hilariously presumptuous because by saying I'm a typical observer in the universe you're saying typical observers in the universe are like me and that is completely unjustified by anything so I'm not telling you what the right way to do it is but these kind kind of questions that are not quite grounded in experimental verification or falsification are ones you have to be very careful about that to me is one of the most interesting questions and there's different ways to approach it but like what's outside of this how did the Big M start how do we get something from nothing that's always the thing you're sneaking up to when you're studying all of these questions you're always s that's where the black hole and unifying getting quantum gravity all this kind of stuff you're always sneaking up to that question um where did all of this come from and I think that's probably an answerable question right no it doesn't have to be so you think there's there could be a turtle at the bottom of this that's that refuses to reveal its identity yes I think that um the specifically the question why is there something rather than nothing yeah does not have the kind of answer that we would ordinarily attribute to why questions because typical why questions are embedded in the universe and when we answer them we take advantage of the features of the universe that we know in love but the universe itself as far as we know is not embedded in anything bigger or stronger and therefore it can just be do you think it's possible this whole place is simulated sure it's a really interesting dark Twisted video game that we're all existing in you know my own podcast listeners mindscape listeners tease me because they know from my AMA episodes that if you ever start a question by asking do you think it's possible that the answer is going to be yes that might not be the answer that you care about but it's possible sure as long as you're not you know adding two even numbers together and getting an odd number when you say it's possible there's a mathematically yes and then there's more of like intuitive yeah you want to know whether it's plausible you want to know is there reasonable non-zero Credence to attach to this I don't think that there's any philosophical knockout objection to the simulation hypothesis I also think that there's absolutely no reason to take it seriously do you think humans will try to create one I guess that that's how I always think about it you know I I see what I've spent quite a bit of time over the past few years and a lot more recently in Virtual Worlds and just them always captivated by the possibility of creating high and high resolution worlds and uh as we'll talk a little bit about artificial intelligence sort of the the advancement on the Sora front that you can automatically generate those worlds and the possibility of existing in those automatically generated worlds is pretty exciting as long as just a assist in physics quantum mechanics and general relativity that governs the generation of those worlds y uh so it just seems like humans will for sure try to create this yeah I think they will create better and better simulations I think the philosopher David Chalmer has done a what I consider to be a good job of arguing that we should treat things that happen in virtual reality and in simulated realities as just as real as the reality that we experience I also think that as a practical matter people realize how much harder it is to simulate a realistic world than we naively believe so this is not a my lifetime kind of worry yeah the Practical matter of going from a sort of a a prototype that's impressive to a thing that governs everything similar question on this front is in AGI yeah you said that we're very far away from AGI I want to eliminate the phrase AGI so uh basically when you analyzing large language models and seeing how far they from whatever AGI is and we can talk about different right Notions of intelligence that we we're not as close as kind of uh some people in in public view are talking about so what's your intuition behind that my intuition is basically that artificial intelligence is different than human intelligence and so the mistake that is being made by focusing on AGI among those who do is is a an artificial agent as we can make them now or in the near future might be way better than human beings at some things way worse than human beings at other things and rather than trying to ask how close is it to being a human-like intelligent we should appreciate it for what its capabilities are and that will both be more accurate and help us put it to work and protect us from the dangers better rather than always anthropomorphizing it I think the under in idea there under the definition of AGI is that the capabilities are extremely impressive that's not a precise statement but mean no I get that completely agree and then the underlying question where the a lot of the debate is is how impressive is it what are the limits of large language models can they really do things like Common Sense reasoning how much do they really understand about the world or they just fancy McRee machines mhm and uh so where do you fall on that as to the limits of large language models I don't think that there are many limits in principle I I'm not I'm a physicalist about Consciousness and awareness and things like that I see no obstacle to in principle building an artificial machine that is indistinguishable in thought and cognition from a human being but we're not trying to do that right what the large language model is trying to do is to predict text that's what it does and it is leveraging the fact that we human beings for very good evolutionary biology reasons attribute intentionality and intelligence and agency to things that act like human beings as I was driving here to get to this podcast space I was using Google Maps and Google Maps was talking to me but I wanted to stop to get a cup of coffee so I didn't do what Google Maps told me to do I went around a block that it didn't like and so it it gets annoyed right it it says like no why are you doing it doesn't say exactly in this but you know what I mean it's like no turn left turn left and you turn right it is impossible as a human being not to feel a little bit sad that Google Maps is getting mad at you it's not it's not even trying to it's not a large language model it's not has no aspirations to intentionality we attribute that all the time Dan Dennett the philosopher wrote a very influential paper on the intentional stance the fact that it's the most natural thing in the world for we human beings to attribute more intentionality to artificial things that are really there which is not to say it can't be really there but if you're trying to be rational and clear thinking about this the first step is to recognize our huge bias toward towards attributing things below the surface to systems that are enable that are able to at the surface level act human so if that huge bias of intentionality is there in the data in the human data in the vast landscape of human data that AI models large language models and video models in the future are trained on uh don't you think that that intentionality will emerge as fundamental to the behavior of these systems now naturally I well I don't think it will happen naturally I think it could happen