The Black Hole Wars: My Battle with Stephen Hawking

good evening everyone my name is andrew frak noi i'm the astronomy instructor here at foothill college and it's a great pleasure for me to welcome everyone in the auditorium and everyone watching or listening on the web to the 10th annual silicon valley astronomy lectures which start tonight these lectures are designed to introduce some of the most interesting new results and ideas in the field of astronomy and we invite noted astronomers and physicists from around the Bay Area and the country to update us six times during the school year the lectures are sponsored by NASA and NASA's Ames Research Center which is one of the premier research centers in the NASA circuit by Foothill College which is a community college here in Silicon Valley that offers both day and evening classes for students from age 16 to 80 and we actually have students from both those ranges in my evening class this quarter so it's a it's really a delight to see people from the community come up and take classes here other co-sponsors are the Astronomical Society of the Pacific a venerable organization that since 1889 has been doing what we do in these lectures which is sharing the excitement of astronomical discovery with the world at large and they have a number of educational programs which are outlined on the back of your program and finally the SETI Institute the search for extraterrestrial intelligence Institute which is an organization devoted to the scientific investigation of life elsewhere now for those of you who are here I want to announce formally that we are also delighted to have working with us the local amateur astronomy organization called the peninsula Astronomical Society and they as many of you know also run the Foothill College Observatory which has a new telescope donated to us by a Gen donar and is open every clear Friday evening for viewing from 9:00 to 11:00 as was Saturday morning for solar viewing but that's not quite ready and to show off the new telescope they have graciously agreed to hold open the telescope tonight after the lecture so if you are not busy and you want to walk over to our Krause center on the other side of campus ah they will be glad to have a kind of star party and show off the telescope tonight it was just clearing up as we were coming in so as long as it remains clear right Sarah that's the requirement all right so without further ado let me then introduce our speaker our speaker is the author of a best-selling book about black holes or the black hole war and it's the topic we've asked him to address tonight dr. Leonard Susskind is the Felix Bloch professor of theoretical physics at Stanford University and the author not only of the black hole war but also the cosmic landscape another introduction to the far-out frontiers of physics and astronomy he's written many articles on recent developments in science and their meaning he teaches a popular continuing studies course at Stanford on modern physics and has won the American Institute of Physics science writing prize for an article explaining black holes in everyday language his scientific research focuses on particle physics quantum theory and the nature of gravity small questions right but in fact he is as well known for being a superb explainer of science and so we have asked him tonight to explain a little bit about his ongoing intellectual battle with Stephen Hawking on the subject of some of the most mysterious objects in the universe black holes ladies and gentlemen it's a professional privilege for me to introduce dr. Leonard Susskind is this better okay I can one-up your Andrew you know right I do teach a class for the general public at Stanford the name of the class incidentally I don't remember the precise real name of the class but we all call it quantum mechanics for old farts anyway I am NOT an astronomer I've only once in my life looked to an astronomical telescope so I may disappoint you I don't have wonderful pictures of this or that galaxy and so forth what I'm going to tell you about is a big controversy that took place in theoretical physics that had to do with black holes now if you buy my book and please buy my book I get about a dollar and a half for every book you buy if you buy my book and you open up to the central chapter you'll find that the absolute central chapter the center of the book is called the Battle of Santa Barbara the Battle of Santa Barbara was a physics conference a bunch of theoretical physicists got together to battle out one of the central questions one of the deep questions of theoretical physics and I didn't know this when I wrote the book but after I wrote the book I discovered that one of my friends had taken a picture of the conference and here it is let's see if I can remember who's who here that's a joke but maybe in any case the black hole war was not really a war between people it was certainly not a war between armies of people it was a war between concepts if you could photograph ghosts this ghost this photograph would have a ghost of Einstein hovering over the whole thing and the ghost of Einstein would be weeping he would be weeping because the battle was between two of his children two of his favorite children it was a battle between the principles of general relativity the so-called equivalence principle on the one hand and on the other hand quantum mechanics these two theories clashed with each other from the very very beginning they were like angry enemies that simply couldn't reconcile each other but the real battle broke out over the properties of black holes now again this is not a real photograph of a black hole I wish it were this is an artist's rendition I suspect the background is quite real but the black hole at the center is an artist's picture but it's actually quite accurate the boundary of the black hole of course is called the horizon you can't see anything from inside the black hole and of course all of these rings and distortions around the black hole are due to the fact that black holes Bend light so this is a picture of a black hole this is a picture of an imaginary astronomical black hole but the debate was not really over the properties of real astronomical black holes there was over the principles the principles of quantum mechanics gravity and how they relate to black holes one of the deepest principles of physics perhaps the deepest in fact in my view I would have to say it is the deep principle of physics it's a quantum mechanical principle is that information is never lost information comes in bits I'll explain to you what that means what does it mean for information to come in bits you all know that your computer is full of bits well here's a piece of information I doubt that it's true maybe it is true but it is a piece of information King Canute had warts on his chin everybody will agree either true or false this is a piece of information but how do you quantify the amount of information that's in this sentence so let me quantify it for you to quantify a bunch of information what we do is reduce it to bits reducing it to bits is the same thing as reducing it to Morse code here's Morse code for King Canute had warts on his chin and it consists of a bunch of dots and dashes information comes in bits bits are the same as dots and dashes King canoe had warts on his chin is a 65 bit sentence a 65 bit message and that's what the quantity of information means the number of bits are the number of dots and dashes that it takes to express a given thought idea message that's how much information is in it now as I said one of the deepest principles of information or of physics in general is that information is never ever lost if you have some information in your computer you can erase it if you couldn't erase the information in your computer we get overloaded but really in fact that information is not lost what happens to it is it's ejected out of the computer in a little bit of heat it is not lost information it is scrambled information a little bit of something gets ejected out into the atmosphere scrambled around hit by molecules and so forth for all practical purposes it's lost but if you could examine every molecule in the room every molecule of the computer you would find that bit lurking someplace so bits of information are never lost as I said that is one of the very very deepest principles of physics it goes way back it actually goes back past quantum mechanics to classical mechanics and it is sacrosanct or always was sacrosanct however in 1976 Stephen Hawking put forward an idea that seemed to undermine that basic principle the principle the idea had to do with black holes Stephen was a great expert on got black holes you are not great experts on black holes I'm only a medium expert on black holes but I have my way of thinking of them and I'm going to share with you my way of thinking about them imagine an infinite lake a lake that spread out in every direction horizontally forever and ever and it's not a very deep lake a metre deep one meter deep but in that lake lives fish the fish communicate with each other how do they communicate with each other by sound they're blind fish they can't see they communicate each other only by sound and there's a rule whether it's a law of physics or a law of fish or a law of our legalistic law doesn't matter to us very much but the rule is no fish is allowed to swim faster than the speed of sound in the water that means he's not allowed to swim faster through the water than the speed of sound it could be a law of nature as I said or it could just be a law of fish well this lake is a rather dangerous lake and the reason it's dangerous is because right at the center of it is a drain hole and the drain hole empties out underneath into a cave and in that cave is very sharp rocks anything that gets sucked into the drain is doomed is dead if it gets sucked into the drain and what makes that drain hole so very very dangerous is that at some point at some distance away from the drain hole the inflow of water is moving faster relative to the ground than the speed of sound what that means is that any fish that passes that point let's call it the point of no return any fish that passes the point of no return has no chance of getting out he can't swim the current the current is moving faster toward the center than he can swim he's lost he's doomed nothing yet has happened to him he's floated freely past the point of no return may not even realize it everything else is flowing with him the dirt the sand whatever it is is flowing along with him has no concept that he has passed the point of no return and yet he is doomed