Your Daily Equation | Live Q&A with Brian Greene

everyone welcome to this Friday live discussion as part of your daily equation that you had a chance to join me here for our little conversation those of you who have been here in previous Friday's knows that sometimes little is very much in the eye of the beholder it is absolutely not absolute it is certainly one of the words of relativity I don't know how long we'll go today but you know if the past is any guide we may be sitting here for a while which can be fun I've certainly enjoyed the discussions that we have had and let me just quickly also note that I think as I mentioned last time as I head into next week I began to teach back at Columbia I'll be teaching a course there in the summer so it's going to be more difficult for me together with a bunch of other things that we're doing some of you have also asked about World Science Festival the regular programming that we do we're gonna start rolling those programs out over the next few weeks so there's obviously a lot of effort and time that goes into putting those together so your daily equation the word daily may also be relative I will continue to do some of the episodes but I won't be able to do them at the same frequency I don't think as I've been doing them before but you know we'll play it play it by ear so just if you have a little patience with me flexibility with the the rate at which we create them that that would be great alright so let's let's get into the discussion here and I realize that I've got the wrong chat window open so let me just fix that so I actually see yeah I think this is the right one Justin attends it says sup chat I think that means that I'm on the right page if I'm not thinking about things wrong good okay so there was one question that caught my eye yeah there it is Andrew Hanny asks is it right to say that reality is not absolute since what's real differs with different perspectives and that's um that is a subtle that is a subtle question what I would say is there are certain qualities of the world that are absolute in the sense that a very specific sense that anybody who is following a particular procedure to measure or observe or quantify certain aspects of the world around us will get the same result for instance if you're talking about the electric charge on the electron or the mass of an electron anybody who is using the appropriate equipment in the right manner regardless of where they are say on planet earth or as far as we can tell regardless of where they are you know throughout at least the observable universe we believe that they will get the same value for the electric charge of an electron or the mass of an electron so those qualities of reality do seem to be absolute in the sense that everybody agrees on them in Einstein's relativity there are other qualities of the world that we believe to be absolute to in fact you may be surprised to hear and I'd be interested to know if you're surprised here I mean look those of you who've read popular physics books or know the subject well know exactly what I'm about to say but for those of you for whom this material is new Einstein didn't want to call relativity theory relativity he wanted to call it invariance theory invariant the things that don't change you see because the right way of thinking about say the special theory of relativity is not that Einstein made everything relative like you hear people say that kind of silliness a lot and if it's tongue-in-cheek or if it's just meant in a colloquial sense fine I mean use language however you want in everyday life but when you're talking about the precise description of Einstein's special theory of relativity it's not that everything is relative what Einstein showed is there are qualities of the world that in the past we thought were absolute and those qualities of the world turn out to be relatives space and time being the great examples but he also showed that there are other qualities of the world that are absolute they're just not the qualities that previous generations thought to be absolute for instance if you have two events that take place in the universe a firecracker goes off over here and then another firecracker goes off over there you can think about the distance between them in space how far apart the events took place you can also think about the distance between them in time the time difference between them from your perspective or anyone's perspective different observers will disagree on the spatial separation between those events and the temporal separation between those events however and here's the beautiful thing I'm Stein shows that there's another quality another quantity depending upon space and time that everybody will agree on and in units where the speed of light is equal to 1 that quantity is delta T squared the time difference according to any observer squared minus Delta x squared the spatial separation squared according to any observer so that particular combination of space and time is something that everybody will agree on regardless of how they're moving regardless of the configuration in which they find themselves relative to the events that they are witnessing so so there you have it there is an absolute quality of the world it's just not the qualities that we thought to be real so I would say in answer to the question that there are absolute qualities of the world reality is something that's out there there are many features of reality that are in the eye of the beholder both metaphorically poetically and scientifically but there are other qualities of reality that everyone will agree on I think they have every right to be called the absolute qualities of reality ok so that was a long answer to our first question so anybody who's still with me after that one let's see what else we can get to here all right from Kuwait great to see you guys from friend Vancouver Canada and scroll in Pakistan California yeah do do tell us where y'all are coming from and in the chat here oh here's one here's one and many people have been asking me this question so I think I should dispense with it right now there was a report that you may have seen that NASA has found evidence of a parallel universe where time goes backwards anybody see that particular news report and so a lot of people have asked me well well okay is that is that really true what is that what does that really mean and and here's the situation so there were some observations that have been made of certain cosmic ray particles what are cosmic rays you know the Sun emits particles that travel through space to hit our atmosphere they cause various kind of interactions to take place and showers of particles rain down from the the sequence of processes that I just just described and some of the folks who were investigating these down I guess it must be at the South Pole a particular experiment called Anita they found a strange result they found a result is actually I think way back in 2016 so it's not a new result it's just people are really thinking about it and trying to understand it and they found what seemed to look like the shower is going up as opposed to down and and that was quite confusing and it's hard to make sense of that and many people have put forward ideas for instance maybe some of these particles that they are observing somehow we're produced by the ice and they're going that direction as opposed to coming at us from space and so forth so so the bottom line is many people have tried to come up with explanations for the data and my understanding I've not actually gone through the papers myself my understanding is that none of those explanations really are yet convincing so it's an anomalous observation which is not all that infrequent in science it's one that's been around for a handful of years and when you have difficulty explaining an anomalous observation after a couple of years some of the more far-out explanations begin to bubble up to the surface and one of the farthest out explanations is that we are witnessing particles in a parallel universe that relative to our orientation of time are travelling backward in time and therefore they're going in the wrong direction explaining the weird observations so so do I consider that to be evidence for a parallel universe number one I don't I consider it that's an interesting explanation I'm glad it's on the table I'm glad people kick it around but it's gonna take a lot more than that to convince me and I'm open to these ideas I wrote a whole book on parallel universes the hidden reality is all about different flavors of parallel universes you have to be very careful when you claim that you've got evidence for something so so radically distinct from established science and it's going to take a mountain of observational experimental data to really convince us of the possibility that these parallel universes are real or that this particular explanation is the one that we should take seriously bottom line is you know Carl Sagan perhaps said it best I don't remember the exact wording but something like extraordinary claims require extraordinary evidence it's a great quote right the notion of a parallel universe or time runs backward is an extraordinary claim it will require extraordinary evidence and we do not have that extraordinary evidence in hand now sociologically culturally the second certain publications here of the possibility that scientists may at least be considering the possibility of parallel universes with particles traveling backward in time they kind of tend to forget about all of the caveats and all the other explanations that people are kicking around and focus only on that and then the word spreads outward so I don't like to throw cold water on excitement but I do have a certain resistance and a certain allergic reaction to the hyperbole and the over-the-top headlines and the grand excitement about some far-out sounding idea because then when it's not true people roll their eyes later on when there is some extraordinary claim and it is something that people really are taking seriously and I would say that the vast majority of physicists are not at the moment coming to the conclusion that the headline that I certainly read in one of these articles that NASA finds evidence of a parallel universe where timing runs backward you ask most physicists in the world today and they will not say that that summarizes their perspective all right so Dom Cass Moreau said that was too long an answer all right Dom I will try to speak faster or use less words going forward thank you for your constructive criticism but right below you someone said love you professor so maybe there multiple perspectives on on how much information I should give you but whatever whatever you want to ask I'll do my best answer it as concisely as possible all right so what else do we have here I've got to take my finger off the scroll all right Maximilian agar says what would be evidence for such a claim then that's it that's a very good question and well first of all you want to make certain that the data is real so you want to make certain that this is not some one-off perhaps anomalous experimental error right you may recall that there was claimed some years ago that particles were traveling faster than the speed of light and it was an experiment where particles neutrinos are being shot through rock from one location in gran sasso Italy I think it's from CERN to Gran Sasso Italy and the particles were arriving too soon right and and so there were these claims of faster than the speed of light the speed of light limit has been broken that speed limit has been broken and most of us who said to ourselves no I don't trust that relativity it's been around so long anything that violates it it's got to take a mountain of experimental evidence to support it and when the experiment have went back and checked the equipment very carefully you found that there was a problem with equipment and when they fix the problem the equipment the the data went away so that's number one you want to make sure that this is replicable experimental data that you see at a sufficient frequency that you can really gain some statistical confidence that this is not just some weird anomaly with either the equipment or some kind of other fluke in the environment and when you rule out every single possibility of a sort that is closer to our perspective on the world then parallel universes were time run backward then then you then you get to a place where you start to take it seriously we're not run out there yet all right so let's see hmm there's one question I think I understand but maybe it's an internal conversation so I'm going to let that one go let's see garden ask isn't it crazy how time breaks down at the beginning of the universe is it because time and space work together and well partly that is the answer again the lesson that we learned from Einstein is that the Newtonian perspective that space is one thing and time is another that is a perspective that needs to be jettisoned and we learn that space and time more or less as you described guard and they're kind of woven together that's why we use the language the fabric of space-time as if they're woven together in a particular pattern dictated by the equations of relativity and when you go back in time with your mathematics not for real but use your equations to turn the cosmic film ever further back in time what you find in our understanding of the universe is that the density of matter and energy gets higher and higher and when the density as you head back toward the beginning soars toward the number infinity as basically what the math tells you you realize that it's not just that sort of time is breaking down it's at our whole mathematical architecture for understanding what happens in the earliest moment of the universe that is breaking down you know sometimes I think I said it before people have a sense that the word singularity is some mysterious concept some beautiful mysterious Engel arity is coming the singularity is near right and depending what you mean by that it can have a real meaning I'm not trying to denigrate some of the folks who speak that way but the bottom line is in physics when we talk about singularity it is a euphemism it is a metaphor it is a word that actually tells us that we don't know what is going on singularity means math breaks down we don't know what's going on so it's not that we can really say that time stops at the Big Bang we can't say that time begins at the Big Bang these are all real possibilities but what we can say is we don't have the math to give us insight into what happens at time zero and until we have equations that do not break down under any circumstances however extreme the environment may be however dense the energy might be then we are at a loss so we need those equations that will never break down under any circumstance we hope to one day have them but I would say at the moment we are lacking that kind of technical understanding and that's what prevents us from saying what happened at time zero itself little bit von Beethoven a regular on this discussion professor me and some others have now a subreddit called your daily equation with an R a reddit slash