Leonard Susskind on The World As Hologram

I'm having a bad week I'm having a really bad week and I'm feeling a little bit down the first bad thing that happened to me is at the beginning of the week a whole bunch of students at that perimeter came running over to me and they said we just read in a blog and on the in the newspaper that one of your students X students has been arrested for running an Internet prostitution ring that's oh my god turned out it was true the next day immediately afterward they brought me the Scientific American and there's a great big page that begins with a page with a great big picture of me the bad boy of physics oh my god what did they find out well I called up the editor I did call up the editor and I asked him why do you call me the bad boy of physics of course I knew that it had nothing to do with the previous bad thing that happened but he said well it seemed every five years you seem to say something totally outrageous which nevertheless winds up being true um you seem to be a kind of bad boy I have some that occur to you that maybe I was thinking about these things for five years in between is it oh no I didn't think of that what I'm going to talk about tonight is one of those things but there's a quote that I like there's a quote that I like very much it comes from a famous intellectual by the name of shriyak Holmes and it says when you have eliminated all that is impossible which by the way sometimes takes five years when you have eliminated all that is impossible whatever remains must be the truth no matter how improbable the thing I'm going to tell you tonight is one of those things which seems nutty it seems wildly improbable but it wasn't just something that some of us I wasn't alone and saying this that some of us just said oh one day oh you know maybe the world is a hologram that's not the way it happened the way it happened was exactly this way when you eliminate everything that's impossible whatever is left over must be the truth so let me tell you a little bit about where we're going good ok what is this thing which Sherlock Holmes might have eventually concluded after trying everything else and the answer is that in a certain sense and a certain peculiar sense the world is a hologram now not everybody knows that a hologram is here you know you've all seen these pictures which look three-dimensional they're made out of a film which is a flat piece of film nevertheless they look fully three-dimensional I'll tell you eventually what a hologram is but the idea that the world is a hologram is a wild idea or at least a seemingly wild idea it all began we're thinking about black holes black holes are those objects the most in some sense the most exotic objects in the universe they're dense they're heavy they're dangerous but they're also ubiquitous the universe is filled with them and not only that almost all of the information that will come to what information means but almost all of the bits of information in the universe by a vast majority exist in black holes so in a certain sense although they may be very very exotic they're almost everything at least almost all of the information of the universe so I should begin by telling you or giving you a picture of what a black hole is now I assume that I'm not talking to physicists for those people who are physicists you know what a black hole is but for those who are not I'll try to give you a picture in the picture is an analogy all analogies are defective and I get some very funny emails from people who read my analogy somewheres and pulled out completely the wrong thing out of it I hope you won't but I can't protect myself against it but let me give you my picture very simple picture that I actually learned from a famous Canadian physicist named Bill Unruh but here's the picture of what a black hole is begin by imagining a shallowly lake it's an infinite lake it goes on and on and on forever in two directions but it's only about a foot or a foot and a half deep it's not very deep and fish live in it fish swim around now these fish have a rule whether or not the rule is a law of nature or a legislated law that was legislated by the kingfish that's not important the law is the law and the law says that they may not swim faster than the speed of sound all right that's the rule now this Lake happens to have a very dangerous place some ways in the middle of the lake there's a drain hole and the drain hole drains out onto rocks below these rocks are exceed exceedingly sharp so dangerous that anything that comes in contact with them will be comedian I elated and this drain hole has the property is all real drain holes would as you get closer to it from far away the water flows faster and faster the flow of the water or the velocity of the water becomes faster as you approach the drain the drain is sucking water out at a sufficiently rapid rate that there happens to be a distance represented by the red line here at which the in flowing water is moving with the speed of sound and as you go in even closer than that it's moving even faster what happens to a fish let's call her Alice poor Alice has passed the point where the infalling water is falling faster or moving faster than the speed of sound it's also moving faster than she's allowed to swim she's stuck nothing bad happens to her when she crosses this place she probably doesn't even know it you know what it's like it's like rowing down Niagara Falls and passing the point at which you can't row faster but you don't realize it nothing bad half to you yet nothing bad happens to Alice when she crosses the point of no return let's call it the point of no return but nevertheless she's doomed her friend Bob is on the outside and Bob is waiting to hear from Alice Alice has been calling to him maybe saying help help help but after she