not yet dead but doomed he can try to shout to his friends he can say save me save me but even his sound waves can't escape because the water is moving faster than the speed of sound even they get pulled down into the drain well this is a model of a black hole and it's a rather accurate model of a black hole down at the center is the singularity of the black hole the dangerous dangerous place which as you approach it you will be crushed squeezed stretched turned into whatever the horizon of the black hole appears at first sight to be completely innocuous non dangerous in itself you just float freely past it the point of no return I called it the horizon that's what it is the point of no return is called the horizon of the black hole nothing including sound or in the case of a real black hole light or anything else can escape from the black hole that's really all you need to know about a black hole that it's horizon is a point of no return and the singularity at the center is a very dangerous place that's one picture of a black hole here's another picture showing the same thing it's just another form of describing a black hole as a curvature in space here's a fish if that fish accidentally passes the point of no return for some reason I've always called that fish Alice Alice and her bits everything about Alice everything that makes Alice Alice all the bits of information in her DNA and everything else are lost to the outside world apparently bits of information can be lost and they get lost by falling into a black hole or so Stephen Hawking said to make things even more confusing Hawking had discovered that black holes evaporate Alice falls into the black hole and now you wait and the black hole evaporates how does it evaporate it gives off heat and light it gives off photons as it gives off photons the energy of the photons is carried away and the black hole shrinks it shrinks because it's losing energy very very much like a puddle of water out in the Sun as it evaporates it shrinks and shrinks and it shrinks until there's nothing left but where is Alice what happened to her bits they're gone they fell behind the horizon they couldn't get out because they can't exceed the speed of light or so said Stephen Hawking and so on saying so he basically announced a violation of the most sacred principle of physics information is never lost well was it really that simple some of us didn't think so that was in fact the origin of the black hole war the black hole war was a controversy a controversy involving Stephen who said yes information is lost when it falls into black holes and myself and a physicist by the name of Jerrod a tuft a very very famous physicist incidentally one of them - most physicists incidentally - most theoretical physicists Jerrod it hoofed is number one he is the great physicist of my generation we said no that's too easy to say that information is lost you're under mine in something too deep too fundamental it can't be true but we couldn't understand what was wrong with what Stephen was saying if something falls into a black hole it can't get out if it can't get out it's lost if the black hole evaporates it's gone we didn't understand what was wrong with what he was saying but we were sure he was wrong that was the origin of the black hole war all right so let me tell you now a little bit more about what was learned about black holes since around the early 1970s a little bit before Stephen made his claim let me start with the observation of a physicist whose name is jacob bekenstein again the very famous Israeli physicist in 1972 jacob bekenstein was an undergraduate student a graduate student at Princeton and he discovered something very very remarkable about black holes he didn't discover it by doing an observation he didn't discover it by doing an experiment he did it by doing a thought experiment and he was a stór experiment he began with the idea of entropy what is entropy well entropy was something that was first discovered and first talked about by steam engineers it had to do with the quality of a given amount of energy is it useful energy is it not useful energy not useful energy is called heat you can't do much with heat well sometimes you can but heat is harder to do things with and mechanical energy and a measure of how useless energy is was called entropy it's a measure of confusion how confusing how confusing the little constituents which carry the energy are if there are lots of the molecules moving around and also two crazy directions there's lots of entropy if all the molecules are moving together there's only a little bit of entropy entropy had to do with steam engines what could it possibly have to do with black holes well the connection with black holes was a principle namely the second law of thermodynamics the second law of thermodynamics said entropy always increase you cannot decrease the amount of confusion in the universe you may be able to decrease decrease the amount of confusion in one place but it will always show up someplace else and here was the puzzle that bekenstein addressed he said oops one cook before he's before what he said let me tell you a little more about entropy entropy has it there's another idea of what entropy is if I were to take a bathtub full of water we would all agree anybody who knows anything about water and about thermodynamics that has lots and lots of entropy in that water what is that entropy that entropy is the same as hidden information when you look at that bathtub full of water you don't see much you see the amount of water you see the temperature of the water that's about all but there's an enormous amount of information in that bathtub and that information is stored in the position and velocity of every single molecule it's there if only we had the patience to detect it and the count every molecule that information those bits of information would be there another way of thinking about entropy is that it's hidden information information which is hidden because it's in too many degrees of freedom too small too mixed up and too difficult to get at then it's called entropy the principle of physics the second law of thermodynamics said that entropy always increases but bekenstein said wait a minute supposing I take a bunch of entropy and I allow it to fall into a black hole after it's falling into the black hole a black hole increases its size a little bit but the entropy is gone the steam engine that carried the entropy is gone all we have left is the black hole entropy has disappeared bekenstein said no there's something wrong with this so what's wrong with it as black holes must have entropy when the black hole gets a little bit bigger when it swallows the entropy it gets a little bit bigger it must be that somehow bigger black holes have more entropy more hidden information in them than smaller black holes said when we're going to count the entropy of the world we must count entropy for black holes well he was more interested in quantitatively knowing how much entropy how many bits of information were hidden in a black hole and he was his argument I'm going to show you his argument that's very beautiful ah there's a little bit of mathematics to it I'm not going to do the mathematics he said let's start with a very tiny black hole very very small black hole have very little information in it a black hole as big as a proton let's say no bigger and now let's start making that black hole bigger by dropping things into it and we're going to drop things in one bit of information by at a time how do you drop a bit of information into a black hole you drop in a single elementary particle a photon so we said let's drop in one by one bits of information the only information that's there in an elementary particle is either it's there or it's not there it's like a dot or a dash it's either there or it's not there if we drop a particle into a black hole there must be a particle in the black hole we may not know where it is but that's a piece of information what happens when we drop there Potter when we drop a bit of information in the black hole grows a little bit it absorbs the energy of the photon grows a little bit because the more energy that it has the bigger it is and then we throw in another one and the black hole grows and so on and so forth until we build up ourselves the black hole that were interested in well what what bekenstein discovered was quite remarkable when he sat down did the mathematical calculations he discovered that the number of bits of information that could be in a black hole if you think about it for a minute before I address this how many bits of information are in a full of water the answer is the amount of water that's there roughly and the amount of water is proportional to the volume of water in the bathtub up until bekenstein it was always the case that the amount of information information the air in this room is proportional to the volume why because the number of particles is proportional to the volume but what bekenstein found when he did his little thought experiment of throwing in bits as the black hole grew in such a way that the number of bits that could be inside the black hole was proportional for the area of the black hole the area of the black hole and some tiny unit called the plunk unit what did they say this said that somehow the interior of the black hole had nothing in it only the horizon of the black hole the horizon of the black hole was storing all the information and it was storing it very very much as if the black hole horizon was made out of bits of information which were impenetrable and each time you put another bit in it increased the area of the black hole a little bit that was beckon Stein's resolution of the second law of thermodynamics throw things into a black hole they appear on the horizon as bits of information bits of entropy and as you fill up the black hole it simply grows its horizon gets bigger and bigger but the surprising thing was there's no idea that entropy somehow resided only on the surface it was as though all of the information in this room was on the boundaries of the room not in the interior of the room and this was very very confusing well let that raises a question I'm going to take a little time out to answer a particular question what are the hidden microscopic structures these little bits that make up the horizon of a black hole that make up the entropy of a black hole I want to tell you very quickly now that's faith theorist over the last decade have put together a theory of what is on the surface of a black hole it began with the basic ideas of string theory that elementary particles are little