again I'm not against the the principle but again the way that large language models came to be and what they're optimized for is wildly different than the way that human beings came to be and what they're optimized for so I think we're missing a chance to be much more clearheaded about what large language models are by judging them against human beings again both in positive ways and negative ways well I I think sort of to push back on what they're optimized for is different to describe how they're trained versus what they're optimized for so they're trained in this very trivial way of predicting text tokens MH but you can describe what they're optimized for and what the actual task in hand is is to construct the world model meaning an understanding of the world and that's where it starts getting closer to what humans are kind of doing we're just in the case of large language models know how the sausage is made and we don't know how it's made for us humans but they're not optimized for that they're optimized to sound human that's the fine-tuning but the actual training is optimized for understanding uh creating a compressed representation right of all the stuff that humans have created on the internet and the hope is that that gives you a deep understanding of the world yeah so that's why I think that there's a set of hugely interesting questions to be asked about the ways in which large language models actually do represent the world because what is clear is that they're very good at acting human the open question in my mind is is the easiest most efficient best way to act human to do the same things that human beings do or are there other ways and I think that's an open question I just heard a talk by Melanie Mitchell at Santa Fe Institute an artificial intelligence researcher and she told two stories um about two different papers one that someone else wrote and one that her group is following up on and they were modeling aelo aell the game with a little rectangular board white and black squares so the experiment was the following they fed uh neural network the moves that were being made in the most symbolic form like E5 just means that okay you put a token down E5 so it gives a long string it does this for millions of games right real legitimate games and then it asks the question the paper asks the question okay you you've trained it to tell what would be a legitimate next move from not a legitimate next move did it in its brain in its little large language model brain I don't even know was technically large language model but a deep Learning Network did it come up with a representation of the aelo board well how do you know and so they construct a little probe Network that they insert and you ask it what is it doing right at this moment right and the answer is that uh you know the little probe Network can ask you know would this be legitimate or is is this token white or black or whatever um things that in in practice would amount to its invented the the aelo board and it found that um the probe got the right answer not 100% of the time but more than by chance substantially more than by chance so they said there's some tentative evidence that this neural network has discovered the aelo board just out of data raw data right but then melan's group asked the question okay are you sure that that understanding of the of the Aela board wasn't built into your probe and what they found was like at least half of the Improvement was built into the probe you know not all of it right and look a a fellow board is way simpler than the world so I that's why I just I just think it's an open question whether or not the I mean it would be remarkable either way to learn that large language models that are good at doing what we train them to do are good because they've built the same kind of model of the world that we have in our minds or that they're good despite not having that model either one of these is an amazing thing I just don't think the data are clear on which one is true I I think uh I have some sort of intellectual humility about the whole thing because was humbled by several stages in the machine learning development over the past 20 years and I was just would never have predicted that llms the way they're trained on the scale of data they're trained would be as impressive as they are and there that's where intellectual humility steps in where my intuition would say something like with Melanie where you need to be able to have very sort of concrete Common Sense reasoning symbolic reasoning type things in a system in order for it to be very intelligent but here you're I'm so impressed by what it's capable to do train on next token prediction essentially that's I I just my conception of the nature of intelligence is just completely um not completely but uh humbled I should say look and I think that's perfectly fair I also um was I almost say pleasantly I don't know whe it's pleasantly or unpleasantly but factually surprised by the recent rate of progress clearly some kind of phase transition percolation has happened right and the Improvement has been remarkable absolutely amazing that I have no arguments with I'm that doesn't yet tell me the mechanism by which that Improvement happened constructing a model much like a human being would have is clearly one possible mechanism but part of the intellectual humility is to say maybe there are others I was chatting with the CEO of anthropic darad so behind Claud and that company but a lot of a lot of the AI companies are really focused on expanding the scale of compute soort of if we assume that AI is not data limited but is compute limited you can make the system much more intelligence by using more compute so let me ask you on the almost on the physics level do you think physics can help expand the scale of compute and maybe the scale of energy required to make that computer happen yeah 100% I think this is like one of the biggest things that physics can help with and it's an obvious kind of loow hanging fruit situation where uh the heat generation the inefficiency the waste of existing highlevel computers is nowhere near the efficiency of our brains it's hilariously worse and we kind of haven't tried to optimize that hard on that Frontier I mean your laptop heats up when you're sitting on your lap right it doesn't need to your brain doesn't heat up like like that um so clearly there exists in the world of physics the capability of doing these computations with much less waste heat being generated and I look forward to people doing that yeah are you excited for the possibility of nuclear fusion I am cautious ly optimistic excited would be too strong I mean it' be great right but if we really tried solar power it would also be great I I think alas discovered said this that the future of Humanity on Earth will be just it the entire surface of Earth is covered in solar panels and data centers why would you waste the surface of the Earth with solar panels put them in space sure you can go in space yeah space is bigger than Earth yeah just solar panels everywhere yeah just I like it you already have Fusion it's called the sun yeah that's true and and there's probably more and more efficient ways of catching that energy sending it down is the hard part absolutely but um that's an engineering problem yeah so I I just wonder where data centers