passes the point of no return not only can't she swim out but her sound waves that she tries to send the message with are also pulled in faster than the speed of sound and so she becomes permanently disconnected from the outside she cannot get a message out she cannot swim out and so as far as Bob is concerned poor Alice has disappeared out of the world well that's about what a black hole is a black hole is a kind of inflow it's a kind of place where space itself is falling in at a certain distance out it's falling in so fast that to get out beyond it you would have to exceed the speed of light the local speed of light and if you pass that point of no-return again nothing bad happens to you but you're doomed okay so I've put this in a couple of notations here nothing special happens at the horizon but Alice nevertheless is lost to the outside world all of our bits and pieces when I use the word bits you might think about information bits if you like but all her bits and pieces are lost and the horizon is a point of no return but itself is harmless a place which is harmful at the center of the black hole that's called the singularity but we're not going to be even interested in the singularity all right now let's move on to another subject of course we're not moving really moving on to another subject we're going to examine a few related subjects and then put them together information now information whatever it is we'll talk a little bit about what information means but information comes in in discrete units let me give you an example of some information a sentence King Canute had warts on his chin I don't know if King Canute had warts on his chin or not it doesn't matter this sentence here expresses a certain amount of information but when information physicists physicists information theorists when they talk about information they're really not even talking about the meaning of the information the meaning doesn't count what counts is the symbols this is us this is a sentence or bit or not a bit of information but a collection of information which consists of the sequence of letters whether or not you can read English and decipher it is not the important thing the important thing is it takes a certain number of letters to describe it you could convert the message to Morse code Morse code is of course thought that there's not that and in converting this happens to be a if you leave out the symbols that you need to put the the spaces between the words this sentence here is a 65 bit message in Morse code and the real information is in this sequence of pluses and minuses or dots and dashes this process of going to Morse code has replaced the sentence by a collection of bits a bit is a dot or a dash that's what it stands for it's the same concept as in your computer except in computers we talk about bytes byte is eight bits megabyte is eight million bits so this is the same concept that you use when you ask how much storage space you have in your computer now let's go to the - first law of physics why is it the - first law of physics well the first law of physics there are at least two first laws of physics already one of them is in thermodynamics the others Newton's so I didn't want to call this the first law of physics it's more important and deeper than either of those two first laws of physics there's also because people realized there was a deeper law they defined the zeroth law of thermodynamics so the zero flow was also used up but there's an even more fundamental law so what could we call it the - first law of physics I will call it now of course it may turn out the dick will discover the - second law of physics and so forth but at the moment this is the deepest law of physics I know and it's that bits of information are indestructible the meaning of that is that distinctions between situations distinctions between configurations are never erased they never disappear from the world let me give you an example here's again the 65 bit message but now it happens to be stored on my computer screen well it doesn't matter whether it's on the computer screen it's buried somewhere is in the computer memory and it consists of a bunch of our on and off switches and it's a 65 bit message can you erase some of the message can you get rid of a bit can you erase a bit well of course you can if you couldn't erase some of your computer your computer would very quickly fill up and you wouldn't be able to put anything new in it so you have to be able to erase information but when you erase information in fact you're not really erasing it you're ejecting it out of the computer by one means or another into the environment the result is the environment may actually be part of the computer it might be the plastic of the computer case or so forth or it might actually be the atmosphere when you eject a bit in that way the indestructible bit which cannot be destroyed when you reject the bit it adds a little bit of energy to the environment and thereby heats the environment that is why your computer has to be cooled your computer has to be cooled because whenever you want to erase information the bits are little bits of not only as a matter of fact I'm not only bits of information there are also bits of energy and therefore you have to cool your computer whenever you erase but the lesson here is that bits are indestructible information is forever well now we have a very funny little paradigm on the one hand the - first law physics says that bits are never erased on the other hand when Alice crawls into the black hole and falls behind the horizon as far as Bob is concerned her bits have disappeared from the world so in effect for all practical purposes for all physics purposes Bob sees a world in which information is erased can this be right this was Hawking's central point in 1976 when