your daily questions discussed topics discussed here or to ask for additional questions do you approve of this initiative yeah sure why not I love conversations about the things that we are focusing on and and look like I might also mention to ever is interested sorry I just took a shower and they got war in my ear I'm going to be doing a semi-regular reddit discussion conversation QA you may know that reddit has this thing called our pan reddit public access network I did it a couple weeks ago is kind of fun a lot of people were discussing the kinds of things that we discuss here so I think that's going to be Friday's from two to three maybe every other week so I don't know how long we'll continue our live sessions but for at least a while you can join me a two o'clock on that reddit access network I'm sure you guys can find it I don't even know where you gonna find it and but yes of course anything that you guys want to do to continue the conversation that's that's that's fantastic alright Gayatri Pandit asked professor why does string P require ten or eleven dimensions and does having different dimensions mean different universes or shapes of objects and I wish I could give you an answer for why string theory requires 10 or 11 dimensions in the sense of why 10 or 11 I think it may have mentioned before I've never been able to come up with anything but the mathematical explanation of that so let me just frame it this way there is an equation in string theory which to be satisfied for the theory to be mathematically coherent if this particular equation is not satisfied you can prove that all sorts of weird things would happen which would destroy the viability of the theory you lose energy conservation you lose all of the essential details that make a mathematical theory of the universe viable worthy of attention in this equation in some sense it counts the number of vibrations of a given energy of a vibrating string if a string is vibrating say in just the plane in your mind you can picture there are just so many distinct vibrational patterns that it can have if you go to a third dimension now there are more distinct vibrational patterns of a given energy because not only can it vibrate this way the string can also vibrate this way and it's harder to picture but if you go to four dimensions of space there yet more vibrational patterns that are accessible five dimensions more six dimensions more and so forth so here's the thing when you calculate the number of vibrational punters necessary to solve that equation that I mentioned a moment ago there aren't enough vibrational patterns in two dimensions of space and three at four five and six and so on only when you get to nine dimensions of space and one dimension of time are there enough vibrational patterns to satisfy that equation I cannot convince you of the number nine spatial dimensions but I hope it gives you the flavor of reasoning that connects the number of dimensions of space with the viability of the theory it's not that someone sitting there and say wouldn't it be fun to have extra dimensions of space people did follow that approach way back in the early part of the 20th century Colusa klein they weren't being as facetious as that of course but they were examining the possibility of extra dimensions just because it was an interesting possibility and they were curious to see whether physical law could make sense in a world with extra dimensions and I found some very interesting results that's not what happens in string theory in string theory you do not posit the extra dimensions in string theory you study the fundamental mathematical equation of a vibrating string in an existing space-time arena and you find that that space-time arena must have more than three spatial dimensions for the fundamental equations to be internally consistent that's a completely different way of getting to this idea of extra dimensions of space and that's why it's much more convincing finally to end this answer to this question when you go to M theory this more refined version of string theory you learn that the approximations that we had been making in conventional string theory left out one spatial dimension they were insensitive to one spatial dimension and therefore nine dimensions of space went up to ten dimensions of space with time takes us to eleven space-time dimensions so that's the chain of reasoning and you know some of you have asked me in one of these episodes to explain this curious fact you know that one plus two plus three plus four plus five what does that add up to someone just tell me in the chat I'm sure some of you guys know what that adds up to and infinity is one answer and it's a fine answer but that's not the answer that I'm looking at I'm looking at a finite answer for adding up all of the numbers and I think there's a let me just see if I can see if anyone has that answer for me well I'm waiting I'm waiting maybe it will come in I think there's a bit of a tight time delay between when I there it is thank you walking Android minus 1/12 thank you walking Android and and so people wanted me to explain how it could be the real flew non minus a12 how could be the one plus two plus three could add up to minus 1/12 and at some point I will do that but that minus 1/12 it turns out is one of the key ways of understanding how it is that string theory requires the extra dimensions that it does now a lot of people now I guess that's the bit of time delay between what I say and when you hear it so I see many people while while coming in with - at 12 wow you guys are good how many of you who know that the answer is minus 1/12 think you really understand why it comes to minus 1/12 or you can give the argument I'd be interested to see your answer on that just say yes if you understand it and know if you're a little bit shaking on it but the reason I ask this is because this is deeply connected to the technical explanation for why there are extra dimensions and string theories so that's the kind of thing that we would need to cover in order to give a full answer to the extra dimensions in string theory ok I see a lot of - 2/12 and some are saying that they understand and some are saying yes and Ramanuja n-- is uh no dad teach us as Justin and in a subsequent episode I will not try to do it now I know it's minus 1/12 and I know how this comes about yes great perfect so so some of you are quite advanced which is fantastic some of you are saying that you don't okay so I'm gonna jump over to a different question now john smith ii asks how do you derive the time that inflationary expansion occurred for and you may recall in the episode which repa sowed was i think was the last one number 30 well that was an inelegant sip of water so glad that that's i'm on film so in the episode number 30 I described how this burst of repulsive gravity this inflationary expansion just last for a tiny fraction of a second I said it was something like 10 to the minus 30 to 10 to the minus 33 seconds and the question is what determines the duration of the inflationary burst and the answer is it's nothing fundamental so you may recall that I put an inflationary potential deify is what I called it and via Phi I don't bother drawing it but you recall it was a very gentle slope and then it had a steeper section to the curve and that ensured that the value of the in photon field would stay pretty constant for a while and it's that constant value of the energy and pressure densities that yields they were pulse of gravity that pushes everything apart but then the in photon rolls down the field so the question is how long does it stay on the top part which is the span of time during which the inflationary expansion takes place and that's totally dependent on the slope of that top part and the length of that top part right is V of v so how much does phi a have to change before it hits that other part of the curve in which it falls down and all that's chosen by hand all that's chosen by the physicist all that's chosen by the definition of the model and once you choose that definition of the model you then work out how long the field stays up on the hill and I noticed that half of my heads being cut off so I'm gonna shift this a little bit so that's that's really the answer to to the question we would love it if we had a fundamental explanation where you could say from first principles here's what the potential looks like from first principles here's how long the field therefore will stay on that plateau from first principles therefore here's how long the inflationary bursts will last and we can't do that yet so that's a goal for the future maybe one of you guys will figure out how to do that but as of today it's all set by hand it is not set by any fundamental principle okay yeah teach our goal all loved you in Startalk sir could there be a component of the Higgs field in the time dimension which is why we only travel forward Wow well first yeah taste thank you for the kind words on that Startalk episode it was a lot of fun talking about the end of time with my friends over there at star talk Neal but your question is um is an interesting one a perplexing one so when we talk about the Higgs field we do talk about it filling space for a duration of time so it really does fill a region of space-time so I think you may be imagining that the Higgs field only talks to space and it doesn't have any conversation if you will with the temporal the time direction but that's not true so for instance it's possible in the very early universe that the Higgs field did not fill space there are many in fact the most common models imagine that when you heat up the universe sufficiently high the Higgs field evaporates it goes away so the early universe was so hot that in many of these models there was no molasses filling space there was no Higgs field filling space which means at that moment all the particles would have been massless and then as the universe expands and cools the idea is that the Higgs field can condense kind of freeze out if you will from the evaporated environment and then from that point forward space is filled with the Higgs field so if you think about it that way I think you'll recognize that the Higgs already fills space and time in this very specific way that I described so we're not missing that possibility if I if I didn't interpret your question correctly do ask it again but I hope that addresses it ooh what happened I went away for a minute I I must have missed must have disappeared for a minute folks I have no idea if you heard my answer I just gave one of the best answers of my life and I hope that no I assume that you guys heard I don't know what happened but anyway I think we're back in business here which is good Marin who you'd COO I'm gonna get this coup Kendall Marin COO Kendall I love you new book thank you appreciate that always like kind words when you're thinking about the end of our universe in the far far future change if there were proof of other universes and to some extent it would affect my thinking you you may recall and it was only a brief mention but in in chapter chapter 10 I think it was chapter 10 toward the end yeah in chapter 10 toward the end I do note this interesting possibility that the wonderful creative influential physicist Alexander the Lincoln and his collaborator came forward with some years ago where they imagined the possibility that as our civilization or more generally our universe comes to an end maybe we could pack up all of our knowledge and insight into some kind of capsule and launch it into another universe if the multi-verse were real sort of send it out in space and it could reach sufficiently distant locations where those regions would not suffer the same fate that we might be suffering and that's an interesting possibility it would it wouldn't change my view on how reality would end in our universe the part that we have direct access to and and the environment that we have been living within and measuring and having a civilization on planet Earth and so forth but at least conceptually the idea that we might launch our understanding into a distinct realm that might last longer than us at least gives us some kind of symbolic carrying on I was gonna say symbolic immortality but that's not quite true because that other region will also have a finite duration and what they show though and this is the part that is perhaps curious of all if there truly is a multiverse then you can argue that there is some region in fact many reasons out there that will last arbitrarily long through weird quantum fluctuations that cut against the grain of the likelihood is given by the probabilistic mathematics you know if something has a 1 million chance of happening if you have enough universes where every possibility takes place then clearly there's gonna be some universe and which then one and a million weird possibility happens and sometimes the one in a million or one in a billion and one in a trillion weird possibility is such that it will extend the duration of life and consciousness in that universe and yeah so that definitely slaps your brain around a little bit maybe gives you a little bit of comfort that even if life and consciousness come to an end in our universe there's some place it's very abstract because you don't have direct access to it but there's someplace out there where life and mind continue so do I take solace from that I don't know number one I am a multiverse skeptic some people like why would he talk about man you're the guy that's always talking about of the universes I talk about other universes as an interesting possibility I wrote a book about it because I find that possibility exciting interesting worthy of attention but in that book and in any interview where they don't cut out the caveats I always say we need evidence we need observation to establish that these ideas are correct at the moment I view them as a powerfully interesting tool in our toolkit as you try to understand things in the world around us so you know with the recent observations of those strange particles sure bring out your toolkit and imagine the possibility of other universes but I'm a skeptic of this so in terms of taking solace from this idea it feels too too tentative for me to hang any existential hope on the continuance of life in mind in a parallel universe so it doesn't really help me in that regard in any deep way rather the approach I take in the book does help me you know when I recognize how unlikely it is that we're here when I recognize how spectacular it is that particle is governed by physical law can do the things that we do that to me lessens the blow of realizing that life in mind in our universe are finite that's what works for me thank you for the question though of course all right what else we have here she Creole asked the Supreme please explain the equivalence principle well hmm and then the question about particles accelerating space creating curvature and so forth you see the equivalence principle is the heart of Einstein's general theory of relativity the way that I like to think about it is that a sufficient ly well chosen accelerated trajectory can either Mach up a gravitational force or cancel a gravitational force