the compute centers can expand to if that's the future if AI is as effective as it promis as it possibly could be then it's the scale of computation will keep increasing and perhaps it's a raise between efficiency and and uh scale there are constraints right you know there's a certain amount of energy certain amount of damage we can do to the environment before it is not worth it anymore so yeah I think that's a new question in fact it's it's kind of frustrating because we get better and better at doing things efficiently but we invent more things we want to do faster than we get good at doing them efficiently so we're continuing to make things worse in various ways I mean that's that's the dance of humanity we we constantly creating better better better technologies that are potentially causing a lot more harm and that includes for weapons includes AI used as weapons that includes nuclear weapons of course which is surprising to me that we haven't destroyed human civilization yet given how many nuclear warheads are out there look I'm with you between nuclear and bioweapons uh it is a little bit surprising that we haven't caused enormous Devastation of course we did drop two atomic bombs on Japan but compared to what could have happened or could happen tomorrow it could be much worse yeah it does seem like there's a underlying speaking of quantum Fields there's like a like a like a field of goodness within the the human heart that like in some kind of game theoretic way we create really powerful things that could destroy each other and there's greed and ego and all this kind of power hungry dictators that are at play here with in all the geopolitical landscape but we somehow always like don't go too far yeah but that's exactly what you would say right before we went too far right before we went too far and that's why we don't see aliens uh so you're like I mentioned associated with Santa Fe Institute I just would love to take a stroll down the the the the landscape of ideas explored there um so they look at complexity in all kinds of ways uh what do you think about the emergence of complexity from simple things interacting simply I think it's a fascinating topic I mean that's why I'm thinking about these things these days rather than the papers that I was describing to you before um you know all of those papers I described to you before are guesses like what if the laws of physics are different in the following way and then you can work out the consequences at some point in my life I said like what is the chance I'm going to guess right you know Einstein guessed right Steven Weinberg guessed right but there's a very small number of times that people guessed right whereas with this emergence of complexity from Simplicity I I really do think that we haven't understood the basics yet I think we're still kind of pre-paradigmatic there have been some spectacular discoveries um people like Jeffrey West at Santa Fe and others have really uh given us true insights into important systems but still there's a lot of the basics I think are not understood and so searching for the general principles is is what I like to do and I think it's absolutely possible that I mean to be a little bit more substantive than that I I think this is kind of a cliche I think the key is information and I think that what we see through the history of the universe as you go from simple to more and more complex is really subsystems of the universe figuring out how to use information to do whatever to survive or to to thrive or to reproduce I mean that's that's the sort of fuel The Leverage the resource that we have um for a while anyway until the heat death but uh that's where the complexity is really driven by yeah but the mechanism of it what I mean mentioned Jeffrey West what what are interesting in clings of progress in this realm and what are systems that interest you in terms of information so I mean for me just as a as a fan of complexity uh just even looking at simple cell autom is always just um fascinating way to illustrate the emergence of complexity so for those of the listeners who don't know viewers cellular autometa come from imagining a very simple configuration for example a set of ones zeros along a line and then you met a rule that says okay I'm going to evolve this in time and generally the simplest ones start with just each block of three ones and zeros have a rule that they will determinedly go to either one or a zero and you can actually classify all the different possibilities a small number of possible cellular autom of that form and what was discovered um by various people including Steven Wolfram is some of these cell automa have the feature that you start from almost nothing like 000000 1 00000000 and you let it rip and it becomes wildly complex okay so this is very provocative very interesting it's also not how physics works at all because as we said physics conserves information you can go forward or backwards the cellular aom do not they're not reversible in any sense you've built in an arrow of time you have a starting point and then you evolve so what I'm interested in is seeing how in the real world with the real laws of physics and underlying reversibility but macroscopic irreversibility from entropy in the arrow time Etc how does that lead to complexity I think that that's an answerable question I don't think that celom are really helping us in that one so what is in that what is the landscape of entropy in the universe look like well entropy is hard to localize it's a property of systems not of parts of systems right um having said that we can do approximate uh answers to the question and the answer is black holes are a huge in entropy most of let's put it this way the whole observable universe that we're in had a certain amount of entropy before stars and planets and black holes started to form 10 to the 88 I can even tell you the number okay the single black hole at the center of our galaxy has entropy 10 to the 90 single black hole set of our galaxy has more entropy than the whole universe used to have not too long ago so most of the entropy in the universe today is in the form of black holes okay that's fascinating first of all uh but second of all if we take black holes away what are the different interesting perturbations in entropy across space what is uh where do we earthlings fit into that the interesting thing to me is that if you start with a syst system that is isolated from the rest of the universe and you start it at low entropy there's almost a theorem that says if you're very very very low entropy then you the system looks pretty simple because there's low entropy means there's only a small number of ways that you can rearrange the parts to look like that so there if there's not that many ways the answer is going to look simple but there's also almost a theorem that says when you're at maximum entropy the system is going to look simple CU it's all smeared out if it had like interesting structure then it would be complicated right so entropy in this isolated system only goes up that's the second law of Thermodynamics but complexity starts low goes up and then goes down again sometimes people mistakenly think that complexity or life or whatever is fighting against the second law of Thermodynamics fighting against the increase of entropy that is precisely the wrong