he created something that came to be known as the information paradox it was an extremely deep observation it was a very important observation it is not important that Hawking didn't get the right answer he asked the right question and this became a central debate a central question that took basically 20 or 25 years to resolve we now know the answer and we'll come to it the answer is that bits of information never are lost but nevertheless the things that came out of the question is so deep that one can hardly say that it was Hawking's mistake it was one of the deep observations about physics that let the great things okay so but you might say wait a minute wait a second the bits Alice's Betts fell into the black hole and there they are they're in the black hole maybe you can't get access to them it's not too different than locking him in a room and throwing away the key we don't say that information is lost then but to make things even more confusing and this was another discovery of Hawking's and earlier discovery of Hawking's black holes evaporate they disappeared it's as if the box that you hid some information in after a while disappears how that evaporation takes place is not so important basically anything evaporates everything evaporates if you give enough time little pieces of it break off and disappear into the atmosphere and if I were to just draw or two I use my extremely crude computer skills to try to make a movie of a black hole evaporating what does it evaporate it evaporates photons light gravitons other kinds of particles and as it evaporates it loses energy in the process of losing energy it shrinks and eventually shrinks down to a very tiny black hole and then it's gone but when it's gone where is Alice or more to the point where are Alice's bits where are the bits of information that - first law of physics says can never disappear the black hole is gone Alice's bits could not have gotten out from behind the horizon why not because to get out from behind the horizon they would have had to exceed the speed of light just like the fish would have to exceed the speed of sound and so we had a real dilemma we have a conflict of principle on the one hand black holes seem to erase information on the other hand the most basic law of physics that I know says that information is never erased next what is entropy you've all heard the word entropy and you probably heard that entropy has to do with confusion and entropy has to do with chaos and entropy has to do with the world coming to an end because everybody gets too confused to tie the shoelaces or whatever but entropy has a very distinct meaning so let me tell you what it is here I've imagined the bathtub full of water just to get away from black holes for a while let's think about a bathtub full of hot water or warm water and how much information do we need to know about that bathtub full of hot water how much information is there and how much do we need to know in order to know whether we should step into it and take a bath well really there's about two things that we really want to know we want to know whether there's any water in the bathtub so we want to know the volume of water that's in the bathtub that's important how much water is there and the other thing we want to know is the temperature of the water right when you get in the bathtub you want to the water okay that's about all that's about all the information you need that's about all the information that would be easy to get how much more information is there about that bathtub full of water well the answer is a huge amount an enormous amount of information the physicists all know that and what is it well if you looked at the water through a microscope you would of course see molecules the position and velocity of every one of those molecules is information that information may be extremely inaccessible let's call it hidden information why is it hidden it's hidden because it's stored in a huge huge number of degrees of freedom many many too many to keep accurate they take account growth and they're too tiny to see that's all so yes the bathtub has a huge amount of hidden information hidden as I said because it's stored in things which are too small and too numerous to keep track of that's what entropy is it is simply the information that's hidden usually for the reason that I said but for any reason if information is hidden from you we call it entropy that's all it entropy is what was extraordinary was that sometime around 1972 a young physicist by the name of jacob bekenstein this is not a picture of jacob bekenstein in 1972 but jacob bekenstein was a student and he announced black holes have entropy where that mean that meant that black holes have in them hidden information well that's not surprising there's no surprise in that of course black holes have hidden information the stuff that fits exactly what black holes are they're a place where information falls in and it gets hidden you can't see it when it's behind the horizon of a black hole but the real importance of what bekenstein did was to be quantitative and say how much hidden information is in a black hole what is the maximum amount of information that can be hidden inside the num maximum number of bits that can be hidden behind the horizon of a black hole here is the way he approached there I'm going to tell you just rough it out for you how he approached the problem I'm not going to do the calculation for you going to show you what he did he has the question which is pretty similar to the following supposing you want to know how many atoms it takes to fill up a bathtub full of water what's a simple way to do it you drop in one atom at a time and you count how many it takes until the level of the water is up to where you want you know what the answer is going to be the number