tiny strings a weird idea but let's accept it little tiny strings no bigger than the Planck scale vibrating and doing whatever they do but if you heat them up how can you heat them up you can put them in a frying pan and heat the frying pan well that doesn't do very much but if you collide them together at enormous energies you can heat them up and when you heat them up they grow they get more tangled they expand they expand the string grows more energy more string and eventually they form huge tangles of string when you pump enough energy into them well those huge tangles of string gravitate the parts of it pull themselves together by gravity and that oops excuse me that forms a black hole well we now believe at least those of us who have some confidence in the ideas of string theory is that a black hole is nothing but a huge tangle of string which has been pulled together by gravity but on the surface of that huge tangle of string little bits of string carry the information that is on the horizon of the black hole that's what is now believed about black holes that their surface is a tangled mess of hot bits of information and they are very hot they won't have time to tell you why they are very hot but if you were to lower thermometer down to the surface of a black hole you would discover this hot bath of bits of information well that is a bit confusing the first picture I gave you of a black hole is that it was nothing but a point of no return or a black hole of horizon that the horizon was nothing but a point of no return which you could freely fall past Alice would freely fall past it nothing much what happened to her she would pass the horizon of the black hole be trapped you can't get out but she would feel no pain as she passed the horizon of the black hole that was one picture of the black hole horizon a harmless point of no return but now let's think about Alice falling through the black hole according to that picture Alice would fall into a black hole and this theory that it's just a point of no return says that she would see nothing out of the ordinary at the horizon she would happily sail through right through the point of no return cool as a cucumber nothing would happen to her on the other hand the other picture is that the horizon of the black hole is a terribly hot bit soup of bits a tangle of string of super bits and hot how hot if you were to lower a thermometer down to the surface of a black hole and then retrieve it to see how hot it got the closer it got to the surface of the black hole surface means the horizon the closer it gets to the horizon the hotter it would be it would heat up to a million billion billion billion degrees something's funny here we have two distinct pictures which is true is it a harmless point of no-return the horizon or is it a hot soup of bits where Alice would get destroyed destroyed by the heat here's two pictures the two pictures are Alice falling freely through the horizon of the black hole nothing happening to her that was one picture and incidentally this is the picture that followed from a naive application of general theory of relativity the other picture says that when she get to the horizon she would encounter a super hot super bits at the horizon she would be cooked thermalized and then radiated back out as photons here she is falling into the black hole the black hole is surrounded by this hot soup of bits as she falls in she encounters it it's a million billion billion billion billion degrees what happens to her she gets evaporated ionized turned into photons and radiated back out obviously both of these things cannot be right does Alice fall safely through the horizon or is she thermalized and eventually radiated back out in the form of scrambled toms that was the big controversy that physicists were dealing with when they when they entered into this black hole war well what is the answer the answer is that both are true how on earth can both be true either alice is destroyed at the horizon or she's not destroyed at the horizon it stands to reason to things which are contradictory can't both be true and yet the more we thought about it the more we came to the conclusion that both things are true how can that possibly be well the answer has to do with what you can really measure about a system there are all kinds of circumstances in physics where apparently contradictory things are both true I'll give you an example if a light bulb over there goes off and a light bulb over there goes off one and then the other or the other and then the one one of them must go off first right it stands to reason if that one goes off first then that one could not go off first if that one goes off first then that one could not go off first but we've learned from Einstein that there is no definite answer to the question of which one goes off first it depends on how the observer is moving if the observer is moving fast you will see that one goes off first if he's moving in the other direction you'll see that one go off first and so there is a relativity to observations it's not necessarily the case that two apparently contradictory things can't both be true it depends on how the observation is done well what we learned is that in fact both things were true here's Bob Bob stands outside the black hole he watches Alice for into the black hole Alice falls into the black hole and she says when she passes the horizon she says I'm okay I've just passed the point of no return I haven't gotten to the singularity yet I'm perfectly healthy I haven't been cooked I haven't been heated up the problem is she can never communicate that information to Bob if the information can never be communicated to Bob then Bob has no way of knowing that Alice is okay Bob sees on the other hand radiation coming out from the black hole he counts up all that radiation and he discovers there's one bit for each bit of Alice that fell into the black hole he finds Alice having been cooked and radiated and sent back out but is there a contradiction not in the strict sense of the word because Alice can never communicate that information to Bob and so there's no observable contradiction that idea believe it or not has infected itself into physics and it is now generally accepted that both views are true Alice falling into the black hole encounters nothing crazy at the horizon and it's perfectly safe until she gets to the singularity Bob watching the whole thing discovers Alice being disassembled cooked radiated and sent back out as photons so the lesson is that objectivity is not really what we thought it was the idea of where information is how things behave is relative it's another example of relativity and action but wait a minute you say what happens if Bob looks at Alice not after she crosses the horizon but just as she's about to cross the horizon I told you a moment ago that near the horizon if you drop the thermometer down not through the horizon but near the horizon that it's extremely hot Bob doesn't have to wait until Alice falls through the Hirai to ask her Alice are you okay or he can shine a light on Alice and try to make an image of Alice and see if Alice is okay well it turns out that it's very interesting in order for Bob to take a good look at Alice as she gets very very close to the horizon he needs to use photons of very small wavelength if he wants to resolve the same way you need a telescope of short wavelength to resolve a small object in order to in order to resolve Alice as she gets closer and closer to the horizon she has to be illuminated with very short wavelength photons short wavelength photons mean very high-energy photons the lesson is in the process of trying to find out if alice is okay he has to hit her with incredibly high energy photons which in the process of looking at her will cook her just the thing that Bob wanted to show didn't happen by observing Alice he causes to happen by observing Alice and so what we found over the years is that there really is no contradiction if Bob chooses to look at Alice he will find that she get does get cooked at the horizon if he leaves her alone he will still think she gets cooked at the horizon because he will discover all this radiation coming out but Alice will pass smoothly through feel no pain and in her frame of reference relative to her frame of reference she will discover nothing unusual that is the ultimate upshot of this confusion that was raised by Hawking in the first place but it's a big deal it's not a small deal it meant we were thinking completely wrong about information how it was stored where it is found how relative it is and how objective a piece of information is the whole subject got turned on its head now an even more startling conclusion that came out of this series of investigations the world is like the ghostly three-dimensional illusion cast by a hologram that sounds very weird most of you know what a hologram is but before I get to Holograms let me explain something about information and how it's stored ordinarily this is supposed to be a picture of a library in fact it was supposed to be the picture of the library in Alexandria it's my artist rendition of it it was known to be about I think 200 feet by 40 feet by some number of feet in this direction here question I thought I heard a question this is the library this is the library in Alexandria reconstructed according to my own imagination and I had a certain size we can ask how much information could be stored in that library well it turned out that about a trillion bits of information was stored in the library in Alexandria in the form of Scrolls a trillion bits of information in other words information could be turned into a billion dots and bashes a billion is not very much why couldn't you store more information well you certainly could you could shrink it down from Scrolls to books or from books to microfiche or you could squeeze it down onto um you know digital tips and get a lot more information in there but what's the maximum amount of information that you could put into a library this big and the answer most physicists always thought was that there was a limit you could not make a bit of information smaller than one cubic Planck length if that's the case you can calculate the number the volume of this library in plunk units and you would discover that it was about 10 to the 100 viii that's a huge number that's more than all the particles in known universe then it can hold 10 to the 108 bits of information a huge amount could be stored in there well what if the owner of this library passed a law a crazy law the crazy law is that you're not allowed to put any information and the