way to think about it we are Surfers riding the wave of increasing entropy we rely on increasing entropy to survive that is part of what makes us special this table maintains its stability mechanically by which I mean there's molecules they're have forces on each other and it holds up you and I aren't like that we maintain our stability dynamically by ingesting food fuel right food and water and air and so forth burning it increasing its entropy we are non-equilibrium Quasi steady state systems we are using the fuel the universe gives us in the form of low entropy energy to maintain our stability I just wonder what that mechanism of Surfing looks like I mean that's where first of all I mean one question to ask do you think it's possible to have a kind of Science of complexity where you have very precise ways or clear defined ways of measuring complexity I think it is and I think we don't it's possible to have it I don't think we yet have it because you know in part because complexity is not a unve valent thing there's different ideas that go under the rubric of complexity one version is just kogo of complexity right if you have a configuration or a string of numbers or whatever can you compress it so that you have a small program that will output that that's K complexity but but that's the complexity of a string of numbers okay it's not like the complexity of a problem right computational complexity the traveling salesman problem or factoring large numbers that's a whole different kind of question that is also about complexity so we don't have a sort of unified view of it so you think it's possible to have a complexity of a physical system yeah in the same way we do entropy yeah you think that's a Sean Carol paper or what we're working on various things my the the glib thing that I'm trying to work on right now with with a student is complexo Genesis how does complexity come to be if all the universe is doing is moving from low entropy to high entropy it's a sexy name it's a good name yeah I like the name now he's got to write the paper sometimes a name arose By Any Other Name uh what which which uh uh in which context uh the the the the birth of complexity are you most interested in well I think it comes in stages right so I think that if you go from the I'm again a physicist so biologists studying Evolution will talk about you know how complexity evolves all the time the complexity of the genome the complexity of our physiology right but they take for granted that life already existed you know and and entropy is increasing and so forth I want to go back to the beginning and say the early Universe was simple and low entropy and entropy increases with time and the universe sort of differentiates and becomes more complex but that that statement which is indisputably true has different meanings because complexity has different meanings so sort of the most basic Primal version of complexity is is what you might think of as configurational complexity that's what kolov gets at how much information do you need to specify the configuration of the system then there's a whole another step where subsystems of the universe start burning fuel right so in many ways a planet and a star are not that different in configurational complexity they're both spheres with density high at the middle and getting less as you go out but there's something fundamentally different because the star only survives as long as it has fuel right I mean then it turns into a brown door for a white door for whatever but as a star as a main sequence star it is an out of equilibrium system but it's more or less static right like if I spill the coffee mug and it falls in the process of falling it's out of equilibri but it's also changing all the time a specific kind of system is where it's look sort of macroscopically stationary like a star but underneath the hood it's burning fuel to beat the band in order to maintain that stability so as stars form that that's a different kind of complexity that comes to be then there's another kind of complexity that comes to be roughly speaking at the origin of life because that's where you have information really being gathered and utilized by subsystems of the universe and then arguably there's any number of stages past that I mean one of the most obvious ones to me is we talk about simulation Theory but you and I run simulations in our heads they're just not that good but we imagine different hypothetical Futures right bacteria don't do that so that's the kind of information processing that is a form of complexity and so I would like to understand all these stages and how they fit together yeah imagination yeah mental time travel yeah the the things going on in my head when I'm imagining worlds are are super compressed representations of those worlds but it get to the essence of them and maybe it's possible with nonhuman Computing type devices to do those kinds of simulations in more and more compressed ways there's an argument to be made that literally what separates human beings from other species on Earth is our ability to imagine counterfactual hypothetical futures yeah I mean that's one of the big features I don't know if it's everyone has their own favorite little feature but that that's why I said there's an argument to be made I did a podcast episode on it with Adam bully it developed slowly I did different podcast sorry to keep mentioning podcast episodes I did but Malcolm mcgyver who is an engineer at Northwestern has a theory about um one of the major stages in evolution is when fish first climbed on the land and of I mean of course that is a major stage Evolution but in particular there's a cognitive shift because when you're a fish swimming under the water the attenuation length of light in water is not that long you can't see kilometers away you can see meters away and you're moving at meters per second so all of the evolutionary optimization is make all of your decisions on a time scale of less than a second when you see something new you have to make a rapid fire decision what to do about it as soon as you climb on to land you can essentially see forever right you can see stars in the sky um so now a whole new mode of reasoning opens up where you see something far away and rather than saying lookup table I see this I react you can say okay I see that thing what if I did this what if I did that what if I did something different and and that's you know the birth of imagination eventually you've been critical on pens psychism yes you've noticed that right can you make the case for pans psychism and against it so psychism is the idea that Consciousness permeates all matter it's maybe it's uh a fundamental force or it a physics of the way of the fabric of the universe pan psychism thought everywhere Consciousness everywhere right it it's one it's to a point of entertainment the idea of frustrates you which sort of as a fan is is wonderful to watch and you've had great episodes with with panus in your podcast where you go at it I had David schmers who's you know one of the world's great philosophers and he is he is pan psychism curious yeah know he's not he doesn't commit to anything but he's certainly willing to entertain it Philip Goff who I've had who is a great guy but he is devoted to P in fact he is almost single-handedly responsible for the upsurge of interest