of atoms or the number of bits or the number of drops of water is going to be proportional to the volume of the bathtub right if you double the volume of the bathtub you'll have to put in twice as much water and therefore twice as many atoms alright so that's the kind of usual thing what bekenstein did is he said let's actually count how many bits of information it takes to drop into a little tiny black hole in order to build it up to a large black hole so we said let's start with a tiny black hole tiny black hole is practically no black hole at all a tiny one as big as a peanut where a peanut is in fact actually a gigantically heavy black hole about as heavy as the earth let's start with a lighter one that's about as heavy as a dust mote and that's about the smallest black hole that you can have and drop a bit of information into it now what does a bit of information mean a bit of information means an elementary particle it could be a photon let's say it photon we drop one photon in and the only information is that we drop the photon in or perhaps it's the information that we dropped a photon of one polarization instead of another polarization but we drop our elementary particle now there's a deep thing going on here that information in quantum mechanics comes in discrete units and they're called particles so what bekenstein did is he said throw in a particle throw in a bit the effect will be to increase the energy and therefore the mass of the black hole and the black hole will grow a little bit do it again drop the second drop in black hole will grow a little more do it again do it again until the black hole achieves the size that you're interested in and count how many photons of the appropriate wavelength does it take to build the black hole of an appropriate size what did bekenstein find that one that there's another one after this know what he found well first what was the natural expectation the natural expectation would have been but just like the bathtub just like the bath tub with a number of drops of water is proportional to the volume the natural expectation would be that the number of bits of information that it takes to build a black hole of a certain size would be proportional to the number of cubic meters a number of cubic kilometers or whatever it is the volume that is not what bekenstein found what bekenstein found was that the number of hidden bits of information the black hole is equal to the area of the horizon measured in a unit called the planck unit first of all that was very surprising that it was area and not volume what it meant was that when the bits of information fall onto the horizon they behaved as if they were little impenetrable objects which collected on the horizon and simply couldn't push each other out of the way and achieved some density almost as though you had a bunch of coins on the table and you try to pack them in as tightly as possible but on the horizon and not in the interior of the black hole so that was the first surprising thing the other surprising thing well it wasn't surprising at that time at that point but it might surprise you that the size of one of these little bits in other words the area occupied by one of these little bits what is very very small one plunk area plunk does not mean bored it's the name of the famous physicist Planck who has a constant named after him called H G here is Newton's gravitational constant and C is the speed of light and if you work it out it's 10 to the minus 66 square centimeters it would take about a thousand trillion trillion trillion trillion trillion of these little Planck areas to wrap a proton to wrap the surface of a proton so this is a very very small unit but nevertheless it's a discreet little unit and this is what bekenstein calculated from the combination of quantum mechanics and properties of black holes this was interesting now what are you could ask about a bathtub full of water if a bathtub full of water has an entropy it means it has hidden information what is that hidden information well we know now today it was not known incidentally around 1900 was not known for certain that it was atoms the motion of atoms in the positions of atoms which made up the entropy of a bathtub full of water in fact was Einstein who nailed that concept in place ultimately but you could ask the same question about the black hole if the black hole has entropy it means there are hidden tiny microscopic degrees of freedom on the horizon which we don't know about which are somehow making up that that entropy was sort of in the same situation as just before Einstein when it was known that fluids and gases and materials had entropy but it wasn't known for sure what the degrees of freedom the little objects which constituted the hidden information we're kind of in that situation there are examples theories mathematical constructions one of them is in string theory and I'll just tell you very very briefly what according to string theory the entropy of a Schwarzschild black hole is forget or black hole is string theory is a theory where elementary particles are little tiny pieces of string little loops of string a single elementary particle is a smallest possible loop of string and it looks about like that except a zillion times smaller now you can take that little bit of string and you can heat it up you can how do you have you put more energy into it you could put it into a frying pan and let it hop around but that won't work very well you collide other particles with it you collide other particles with it you smash it together with other particles and the result is to add energy to it and adding energy to it makes it vibrate and makes it get spread all over the place just like a wildly excited rubber band oscillating all over the place it gets tangled and it gets bigger so you shake them