interior of the library all you're allowed to do is decorate the outside of the laboratory with writing with information arbitrarily small you can make your letters no bigger than the Planck scale but then how much information can the library store if it's only allowed to have its bits of information coding the surface of the library a lot less it's proportional to the area of the surface of the library only 10 to the 72 well that doesn't sound like a big difference 10 to the 72 and 10 to 108 but if you're familiar with thinking about numbers 10 to the hundred and eight is vastly vastly bigger than 10 to the 72 and so you lose a lot of possibility of storing information if you can only put it on the outside well it's a strange law of nature and it is now believed by everybody who works in theoretical physics to be a law of nature that you can never put more information into a library or into a volume of space than the amount that you can store on the boundary it is as if all that you could never have more information in this room than the amount that you could store on the boundaries of this room if you reduced it down to little pixels pixels on the boundary of the room and that seems extremely counterintuitive extremely so to illustrate the difference between information being stored in volume and being stored on surface area I just invite you to look at this picture here this picture has a grid this is a Rembrandt anatomy lesson and it sure looks three-dimensional it looks like there's all kinds of three-dimensional information here the dead man here looks foreshortened he looks more or less as if you're looking at him from from the feet on because he's so short there's information behind this guy's head here in a scroll everything looks very three-dimensional but of course it's an illusion there is no three-dimensional information here you cannot tell whether this dead man is foreshortened or whether he's just short you cannot walk around the picture and see what's on the scroll behind them behind the tall man's head here in fact you can't even tell whether this is a real 3-dimensional object or whether it's just a flat painting of a 3-dimensional object it doesn't really have three-dimensional information the three dimensionality of it is an illusion it's in your head information is being stored since this was actually a photograph taken with a digital camera that information is stored in pixels two-dimensional array of pixels obviously that two-dimensional array of pixels cannot really store three-dimensional information it's an illusion can you store three-dimensional information sure you can store it by storing it three dimensionally instead of pixels you store it in the form of voxels voxels mean three dimensional arrays of dots and dashes in other words a three-dimensional tic-tac-toe puzzle if you allowed yourself to store information bits of information on a three-dimensional lattice like this of course you could store all the information in a three-dimensional picture but obviously you can't store three-dimensional information on two-dimensional pixels well that's not actually true Holograms are examples of the storage of three-dimensional information on a two-dimensional film to a hologram is a two-dimensional film this is a picture of the film on which a three-dimensional figure is depicted by the method of holograms what do you see you see a scramble of meaningless scratches and dots and dashes impossible to decipher what's this is a picture of completely scrambled but it is two-dimensional however if you know the rule and in this case the rule is simple you just shine light on the hologram it will create a three-dimensional image and it's not like Rembrandt's painting of the anatomy lesson you can if I was any good at making videos I would have you turn this thing around and look at the clown from the back but a hologram is a picture like this stored on a two-dimensional film that allows you to reconstruct a full three-dimensional image that you can walk around look at it from the back look at it from the front and in principle you could even make a hologram of the interior of his head his brain and see every bit of information that's going on inside the clown's head but stored on the two-dimensional hologram so it's not really true that you cannot store three-dimensional images in two dimensions well one of the things we found out and I'm going to explain to you how we found it out was that in a certain mathematical sense the entire universe the entire world can be thought of as a hologram out on the boundaries of space at the very edges of the universe ten billion light years away a kind of two-dimensional holographic image encodes and codes all of the information that's there filling up the universe in the form of stars planets people and everything else this is one of the weirdest and most unintuitive extrapolations in physics since quantum Thanks it is truly weird but it has taken over physics and it has become a principle of physics it's called the holographic principle I'm going to show you how we came to that we came to that by thinking about black holes so how did we ever come to such an unintuitive thing let's start with a box I have made a round box around spherical box because it's easy to think about it a round sphere a box is just a thing that could contain something it's not even necessary that the walls of the box are real just a region of space and let's put some information into that box that information could be in the form of matter here it's cheese and wine it could be in the form of a bunch of a gas of elementary particles it could be vapor it could be anything it could just be dots and dashes on a page in a book that you could throw in here let's put some information in there inside a certain volume and that volume is bounded by a certain area now let's take that information this is a good this is the kind of experiments when you can't do real experiments you do thought experiments here is the thought experiment one would love to be able to do this but it's quite impossible technologically let's surround that stuff by a shell of material it could be steel or it could just be light coming in a shell of material that's been accelerated inward so that it's about to collapse let's make that shell of material just massive enough so that when it gets to the boundary over here it creates a black hole everybody who thinks about black holes will admit that this is a possibility that you can add to a system and amount the material squeeze it down until what's left over is a black hole well if no information is lost during this process and remember it's a basic law of physics that information can never really be lost if no information is lost then the in the initial information in there in the wine the cheese and the particles must be less than the amount of information in the black hole but we know how much information is in the black hole it's proportional to the surface area that's what bekenstein taught us one bit of information for each square plunk area on the black hole what does that tell us that tells us that there could never have been more information in this region than what can be stored on the surface you cannot store more information in the region that were can be on the surface in the form of one bit per plunk area why because you can always shrink it down into a black hole and then the amount of information is known and if none can be lost then there must have been less information to begin with if there's less information or at least no more information than can be stored on the surface that's as good as saying that everything that was in there can be represented by information on the boundary of the black hole another way to say it is the boundary of the black hole the horizon is a hologram it is in fact a hologram there are two reconstructions of the hologram one reconstruction Alice sees when she jumps into it when she jumps into it she sees the images that are reconstructed from the hologram planets stars even her own head in her arms when she gets inside the black hole but on the other hand Bob watching from the outside sees the boundary of the black hole as a collection of bits in other words like a holographic film that holographic film eventually evaporates just like any real film a real film that's left out in the warm air will eventually evaporate and that's the Hawking evaporation process so we have a very very surprising conclusion it's called the holographic principle the world what did I write the world is pixelated not Vox elated in other words this entire room everything in it is really represented mathematically by a theory on the boundary which is very much like a hologram or that idea that idea has now become a central pillar of physics it is not any longer a conjecture is now a mathematical reality that the universe the entire universe can be represented as a boundary theory with everything on the boundary where the boundary is out near the horizon the horizon of the universe well this is something that of course has never and and probably will never be directly experimentally tested it involves things which are far too small Planck area sized things far too small but it is through the extraordinary ingenuity of physicists not just string theorists that the holographic principle is no longer what speculation but today it has become a basic principle and a mathematical tool of theoretical physics its influence is being felt from everything from nuclear physics to cosmology for more you have to read my book but what's the final conclusion nobody knows the final conclusion but we no longer disagree are the bits of information that fall into a black hole completely lost to the outside world no they form a kind of hologram on the boundary of the black hole which eventually evaporates with every bit being accounted for we now all agree nobody disagrees anymore Stephan myself a tuft in fact here is a an image of a bet that was made about it not between myself and Steven but between a physicist named John Dante and you can read it it will not say anything that you will recognize but the content of it is is it true that information will always be readmitted from the black hole or will it be lost as Stephen Hawking said will it come out as Susskind and the TUF said or will it be lost to the interior of the black hole never to come out that's the question and here is Stephens concession that he lost the bet and here's his thumbprint no it really is there really is a thumbprint all right well it sounds crazy it sounds completely insane the world as a hologram it came out of a clash of principles it