the example that I gave in one of the earlier episodes I can't really do it here you know I did this thing with a bottle of water this is glass somebody got mad at me for having plastic bottles last time so I listened to you guys so here is a glass bottle but imagine it had holes in it which you can do in a plastic bottle if the water therefore would be spraying out of the holes if I'm holding it like this and I noted if you recall that if you let this go into freefall accelerating downward from my perspective the mat is able to cancel out the pull of gravity on the water to the water stop spraying out of the holes accelerated motion cancelling out the force of gravity Einstein's version of this was the painter who fell off a ladder and while descending in that accelerated trajectory from our perspective toward the surface of the earth that painter doesn't feel his or her own weight I ain't if the painters on a scale the scale Falls with the painters feet so the painters no longer pressing down on the scale and so the reading on the scale goes to zero so that's beautiful that's a beautiful unexpected link between accelerated motion and gravity in this case accelerated motion canceling out gravity and what Einstein emphasized and I described in earlier episode the reverse is also true accelerated motion upwards say in space if you're standing say on the platform and someone accelerates things so that the platform is pushing up against your feet if the acceleration is the right magnitude you'll think that you're standing on planet Earth it'll feel like the force of gravity so it's this equivalence between accelerated motion and the force of gravity and this is what was critical to Einstein being able to work out the general theory of relativity now something occurred to me as we were talking about that oh yeah here's the point that I wanted to make so oftentimes we talk about Newton in the Apple right Newton is sitting under the tree the Apple falls hits him in the head and the idea is that that kind of inspires or at least as the story goes that inspired Newton in understanding the force of gravity in the Einsteinian description it's completely different right yang steinem description the state of freefall is the natural state of existence that's the one where the body doesn't feel a gravitational force the painter does not feel his own way or her own weight or their own weight during the descent the water doesn't come out of the holes of the bottle because the water no longer feels its own weight so the natural state of being is freefall and therefore the natural perspective in the apple hitting Newton on the head is not Newton's perspective he's not in freefall he's on planet earth he's not falling it's the apples perspective so the story of the Newton Apple from the apples perspective is the Apple detaches from the tree the tree accelerates upwards the apple looks down and sees Newton's head approaching it and Newton's head slams into the Apple that's the description of that famous story from the more natural perspective of the body in freefall which in this case is the Apple okay carry on on Alexes so that means we are all gods I'm not sure gods what so if you want to clarify that I'd be happy to answer it pry out - who's also here as a regular thank you God I'm happy to see the regular participants your podcasting star talk was really knowledgeable thank you but I have a doubt can we interpret the notion of quantum entanglement - the stitch fabric of space and time so so so look prior you should have a doubt nobody right now is saying that we really understand what the fabric of space-time is made of we use the language all the time Einstein either used exactly that language in the German perhaps or something equivalent this notion that there is a stuff out there that can warp and curve and using the idea of a fabric is a nice poetic way of talking about it but what really is the fabric made of people to ask that for a long time and what I find exciting is that at least now we have some proposals some strategies for how to go about addressing that question and quantum entanglement is one of the most fruitful strategies that have been pursued again quantum entanglement tells us that distant particles are connected if they're set up in the right way with kind of threads of quantum entanglement in an earlier episode I made them these yellow threads or I didn't make him these yellow threads Josh Zimmerman made them these yellow threads who's actually behind the scenes right now making sure that all this is working spectacularly creative editor and animator but anyway so we have these yellow threads between the particles and that allows them to correlate their behaviors now when you think about that distant particles connected by a thread of quantum physics you began to wonder could it be that space itself is stitched by these threads of quantum entanglement and there is now mathematical might behind that idea people like well many people have been involved in this idea from many Susskind to one maldacena mark from roms doc many many people we had a program a full program at the World Science Vessel so if you want to have a disc and you know what we're gonna do it again a more refined version of that program this summer we're gonna have a program on quantum entanglement and wormholes and stitching the fabric of space-time so so we'll go into it much more detail there but I would say Priok that having doubt that that is the right way of thinking about space that it is a fabric stitch by the threads of quantum entanglement have doubt but have an open mind and let's allow the research to progress and let's see where it goes because honestly I'm shocked that we even have ideas that are sufficiently well formulated for mathematical analysis regarding the fabric of space and what it's made of I wouldn't have thought that in my lifetime frankly we'd be able to make progress on that and the fact that there are some real interesting possibilities that people are pursuing that to me is the big story whether it's the right explanation I don't know but the big story is that we can actually begin to address these questions with a degree of mathematical seriousness and that's very very impressive so let's see so a couple people are asking about wormholes maybe because I mentioned it Abu Bakar Faruk we asks professor Bremen was the likelihood of the existence of intergalactic wormholes and then right underneath that Gayatri Pandit asks do you think quantum entanglement can make travelling through wormholes possible all interesting questions number one there is zero evidence for the existence of any wormholes whatsoever no events all right it is an idea that naturally emerges from Einstein's general relativity you can solve the field equations with certain assumptions and come up with these shapes that have this tunnel-like quality this throat like quality Einstein himself in a paper with Nathan rose in 1935 wrote down one of the early solutions of this form so the math allows for it does that mean that these entities are real well you remember what Einstein said Tula maitre your calculations are correct but your physics is abominable he was talking about the expanding universe in that example and there Einstein was dead wrong physics was not abominable now you could say the same thing about wormholes they naturally come out of calculations entrenched within the general theory of relativity but not every mathematical solution is realized in the real world I think and therefore you have to have real observational evidence and we do not have any now could quantum mechanics help make wormholes traversable and the answer to that is yes so when you create mathematically a wormhole you then often investigate its properties and scientists have found that they tend to collapse in on themselves such that it be very difficult if not impossible for something to pass through however people have found that if there's an exotic form of matter that has a negative energy density sorry excuse me ate too much for lunch negative energy density then that matter can create an outward force that can keep the throat the tunnel part of a wormhole open and that yields what's known as a traversable wormhole now again we don't know if wormholes are real so we don't know if traversable wormholes are real but at least the math does allow for quantum mechanics to yield a kind of substance that would keep a wormhole propped open so a lot of tentative things in that sentence but the bottom line is at least mathematically speaking mathematically speaking I don't know if this is in the real world you can in principle have wormholes that would be traversable that you could pass through and you know that's pretty exciting because if you had a traversable wormhole you can turn it into a time machine you move the openings of a traversable wormhole relative to each other put one near the edge of a black hole one far away time elapses at different rates at the two openings of the wormhole makng have a tunnel with two openings and you're somehow able to make time elapse at different that the two openings of the tunnel that means as you pass through the tunnel you'll start at one moment in time but you can end up in a very different moment of time either in the future or in the past and that's why these ideas are shocking and strange some would say that's proof that you'll never have a traversable wormhole because you can't travel to the Past some would say I think it's too quick but nevertheless it would be monumental if there is any real evidence for any of these wormhole ideas to be actually real hmm Marilyn Kozak so many questions but hoping your back is feeling better Mountain thank you you must have seen the interview with Joe Rogan where at the end he nicely inquired I guess why I was sitting in such a strange angle no no we'd spoken about beforehand that's what it is I was of course I showed up there on crutches now it's all coming back to me and so Joe had various suggestions in fact he actually took me after the interview to his his workout stations right in the same space where we we did the conversation and he put me on all sorts of machines and I have to say that was the beginning of the road to recovery for me you know so then he also suggested all sorts of treatments it was really great really nice guy but yes the answer is my back is is feeling much better so you know you talk about you know a life of contemplation thinking about the universe and math and physics if your back is hurting or you've got any physical ailment it all goes away you can't do anything you can't think about anything else if the pain is great so man we we are these creatures whose brains can soar to the edge of the cosmos but you fiddle with us physically and you break a little something or you imbalance in the chemical makeup and that's it we fall apart we are just these bags of particles how amazing that when they're doing the right thing we can engage with the world in such deeply interesting and profound ways okay what else do we have to talk about here um Philip asks if time is not fundamental where is the point that it emerges from from more basic principles and how can the universe evolved from a fundamentally timeless basis and I wish I had something good to say on that but let me just give a couple of quick thoughts we are familiar with qualities of the world that you might have thought to be fundamental but they're not refined investigation and knowledge shows us that these qualities of the world emerge from more fundamental starting points in the example that I I like to give it's very intuitive is temperature you know there is a time when you might have thought in the history of our understanding I'm we here is now the entire species there's a time when we would have thought that hot and cold to these fundamental qualities of the world but then physicists chemists dig deeper and they realize oh temperature that's nothing but a measure of the average kinetic energy of the particles that make up a substance whether that be the environment the air or that be you know a pan that we're holding right and if the molecules are moving very quickly in the handle of that pan and you grab it you scald and you burn your flesh hot if on the other hand the molecules are moving much more slowly you grab it and it feels comfortable so temperature hot and cold is now recognized to emerge from a more fundamental idea the motions of the particles that make up a substance could it be as people have kicked around and as Philip is asking that time is also emergent could it be that there are more fundamental qualities of the world I don't know what to call the molecules of time atoms of time people use this language but really making that precise is difficult but imagine that there are these particles that only when they arrange themselves in a particular configuration not moving quickly or slowly that's tempered but rather arranging themselves in the right pattern when they do that a concept of time emerges just like when the particles are in the arrange the moving quickly the concept of hot emerges could that be it and could it be therefore that when the particles of time are not arranged in that configuration time as we know it doesn't exist so to answer your question Philip imagine imagine a universe hard to do is our language is so temporal from the get-go it's difficult for me to even talk about things without time slipping in but imagine a time there it is long ago another reference to time when the universe was in a configuration in which those particles were not arranged in the manner that yields the conventional notion of time and then at some moment a temporal notion has slipped in again at some moment the particles do arrange in the manner that yields conventional notions of time and then the universe progresses from there now I don't have the language to even talk about the era prior to the particles arranging in a manner that yields time but intuitively I think you can grasp the idea that there could have been a realm where time had not yet emerged and only when the particles coalesced in the right way that sounds like a temporal process there you go I'm slipping in again but somehow when the particles coalesce in the right way time emerges so you see the challenge is to develop a completely different vocabulary and a completely different mathematical structure that allows us to talk about processes without time creeping in and people have worked on this people have worked on versions of physics where there isn't time and space from the outset rather there's the relationships between the ingredients I've never been completely convinced that those approaches have achieved what they seek to achieve but it's just to say that people do try to develop the language and the math to make more precise the answer that I just gave but I hope that gives you some feel for how time could be emergent and how the universe itself could have an era in which time as we know it did not exist so Rajeev dar asks linear or cyclic cosmology and I would say I fear strongly toward linear cosmology right now I have been struck over decades as have many of my colleagues by the successes of