one way or another and you increase their energy and you increase their size you add even more energy and they get more complicated eventually if you add enough energy remember that energy is mass if you add enough energy you'll get a great big huge tangle of string does this tangle of string have entropy of course it does if you don't if you're not smart enough or small enough or capable of following every little turn of the string and you simply say that's hidden from you because it's too small and too numerous you would say this complicated ball of string has entropy it's a string tangle now this is not yet a black hole on top of that there's gravity gravity pulls it together if you collect enough string with enough energy eventually gravity will pull it together into a black hole so what is left over after it forms a black hole something which looks metaphorically sort of like this little bits of strings still hanging out of the horizon and it's those little bits of string in string theory which constitute or comprise the degrees of freedom which carry the entropy but I'm not here to sell you string theory what ever the entropy of black holes is it's something that's very microscopic too small to see very numerous very chaotic and I also should add in a constant state of agitated motion and a constant state of agitated motion because it's in a constant state of agitated motion and because it has entropy motion and entropy mean heat that means that the surface of the black hole is hot it's a hot soup of bits a hot 2-dimensional super bits that's a funny kind of soup two-dimensional soup but it's a hot bit soup and you can ask then how hot is it if somebody would to go down near the horizon of the black hole and measure the temperature of the region near the black hole you could do that you take a long cable with a thermometer on the end you lower it down the thermometer is connected by electronics to whoever it is who's out here lowering it down reads off the temperature the answer is that the temperature near the horizon of the black hole as close as you can get to the horizon of the black hole is about a million billion billion billion how many did I say a million billion billion billion degrees is anybody going to ask me whether it's centigrade or Fahrenheit right oh you should probably add 273 or something yeah okay it's really hot down there oh boy but now we have a problem we have a conflict I originally told you that the horizon of a black hole is a harmless point of no return remember Alice Alice sailed through the horizon nothing happened to her yeah exactly remember Alice one theory that we've postulated or that we said or that we've described says that she sees nothing out of the ordinary at the horizon perfectly safe crossing the horizon it's true she's doomed she's going to hit the singularity but nothing special at the point of no return and she happily sails right through the point of no return cool as a cucumber the other theory says quite the opposite the other theory says she encounters and falls into a soup of super hot a super hot soup of bits at the horizon what happens when something falls into such a superheated region it is evaporated it is ionized is thermalized it's turned into evaporation products which in this case basically means photons or other elementary particles which are just radiated out so here's the other picture alice falls through the horizon when she gets within this thin layer near the horizon the temperature becomes so hot that she's evaporated and just radiated back out with the Hawking radiation with the evaporation radiation this is odd this is certainly an odd situation we have a conflict we have a conflict of principles does alice safely fall through the horizon that's what one theory says or is she thermalized at the horizon and eventually radiated back out in the form of scrambled scrambled bits just means you all mixed up what's the answer the answer is that both are true now how on earth can both be true they say contradictory things apparently one says Alice gets to be blunt she gets killed with the horizon the other says she safely passes through with no problem whatever ok so here's something that illustrates the paradox Bob on the outside watching the whole thing who doesn't get to see Alice actually fall through the horizon a cease radiation coming out he sees evaporation products coming out those evaporation products he says well they must be Alice's bits Alice is being thermalized and radiated back out poor Alice Alice sails through the horizon and in her own frame of reference in her own reckoning she says I'm fine nothing happened to me but there's no obvious conflict operational conflict why not because Alice saying she's ok cannot get the message out to Bob Bob sees no contradiction he never gets to find out that alice is ok Alice sees no contradiction she just falls through the horizon and finds nothing dangerous but still this seems ridiculous that we could be that confused about whether alice is thermalized and destroyed at the horizon or falls cleanly through it ok let's suppose let's let's even push the experiment a little bit further let's suppose that just before alice falls through the horizon she's already encountered this very very hot region remember it's just above the horizon the thermometer lowered down very very hot she's in the soup in the hot stuff before she crosses the horizon before she crosses the horizon Bob takes a look at her now what does it mean to take a look at her it means he shines photons on or he shines electromagnetic radiation on her which bounces off into his eye and he asks is she getting thermalized there isn't she getting thermalized it's a fascinating story but I'll tell you what the upshot is in order for Bob to actually see Alice in order to make the determination