came out of the impossibility of apparent impossibility of putting together gravity with quantum mechanics I like the quote at this point Sherlock Holmes when he said when you have eliminated all that is impossible whatever remains must be the truth no matter how improbable thank okay I'm a jet lag so I had to sleep but at the beginning I didn't sleep yet so you said something about the information being encoded in the Morse code and to me that's sort of arbitrary about 65 bits that information what kingka note seems to have just one bit of information either he has the warts or not and that's one bit why is it 65 yeah well of course part of the problem is we use information in a colloquial sense and we use it also in a very technical sense in the technical sense saying that somebody has warts on his chin is not really a collection of bits of information bits of information do really correspond to physical realities and how many yeses and noes you would have to answer in order to state what the physical what the physical configuration of a system is so for example ah we could divide this room up into lots of little voxels let's forget whether it's pixelated of ox elated divided up into lots of little pixels and for the simplicity let's suppose there's only one kind of elementary particle let's call it an electron and then the only thing that we could ask is in each little voxel is there or is there not an electron if we knew in every voxel whether there was or was not an electron we would know everything about this room how many yeses and no questions are there to answer to know everything about this room well it's the number of voxels so that's that's the technical of idea of information how many yes/no decisions or how many yes/no statements do you have to make in order to say everything that can be known about this room perhaps King Canute chin was not really a good example I only used it to illustrate the idea of dots and dashes hi my name is Venki I have a couple of questions so there's these classic definition of a black hole as something from which nothing can escape not even light is that not right I'm having trouble hearing you did you hear is the classic definition of a black hole where nothing can escape not even light not correct no it's correct the point from which nothing can escape not even light yes that is correct that's correct but we have stuff coming out of the black hole right like Hawking radiation no no okay well good good good is it coming out of the black hole or is it coming off from just above the surface of the black hole so one way of thinking about it is that the material that falls onto a black hole never really falls into the interior of the black hole when watched from the outside when watched on the outside it takes an infinite amount of time for anything to actually fall through the black hole so one way to say it is nothing ever really does fall into the black hole it just collects on the surface heating it up in thinner and thinner layers as time goes on and the radiation that comes off from the surface of the black hole is really coming off from a fat thin little layer just above it or at least that's what Bob says watching it from the outside Alice she seems to think that she's fallen right through the surface of the black hole that is what the puzzle is all about so you could say on the one hand when watched from the outside nothing if it does get into the black hole on the other hand falling through with Alice you would swear that she fell through unharmed through the black hole that is and which is correct both are correct and we are going to have to live with that for a long time thank you is this evolution and understanding a step in the direction of the grand unified theory well I think this these questions in order to experimentally access them would require let's call them microscopes which could see down two scales size scales 10 to the minus 33 centimeters on a saw on a side the questions that are taking place in particle physics at the present time questions about grand unification and so forth are much more coarse-grained than that they're on scales thousands of times larger than that so no questions about the sorts of questions which we can hope will be answered let's say at the LHC won't directly bear on this somewhat indirectly they will are if it turns out that string theory is a good description or what happens at the LHC then it will tell us that perhaps string theory is a good description of a black hole but the connection is at best a distant one I wish you were otherwise thank you for the lecture how certain are we on the actual physics existence of black holes I mean people were quite certain of classical mechanics before I understand and you know like some observations that were made so how certain are we that you like there's no some unbeknown to us physics at that energy scale I would say pretty certain from a theoretical point of view if you believe the general theory of relativity there seems to be no escape from the idea that matter will collapse stars will collapse into black holes that's a theoretical statement from an observational statement we certainly see things out there which look remarkably like black holes are supposed to look I don't think you can ever know without getting up much closer to them whether they really behave exactly like black holes but it certainly looks very compelling to most astronomers that the things that we see in the Centers of galaxies are giant massive black holes that collapse stars when the star is bigger than maybe ten times the mass of the Sun that those collapsed stars are also black holes so out is there any room at all for saying maybe black holes don't exist yeah I suppose there's some tiny tiny room but I think I would have to say that the smart money in both theoretical physics astronomy and cosmology would say that black holes are very definitely real you would it would be it would be more radical much more radical to say that they don't exist than to say that they do exist that's the way I judge it how radical is it to say they do exist not radical at all by now how radical is it to say that black holes don't exist you'd have to completely change the theory and you have to blame the observations on something that we have no idea what it could be so be very radical to say they don't exist is in a relationship between the dark force and black hole dark matter Tashia dark matter or dark energy not energy and black hole dark energy there is a funny relationship I showed you how to think about a black hole as a drain hole where as the water is moving in at some point that exceeds the speed of light or sound or whatever it happens to be well dark energy causes the universe to expand more rapidly than it would otherwise it's called the accelerated expansion of the universe because of it if you go out to a far enough distance the universe will be receding or matter will be receding away from you with greater than the speed of light it is as though the universe was a lake with an outward flow and as you go further and further out the flow gets faster and faster if you go out far enough the water let's call it water the water will be flowing away from the Center with faster than the speed of it could be sound in the case of a fish's pole in that case anything that's out past that point is beyond a cosmic horizon we are in the interior not in the interior of a black hole but we are in the interior of a cosmic horizon and we are surrounded by a cosmic horizon we can throw things what things stars planets and so forth when they pass outside the cosmic horizon they lost to us they're gone and it is very very much like when things fall into a black hole as seen from the outside where we see from the inside is almost like an inside out black hole so yeah there is a connection between the dark energy the accelerated expansion of the universe and the existence of cosmic horizons which surround us rather than we surrounding the horizon of a black hole dark matter and it's dark matter break hole and it doesn't seem so first of all let me just explain to the audience difference between dark matter and dark energy dark energy is somewhat weirder and it really corresponds to a universal repulsion gravitational repulsion between things which is pushing the universe apart at an accelerated rate it's not formed from particles it's not ordinary matter of any kind it's not even particles of unknown type it's not particles period it's a form of energy which is there in empty space dark matter by contrast is a totally different thing it's simply most likely it is simply elementary particles which are electrically uncharged and therefore don't emit electromagnetic radiation therefore they are invisible what kind of particles well they're not neutrons we know that neutrons don't live very long long they're electrically neutral we know they're not neutrons because neutrons have a lifetime of about about 12 minutes and there have been out there for a long time they're not lute Reno's for another reason so most likely they are a form of particle that we have not yet discovered in the laboratory it's a pretty safe bet all physicists who work on elementary particle physicists physics do not believe they believe that we have not discovered the entire zoo of elementary particles almost every physicist has 10,000 new particles that he wants to postulate so there's plenty of room in physics for many many more kinds of particles that we haven't seen yet most likely and when I say most likely I'm judging basically on the number of physicists who believe in a certain thing I being one of them most physicists believe that dark matter is simply elementary particles that we haven't discovered yet and they're out there they're out there they surround galaxies they form the halos of galaxies and but they're really not in any very deep and significant difference different different way different than ordinary particles so Dark Matter I think is less of a mystery than sometimes it's made out to be in the public press you said that we can only get two dimensions worth of Planck length so we can't get the volume of it the amount of information that can be stored in a region so so that's like from a two dimensional to a three dimensional but there's 11 dimensions yeah well if they're erasing that these two dimensions create 11 dimensions as well as everything including light and gravity in the universe there are three there are three obvious dimensions of space that way that way in that way I can't I can never find the other seven of them but they're that tiny I yeah if you really wanted