the inflationary theory I am NOT saying as I noted in the episode I feel again was episode 30 I'm not saying that inflation has been proven I am saying that it's a very compelling framework for dealing with a great number of cosmological issues and giving rise to a very economical compact description of how the universe got to be the way it currently is now there are critics of the inflationary theory including the one of the gentleman who was responsible for the theory itself Paul Steinhardt and again as I emphasized in the earlier episode I think it's spectacular that Paul who developed a theory is willing to take a sledgehammer to it to try to break it down and suggest an alternative possibility doesn't mean that he's right it does mean that there's a vibrant conversation that would not otherwise be happening if Paul and his colleagues were not developing these alternate ideas in the end of the day it's got to be observation and experiment mathematical consistency the predictions that emerge from a theory that determines whether it's the linear version of inflation or Paul's suggestion as others have worked on to a cyclic cosmology of bouncing cosmology so we will see I would think that in the next 5-10 years we will have enough new mathematical insight enough new data that we'll be able to answer your question more forcefully but at the moment there are these competing proposals I think the vast majority the cosmologists are in the linear camp but that could change over time ok let's see what else let's see okay that's interesting so I get any inspector Levin says I'm the original Ludwig van bond Beethoven I don't think original in this ends I've got original but probably original in specific count and there have been copycats Wow and then you've been put out oh wow I don't know all sorts of political intrigue happening on the live chat so I have not much to say about that but hopefully everybody's having a good time that's all that really matters all right on to other questions easy Sparky does the future already exist right now certainly in in Einstein's special relativity if you allow me to answer this from the perspective back in the early part of 20th century back then I think Einstein would have had a certain degree of warmth and sympathy and agreement in that view that the future already exists well I should not have chosen this bottle I just got water all over my face just excuse me one second as I wipe ma'am I'm gonna get a better cup out here anyway I was trying not to use a plastic bottle but you know Einstein's view is that the whole notion of now right the whole notion of what's happening at a given moment in time is highly in the eye of the person they observer the beholder because if you and I are moving relative to each other we have different clocks ticking off at different rates we have different notions of simultaneity in that episode I don't remember what it was it was a while back now but there was a your daily equation on the relativity of simultaneity where if you watch that or if you go back to it if you're interested I established that in the special theory of relativity we learned that things that I say happen at one moment in time if you're moving with respect to me you will not agree that those events happen at the same moment in time right we're like right now I would say I snapped my fingers simultaneously at the same moment but if you were moving relative to me in one or another direction and you observe those snaps from your perspective you would say what happened was snap snap or if you're moving the other way you'll say what happened is snap snap so the notion of simultaneity what's in the present depends upon your state of motion and that's exciting and interesting in its own right but one implication is that you and I if we don't agree on the now we don't agree on the past and therefore we also don't agree in the future right the person moving by would have said that happened first and then in the future this happened the person moving the other direction would say this happened first and then this happened in the future while I say that happened at the same moment so observers in relative motion mix up their conceptions of past present and future and therefore the things that I consider to take place in my future that's a real motion I have a unassailable conception of the past I have an unassailable conception of the future but it's my future and my past and things that are in my future can be in your present or can be in your past depending on how you're moving relative to me and if my future can be in your past then in a sense my futures already taken place now when you look at this really closely many of the things that then come to mind are not possible it's not like you can learn about my future before I know about it and tell me about no no can't happen none of those games can be played because it takes time for you to learn about what happened in my future even if it's in your past it takes time for the signal to reach you right when I look out at the distant stars I'm seeing the past it took a long time for that light to travel to my eyes so I'm seeing something a long time ago but by time I am aware of it it's long past it's long gone and therefore has none of the funny things that might come to mind in terms of spoiling causality or possible but in an abstract sense is the future already in existence yeah according to special relativity it is quantum mechanics generativity interesting nuances complications if you're interested ask about it I'm happy to go down but this according to that way of thinking about special relativity the future in some sense is already real so let's see I'm going to take a risk and try to drink some more particularly thirsty today what do we got here well so divyam single asks I just wanted to ask what your viewpoint of m-theory it's progress since 1995 how does it explain dark energy and look my view is this I've said this before I'm happy to say it again I am thrilled in the rate of progress and string theory or m-theory in certain kinds of questions I mentioned one before that insight into the fabric of space-time may be stitched by the threads of quantum entanglement that ultimately relies on insights from string theory that's great some of the insights into black holes that string theory has yielded spectacular some of the insights into pure mathematics that have come from string theory my own contribution I'm happy to a participating mirror symmetry and topology change these are exciting developments what we have not done is make contact with observation and experiment in the manner that we hoped would happen by today so anybody who's a research scientist that's listening to this anyone who's a graduate student who's in the middle of their dissertation the research program will know you can't predict how long it's going to take you can't predict what area of science is going to develop rapidly and what area of science is going to develop at a snail's pace if you interviewed me as a graduate student back in the 1980s I would have thought that by today we'd only made contact with the supersymmetric particles that string theory requires or that would have seen some exotic process that would give indirect evidence for string theory that has not happened but again if you ask me back in the 1980s will we be able to talk about what makes up the threads of the space-time fabric or will we be able to truly understand the entropy count for black holes I would have said I don't think so it's gonna take longer and yet we've gotten headway made progress in these areas so unbalanced it's exactly what you'd expect the rate of progress of science is unpredictable as long as it is making progress in some areas that means that theory is alive well and healthy and I think that's the best that I can do in describing the state of play in string theory okay all right what have we got here they may switch over to YouTube for a second as there are some that I remember over there liking a lot all right so one one technical question I think it's worth spending ten seconds on from Martin tope inca why do people use the via five plot with a rolling ball in the direction of the gradient of the potential and not Phi of T plot to describe inflation and and so what what Martin is referring to is my head's on the blink right now so I can't draw it for you but you remember I mentioned before ready I drew this curve that was the plot of V as a function of Phi or maybe this is the direction I drew it that's probably how I drew it and I imagine that the Phi value was like a ball that's metaphor but it's a ball in the sense that it's value changes over time and rolls down the hill and the reason why we typically write Phi of T is that it via Phi we could do five T you're absolutely right five starts at a certain value it stays constant at that value over a stretch of time and then it drops down the reason why we frame in terms of via Phi is via Phi is what we choose and put into the model that's the user chosen quality of that model of cosmology we then use via fine to write down the equations that determine how Phi changes in time so Phi of T for us is generally a derived quantity whereas V of Phi is a quantity that we put in by hand so we tend to define the model by the things that we put into it and then we extract from it through calculation certain qualities and that's why we write down the thing that we pick by hand and then we figure out Phi of T we determine it by solving the equations of motion so that's that's but you're right you can you can do it either way doesn't matter okay so van wrong says dr. green huge fan of your work thank you van Ron can you recommend a great book on the history of quantum mechanics yeah a great book on the history of quantum mechanics I dunno some I'm having trouble bringing them into mind directly right now it's on the tip of my tongue that's why I'm struggling to it there's a book called quantum and there's one word after it quantum ages quantum yeah it hopefully it'll come to me but there there are a lot of really good books on the on the subject not I understand you're asking for the history as opposed to the extra subtly I'm gonna have to come back to it hopefully it will come to me or maybe believe and put it I'll put it in the comments if it comes to me later ok so Oh what if we go to the odd abide choco asks does a particle without mass would it could it be motionless and the answer to that is no it's a strange idea if a particle doesn't have any mass it cannot sit still I successfully took a sip of water Wow congratulate me don't have water in my face on that one a particle that has zero mass is a particle that will always and forever be traveling at the speed of light so the photon of course is the prototypical example and the proton opposite photon that proton the photon the particle of light is always traveling at light speed it's never not traveling at light speed and you know there's a lot of intuitive ways you can think about it you know as a as a particle gets ever lighter obviously the wispy 'us force will give it the largest of accelerations right F equals MA fix of small value of F let em go smaller and smaller the acceleration is F over m as M goes to zero the acceleration goes infinite infinity goes to infinity and therefore the particle accelerates arbitrarily quickly more specifically when you really look at RN Stein special theory of relativity it is the trajectories of masses particles that define the causal structure of the universe they are the ones that set the limit on how quickly a signal can travel from one point in the universe to another and therefore they delineate what influences any given process can exert on other events and so the the speed of light is an interesting concept because we name it the speed of light because it is the speed of light but it's more than that the specialty of relativity is not so much about the speed of light per se as is about the causal connections the events that can influence each other by any kind of signal sent with any kind of particle light being one particle but gravitons masses particles that we believe exist would also be traveling at the speed of light or call it speed of gravity as with any massless particle they all fall into the same category of articles that cannot be motionless always traveling at 1:00 in the same fixed speed okay we got here al-bayan as I've read once there's a mathematical relationship between dividing by zero and black holes is it true well sort of not really I mean not in any deep sense when you look at the solution to Einstein's equations and the general theory of relativity and you look at the amount of curvature at the origin at the zero point say of your coordinate system for a black hole you find that the curvature explodes it gets arbitrarily big and depending on the exact solution you're looking at it goes like a power of your distance from the origin so imagine it's the sixth power that the curvature goes like one over R to the sixth power for the black hole solution then as R goes to zero one over zero to the six is zero so it's like dividing one by zero so the curvature at the origin of a black hole is like dividing by zero but that's the nature of a certain kind of curvature singularity that need not be associated with a black hole it could be associated with you know any solution as some would say you know aren't aren't singularities always cloaked with a black hole horizon and if that's the Association you have in mind that's that's fine that's true but I guess why my gut reaction say yes and no is there is some quip I don't know if it was Stephen right or comedian or maybe it was Einstein or somebody like that I don't know don't quote me on this quote but somebody said black holes are the result of God dividing by zero and when I hear it framed in that way as you no doubt can tell by the look on my face it's funny clever perhaps but there's nothing more than that to the statement so I think my interpretation of the curvature going to infinity at the origin of the coordinate grid for black hole solutions probably the best real connection between / 0 and black holes that you can get so DM asks and is very excited about this question so exclamation points says even though things can perceive the same event at a different time isn't there an absolute time that an event happened and and the answer to that is is no your intuition says that DM exclamation point question mark but your intuition is something that we've learned from Einstein is a generally a poor guide to understanding the true nature of reality so really what Einstein taught us is that there is no universal notion of time so an event can take place and you may use a notion of simultaneity to determine when that event happens what do I mean the firecracker goes off and you look at your watch you're like okay it went off at 12 noon and you're saying that those two events are simultaneous that's what it means to say that an event happened at 12 noon you mean the event happened at my watch struck twelve simultaneous events that's what I mean by the event took place at 12 noon but as I described before different observers moving relative to you