of whether she's being thermalized or not he has to hit her with short enough wavelength photons enough of them that these photons will themselves thermalize her roaster so in the this is the way quantum mechanics works quantum mechanics is always like this that you try to show that something doesn't happen by doing an experiment and the experiment itself makes it happen very frustrating Bob comes to the conclusion that alice was fried why he sees all this radiation coming back out one could say Bob did it to her but the operational fact is that Bob discovers that Alice was roasted so there is no contradiction and yet somehow it's not completely satisfying something's going on here something deep is going on here about information about black holes well it seems and I think this is correct that there are two distinct representations of the same reality the same information one of them the three-dimensional reality of Alice falling through the black hole she looks around she sees herself she's three-dimensional nothing has happened to her and the other two-dimensional the two dimensionality being this thin surface of extremely hot fluid which absorbs Alice thermal eise's her scrambles her and radiates her back out now can there be two distinct descriptions of the same thing one three-dimensional and one two-dimensional well sure there can be a painting a painting is a painting a painting a drawing or a painting a painting is a representation of three dimensional object let me just put up a painting for you kind of grim painting yeah it's extremely three-dimensional with showing all sorts of three-dimensional features but really it's not giving three-dimensional information it's a trick of the eye familiarity with the subject matter familiarity with the way human beings look familiarity with the way light scatters off things in your brain creates a three-dimensional fiction what's really there is two-dimensional layer of paint there's only two dimensional information there for example can we tell whether the cadaver is a really short fellow or is he foreshortened because he's sticking out out of the blackboard a little bit you can't tell there's no way to tell you can't touch him you can't feel him you can't stick your head under him you can't do anything to find out if he looks short because he's foreshortened oh because he's short let's see I can you see what's behind this guy's head there's a plaque behind his head if it were a real three-dimensional figure I could go over to here around over here and look at it but I can't see anything it just isn't there the information the three-dimensional information is just not there it's two dimensional information end of story so let's talk about coding two-dimensional and three-dimensional information with bits I could take that painting let's forget the fact that it has several different colors in it you can always reduce the color store what is it red green and blue you can always reduce it to red green and blue and make a lot of little pointillist pixels out of it and then represent the painting as a bunch of well it would take three three types of pixels and are two types of pickled pixels but you could represent it as a series of pixels where the information would be coded discretely in this case in X's and zeros X's and zeros you could represent the two-dimensional painting that way but supposing I wanted to represent a real three-dimensional reality let's say this room how might I represent what's going on in this room I might divide the room not into pixels you know what a three-dimensional version of a pixel is called it's called a voxel a voxel V for volume they're called voxels you could divide the room up into tiny little voxels let's say each voxel was about as big as an atom and let's simplify the story and say there's only one kind of atom everything's made out of hydrogen then I could completely describe what's going on in this room by saying yes or no in each pixel at each voxel whether there's an atom there or not if I know where in every box whether there's an ant or there's an atom there then I know everything about the room and I can represent it that way so in fact I should be able to represent the world or this room or even way beyond this room if I get into real micro physics I might have to make my voxels smaller but I should be able to represent that as a 3-dimensional array of information can it be that somehow our world or at least the surface of a black hole can be described both in three dimensional terms and two dimensional terms it seems impossible on the face of it three dimensions and two dimensions just seem very different can you take three dimensional information and re-express it voxels instead of pixels well the answer is yes but there's always a big cost and the big cost is when you take the three-dimensional data and try to lay it out in two dimensions the result is always to scramble it horribly it's always going to be incredibly mixed up an example is a hologram a hologram is a piece of film when I say the word hologram I don't mean the image I mean the piece of film that the hologram is stored this is about what a piece of holographic film would look like incredibly scrambled lots of scratchy little things if you looked at it through a microscope you would see no pattern and you would not be able to tell in a million years what this thing was a hologram of it's incredibly scrambled and it's two-dimensional but if you know the rule and in this case the rule is an experimental rule you shine light on the hologram and an image forms a full three-dimensional image you can find out whether this clown has hair on the back of his head how do you do it you go around to the back of the hologram and you take a look three-dimensional information of course it doesn't contain the