in pan psychism in the popular imagination and the argument for it is supposed to be that there is something fundamentally uncapturable about conscious awareness by physical behavior of atoms and molecules so the pain psychist will say look you can tell me maybe someday through advances of Neuroscience and what have you exactly what happens in your brain and how that translates into thought and speech and action what you can't tell me is what it is like to be me you can't tell me what I am experiencing when I see something that is red or I taste something that is sweet you can tell me what neurons fire but you can't tell me what I'm experiencing that first person inner subjective experience is simply not capturable by physics and therefore this is an old argument of course but then the therefore is supposed to be I need something that is not contained within physics to account for that and I'm just going to call it mind we don't know what it is yet we're going to call it mind and it has to be separate from physics and then there's two ways to go if you if you if you buy that much you can either say okay I'm going to be a dualist I'm going to believe that there's matter and mind and they are separate from each other and they are interacting somehow or that's a little bit complicated and sketchy as far as physics is going to go so I'm going to believe in mind but I'm going to put it prior to matter I'm going to believe that mind comes first and that Consciousness is the fundamental aspect of reality and everything else including matter and physics comes from it that would be at least as simple as physics comes first right now the physicalist such as myself will say I don't have any problem explaining what it's like to be you or what you experience when you see red it's a certain way of talking about the atom and the neurons Etc that make up you just like the hardness or the brownness of this table these are words that we attach to certain underlying configurations of ordinary physical matter likewise sadness and redness or whatever are words we attach to you to describe what you're doing and when it comes to Consciousness in general I'm very quick to say I do not claim to have any special Insight on how Consciousness Works other than I see no reason to change the laws of physics to account for it if you don't have to change the laws of physics where do you think it emerges from is consciousness an illusion it's almost like a Shand that we humans used to describe as certain kind of feeling we have when interacting with the world or is there some big leap that happens at some stage I almost never use the word illusion illusion means that there's something that you think you're perceiving that is actually not there like an oasis in the desert is an illusion it has no causal efficacy if you walk up to where the Oasis is supposed to be you'll say you were wrong about it being there that's different than something being emergent or non-fundamental but also real like this table is real even though I know it's made of atoms that doesn't remove the realness from the table I think that Consciousness and Free Will and things like that are just as real in tables and chairs Oasis in the desert does have causal efficacy in that it leads you to draw incorrect conclusions about the world sure but imagining a thing can sometimes bring it to reality as we've seen and that has a kind of e a causal efficacy sure but your understanding of the world in a way that gives you power over it and influence over it is decreased rather than increased by believing in that Oasis that is not true about Consciousness or this table you don't think you can uh increase the chance of a thing existing by imagining it imagining it existing unless you build it or make it no that's what I mean like imagining humans can fly if you're the right imagining that humans are flying right in terms of counterfactuals in the future absolutely imagination is crucially important but that's not an illusion that's just a oh okay the possibility of the future versus what reality is I mean the future is a concept so you can in time time time is just a concept so you can play with that but yes reality um so to you so for example I have love asking this so Donald Hoffman um thinks that the entirety of the conversation we've been having about SpaceTime is an illusion is it possible for you to steal man the case for that can you make the case for and against reality as I think uh he writes that um the laws of physics as we know them with SpaceTime is a kind of interface to a much deeper thing that we don't at all understand and that we're fooling ourselves by constructing this world well I think there's like part of that idea that is perfectly respectable and part of it that is perfectly nonsensical and I'm not even going to try to steal man the nonsensical part the real part to me is is what is called structural realism so we don't know what the world is at a deep fundamental level right let's put ourselves in the in the minds of people living 200 years ago like they they didn't know about quantum mechanics they didn't know about relativity that doesn't mean they were wrong about the universe that they understood they had Newton's Laws right they could predict what time the sun was going to run perfectly well in the progress of science the words that would be used to give the most fundamental description of how you were predicting the Sun would rise changed because now you have curve SpaceTime and things like that right and you didn't have any of those words 200 years ago but the prediction is the same why because that prediction independent of what we thought the fundamental ontology was the prediction pointed to something true about our understanding of reality to call it an illusion is just wrong I think we might not know what the best most comprehensive way of stating it is but it's still true is it true in the way for example belief in God is true because for most of human history people have believed in a God or multiple gods and that seemed very true to them uh as an explanation for the way the world is uh some of the deeper questions about life itself with The Human Condition and why certain things happen that was a good explainer um so do you that's not an illusion no I think that was completely an illusion I think it was a very very reasonable illusion to be under there are Illusions there are you know substantive claims about the world that go beyond predic that we can make and verify uh which later turn out to be wrong and the existence of God was one of them um if those people at that time had abandoned their belief in God and replaced it with a mechanistic universe they would have done just as well at understanding things right uh again because there's so many things they didn't understand it was very reasonable for them to have that belief it wasn't that they were dummies or anything like that but that is you know as we understand the universe better and better some things stick with some things get replaced so like you said you are a uh you're a believer of the mechanistic universe uh you're a naturalist and as you've described a poetic naturalist that's right what's the word poetic what is naturalism and what is poetic naturalism naturalism is just the idea that all that exists is the natural world there's no Supernatural