will not say that those two events were simultaneous they will say either that your clock struck noon before the firecracker exploded or they will say that the firecracker exploded and then your clock struck 12 noon and so the conception of when an event took place depends upon who is doing the observing who's doing the measuring the clocks and the state of motion that they are undergoing why does that matter why does that matter why is it matter because it radically changes our perspective of the world our view of the world according to Isaac Newton was there's this Universal clock ticking out there in some metaphorical abstract way and the events of the universe simply unfold as that clock ticks off time forward and because the clock Universal you and I and everybody else will agree on when events take place and what Einstein did is he took a sledgehammer and he smashed the universal Newtonian clock and the shards that shot through space are the individual clocks that each and every observer carries with themselves and so time now is not universal time is in the eye of the observer a completely different perspective on how the world works I mean don't you find it mind-blowing that if you and I diem imagine you and I on opposite ends of the universe billions of light-years apart and let's say initially we're not moving relative to each other which means we will agree on what things happen at the same moment but then if I get up and I start to walk toward you or away from you my conception of what happens right now may swing a hundreds of years into your past or hundreds of years into your future things that you would say have not yet occurred I would say are you kidding me they already occurred things that you would say our long past that's a no-no they just happened right now that's crazy sounding but it's true that's why it matters that's what Einstein's relativity of simultaneity gives us okay Chetan asks is it true the photons do not experience time and this question comes up now and then and I ask you to think about your question a little bit so you say photons do not experience time normally I don't need to parse a question carefully but this one I do because what does it mean for a photon to experience something we anthropomorphize the particles of the world and we imagine that they kind of have some experience of time like we do some conception of time passing and that's not true I don't think I don't think photons have any conscious awareness so the question of time passing for them is a very different proposition from the notion of time passing for us and therefore I always find it a little uncomfortable to answer this question as if it were the case that a photon is consciously aware now why do I say that I say that because yes poetically speaking there is a sense in which if a photon did have conscious awareness it couldn't experience the passage of time in a sense that it's clock would be dead fixed at one moment relative to our clock or said differently from its perspective it would see time on our clock elapsed infinitely quickly all events would happen at the same moment so the notion of the photons being able to see the world as we'd like to see it events happen one after another after another with some finite separation in time between the events that would not be the photons experience but I urge you to take this with a grain of salt because photons don't have that experience whatsoever and therefore if it excites you and you finally interesting to think about how the world looks from the perspective of a photon beam I guess it's fun to play those games but don't take it too seriously because no conscious awareness is ever going to have the perspective of a photon okay what do we got going on here yes a garden asks again so what would a photon see in its one moment again I'd say the same caveat I don't even know what it means for a photon to see has it seen with another photon another photon brings the image of light to the eyeball of the photon the fruit you know so you see we get into a bit muddled very quickly putting all that to the side which I shouldn't do but just because you asked and that's an unsatisfying kind of answer in some sense the photon would see all of space in the direction that it's moving infinitely compressed right because it's going at the speed of light which means the gamma factor would be infinite so distances that it looks at whatever the heck that means would be infinitely compressed and moreover because it's clock is ticking off the infinitely slow compared to the clocks that it's moving by if we see those clocks ticking off you know at a rate of time that would be very strange you know so I it's hard it's hard to really it's hard to really answer this question you know as a wheat we can talk about our view of the photon our view the photon is that if it were carrying a watch that watch would be ticking infinitely slowly you can say that but the real way to answer that question is don't talk about photons talk about a particle traveling at ninety nine point nine nine nine nine nine nine nine nine nine nine nine nine nine nine nine nine percent of speed of light that's pretty darn close to the speed of light but not exactly equal to the speed of light none small difference is kind of vital because that is a perspective that in principle a particle or even a human being can be within I mean if a particle is traveling at that speed in the opposite direction from its perspective whatever that means I am traveling this way at that high fraction of the speed of light and again we know what happens in those circumstances I look at your watch see it going slow you look at my watch I see it going slow you know so so those are the things that you know if I look at an object moving by me I see it compressed in the direction of motion so that if an object is moving by me an incredibly high speed close to speed of light it will be like a pancake twisted pancake as it turns out so these are the things that we can say but really thinking about the perspective of a photon always is going to get you into trouble you know Niels Bohr was famously fond of saying that if you ask a question that refers to a quality of the world that it is impossible fundamentally impossible for you to ever access then you're likely to find that your attempt to understand it is going to hit a brick wall and that's this perspective of a photon you can talk about it you can poetically think about it but you can't ever access it and therefore when you head down that trajectory it's a dangerous one to take seriously our Yong Tiwari asked hey prof love the quantum series what is nothingness the probability of you seeing this is 1 522 1 in 526 right now apparently so look at that you've won the lottery yeah I'm sure you'd rather have won the real lottery over this one but so what is nothingness subtle question you wouldn't think so nothingness is the absence of stuff stop right we should stop right there but the problem is you have to carefully delineate which stuff you are imagining being absent sure if you imagine that material object you know like my contact lens box and you know my water bottle if all of that kind of stuff was gone you'd have a certain kind of nothingness you'd have emptiness empty space but space would still be there time would still be there and if you look really closely in the quantum description even the fluctuations of the fundamental fields would be there the electric field magnetic field all bubbling around in the quantum vacuum so that doesn't all of a sudden seemed like nothingness at all that seems like a whole lot of something it's just not the usual some things from everyday experience so then you want to go further and say can I really imagine a nothing that doesn't even have any space no time a true nothing and you can imagine that and it's something that imprints of all you can write down a mathematical formalism that would make use of you know it's a it's a spatial manifold if you'll read the size of the manifold they shrunk all the way to zero so the space-time itself has gone away it's not that it's shrunken within a environment which is itself got the qualities of space and time we're actually imagining all of space-time itself you know the cosmological solutions where you wind the film those guys are getting smaller and smaller and not in an existing realm but the realm itself is disappearing so you can approach the ideas of nothingness but it is a surprisingly subtle and curious idea if you want to have a full look at it we have a from time to time I do this just as I think it's interesting for you to look at things there is a World Science Festival program called what is nothingness or what is nothing or the meaning of nothing or something like that and it is the parsing of the conception of nothing from various distinct points of view and it's interesting to see how different ways of approaching that question yield different answers Amanda asks can you elaborate on the different types of infinities yes you know I should do a whole episode on your daily equation on the different kinds of infinities the two that are most prominent easy to understand are the infinity that we all use when we were kids you know 1 2 3 4 5 you know the various incarnations of that you know you you you you say something against and they say well I twice on you 3 times 4 you know you have this bickering going on and only if some one kid is always going to jump to infinity to try to win the argument and that's one type of infinity just counting the natural numbers 1 2 3 4 5 up to infinity but you can ask yourself how does that infinity compare to the infinity that also allows decimals and fractions point 1 2 4 1 3 9 7 5 9 and so on or PI you know that's a decimal 3.14159265 goes on I can't go any further than that many of you can beat me in that no doubt so the infinity of the counting numbers versus the infinities of the decimal numbers is an interesting question to ask yourself and you can prove that the Infinity associated with the counting numbers is a smaller infinity a small infant it's like a weird idea he'd say well infinities infinity right but you can ask yourself can you partner up all of the counting numbers with all of the decimal numbers so you say let me call one the number of point zero one two six let me call two point zero one two nine and so on you try to pair them up and you can prove that you will run out of the counting numbers and when you try to marry them in that pairwise fashion they'll be left over decimals that don't have a whole number partner in that kind of attempted pairing and the beautiful argument that comes from Cantor Cantor's diagonal argument and I'll do that in an episode at some point maybe if I find the time to do it I would love to do that but you should look that up because it's a very simple argument and kind of mind blowing Cantor tries to line up the whole numbers in the manner that I just said with the decimals and he's able to prove the existence of a decimal that will not be partnered with a whole number and therefore that the decimals have a larger cardinality a larger infinity than the counting numbers and they're various games further that you can play with this and get various levels of infinity very curious very puzzling idea but one that is very powerful and very interesting all right so what else do we have going on here yes thank you Brian DeGraw was the book quantum generations it was quantum generations that's exactly the book that I had in mind I haven't looked at it in a long time but I remember thinking that it did a very nice job on the history of quantum mechanics so we just crowd-sourced the answer I used up one of my lifelines to get Brian DeGraw to chime in with the correct answer to the question about a good book on the history of quantum mechanics oh thank you Steve Baggins hello greetings from Greece can you explain the function of the Z boson and sure when people were trying to understand the basic forces of nature obviously we knew about gravity for a long long time we knew about electricity and magnetism for a long time Maxwell and Faraday and others gave us a deeper description of electricity and magnetism that blended them into a unified whole called the electromagnetic force and in the early part well the middle part of the 20th century people began to go further to describe the nuclear forces not gravity not electricity not magnetism but the nuclear forces at work inside the nuclei of atoms for the most part and there is a force called the weak nuclear force that was discovered experimentally and understood theoretically in a handful of papers but ultimately the ones that won the Nobel Prize is the paper of glass sheldon glashow from 61 and the paper in 66 67 by abdus salam and another paper by Steven Weinberg and in this so-called electroweak theory we recognize that the weak nuclear force is transmitted not by one particle the way the electromagnetic force is so the electromagnetic force light is communicated by photons one type of particle the weak nuclear force is transmitted by three types of particles and those particles are called the W plus the W - and the Z 0 or the Z boson so what is the Z boson the Z boson is one of the three particles that transmits the weak nuclear force it is the only particle of the three that doesn't carry any electric charge so whereas the W plus plus charge W - negative charge they carry the weak force and also they have electric charge so the electromagnetic force right in there blended with them the Z is the weak nuclear force carrier that does not also carry the electromagnetic force the electric charge of it is zero thanks for that question from Greece so Mohit asks if we assume that the guiding wave is real for a quantum particle is it possible to not get the interference pattern when we don't see a flash in the photon and electron interacting somehow I understand the first half of the question I'm not fully appreciating the second half so I'll take a stab at it there's an episode in your daily equation it is the mystery episode episode 24 in episode 24 I discussed the approach to quantum mechanics called the Dubrow Bohm theory and at the very end of that episode I was rushing and it made one little mistake in an equation I wrote down none of you caught it but I was so uncomfortable with this little mistake I probably should have left it that I took the episode down and I was gonna redo it or fix it and haven't gotten around to doing it but this question is associated with that theory because in that theory in the debris Bohm theory it's not as in traditional quantum mechanics where we say you've got a particle or you have a wave right and you have both of those blend it in some strange manner but when you observe the entity using equipment that's sensitive to its particle qualities you only see the particle aspect of the wave and the particle aspect of the entity I should say and when you're using equipment that's sensitive to the wave-like qualities of the entity then you only see the wave-like qualities in the debris boom theory that's not the case it's not particle or wave it's particle and wave because the wave function in quantum mechanics the probability