to think about the world the way string theorists think about it is 11 dimensional with some tiny dimensions I think you could probably say that in that 7-dimensional world that all information is stored on 10 dimensional boundaries but from the gross macroscopic viewpoint it would translate into our world saying that that the three-dimensional world becomes two-dimensional you know what I'm going to refer you to my book the black hole war for the answer to that question I just have one quick question so if the universe is to be viewed as a yeah okay mute if the universe is to be viewed as a hologram with the cosmic sort of background as being the edge what is the light source that illuminates the hologram that we all see well yeah because there's nothing wrong right right I I don't think there's a light source in that sense what you can say about the hologram the hologram stores three-dimensional information even if you don't illuminate it or if you don't illuminate it that three-dimensional information is stored illuminating it is just a way of seeing it as a way of seeing it what is believed is that the mathematical description of the three-dimensional world is equivalent to a mathematical description of a two-dimensional surface far away now the faraway world is as scrambled as a hologram in other words if you could reconstruct that two-dimensional hologram at the edges of the universe you wouldn't recognize if you looked at it through a microscope you wouldn't recognize the ordinary things in the world unless you knew the special code for reconstructing fortunately in the case of ordinary Holograms the code is pretty easy there's a mathematical code that you could decipher if I showed you the hologram and I told you what mathematical process to do you could reconstruct that it was a picture of but fortunately it's a simple away you just shine some light on it I wish I knew how to do the same there is no analog for how to shine light on the cosmic hologram and reconstruct the world in the sense it's a mathematical equivalence only the people standing now are going to have their I I don't decide away it's questions I can't even see them familiar what can you announce that they can't hear me Oh only people who stand can ask questions I don't make the rules I'm going to answer questions this is taking it from Alice's point of view inside the black hole you're out from Bob's yes there was a book written about 20 years ago about a fellow named Kaufman not that well-known I don't remember his first name Stewart Kaufman Kaufman ka uff ma n coming up yeah I don't know and the subject matter of his book was that if you got a black hole that was a right size and the right spin a spaceship could go into this black hole or skip off of a black hole I'm not sure which and end up very fast in another part of the universe yeah this guy this is a sort of urban myth that the black holes can be tunnels to other places in the universe and the origin of the myth the urban myth is actually the mathematics of Einstein and Rosen who constructed a mathematical solution of a black hole where the black hole consisted of sort of two pieces two mouths a black hole is like a mouth right that sucks things in and two mouths connected by an alimentary tract one of them here and the other one very very far away it was a legitimate mathematical solution of Einstein's equations but there were two things wrong with it first of all the tunnel that it's called an einstein-rosen bridge the einstein-rosen bridge is a kind of tunnel but at first it's closed no tunnel opening up the tunnel opens in up and then closes again very quickly and it always does it in such a way that nothing including light can pass through they called non traversable wormholes you can't get through it just doesn't stay open long enough but the other fact is that what Einstein and Rosen were talking about were very idealized black holes that had been there for an eternity into the past our universe was not like this for an eternity into the past that originated in the Big Bang black holes can't be older than the Big Bang black holes what you are created by let's say the collapse of stars or the collapse of galaxies or anything like that are not bridges from one place to another they're simply collapsed objects so this is a you know it's a wonderful line for a science fiction story black holes connecting collecting connecting us to very very different places but there's no good physics reason to believe that idea so I would say that's probably science fiction now Never Say Never in your example you say Bob sees Alice getting thermalized and that the data the information is then bounced or evaporated right off the surface of the right off the horizon right and Alice at the same time experiences being in the hole but can't communicate that out does that mean that the theory transition form from bits of information get lost - then no bits of information get lost but it almost seems like it ends up being information gets duplicated Wow very good yes there's a sense in which information gets duplicated information that falls in an information that's bounced off appears like duplicated information now I don't know your voice from your voice I don't recognize your voice but I sort of recognize the voice of a physicist am i right rocket scientist Oh rocket scientist are you what are you a person who knows that it's a quantum no no to duplicate information no but it seems like a bad thing it is a bad thing it is a bad thing as a theorem that information cannot be observably duplicated but it's a very interesting thing that nobody can ever see the duplication of the information those that are behind the horizon see one thing those that are outside the horizon see the other thing and now you might ask well what happens if Bob was outside the horizon and collects this duplicated bit of information which is the same as Alice's what happens if he jumps into the black hole then can he compare his bit of information with Alice and that's been studied and it always turns out that before Bob can get a message from Alice about what her bit of information was they both crash into the singularity and are killed really so so there seems so there seems to be a conspiracy that nobody ever detects this duplicated information but one way of thinking about it is that the horizon of the black hole is is made up out of a bunch of miniatures Xerox machines quantum Xerox machines which duplicate the information and send some of it sailing through with Alice and send some of it back out with Bob as this holographic principle led to doubts as to that the center of the black hole is actually a singularity no not in the following sense there are two ways you could make sense out of the question first of all you could ask watch the black hole as it evaporates and as it evaporates it will get smaller and smaller and smaller and eventually at the last gasp it will look like a singularity from the outside now you have to take with a grain of salt what's meant by a singularity a singularity just means something which is so dense and so extreme in its in its a compression that all of the standard laws of physics break down and we can't though we can't think about it by the normal laws of physics something getting squashed to plunking in proportions we can't follow it past there we call that a singularity we expect that if you could watch a black hole evaporate then its last gasp it would look like a singularity that's one statement the other thing is we have no reason to believe that Alice won't get killed at the singularity when she goes in as far as anybody can tell Alice's fate from her own point of view from Bob's point of view Alice's faith was he was cooked at the horizon from Alice's point of view she gets disassembled or whatever it is when she hits the singularity so as far as we know that that has not changed no okay back to the library yeah you spoke of you and I supposing you and I are there mm-hmm and a library is absolutely full of information ten to the 172nd was it I don't know is it packed the the volume or is it the set on the surface ten to the 72 okay and you're outside and and you have access you can see all that you have access to all those bits I'm there too but I'm inside the library well and I'm looking at the same surface and I see all 10 to the 72 bits right except I'm sitting in a chair and I'm reading a book are the pages of the book blank well you might think of them as the holographic image you might think of them as the holographic image we could imagine we could imagine that somebody is shining coherent light on the outside of the Ptolemies library and it's reconstructing itself into the pages of a book on the inside and you're sitting looking and reading the pages of the book and I'm that image also well you know I from my point of view outside you're also plastered onto the outside of you and the book are plastered onto the outside of the universally have been losing bits of information for quite a while yeah I know that's what happens after the age of about 50 I think I wanted to play the devil's advocate a little bit with your Sherlock Holmes idea you eliminate the impossible because I see so the things that you were describing is impossible the idea that she's both burned to death and goes through without any problem right that and you kind to me it's kind of like weaseling around talking about different points of view but to me it is impossible to be thinking of both things being true at the same time so right if that that's my idea of impossible so it's hard to go from there plus it just and also with light it's both the Corbett's both the particle and its a wave at the same time yeah now it's a wave down with it I I don't see how an ordinary person can accept these things yes one of the themes of my book is exactly that that our minds our intellects were created by a process of evolution which was intended to give us the tools for ordinary experience an ordinary range of parameters we were not equipped by evolution to be able to think about motions near the speed of light that's why relativity is so hard for us because our minds weren't created for it our minds were not created to think about higher dimensional spaces in fact I often ask people this question in this kind of situation how many of you can visualize four-dimensional space try to be you know visualize it not make a trick to think about it but visualize it in the same sense that you can visualize a three-dimensional scene is there anybody here who thinks they can visualize four dimensions in the genuine sense good we don't have to we don't have to