world you can have arguments about what that means but I would claim that the argument should be about what the word Supernatural means not the word natural the natural world is the world that we learn about by doing science the poetic part means that you shouldn't be too I want to say fundamentalist about what the natural world is as we went from Newtonian SpaceTime to einsteinian SpaceTime something is maintained there there is a different story that we can tell about the world and that story the Newtonian regime if you want to fly a rocket to the moon you don't use general relativity use Newtonian mechanics that story works perfectly well the poetic aspect of the story is that there are many ways of talking about the natural world and as long as those ways latch on to something real and causally efficacious about the functioning of the world then we attribute some reality and Truth to them so the poetic really looks at the at the uh let's say the pothead questions at the edge of science is more open to them it's doing double duty a little bit so that's why it's confusing the the more obvious respectable Duty it's doing is that tables are real even though you know that it's really a Quantum field Theory wave function right tables are still real they're a different way of talking about the underlying deeper reality of it the other Duty it's doing is that we move Beyond purely descriptive vocabularies for discussing the universe onto normative and prescriptive and judgmental ways of talking about the universe this painting is beautiful that one is ugly this action is morally right that one is morally wrong these are also ways of talking about the universe they are not fixed by the phenomena they are not determined by our observations they cannot be ruled out by a crucial experiment but they're still valid they might not be Universal they might be subjective but they're not arbitrary and they do have a role in describing how the world works so you don't think it's Poss to construct experiments that explore the Realms of morality and even meaning so those are just those those are subjective yeah they're human they're personal but do you think that's just because we don't have a uh the tools of science have not expanded enough to incorporate The Human Experience no I don't think that's what it is I think that what we mean by Aesthetics or morality are we're attaching categories properties to things that happen in the physical world and there is always going to be some subjectivity to our attachment and how we do that and that's okay the faster we recognize that and deal with it the better off will be but if we deeply and fully understand the functioning of the human mind won't be able to incorporate that no that will absolutely be helpful in explaining why certain people have certain moral beliefs it won't justify those beliefs as right or wrong do you think it's possible to have a kind of general relativity but but that includes the observer effect where the human mind is the Observer so of sort of like how we morph uh in the same way gravity morphs SpaceTime how does the human mind morph reality and have a very uh thorough theory of how that morphing actually happens that's a very pothead question Lex but don't you think it's possible the answer yes I think that there's no I think that we're part of the physical world and the natural world um physicalism would have been just as good a word to use as naturalism maybe even a more accurate word but it's a little bit more off-putting so I do I did want to snappier more attractive label um than physicalism are there limits to science sure we just talked about one right science can't tell you right from wrong you need science to implement your ideas about right and wrong if you are functioning on the basis of an incorrect view of how the world works you might very well think you're doing right but actually be doing wrong but all the science in the world won't tell you which action is right and which action is wrong you know dictators and people in power will sometimes use science as an authority to uh convince you what's right and wrong studying Nazi science is fascinating yeah but there's an instrumentalist view here you have to first decide what your goals are and then science can help you achieve those goals if your goals are horrible science has no problem helping you achieve them science is happy to help out let me ask you about the method behind the madness on several aspects of your life so you mentioned that your approach to uh writing for research and writing popular books how do you find the time of the day like what's the day in the life of Sean Carol how I find the time on so you don't have a thing where in the morning you're like you you try to fight for 2 hours somewhere I don't I'm really terrible at that you my my strategy for finding time is just to ignore interruptions and emails but it's a different time every day some days it never happens some weeks it never happens to pull it off cuz you're extremely prolific so like you're able to have days where you don't write oh my God and still write the next day right oh wow that's a rare thing right a lot of prolific writers will yes it's true will carve out two hours because otherwise it just disappears right no I get that yeah I I do and yeah it's just like I everyone is you know has their foibles or whatever so I'm not able to do that therefore I have to just figure it out on the Fly and what's the actual process look like when you're writing uh popular stuff you get behind a computer yeah get behind a computer and my way of doing it so my wife Jennifer is a science writer but it's interesting because our techniques are entirely different you know she will think about something but then she will freewrite she'll just sit at a computer and write like I think this I think this I think and then that will be vastly compressed edited in you know Rewritten or whatever until the the final thing happens I will just like sit there silently thinking for a very long time and then I will write what is almost the final draft so a lot of it happens there might be some scribbles for an outline or something like that but a lot of it is in my brain before it's on the page so that's the case for the the biggest ideas in the universe the quanta book and the SpaceTime motion book yeah Quant and fields which is actually mostly about Quantum field Theory and particle physics um that's coming out in May and that is uh I I'm letting people in on things that no other book lets them in on so I hope it's worth it it's it's a challenge because there's a lot of equations I mean you did the same thing with SpaceTime motion you you did something quite interesting which is like you made the equation a centerpiece of a book right there's a lot of equations book is is um goes further in those directions than book one did so it's more cool stuff it's also more mind bendy it's more of a challenge book three that I'm writing right now uh is called complexity and emergence oh wow and that'll be the final part of the trilogy oh that's fascinating so there's a lot of probably ideas there there I mean that's a real Cutting Edge well but you know I'm not trying to be cutting edge in other words I'm not trying to speculate in these books obviously in other books I've been very free about speculating but the point