three-dimensional information of what's inside the clown's head but if you made the hologram from an MRI scan you could actually code the full three dimensionality including the brain and everything else on the holographic surface here so a hologram is a very good example let's call it compressing data down to a two-dimensional surface but in the process scrambling it beyond recognition unless you know the detailed code well what's the upshot the upshot is that a black hole horizon is like the scrambled hologram of everything that's inside two versions of reality two reconstructions of the same reality one construction or one reconstruction the surface of the black hole extremely scrambled hot hot bit soup but containing exactly the same data as what fell in the full three dimensionality of the things that fell into the black hole which in fact were unharmed and unmute elated and just fell cleanly through the horizon that is what we now believe and there's an enormous amount of very very sharp mathematical evidence for this picture it's not something that was just made up for fun or the world is a hologram or a black hole as a hologram there is very sharp mathematics to it I'm not going to do the sharp mathematics so the picture is that the black hole this is this is not supposed to be the moon incidentally this is just a cutaway picture of the interior of the black hole the surface of the black hole which is what Bob sees is this very scrambled representation of reality of the reality of Alice and what Alice is more like is she's more like the image made up out of shining the light now it doesn't have to do a shining of light this is not you don't reconstruct Alice by shining light on the black hole it's a mathematical reconstruction two different mathematical representations of the same reality this is the universe or at least this is somebody's representation of the universe and what I'm going to tell you next is it's not just black holes which are Holograms but in a certain sense the entire universe can be represented as a hologram or any finite region of the universe any big chunk of the universe can be represented as a hologram and essentially exactly the same way it does not have to be the stuff that fell into the horizon of a black hole how did we come to this I'm going to try to explain to you roughly how we came to this conclusion because it's very simple it's very unintuitive that's a crazy conclusion but you can follow the logic of it it's not that hard take some region of space and put some stuff into it some information that information could be in the form of letters of the alphabet the alphabet soup you know the stuff they're real alphabets genuine alphabet soup it could be wine it could be cheese it could be whatever you like it's information all right it tells you something about what's inside that region the question first I'm going to try to answer is or answer in fact is what is the maximum number of bits that you can squeeze into that region of space that's a question how many now you would normally think that the maximum number that you can squeeze in should be proportional to the volume right seems reasonable but let's do the following thought experiment let's surround the region of interest which has a boundary over here let's surround it with a shell of material it could be a shell of Steel it could be a shell of photons it could be a shell of anything that you like and then squeeze down on it squeeze down on it in just such a way give it exactly the right amount of mass so that by the time it together with the stuff which is in here by the time it is squeezed down to that surface over there it forms a black hole if it has if the shell has just the appropriate mass and you squeeze on it just the point where it passes the surface of that region it will collapse into a black hole all right now let's assume that the - first law of physics is correct information is never lost then the initial information content the wine the cheese the alphabet soup the information could not have been more than the amount hidden in the black hole if it was more that would mean that information was lost but we know how much information is hidden in the black hole it's the area of the horizon and plunk units the conclusion is remarkable the maximum amount of information that can be held in a region of space this room is proportional to the area of the walls of the room it exists as if the walls of the room were divided up into little tiny pixels one plunk area on the side and everything in the room could be described by knowing what was going on in those soles that's the that's the argument it's as simple as that and the conclusion of it is that you can describe a region of space any region of space by data on the surface as if it were a hologram the maximum amount of information in a region of space is proportional to the area of the region region I like to say that the world is a pixelated world and not a voxel ated world let's move on we have a few more minutes yet I think let's talk about cosmology the reason I want to talk about cosmology is because there is another sense in which the world is a holodeck closely related sensor very closely related sense there are other kinds of horizons in the world besides black hole horizons let me explain to you the other kind of horizons that cosmologists real cosmologists not half cosmologists are constantly concerned about and tell you how they play into the story ok let me give you a model for the way the universe works it's another fishy example another fishy story it's the way it has to do with the way the universe expands it has to do with the way the universe accelerates as it expands let's go back to the lake let's take away the drain hole we're not interested in the black hole anymore that's there it may it did