Cracking a Black Hole Paradox - Sixty Symbols

so bready one of my favorite subjects after football obviously is and she knows black holes and there's over the last sort of six months or so there's been some quite big black hole news and I think it's time to shared it with you go I'm all the ears what's going on so so as you know I mean this is there's been a problem that's kind of been around my my entire life basically and it's the the famous black hole information paradox which so Hawking first saw and proposed it around the time I was born about about say well should I say how long ago mid seventies it was and so Hawking spent his whole life trying to solve this problem never quite managed it well it seems that in the last year or so we I think we're there I think it's been solved what is the problem very in a nutshell it's that black holes seem to lose information they seem to have sort of information seems to disappear inside black holes and that kind of breaks fundamentally the laws of quantum mechanics quantum mechanics basically tells you that you can't lose information what goes in must come out so Hawking proposed that he seemed to see evidence that black holes were actually losing this information and he figured well that means they're breaking quantum mechanics this is like sacrilege Tony when a physicist says information what do they mean you don't mean like three bottles of milk or there's the Liverpool game will score was three two like what is information I can think that I can absolutely mean that so let let me give you an example I've actually come prepared with an example so obviously what's going to talk about information what we really want to talk about is is in the context of entropy so Jorian lockdown I've been homeschooling my kids and we've been doing some experiment and I'm not very much I'm not very good experimentalist I'm no film re ality right and but we've been trying a few one of the ones we did was we are balancing liquids of different density on top of one another can you see that really I've got a liquid there I've got the blue liquid on top of the the red liquid and then the other one it's the other way around you can't quite see it as well but the red liquid is on top okay so we got two different liquids they look very different right these two liquids they look very different and you would say they're completely different states but what I can do is of course I can stare the liquid right and I can stare the other one nice and now if I show you them you can't tell the difference between those guys right they look exactly the same you can't tell whether this one was the one that had the blue on top or this one was the one that had their the blue on top it's impossible to tell right just by looking at it so the measurements that you're doing just by staring at this thing it could be either state that created it could have been the one with the red on top but it could have been the one in the blue on top they're coming lots of other ways you could have created that same sort of gunky mess right and that gives it entropy that's like an uncertainty a sort of missing information stuff you don't know just by based on the measurements that you're doing of this object similarly you know you have a sort of set of headphones that are all tangled there could've been loads of different ways they could have gotten to that roughly tangled state and that gives this entropy in some sense of missing information now of course in the case of this this liquid I could sort of dive inside and don't pick the microscopic structure of the whole thing and extract the information out of whether it was blue on top of the starter or red on top I could in principle get that out of so you're talking about almost like doing the ultimate crime scene investigation and unpicking this came from that direction and this came from that direction and figuring out all this stuff to say oh it was red and blue at the start totally you could do that in the case of that that the case of this thing right in the case of a black hole however it really does hide the information because you can't get anything out of a black hole you can't go in and then pick the information and feed it to the outside so to see how black holes do carry entropy like it let me imagine a scenario right suppose you wake up one morning and there's a black hole at the bottom of your garden right and okay it's quite alarming and probably it's going to sort of tell you apart but it's sort of tidal effects if you get too close to it but let's say you don't get too close and the next day you wake up again the black hole is still there but it's grown by say the mass of an elephants okay now how do you know that it's swallowed an elephant did it swallow an elephant or maybe did it swallow a car with the same mass or something else with the same mass there's no way that you can know right because when you do a sort of measurements on a black hole the only things that you can measure are its mass its charge and its angular momentum so there's literally no way you can tell whether it was made by an elephant or or made by a car there's no measurement you can do on that black hole that will tell you that it will look the same Tony what why is this not just a problem of access to the information rather than the existence of the information brilliant question Brady okay so if that was all I told you then you'd say yes that's it's just hidden behind a black hole if I dived inside I'd find that information everything would be fine would be no problem okay great the trouble is Hawking then told us that black holes actually radiate that they'll evaporate okay so you have this process by which you think of pairs of particles being