of these books is to say things that 500 years from now will still be true and so there are some things we know about complexity emergence and I want to focus on those and I will I will mention I'm happy to say this is something that needs to be speculated about but I won't pretend to be telling you what one is the right one you somehow found the balance between the rigor of mathematics and still accessible which is interesting I try I mean look this these three books the biggest ideas books are absolutely an experiment they're going to appeal to a smaller audience than other books will um but that audience should love that like my 16-year-old self would have been so happy to get these books I can't tell you yeah in terms of looking back in history th those are books the trilogy would be truly special in that way worked for Lord of the Rings so I figured why not me you and toen just yeah different styles different topics same Ultimate Reality uh like we mentioned mindscape podcast I love it uh you interview a huge variety of experts from all kinds of fields so just several questions I want to ask how do you prepare uh like how do you prepare to have a good conversation how do you prepare in a way that satisfies makes your own curious mind happy all that kind of stuff yeah no these are great questions and I've sort of struggled and and changed my technique over the years it's over 5-year-old podcast might be approaching six years old now um I started out overpreparing when I first started you like I had a journey that I was going to go down many of the people I talk to were academics or you know thinkers who write books so they have a story to tell you know I could just say okay give me your lecture and then an hour later stop right so the mistake is to sort of anticipate what the lecture would be and to ask the leading question that would pull it out of them uh what I do now is much more here are the points here like the big questions that I'm interested in and so I have a much sketchier um outline to start and then try to make it more of a real conversation um I'm helped by the fact that it is not my day job so I I strictly limit myself to one day of my life per podcast episode on average some days take more and that includes not just doing the research but inviting the guest recording it editing it publishing it so I need to be very very efficient at that yeah you enforce constraints for yourself in which creativity can emerge that's right that's right and you know look sometimes if I'm interviewing a theoretical physicist I can just go in and where I'm inter interviewing an economist or a historian I have to do a lot of work do you ever find yourself uh getting lost in rabbit holes that serve NOP purpose except satisfying your own curiosity and then potentially expanding the range of things you know that can help your actual work in research and writing yes um on both counts you know I do some people have so many things to talk about that you don't know where to start or finish right others have a message and it's what's one of the things I discovered over the course of these years is the correlation with age like there are brilliant people and I try very hard on the podcast to sort of get all sorts of people right different ages and things like that um and bless their hearts the most brilliant young people are not as practiced at wandering past their literal research right they are less Mastery over the field as a whole much less how to talk about it whereas certain older people just like have their patent answers and that's kind of boring right so you want you want somewhere in between you know the ideal person who is is has a enough a scope that they can wander outside their specific papers they've written but they're not overly practiced so they're just giving you their canand answers I feel like there's like a connection to the metaphor of entropy and complexity as you said with the there edge of chaos yeah uh you also do incredible amas and people should sign up to your patreon and because you can get to ask questions Sean Carol well for several hours you just answer in fascinating ways uh some really interesting questions is there something you could say about the process of finding the answers to those that's a great one again it's it's evolved over time um yeah so the ask me anything um episodes were first when I started doing them they were only for patreon subscribers to both listen to and to ask the questions but then I actually asked my patreon subscribers would you like me to release them publicly and they overwhelmingly voted yes so I do that so the patreon supporters asked the questions everyone can listen and also at some point I I really used to try to answer every question but now there's just too many so I have to pick and that's fraught with Peril and my personal standard for picking questions to answer is what are the ones I think I interesting answers to give for right so that both means if it's kind of the same old question about special relativity that I've gotten 100 times before I'm I'm not going to answer it because you can just Google that it's easier um there are some you know very clear attempts to ask an interesting question uh that honestly just I don't have an answer to like I read this science fiction novel what do you think about it I'm like well I haven't read it so I can't help you there um what's your favorite color you know I can tell you what it is but it's not that interesting and um so there's I try to make it a mix uh I try to like it's not all physics questions not all philosophy questions I will talk about food or or movies or politics or religion if that's what people want to I keep suggesting that people ask me for relationship advice but they never do yeah I don't think I've heard I don't think I've heard one yeah I I'm I'm willing to do it but uh I'm a little reluctant because I don't actually like giving advice um but I do but I'm happy to talk about those topics I want to you know I want to give several hours of of of talking and I want to try to say things that I haven't said before and keep it interesting keep it rolling if you don't like this question wait for the next one what are some of the harder questions you've gotten do you remember what what kinds of questions are difficult for you rarely but occasionally people will ask me a super insightful philosophy question like I hadn't thought of it things in exactly that way and I try to be you know um I try to recognize that um a lot of times is the it's the opposite where it's like okay you're clearly confused and I'm going to try to explain why how the question you should have asked love those yeah yeah why that's the wrong question or that kind of stuff that's great right that's great but the hard questions I don't know like I don't actually um answer personal questions very much like the most personal I will get are questions like what do you think of Baltimore right you that that much I can talk about or how are your cats doing happy talk about the cats in infinite detail but you know very personal questions I don't get into but you even touched like uh politics and stuff like that yeah no very happy to talk about politics um you know I try to be clear on you know what is professional expertise what is just me babbling what is my level of credence in different things