wave in quantum mechanics in the dubrow Bohm Theory it's a real thing it is the guiding wave in the language that Mohit is using so you've got particles moving around and you got these quantum way and the quantum way simply push the particle around and they push the particle around in an unusual manner a manner that the theory postulates and the manner that it pushes the particle around can yield and does yield the interference patterns of quantum double slit experiment so the double slit experiment in this approach is not described in the usual way of the wave for the particle goes through the two slits it overlaps yields an interference pattern and then when the wave hits the screen it turns into a particle because it's being detected by a detective it's sensitive to particles and that forces the wave-like nature to go away and the particle-like nature too appears a dot on the screen and that gives you the interference pattern in the debris bone theory you've got particles going right from the gun through the openings and hitting the detector screen and there are particles through and through through the entire journey in fact you can plot their entire trajectory it's not as though when you think about them as particles going through one slit or another the interference pattern disappears as it traditionally does in the usual story rather the wave the quantum wave also in addition to the particle goes through the two slits it interferes with itself giving the overlapping interference pattern and that particular wave configuration pushes the particles to accumulate where the wave is big and not to accumulate where the wave is small and that gives you the band like structure on the interference screen so it's a it's a cooler well not a cooler it's a more understandable explanation of the double slit experiment it's less mysterious than the usual explanation it allows particles to have positions and speeds it just augments the influences under which the particles are subject the influence of this new guiding wave comes into the story so you might say well why don't people talk about this theory that's an interesting sociological question I think the only physics part of it is this theory is manifestly non-local all right quantum entanglement has a non-local quality already but it's kind of hidden it's not in the mathematical formalism that you start with it kind of emerges later on that there can be B states that have these long-range correlations but the fundamental Schrodinger equation that you start with doesn't have any nonlocality in it in the dubrow Bohm theory the fundamental equation does have nonlocality in it from the get-go so the nonlocality is more in-your-face and that has troubled many people I don't really know why it's some deep level because if the theory has nonlocality in it who cares whether it's like in your face from the get-go or emerges downstream when you recognize that certain states exhibit non-local correlations be that as it may the Dubrow Bohm theory is hardly spoken of even though it allows you to still talk about particle trajectories and particle speeds and positions Wow quantum mechanics in which particles have positions and speeds easier in some sense to grok to understand to wrap your mind around and yet it has not caught on and is not something that people for the most part take seriously although there are some wonderful receipts researchers around the world who are developing the subject further and happened for decades and who knows how all play out maybe physics class is a hundred years from now we'll be focusing upon the Bohm dubrow theory because that one has been developed and that one wins out and I should say the Bohm Dubrow theory doesn't have a quantum measurement problem when you measure a particle you find it here it was here and is here it's not as though it was in all these other places and then it materialized they're responding to your observation no you don't need weirdness like that in the deployed Bohm Theory what you measure is what was there just like in the old Newtonian point of view so you might say wow it's a return to normalcy however because I have nonlocality and also the difficulty in making it a fully relativistic theory and the difficulty of making a quantum field theory a version of it and being a little bit quick when I don't list all the problems that the theory has but those challenges have kept it from gaining momentum in terms of the level of acceptance that people have of it as a viable approach to quantum mechanics anyway I hope I answered Mohit's question that was my best interpretation of what it what Mohit was asking professor green asks my zombie my zombie lick huh I'm not gonna parse that name program what new technology of physics development do you expect or hope to be released in the next 10 to 20 years um I don't know I'm not I'm not a futurist in that sense I don't really follow the technological trends but if you asked me where do I see spectacular rate of progress how can it not be in AI artificial intelligence in general artificial intelligence I mean I had a conversation just before this whole pandemic thing hit I was in London I had a conversation with demmas Hospice you know one of the folks who really has revolutionized the subject and it was just amazingly exciting to hear about the things that they're doing the possibilities of really for instance making progress on deep physics problems by having a system that can learn the patterns of reality by looking at the data and probably looking at earlier attempts to articulate the patterns in the data mathematically and then perhaps to be able to go further and suggest deeper insights that of today we have not yet our cells made Wow it's like an artificial physicist that's exciting you know and and the whole field of consciousness studies I think can radically change if we get to a point of artificially intelligent beings that seem to really have qualities that we have long thought to require a human brain I think these things are deeply exciting and and we're I just starting out in science right now I'd be quite tempted to work in these areas because it's not that physics has reached dead end everything that we're talking about it's hugely exciting but it's nice to be at the beginning we're not at the begin one maybe that's hubris I was gonna say we're not at the beginning of physics maybe we are but I would say that you know we've been at it let me put it this way there's a corpus there's a literature in physics that goes way back I don't know where you want to begin but let's say there's on the order of three hundred and fifty years of literature in physics there isn't that kind of long literature for artificial intelligence so it's exciting to be at the early stages to write the early papers that really set the agenda for the subject going forward so that that's my best answer I think to the question of exciting development in the next 10 to 20 years Nevaeh ball as Ken schrödinger's cat experiment be a proof of parallel universes well David Deutsch certainly would say so David Joyce I think many of you may know as a deeply insightful physicist philosopher written some spectacularly interesting books that I highly recommend I don't remember all titles but I think one was called the fabric of reality I remember that one because my own book fabric of the cosmos has kind of a similar title so people sometimes mix those up I think he has another book that I've not yet read I thumbed through that is something like the start of infinity or the beginning of infinity I don't recall but in the fabric of reality David Deutsch argues that the kinds of quantum interference processes the superposition that allows objects to occupy distinct quantum states simultaneously he argues that that really is proof of parallel universes that the many-worlds interpretation of quantum mechanics is the only way that picture of the world makes any sense I was not convinced by his argument I found it interesting but I don't by any means think that there's anything that we currently have in quantum mechanics that nails down the many-worlds approach as the only way of thinking about quantum reality some of my colleagues don't agree with me Sean Carroll some of you look at his stuff he's great his a new book something deeply hidden he argues and they are forcefully for the many-worlds approach and these are arguments that are worth taking seriously but it would be premature by a long shot to say that we have reached consensus that the many-worlds approach is the right approach to quantum mechanics there are many people perhaps they write less and are less publicly visible who are very adept at giving reasons why the many-worlds approach is yet to be established either mathematically or observational II so again like multiple universes not in the quantum sense but say in the inflation of cosmology sounds good to have these ideas at your disposal good to think about them but it's going to take much more than we currently have to establish that they are correct ok but if we got to going forward here by the what time is it oh it's a quarter to five it's sorry you certainly lose my boys um I see what we have somebody who have not asked a question before Joelle Jarvan N hello from Sweden hello Joelle Joelle in Sweden I spent a lot of fun time in Sweden I used to go there pays to go to Gothenburg I should go to Gothenburg basically every Christmas and every summer I would spend two to three months in Sweden every year when I was younger I loved the time that I spent there and once went up to the Lofoten Islands I know that I gave him the name pronunciation wrong in Norway that was a great time but anyway enough of that to the question thank you for the inspiration through my theoretical physics master studies my pleasure I'm curious do you think that there is an objective reality similar to a question we asked other can't did but I don't because how would you prove it well yeah so this is a different take on the earlier question that we addressed and look it's it's absolutely the case that we only have access to the purported objective reality through a subjective experience right I mean I look around the world and I imagine that I'm seeing objective entities that are really there you know the ceiling my laptop this display my bottle of water but in reality you and I both know that this bottle of water or this yellow right what is this yellow is this yellow here no no it's deeply in here right there are the photons entering my eye tickling my retina sending a signal into my brain and my brain because of its evolutionary development has become adept at deciphering the signal that my eye is receiving and saying oh yellow even projects it out into the world I I don't I don't see the yellow in my brain I see the yellow out there even though all this crackling this cascading of particles is happening inside my head so all I have access to is the crackling of those particles and in fact I don't even have access to that I can't see the particles coursing through my brain I I'm only able to access the aftermath of those processes how I do that I don't know neither do you neither does anybody how is it that I have this inner experience how is it that I have this world inside my head that evolution has led me to believe is out there even though my experience is just inside so I agree you can't ever prove anything about the objectiveness of those kinds of subjective experiences however there comes a point as a physicist where you put those possibilities you say there's a real possibility that it's all inside my head I mean I'm gonna put it to the side and I'm gonna imagine that there is an objective world and I'm gonna do all that I can to try to explain it mathematically and that's what you do so it's a very pragmatic perspective my language in my books and my language here speaks as though there is this objective world my attitude is that I am working on physics to explain that objective world but you're right in that I only have subjective capacities to engage with whatever that objective world is even if it doesn't exist so so you're right we find ourselves an interesting conundrum but from a flat-footed physics perspective I allow for that possibility I jump it over here and then I say it is useful it is useful for me to imagine that there is an objective world it's useful free to imagine that my investigations are trying to find the patterns in that objective world and then I simply admit the fact that my only means of accessing that objective world is through subjective experience and I leave it at that just because there's not much more I can do with that observation besides marveling at it and then going forward so feel free to answer back on that if that didn't address it enough I'm happy to go further if there's anything more specific that you can guide me toward yah teach agro wall hello dr. Greene love the way you explain physics thank you yeah teach the strings in string theory are said to be made of pure energy so what is that energy is it tangible yes right so tough question and you know as I've described earlier even explaining what energy is in any fundamental sense is a challenge you go to a physics one textbook and physics one textbook says usually energy is the ability to do work it's the ability to move something through a distance right it's with energy that we're able to cause those processes to take place but that's not really telling you what energy is is telling you sort of what energy does you know if you're asking like I just want to know what it is you know what is it made of something you know does it originate from something more fundamental I mean these are tough tough questions but the way that I like to think about it is this even though I don't really know what energy is I know that the universe has it I know that the universe is able to have particles and objects move through distances so so the universe has some energy and then if string theory is correct I would say that the strings in string theory are the most fundamental carriers of the energy of the universe again regardless of what that energy is where it comes from I can't answer questions like that unfortunately but if string theory is correct think of the strings as the most fundamental carriers of the energy that the universe has and how do they carry that energy they carry it through their motion through their vibration through their intrinsic heft perhaps and so in this way the strings in string theory are the most fundamental currency of the energy budget that the universe has okay what else here hmm bonnie asks try a Brita water bottle okay I will try therefore for next time thank you for that suggestion okay what else should we talk about here Nikita asks - Belarus does knowing math behind physics concepts help you to imagine the physics concept for example could you imagine the fourth dimension knowing its math or would you have trouble without knowing the math and without a doubt the answer to that question is yes so the way I go about envisioning things in physics that I understand mathematically I don't understand everything of course but the things that I understand mathematically I use that math