produced near the event horizon and those particles one particle due to the insertive principle might find itself just outside one just inside the outside guy escapes the inside guy falls in and this black hole evaporates it starts to lose its mass that radiation that it produces it's really completely random in some sense so so you know that the event horizon where this all this magic is happening you know there's not you know it could be this particle went out or it could be the other one that went out it's totally random the only thing that the the radiation sees is the shape of the space-time the geometry of the space-time from that radiation you can't extract that there was a it was made from a car that buckle was made from a car or that it was made from an elephants you can't get that from the radiation and then eventually the black hole evaporates away completely and all you're left with is the radiation okay which I've just said and Hawking told us doesn't contain any information that you need so the informations disappeared which is disaster for quantum mechanics I've got one more half-baked brainy theory as to how you could find out the information when I woke up on the second morning and the black hole is heavier could I not do a census of everything outside the black hole and say oh there's one less elephant in the solar system it must be an elephant that fell in no no okay if you have two meters of space that separated from one another if you have a pure constant state over the whole space right then and then you separate them the two regions there could be information in this region which relies on knowledge of this region and vice-versa okay so if you separate the two regions you can have missing information in this and missing information in this but they kind of compensate for one another they account for one another which is kind of what you're asking can I do that and that ought to be what happens that absolutely ought to be what happens but hockey's calculations suggested that it's not what happens okay so it's fair it's a fair point what you said yes isn't the information just kind of sort of account for the missing information on one side versus the other side and everything takes care of itself that's what quantum mechanics demands that should be able to do in some sense hawking said well is the calculation show me how it's done I can't do it all right then so let's let's not get too bogged down in all my stupid questions let's talk about what's actually happened what's the news what's been happening recently that's got you excited okay so before I get to that kind of talk about Hawking's beds okay so hawking spent his whole life trying to solve this problem okay and he was convinced first time that information was lost inside black holes and he had a human Kip Thorne who you probably know from the film interstellar had a bet with a press call from Caltech over whether information was lost on that so Hawking and Thorne said said that it would be lost press will said no no no no no be silly quantum mechanics is two pressures no way it's been lost it's gonna get lost it'll be several survives somehow this information so Hawking then spent a lot of time trying to figure out one way or another then became convinced it probably was survived but couldn't work out how came up with some ideas how to the point where he ended up paying the out the bet to press kill Kip Thorne though thought that Hawking's ideas weren't quite right so I mean you refused to pay the bet and it turns out all his ideas weren't right and but over the years people have become convinced that information was you know it wasn't lost but not really sure how it how it wasn't lost if you see what I mean so then yeah right what's the news we seem to figure out how it's not lost so so information is preserved so this breakthrough has come from from two teams one on the east coast of America centered around Princeton and one one around Stanford on the west coast so the Princeton team did a really nice review just last week actually where they gave a really nice analogy for how how this information is is preserved okay so the story goes you have you have some some faller easy easy lives in a in a posh house and it's full of beautiful extremely valuable paintings okay so he's him but he has no money okay so but he wants so he wants to show off his show off his wealth but he has no cash it's just got these paintings he's really valuable paintings so he says okay then I'm gonna borrow some money off the people of the town okay so it says write borrow some money off the people of town get some cash that way and says he he'll use the paintings as a guarantee okay so he does that he gets this cash nice throws lavish parties the people of the town meanwhile they no longer have any cash because they've lent it all to the guy in the house okay so they're certainly not throwing lavish parties they're living very frugally so you look at this from the outside and you say well who's um who's the guys the townspeople seem quite poor here right they don't seem very rich but of course that's not true they are rich they kind of because that you know they kind of own in a sense those paintings that are locked inside the house they're their paintings right and this is analogous to what's happening with the black hole so in the analogy the house is the black hole okay the townspeople are like the radiation and the the the wealth of the townspeople is the quantum information that's stored in that radiation so very naively you look at this and you think that the townspeople are poor or that the radiation has not what doesn't have much quantum information but actually it does okay somehow got access to the interior of