where you're allowed to disagree whether if you disagree you're just wrong um and you people can disagree with that also but I do think you know and I'm I'm happy to go out on a limb a little bit I'm happy to say look I don't know but here's my guess right I just did a whole solo podcast which was exactly that and you know it's interesting like some people like oh this was great and there's a whole bunch of people like why are you talking about this thing that you are not the world's expert in so you know well I love the actual dance between humility and having a strong opinion on stuff which is a great it's a it's it's it's a fascinating dance to pull off and I guess the way to do that is to just expand into all kinds of topics and play with ideas and then change your mind and all that kind of stuff yeah it's it's interesting because when people react against you by saying you are being arrogant about this 99.999% of the time all they mean is I disagree yeah that's all they really mean right yeah um you know like at a very basic level like people will accuse atheists of being arrogant and I'm like you think God exists and loves you and you're telling me that I'm arrogant I think that all all this is to say just advice when you disagree with somebody try to specify the substance disagreement try not to psychologize them right you know try to say oh you're saying this because of this maybe it's true maybe you're right but if you had an actual response to what they were saying that would be much more interesting yeah I think I wonder why it's difficult for people to say or to imply I respect you I like you but I disagree on this and here's why I disagree like I I wonder why they they go to this place of like well you're an idiot or you're uh uh egotistical or you're um confused or you're naive or you're you know all the kinds of words as opposed to like I respect you as a fellow human being exploring the world of mysteries all around us and I disagree I will complicate the question even more because there's some people I don't respect or like and I I once wrote a blog post I think it was called the grid of disputation and I I had a 2 by two grid and it's are you someone I agree with or disagree with are you someone who I respect or or don't right and all four quadrants are very populated and and that so what that means is there are people who I like uh and I disagree with and there are people who agree with me and I have no respect for at all the embarrassing allies quadrant that was everyone's favorite so and I just think being honest right like trying to be honest about where people are but if you actually want to move a conversation forward forget about whether you like or Don't Like Somebody explain the disagreement explain the agreement but you're but you're absolutely right I completely agree like as a society we are not very good at disagreeing we instantly go to the insults yeah and I mean even on the deeper level I think at some deep level I respect and love the humanity in the other person yep uh you said that general relativity is the most beautiful Theory ever so far what do you find beautiful about it let's put it this way when I teach courses um there's no more satisfying subject to teach than general relativity and the reason why is because it starts from very clear precisely articulated assumptions and it goes so far right and you know when I give my talk you can find it online I'm probably not going to give it again the book one of the biggest ideas talk right was building up from you you don't know any math or physics an hour later you know Einstein's equation for general relativity and the punchline is the equation is much smarter than Albert Einstein because Albert Einstein did not know about the Big Bang he didn't know about gravitational waves he didn't know about black holes but his equation did and and that's I mean that's a miraculous aspect of science more generally but general relativity is where it manifests itself in the most absolutely obvious way uh a human question what do you think of the fact that Einstein didn't get the Nobel Prize for general relativity tragedy he should have gotten maybe four Nobel prizes honestly um he certainly should have got the the photoelectric effect was 100 % worth the Nobel Prize because and people don't quite get this who cares about the photoelectric effect that's like this very minor effect the point is his explanation for the photoelectric effect invented something called the photon that's worth the Nobel Prize Max plunk gets credit for this in 1900 explaining black body radiation by saying that when a little electron is jiggling in a object at some temperature gives off radiation in discret chunks rather than continuously he didn't quite say that's because radiation is discrete chunks right it's like having a coffee maker that makes one cup of coffee at a time it doesn't mean that liquid comes in one cup qua right just that you are dispensing it like that it was Einstein in 1905 who said light is Quant and that was a radical thing so that clearly that that was not a mistake but also special relativity clearly deserved the Nobel prize and general relativity clearly deserve the Nobel Prize not only were they brilliant but they were experimentally verified like everything you want so separately you think yeah yeah absolutely oh humans yeah whatever the explanation there edin huble never won the Nobel Prize for finding the universe was expanding yeah uh but and even the fact that we give prizes is almost kind of silly and we limit the number of people that get the prize and all that I I think that Nobel Prize has enormous problems uh I think it's probably a net good for the world because it brings attention to good science I think it's probably a net negative for science because it makes people want to win the Nobel Prize yeah there's a lot of fascinating human stories Underneath It All science is its own thing but it's also a collection of humans and it's a beautiful collection there's tension there's competition there's jealousy um but there's also great collaborations and all that kind of stuff uh Daniel Conan who recently passed is uh is one of the great stories of collaboration in um in science um so all of it all of it that's what humans do and uh Sean thank you for being the person that makes us um celebrate science and fall in love with all of these beautiful ideas and science for writing amazing books for being legit and still pushing forward the research science side of it and uh for allowing me and uh these pothead questions and also for educating everybody through your own podcast it's uh everybody should stop everything and subscribe and listen to every single episode of mindscape so thank you I've been a huge fan forever I'm really honored that you would uh speak with me in the early days when I was still starting this podcast in means of the world I appreciate it thanks very much for having me on now that you're a big deal still having me on thank you Sean thanks for listening to this conversation with Sean Caroll to support this podcast please check out our sponsors in the description and now let me leave you with some words from Richard Fineman study hard what interests you the most in the most undisciplined irreverent and original manner possible thank you for listening and hope to see you next time