to tell me a parallel story to the visual version that I build up based upon the mathematical understanding so for instance when I'm thinking about the fabric of space ripping to give one example that I had a good time participating in the discovery years ago in order to have a mental image of the fabric of space tearing I have the mathematics right here I have the mathematics of these three-dimensional spheres shrinking down small size and I understand what that means in the equations and then I see this this field a Higgs like field changing its expectation value as I go through the singularity classically created by the shrunken three sphere and as it does that the Higgs field blows up these other two dimensional sphere I can see all that happening in one part of my brain because I can run the mathematical progression in the other part of my brain I'm not talking left right stuff here I'm just talking about the kinds of things that you have in mind and so I'm constantly using the mathematical description to inform my visualization and without that I'd have a lot of trouble and I've often said that I wonder how science the good science writers how they do it maybe they have enough of the background that they also have a mathematical understanding but if you don't have a math understanding I would have a lot of trouble writing about any of these are talking about any of these ideas because if I had knowledge that was already digested into a non mathematical form how would I know if that digested version was leaving out critical things or if my version of the digested version was now taking it in a direction that made it inaccurate or false so I always need to go back to first principles the mathematical understanding have that as my overarching rubric within which I can develop visualizations or everyday language descriptions constantly checking it against the mass and if I violate the math I am in a position to say okay that metaphor that image it violates the math but that's okay that's not a vital part of the story I'm willing to bend the rules there but if I didn't know the math how would I ever judge whether a metaphor or an image was too far away from the actual description to be worthy of articulating so so the answer Nikita is absolutely yes and and to imagine the fourth dimension well look I can imagine the fourth dimension again mathematically can I really turn that into pictures tough I can sort of turn it into three-dimensional pictures but so can anybody so I'd say that just because you have the math doesn't mean you'll have a visualization but if you do have the math it will allow your visualizations to be much more sharply configured okay so what do we got what is the idea behind quantum computers that's a that's a good one and well there are a lot of ideas behind quantum computers but I think the question is what's exactly quantum in a quantum computer because you have a computer on your desk right now or in your pocket your phone's a computer and it relies upon quantum ideas the building of those integrated circuits required quantum mechanics to be able to move electrons on sufficiently precise trajectories to carry out the processes that we want those particular chips to achieve so since quantum mechanics is already part of the story what is a quantum computer well a quantum computer is one that doesn't just use quantum mechanics in the technology per se it actually uses quantum mechanics in the calculations an everyday ordinary computer may have quantum devices within it but it's carrying out classical computations we want to carry out quantum computations because and here's where the many-worlds approach metaphor or real I'm not going to commit one way or another is helpful to think about things if you're able to do a calculation in many worlds simultaneously you could break it up you could have parts of the computation take place in different universes and if you were then able to extract from those many worlds the answer that you were looking for you'd have sped up the computation by splitting it up among these different realities now whether or not those many worlds are real or whether this is just a way of figuratively talking about the mathematical process doesn't matter for the conclusion that you can draw which is that certain calculations can be done much more quickly in the quantum realm because of this divide and conquer if you will approach and people are getting to the point where quantum computing is real and that's that's hugely exciting and so we'll see where this takes us now I should say it's not as though any calculation is a to this huge speed-up that quantum computation process promises there are some calculations that we know how to break them up the algorithm necessary for a quantum computer to win by a huge margin over a classical computer but there are other processes other calculations that we don't really have an algorithm in order to program a quantum computer to do that calculation and to be assured that the quantum version will be lickety-split compared to the classical version so it's not that you should think that once quantum computers are ubiquitous that every calculation will be sped up exponential but some will and some important ones will and who knows as we go forward people may become better adept at using the quantum environment to speed up calculations that today we don't know how to speed up so all hugely exciting all definitely very exciting ok [Music] so I'm gonna ask Ariana's question because I know I had one before but what does it dimension also love that beard so are you mentioned this that what beard I'm cleanly shaken I think maybe it's the lighting or somethin no no or maybe you talk about my birthmark right over here on the side of my face which like when I usually do television I got makeup on to cover but I'm out here just a completely natural if you will so Ariane I'm curious what beard you're talking about but in any event what is a dimension is a damn good question and a dimension is any independent direction a spacial dimension let me do first is any independent direction in which motion is possible so in our world we all know that motion is possible in three independent directions I can go this way back and forth I can go left and right and I can go up and down of course I can also go at an angle but you know if you go to an angle that's just a combination of moving left and right and then moving a little bit back and forth and then a little up and down so an angle is not an independent direction it's a combination of this this and that now when we talk about extra dimensions of space we really mean that there are new independent directions in which you in principle could move that you cannot access by some combination of left-right back-forth up-down that's a curious idea and that's what string theory demands a handful of extra directions that in principle if you were say small enough you'd be able to move that you simply cannot access through the known three dimensions of left-right back-forth and up-down so I've answered your question Ari and I'm curious for you to answer my question but no need if you uh if you don't want to so quantum jump says I hope all our friends from India are well after the cyclone I was not I've not been following the news was there big cyclone I'm sorry to hear that and I as well I agree hope everyone's ok so whose go sorry I had to finance it well life always in other universes after our University so I guess the question will there always be life in other universes after our universe dies and and look number one we don't know if there are the universes big part of my answer to this question but if there are other universes it depends what kind of multiverse we're talking about if we're talking about the many worlds of quantum mechanics then there's something interesting happening because if that is correct and there really are these other worlds in which the quantum probability is sort of branch off and other outcomes of given processes take place then you can argue pretty convincingly that there's a nonzero probability that life can continue indefinitely and if there's a nonzero probability for that it's not as though quantum mechanics has within it a rule that says there's a zero probability that life will persist beyond a certain timescale I'm not aware of any such statement within the laws of quantum mechanics and that being the case if every possible outcome takes place in some universe then however improbable the nearly or literally infinite longevity of life might be there's going to be some realm where that nearly zero probabilistic outcome is realized and that would suggest that life could persist arbitrarily far into the future in some other universe but again it's a funny I saw something somebody mentioned something that I took solace in that and I don't really it's just not true at all for instance in my book until the end of time I spent in virtually no time on the multiverse I was focused and I am focused in that book on how to make sense of the finite nature of life and the finite nature of consciousness in this universe even though the time skills may be large and seemingly abstract my focus is trying to make sense of this reality subjective objective however we want to describe it so it's fun to talk about the possibility of life in other parallel realms but for the serious questions I was asking in the book until the end of time I don't think there's a whole lot of insight that the multiverse provides Ariane says is my attempt at a joke okay sorry I didn't get the joke apologies I must be thick as I don't know what the joke is but in any event viewer asks what is the opposite of entropy and could that have been in place before the Big Bang well entropy is not something that I've yet really spoken about which is kind of surprising because that's where my head has been for a while now when you're talking about the unfolding of the cosmos over arbitrarily long timescales the second law of thermodynamics and the relentless increase in entropy is an essential guiding principle and yet we haven't spoken much about it so what is entropy entropy is a measure in colloquial terms of the amount of disorder in a system but that sounds very subjective what I really mean by that what I mean by that is take any physical system and ask yourself how many ways could have rearranged the fundamental ingredients and Nan have an impact on the macroscopic presentation the look of that system and you know if you have a very ordered system if you rearrange its ingredients it becomes disordered out of order it will recognizably be different in therefore there very few rearrangements an entropy is the count of the number of rearrangements so if something is very ordered the count is very small the entropy is low in a disordered environment like the air in this room right now the particles are rearranging their configuration all the time and yet as I look around I don't notice the difference I don't sense a difference macroscopically has the same properties and therefore the air in this room or your room has a relatively high entropy because there are a huge number of rearrangements of the molecules of air that leave your environment seemingly unchanged entropy is a count of those rearrangements entropy therefore is high for that circumstance now the question was not not only what is entropy but what's the opposite of entropy and if you think about entropy is disorder the opposite is order and therefore the question is could that have been in place before the Big Bang the answer is yes I don't know about the before part but at the Big Bang our best description of the universe imagines that the Big Bang was highly ordered very low entropy and we have been living through the aftermath of that low entropy beginning ever since entropy has been rising steadily in some sense since the Big Bang we are a part way along that trajectory we are highly ordered beings existing within an environment headed toward ever greater disorder the fact that we're here relies on the low entropy starting point because if the universe had a high entropy beginning it would have been disordered at the beginning and disordered all the way through and there'd be no opportunity for ordered structures like you and me to form so the answer is yes it's called the past hypothesis the past hypothesis as its name indicates hypothesizes does improve and i pathi sighs is that the big main the earliest moment of our observable universe had high order had low entropy exactly as you viewer as your name seems to be as I see here have suggested so absolutely right so Christopher says hello why do black holes have different masses and sizes when all of them consist of an infinitely dense singularity yeah that's some a quite natural question and I am going to I do have some more water under here so as you watch me pour I'll start my answer or you probably can't see me pour out of this source here but you'll see the aftermath of that and yes you might say look if a black holes nothing but this dense thing in the middle if that thing in the middle has infinite density then it would seem like all black holes should be the same they all have the same infinitely dense core and number one we don't know what happens at the core of a black hole let's put that out there right now you often think about the core of a black hole as a position in space where all the stuff that fell in is sort of compacted together but that's kind of the wrong image the center of a black hole is more like a moment in time as opposed to a position in space which is one of the subtlety x' that have to do with black holes but the idea is the Infinity that you have in mind that is a misleading number infinity in that setting really is one of those singularities which I said before is the diagnostic that tells us we don't know what's going on so don't think about the infinitely dense core as defining the black hole think about the stuff that fell into the black hole as defining it think about the entire mass of the stuff that fell in as defining moreover if you have a black hole already and more stuff falls in then that increase in mass makes the event horizon larger so the more stuff that goes in the bigger the physical size of the black hole in the sense of the distance to its event horizon the larger that size becomes so the history of the black hole is vital to understanding why it looks the way it does and if you have two black holes where less stuff has fallen into this one and more stuff is falling into that one let's say it began the same lesson here and more and this means this will grow but not as much as this one will have grown this won't be much bigger than that one so from far away we're sensitive to the total mass that's fallen into the black hole that gives a measure of the total gravitational pull exerted by the black hole or the total curvature in the space-time environment created by the black hole but you need to know the history because the size to the event horizon and the gravitational pull that the black hole exerts on something far away is determined by the total mass that falls in even if in both cases the masses gets crushed down to a very small size