black holes all over the place but let's just take a moment uninteresting but there's something new the lake is being fed from underneath by a uniform collection of pipes and these pipes are breathing exit I see dick laughing bringing in new water what is the area what is the effect of this new water the effect of this new water is to cause the puddle force to you know to to expand to grow to stretch poorer portions of it will separate from other poor and the effect of it on these fish incidentally this is ba oh no this is yeah this is Bob this is Alice and this is Charlie over here but Charlie has nothing to do with anything charlie but the water is being pumped in and as the water is being pumped in the lake spreads in fact the way the lake spreads if you work it out is it spreads out according to a law that the further apart that you are the faster you will be separating this is called Hubble's law but this is a special case of Hubble's law which is called the accelerated expanding universe now Bob is sitting there and he's communicating with Alice but Alice is being dragged along by the flow and so she's separating away from Bob eventually a point will come well what happens where she passes a point of no return the point of no return does not have to do now with in flowing fluid it has to do with out flowing fluid from the point of view of Bob at some point the fluid is flowing outward relative to him faster than the speed of sound at some distance and at that point when Alice crosses that point she can no longer communicate with Bob she has passed through let's call it an external horizon it does not have to do with an inflow and a drain hole it has to do with an outflow and expansion well this is exactly the way the universe that we know works it is expanding its expanding with the same pattern of acceleration as if it were being fed new space as if space were constantly being replenished therefore being pushed apart and it has a horizon each person has their own private horizon namely the Reed around them which is moving away from them with slower than the speed of light that region they can see what's beyond that they can't see so it looks something like this here's Bob at the center and at some distance out there's a point of no return and if Alice crosses that point of no return she's as far as Bob is concerned out of this world simply out of communication never to communicate again she's gone as a puzzling thing it looks like there's a region of the world maybe most of the world which is out beyond all possible observation what do we actually know about it in fact we know a good deal about it from observation we know that the universe is at least a thousand times larger in volume than the region that we can ever see ever see means within the horizon within our horizon the universe is at least a thousand times bigger in volume than the horizon region so this stuff out there that stuff is simply beyond observational science period or maybe not but at least in a simple sense in the same sense that you can't see what's behind the horizon of a black hole that stuff is out beyond the Ken of any of any known method of observation what is the meaning I mean this raises deep both philosophical questions scientific questions puzzling questions that really do bother or people who think about this what is the meaning of all the stuff out there the scientific meaning of all the stuff out there if it can never be detected how can we ever hope to confirm it by real observation what is the proper description of a world that is bigger than the cosmic horizon these are all the same question of course but finally is our cosmic horizon the one surrounding us is it a two-dimensional scrambled hologram of all that lies beyond it these are questions which are deep profound questions and the only thing I'm not going to answer them the only thing I can say now is we are all wrestling with them and their big questions and their hard questions that's the physicist incidentally that's the universe so I hope I've given you some flavor for the kinds of questions which we ask but I want to convey something to you that it's an extraordinary remarkable fact it's not a fact about me it's a fact about the way human beings think the way human beings their cognitive abilities that when you think about it for a moment you know a small relatively small band of hairless apes has been able to deduce all of this has been able to deduce such strange and totally unintuitive very very foreign ideas very very abstract ideas about the universe as peculiar and as unintuitive as the world is a hologram I thank

Channel: undefined

Views: 4,008,439

Rating: 4.5071635 out of 5

Keywords: TVO, TVOntario, TVOKids, polka, dot, door, polkaroo, education, public, television, Elwy, Yost, Steve, Paikin, big, back, yard, ideas, Canada, Big Ideas, Science, Physics, Leonard Susskind, Jacob Bekenstein, Stephen Hawking, black hole, entropy, hologram, string theory

Id: 2DIl3Hfh9tY

Length: 55min 26sec (3326 seconds)

Published: Fri Nov 04 2011

Reddit Comments

[u/bartgus]

I have fun reading the youtube comments.

[u/Xoryp]

I couldn't get through the opening talk about him being"the bad boy" of physics. To full of himself.

[u/Origami_psycho]

Can anyone give a short, more or less easily understood precis of what hologram theory is, what it would mean for our understanding of thing if this were true, and why it is/isn't accepted? Cause I've seen this crop up a fair few times recently and all I can gather is that they don't mean hologram like collectible cards or a display projector.

[u/Xoryp]

Yes. That is my biggest issue when watching these presentations, I'm here for the information not the self indulgence.

[u/orbituary]

I love this lecture. Watched it after reading Black Hole Wars.

[u/[deleted]]

[removed]