call the police there's usually one wise guy who says he can do it but apparently not here how many people here think they can visualize a two-dimensional surface I can't hear you well for example yes but how about a curved a curved the surface can you visualize a curved surface okay now admit the truth when you look and think about that two-dimensional surface don't you sort of see it as embedded in three dimensions can you really see that two-dimensional surface as two-dimensional without picturing it as some kind of surface embedded in three dimensions I'll bet you can't I'll bet you can't see a one-dimensional line without thinking of it as a one-dimensional line either in a plane or in three-dimensional space the architecture of your brain was built for three dimensions you can't get away from it but there's nothing in mathematics which which is better about three dimensions than four dimensions or two dimensions it's just the limitations of your mental architecture the same thing is true when it comes to things moving near the speed of light the geometrical relationships between things which are moving near the speed of light are different than your mind was created for you can't visualize them the only way how do you visualize four dimensional things well you don't visualize them it's but it's very easy you just add another letter to the alphabet X Y Z and W and now you have your four-dimensional space you use a mathematical crutch the same is true for thinking about relativity the same is true for thinking about waves and particles or the Heisenberg uncertainty principle our minds were simply not built to the architecture of them were simply not built to be able to I use the word grok then the rock rim and so we are left with having to write equations and having to do mathematics the same is true about the interior of black holes there another extreme environment which is very very far from what our minds were built for our minds were built for our caves walking into and out of cave not falling into and out of black holes the logic of walking into and out of a black of a cave is extremely different than we're walking into and out of a black hole and we're simply not equipped for it so these things always come as surprises and they come to surprises that I can't visualize any better than you but we rewire ourselves we retool ourselves with abstract mathematics and then we try to explain it to a public audience using words that we inherit from ordinary experience and that's where we get into trouble and when we try to explain these things using ordinary words it's hard I do the best I can apparently sometimes I fail thank you my name is Carolyn Zin from China anyway thank you for the talk now I have two questions the first one is the black hole is such a unique thing to study because it's so different from the rest of the conventional physical world and it is in such an extreme condition that there's so much mystery about it now is there any evidence to show that there are things actually more extreme than the black hole well that's an interesting question well again I would say never say never because somebody will eventually cook up something either either logically consistent or not logically consistent but I I think one can reasonably say that in certain senses black holes are as Extreme as it can be they are as dense or as concentrated a form of information as possible they are the heaviest things that can fit in a certain volume so I think this is definitely a sense which they are very very extremal can you think about things wilder than that I don't know I my imagination is limited but but I don't know but I think that for me I think of black holes as sort of the most extreme objects in the universe but there is something interesting you think of them as very exceptional very unusual in the universe not the norm but they're very very exotic well if you take all of the bits of information that exist within the universe then for every 10 billion bits of information 999 million 999 of them are found on the surface of black holes only one bit out of ten billion is an ordinary bit of the kind that you experience all of the rest of them 999 million 999 or a thousand 999 of them are plastered on the surface of black holes so in some sense almost all information in the universe is in the form of black holes and we are the exceptionally unbent rarefied loosely-knit together things I have the second question I think you will appreciate this one talking about the two possibilities that you just Illustrated is it possible because like now we not only prove that there is the assistance of black holes and also we found out there more than you know hundreds of thousands of black holes out there just in one our own galaxy now is it possible that black holes are just banks for empty matters now we cannot find antimatter's is it possible actually thanks for antimatter yeah thanks for energy matters that it will help to serve you know answered question so to me a bank is a place that you can withdraw from as well as things into now that is not clear at the present time but but let us assume a bank is a place that you can withdraw from as well as deposit in our let's take the case of protons protons have anti particle partners which are called anti protons if you create a black hole out of protons and that would be a black hole protons and neutrons made at a star an ordinary star collapses and forms a black hole you create another black hole by using antimatter you create what looks like an anti black hole well the anti black hole and the black hole will be identical there will be no difference between them at all are the stuff that comes out of each of these will basically be photons and photons are their own antiparticles so they are the symmetric with respect to this particle/anti-particle distinction so when stuff falls when stuff falls into a black hole oh and a black hole is made let's say either by protons or anti protons that distinction gets lost that distinction that that's not the same as information being lost but the distinction between whether it was made of protons or anti protons is lost the black holes will be almost exactly the same but in any case you won't be able to tell the difference between them by withdrawing things out of the black hole and seeing whether their protons or anti protons you'll get as many protons out of a black hole as anti protons and so in that sense a black hole is not a good bank for depositing your protons if you expect to get as many out at the end as you put in thank you hi dr. Susskind thank you very much for coming out I appreciate your lectures and follow your work I'm having I'm still having trouble like this last question or what the idea of relativity what we have question sorry what was the question the question is is I was trying to think of another example then the two light bulbs one over here went over there they both go depends on which ones okay right here all right hi you know it I was trying to think of another example like if a bell went off on the other side of town here in Los Altos really loud Bell then one went off one second later right next to my head you know it would sound to me as if that went off first although we both know that objectively the other bell went off first yeah yeah but this is a two-part question if I may the second part is is this whole idea about two conflicting things being simultaneously true of course can't be really conflicting but I thought that was the whole point is that they well they can't really be for conflicting I think the point is that we're suffering from a bad mental picture not from a not from an out-and-out contradiction an out-and-out contradiction occurs when a single experiment can give rise to two conflicting answers or when when two conflicting answers can be compared you take two thermometers and you stick them into the same tub of hot water and one comes out saying 70 degrees and the other comes out saying 95 degrees and you bring them together the same person looks at them and that person knows that there's something wrong in this situation there is no way to bring together the observations which apparently conflict so I would really have to say it's a bad mental picture the mental picture being that information is really stored in a concrete way in a certain place it's apparently much more subtle than that that where information is stored is relative in the same sense that the order of flashing of light bulbs is relative it depends on the motion of the observer but only one can be objectively true no no which question or the question of which light bulb went off first depends on who on the observer let that depend on time okay okay let's get this is the last question hi you said something about black hole's disintegrating over a certain amount of time right and I was wondering if that's really true then where's the contradiction because don't you get that information back when they disintegrate I mean yes but that's of course what what Stephen said is not true they're right what Stephen said is information falls into the black hole past the horizon once it's past the horizon it's trapped that it cannot come out of it but then right go ahead and then he said that it evaporates now it's ooh it sure looked like he was right when we did the mathematics and tried to follow the argument it sure looked like he was right but he was making an assumption and the assumption is that there was an objective sense in which a bit of information is at a definite location in space and that's what turned out to be wrong that the notion that you can attribute a definite precise location independent of the state of the motion of the observer to a particular bit of information so he said it falls into the black hole in order to God you know what it's like it is what it's like when the black hole evaporates it's almost like the drain hole sealing itself up okay the the drain hole the pump that's pumping the water out is slowing down when it slows down the horizon shrinks and eventually the pump stops and the drain hole just ends it's no longer there and space is healed up there's no more black hole there so so when it evaporates there's nothing that comes out of it well it just did ceases to exist that was the picture that was the picture and on the basis of it Stephen said that things that fall down into the drain and can't get back up because they would have to exceed the speed of light to get back up are simply lost down the drain okay I got it now yeah I mean it's hi it's very very hard to explain things which are wrong let's thank dr. Siskin for wonderful