the black hole in the case of the analogy the the the sort of townspeople actually have much more wealth and you can secretly see that by looking at maybe the record of the loan the record of the loan would show that they have some connection with thee with the inside of the house it's my elephant all over again of course he had to be there it had to be right but now let's see how it happened this is this is this is where it gets beautiful how does that play out in the black hole case okay how does the radiation make that connection to the interior of the black hole that that it seems like you shouldn't be allowed that right because this is violating locality in space and time but what happens is the following there's an island forms inside the black hole kind of a sort of region inside the black hole they call it the island and that kind of you start to think about not as part of the black hole but was part of the radiation itself the radiation makes a connection to this island through a wormhole I love wormholes but that's how it makes it so how do you how does the information leak out well what you would do is you would do some complicated sorts of measurements and it can be exponentially complicated right measurements on the on the hawking radiation right and effectively you're creating this wormhole which then accesses the interior of the black hole in Europe and you can get the information out you can figure out whether it was made from an elephant or a car now these wormholes they're really hard to produce you absolutely cannot produce them at all until the black hole is radiated away roughly half its size okay it's passed this time called the page time but after that you can start to create them and it gets easier to create them and actually these these guys have shown that in some simple toy models of gravity that these wormholes are there and actually they dominate the behavior at late times and Hawking never knew about them and that's why he made the wrong conclusion to go back to the painting analogy you told you told me when a black hole radiates Hawking radiation it's a random act there's no control over what particles will happen to form on one side of the event horizon or the other and that's why information perhaps was being lost and if we're going to attach that to the analogy of our rich painting owner surely the problem here is there's no control over whether he's going to pay back the loan pay back the guarantee because the money coming back out to the townspeople has now been randomized right okay and here is that it is difficult to get the information out the black hole and it might be very difficult to get the money back from the from the townsperson back the doors lock the Roxy then set up a barricade but it's not impossible it's there okay it's there and so the way they and the guys outside can prove their worth they say look here's the document here it is I made this loan if you're looking at black hole you need to create this wormhole to get in so Tony if we were creating a very very fantasy situation here and I was going to give you infinite tools and measurement devices and spaceships and all the things you could possibly want right and I said all right I'm gonna send you out to that black hole somewhere in the universe tell me what went down get the information back for me all right I want to know the story what are you doing are you looking for like are you looking for a wormhole is the wormhole near the black hole what how would you go about this investigation yeah so it's really so that's really really difficult and so firstly if the black hole hasn't radiated enough of its of its size away then you can't do it at all it's just impossible to get the information out if it's gone past a certain point services so you know you've gone past a certain stage pass this page time then indeed you can and but it's it's exponentially difficult to do and it gets it gets easier and easier but but it's still really really hard to unpick that to do you basically to do your quantum measurements of the radiation and you're trying to sort of extract the nature of the states but it's really really difficult you know it may be in terms of practical purposes maybe impossible but it doesn't matter the point is is in principle is it possible and it is possible and they showed that these wormholes do actually dominate in this in principle scenario are you using the worm how to go inside the black hole and make measurements or measuring what comes out of the worm so we're going to be really really precise about it the way you can think of it is is this the following so the radiation and you know naively it contains all this missing information it's what we call a mixed state and quantum mechanics it seems very impure in a sense all it's missing all these missing ingredients what the wormhole does it connects it with particles that were once entangled with it and that purifies the state so the wormhole literally enables you to purify the radiation so so you've got all this stuff which is all random over here it used to be connected to stuff that was over here right but now it's been disconnected but actually the wormhole reconnects them and purifies the quantum state and so you actually it has all you doesn't have any doesn't have the missing information that you thought it had Tony is this breakthrough a situation whereby it's like a new discovery and an advance that could be used to you know understand things better and maybe do things in the future or is this more just a case of we found a theoretical loophole that means the current system we're clinging to still works so don't worry there's no exception go about your business I think that's a really interesting question because I think I think one of the things about the black hole information products that people always said was the black olives the information product is so profound it's so incredible that when we solve it and I'm gonna say that I think we have solved it ok that when we solve it it will reveal something dramatic about space and time that's I'll say something about quantum gravity something like that right now I don't think that's happened and then and the reason is is it so Hawking himself could have actually got this solution without any knowledge of quantum gravity it doesn't rely on quantum gravity one of the great ideas that came from looking at the information products was this idea of holography you know that actually the information is stored on the boundary of space-time you know that you know you can basically describe gravity by space of it stuff on the boundary of space-time and that could come and that was certainly an inspiration for these ideas but it doesn't rely on it it doesn't rely on it you didn't need any of that so it's in a way it's that makes it beautifully simple the solution and makes it feel right but where's the amazing new insight that we were promised well we don't know maybe it's very early days yet and there is a little strange thing going on that that's sitting in there which is this this idea that there's almost like a randomness to Quantico it suggests that might be a randomness to quantum gravity that when you talk about quantum gravity maybe the theory isn't just one theory it might be like what we call an ensemble of theories the theories itself there's a little sort of technical subtlety in there in terms of the kind of theories they played with to solve this as things called JT gravity which have this property but is that something that you're going to need for the sort of extended to sort of fall four-dimensional general relativity and so on maybe we don't know that might be the sort of little smoking Condit's hangout that's there really that's the nugget that's gonna take us give us that sort of you know what we were promised from the solution to the information paradox when you look through what they've published and what they've discovered what what do you think the leap or the clever thing they thought of was that all the men and women before didn't think of like what's the thing you'd look at and go ah yes clever I see what you did as ever it's not just one thing Wraiths I've talked about it mentioned the holographic principle the idea that all this that you can describe gravity with a theory and on the boundary of the space-time that's clearly been a major inspiration of major ingredients in terms of understanding in the end we didn't need it but in getting there in the journey it was crucially important and there was a new way of thinking about entropy which was claimed for these guys Rio and taka Nagi and that was really important but actually I want to highlight the contribution of one guy in particular who's a is a young English guy I'm not just saying that cuz I'm biased right and but he's a he's actually just a PhD students at Stanford but actually his work this guy called Jeff Pennington his work and they didn't some of it she did on his own was really sort of a prelim to loss of this and then he's now on the papers with the that finally seem to have solved it but he was the work he was doing before seems to be really really important as well so in a way it's like the new kid on the block just finally sent everybody over the line and I think we've got an absolute star in the making there if I'm honest and I'm funnily enough I was so I had some discussions with him and turns out he he lived on the corner from from where Emma Watson went to school Noah Watson who plays for Miami and air in the Harry Potter films I think that the sisters may his sister may have hung around in a similar circle or something but it sort of makes me laugh it's like did she know there was a real wizard actually just around the corner you mentioned that wormholes have been a key part of this what is a wormhole I always thought a wormhole somewhere where like you know you put your hand in the hole here in on earth and and it comes out on the other side of the universe or something they're like these like ultimate shortcuts Oh am i right or are they something a bit more technically this exactly what it is of course if we're gonna be brutally honest and these calculations are not really done in space-time they're done in space space you actually flip the ten-time into an imaginary time that's how you do these calculators so these are really wormholes in those scenarios it's not a technical detail that I don't want to get bogged down in and but yeah it's exactly you would normally think of a worse space-time wormhole at least there's something like that something that connects two regions of space in these calculations it's connecting two evens of space but there is no time in these settles because you've gone to imaginary time but yeah that's that's like that's that's exactly what they are imaginary time thanks for dropping that bomb shot right at the end well there's all these details right to date I don't take them the extra dimensions angle okay the difference between those sorts of black holes the Astrophysical black holes in the kind that you might produce the LHC that those are those are very large they're very large black holes okay they've been formed from stellar collapse you know death of a star collapses and forms of black hole

Channel: Sixty Symbols

Views: 160,157

Rating: 4.8516903 out of 5

Keywords: sixtysymbols, black hole, wormhole, information paradox

Id: XT_iZ7QEit8

Length: 21min 18sec (1278 seconds)

Published: Thu Jul 09 2020