Channel: SVAstronomyLectures

Views: 538,341

Keywords: Astronomy, space, science, black holes, general relativity, relativity, theory of relativity, Stephen Hawking, space-time, astrophysics, event horizon, quantum mechanics, physics, entropy, quantum black holes, Leonard Susskind, Leonard Susskind (Author)

Id: KR3Msi1YeXQ

Length: 94min 51sec (5691 seconds)

Published: Wed Sep 04 2013

Reddit Comments

[u/[deleted]]

A fantastic introductory book, The Black Hole War illustrates many difficult concepts quite easily. I love Leonard Susskind's way of writing and have yet to read his other book!

[u/poslime]

Susskind is my favorite person.

[u/[deleted]]

[removed]

[u/[deleted]]

If a black hole had an expanding event horizon due to more matter being added to it, would it look like the boundary was receding at faster than the speed of light? Would it look like our universe from the inside?

If we exist on the boundary layer of our universe, could there be a way of changing the boundary close to us, such that the projected universe would be changed at a position that would appear to be far removed from our projected position (like what happens when you scratch a conventional hologram).

[u/IGetRashes]

According to him, Alice does not notice anything unusual as she crosses the point of no return. So I have two questions: What does Alice observe as she approaches the singularity? What does Alice observe when the black hole evaporates? (I have to finish the video later, so I don't know yet whether he addresses these.)

[u/[deleted]]

I'm so glad I watched that. I've always had this prejudice against the hologram theory, but this solid proof really changed that. Thank you OP for posting this!

[u/smallfried]

I was hoping my question would be asked, but maybe someone here would have an answer:

What if you first check the amount of information that you can realistically store in a certain amount of space pragmatically. Like you uniformly float around some datastorage modules in space moving outward to counteract the eventual slight gravity working on them. Now if you then do the thoughtexperiment of making this uniformally filled spaced larger and larger but with the same density of datastore modules, the storage in it increases with a cubed law. The holographic principle states that you cannot do this indefinitely as any cubed function will eventually get bigger than any squared function.

So, what is blocking us from doing this indefinitely?