okay [Music] uh nazma asks why was bicep 2 proven wrong why was bicep 2 proven wrong you maybe call that bicep 2 was this experiment down at the South Pole that reported this very exciting observation of what they believed was the imprint of ripples in the fabric of space coming from the Big Bang itself primordial gravitational waves leaving an imprint on the cosmic microwave background radiation that would be hugely exciting that would be using observational tools to gain fairly direct insight into the Big Bang itself in fact as inflationary cosmology what we did in episode 30 predicts the possibility of these primordial gravitational waves when bicep2 made that announcement there was great excitement in the inflationary cosmology community you may recall there was a video of Andrei Linde a one of the founding physicists of inflationary cosmology someone came to his house with champagne to inform him of this observational result and so great excitement what turned out to be the case however is that the bicep2 team how to describe it some would say they jumped the gun some would say that it's just part of scientific progression whatever but the excitement that their paper initially generated turned out to be premature because analysis of the data showed that dust dust in the Milky Way galaxy can yield the same kind of signature that they may have mistook for primordial gravitational waves I say may have because the writers of that paper they argue that they never said that the data proved the existence of primordial gravitational waves they were just reporting on their observations some reading their paper interpreted what they were saying quite differently so there's been some argument in the community about this but it's not worth read litigating that issue at all if you're interested again there's a nice World Science Festival program on that with some of the you know prime with some of the founding physicists of inflation together with the bicep team and so and so you can take a look at that but the bottom line answer to the science question is dust in the Milky Way galaxy affected the signal in a way that mimicked what you would expect from primordial gravitational waves dust in the Milky Way not so interesting primordial gravitational waves hugely interesting unfortunately it turned out that the dust explanation is the right one that's what happens sometimes you know you think that you've got a big discovery you're so excited your hearts in the right place you want to get the information out there you want people to know about this maybe even thinking nobel-prize you know it's all very human understandable but it turned out that that data was not supporting the idea of primordial gravitational waves so narendra asks what would happen to entangled particles if one of them falls into a black hole with the entanglement still hold and if yes can there be any interaction possible between them so narendra you're asking a question that has puzzled people over the past few years in a significant way if you would have asked that question twenty years ago say the answer was pretty clear because in Einstein's theory classical theory of the general theory of relativity the edge of a black hole the event horizon is not a special location in space there's no signpost that says black hole event horizon do not pass if you want to be able to get out there's nothing like that the location in space that we would mathematically recognize as the event horizon of a black hole is an ordinary region of space with no distinguishing characteristics locally so if you fall over the edge of a black hole you don't know that you've fallen over an edge you're just moving through space just as we're moving through space right now and because of that the perspective was that if you have two entangled particles and one goes over the edge of a black hole they're still entangled there's nothing that happens at the horizon that would cut the entanglement it's after all this empty space what's changed in recent years is people thought about this much more carefully and realized that if the entanglement persists across the edge of a black hole it raises certain puzzles it raises puzzles for the conservation of information that we believe happens with the radiation that leaks out of a black hole requiring entanglement of a different sort that winds up being conflict with the entanglement right across the edge of a black hole this is led some to suggest the edge of a black hole might actually be special quantum mechanically it may be special classically it's not but maybe this quantum mechanically and some have suggested that maybe the edge of a black hole is a firewall nice image firewall what does it mean well it would be a quality of space that basically snaps entanglement if the thread of quantum entanglement is broken at the edge of a black hole energy in some sense is released that energy would power a firewall so your questions potent because if entanglement is snapped then the edge of a black hole is very different from what we would have thought based on Einstein's theory and people debate this idea of a firewall there are others who have even more exotic ideas my friends Sameer Mathur at Ohio State University has developed over the course of many years now the fuzz ball picture of black holes where black holes are more or less like stars in a somewhat exotic state of vibrating strings but there is no event horizon there is no edge in new way that we usually think about it in the classical theory of general relativity so these are these requests and of course obviously entanglement would have different quantities across that because now there's stuff the fuzzy stuff at the edge of a black hole so the bottom line is I'm not sure the answer to your question nobody is it's debated today but it's an important one for us to ultimately resolve okay um what do we got here guy atre asks do I think there's another possible unified theory other than string theory of absolutely possible I am NOT dogmatic about string theory string theory could easily be irrelevant and that hopefully is something that we'll know I'd love to know the answer to that in my own lifetime having spent decades working on the theory itself and only experiment only observation can tell us that and if string theory is irrelevant does that mean the unification program is over now we'll continue to think about it our descendants hopefully will continue to think about it and other ideas will be put forward other unification schemes will be pursued so so I again I just I really want to stress that point I am interested in the truth I'm not interested in string theory being that truth in a sense of it blinding me to truths that might not be string theory at ik I just want us to make progress and if string theory is part of that great that would be happy I've spent my life working on this as of my colleagues around the world how cool that the things that we're doing are part of the stepping stone to the deeper understanding yes I'd love that but that's not the case that that's cool too it was not the case we can throw string theory away in that way we would have made progress not by having the right theory but by discarding the wrong theory and that is a certain kind of progress - maybe less exciting but in the end we're part of a long ongoing journey and we're not going to answer it in our lifetime so that may be the best that we can hope for okay mm-hmm so I had a question and I touched it and it went by uh uh what do we got okay Abbas safar is just try to imagine what space is even if it seems too hard for you if you manage that then you will stop making things up and see reality like the fish that realizes living in water and and I I have sympathy with that comment it is difficult to recognize the ubiquitous qualities of the reality you inhabit it's difficult for the fish to recognize that it's in water if it's never out of water it has nothing to compare that experience with so you begin to become unable to access qualities of reality that are so central that they're always with you now when it comes to space our intuition is moulded by thinking about things in space I mean it's very hard for us to think about taking away space the way we can think about taking away water for the fish but the nice thing is there are mathematical models which do take away space which do allow us to develop our intuition for at least the possibility of removing space so if a fish were able to do that you know an Einstein fish what would you call that fish Stein I don't know so if there's a fish Stein really brilliant physicist I think that's Lenny Susskind's combination there so if fish Stein is this brilliant physicist and comes up with this theory that allows you to imagine a reality for the fish world that doesn't have water it would open their minds and we kind of done the same thing in the world with space but that doesn't mean our theories about space are the be-all end-all that they're the the final description but we've taken your comment to heart and we do try to imagine a reality and a mathematical description of that reality that does not rely upon a pre-existing environment so what what fish Stein did for the fish assists some in our world have done for us let's see what else sobani says I think the great professor is losing it lol I hope I'm not maybe that was a little too off to defend in that description let's see what we got some good questions coming through in the Indies bike is gravity in another dimension and I think the answer to that question is yes well let me qualify it no let me just I'll be quite general I think the answer to that is yes our understanding of gravity as you may have noted from the episode I did 9 science general relativity is that gravity's associated with the geometry of space-time the warps and curves in colloquial language and in that sense once you realize that there's this intimate association between space-time itself and gravity gravity is nothing but the geometry of space-time then you realize that if space-time has more dimensions than the ones that we know about then gravity will be in those dimensions too so that's the sense in which gravity is a universal quality of reality at least reality that is in a phase that has space and time because the geometry of that environment the geometry of the whole environment including all the dimensions is really what we mean by gravity and that gives rise to some interesting implications because the other forces the electromagnetic force and nuclear forces they're not as universal they're not associated with the warpage of space-time and therefore you can find yourself in at least a theoretical possibility that the electromagnetic and the nuclear forces might be confined to certain regions of space-time whereas gravity extends throughout all of them and there are theories that have made use of that idea you may have heard about the brain World Series brain as in B ra and E not be RAIM and those theories imagine that we live on a membrane a three-dimensional membrane hard to picture but using two-dimensional version it'll be just as good imagine that we lived on a kind of two-dimensional membrane floating within a higher dimensional space-time environment that means that everything that we know about would exist on this membrane so gravity extending through all the dimensions we would have some of it because we after all are part of that space-time expanse but the electromagnetic force might only live on our slice the nuclear forces might only live in our slice and that disjuncture between where the forces live in principle can give rise to some very interesting theories that people have developed so yes is the short answer to that question um five-thirty we're getting on time here although my wife has not asked me about dinner and the kids have not yet so I don't know I guess I'll talk a little bit more um Krishna I'm sorry Krishna Krishna evolved is it possible that you would give a course on general relativity like you did for special relativity and um I would love to and you know of late I think because people are at home more is my guess I've had more and more people encouraging me to do that I'd liked I love doing the special relativity course and again I've already mentioned it once before but I got a mention again so Josh Zimmerman did all the visuals for that course and you know there are hundreds hundreds of animations in the special relativity course because I wanted it to be deeply visual I think that's really really understand things but as you can imagine it takes a long time to create those visuals so to do such a course for the general theory of relativity would require developing a whole new set of visuals and it just takes a lot of time it takes a lot of money right time and money are intricately interwoven so we'd have to raise money to do that we'd have to find the time to do it but I am thinking that with this with this lockdown if this happens periodically I hope it doesn't but if it happens periodically and I find myself here we're thinking of setting up a little studio here that would allow me to make headway on those kinds of projects when I'm restrained from working on other things that would require the world to be more opened up so so that maybe a small silver or a tiny silver lining I don't mean to frame it that way in fact let me take that back I'm gonna frame it that way at all that may be one of the things that I'm able to make headway on going forward and I'd love to do it so so keep an eye out again I mentioned world science-u is relaunching in a week or two or three I'm not sure what the answer to that is exactly when but keep your eyes out for it the special relativity will be there as will the master classes and some other additional content as well but you know you should sign up look you should sign up to world science festivals YouTube thing right I think it's my pointing at the right spot I don't think it's some place over here I'm guessing right now because that's where you can really be kept aware of everything that we're doing world science you also has its own YouTube page we don't use it as much you might want to sign up to that but yes it's conceivable that'll do a general relativity course I'd also like to do a quantum mechanic course those are the two other ones that it really really would love to bring out to the world in a visual and mathematical way to try to make these ideas as clear as possible you know from my from my perspective so I hope so I hope so but you know life is short and you have to make decisions on what to do especially on a kind of monster project like creating a full general relativity or quantum mechanics course okay what else have we got uh well there's a question that keeps coming up and a better answer it because it will keep come so Danny smile how can a gravitational field escape a black hole so I'm going to answer your question Danny so you can stop asking it I've seen it like a thousand times written by and so I would say that a gravitational doesn't escape a black hole per se rather what we learned from Einstein is that the environment around a massive body responds to the mass energy of that body and a black hole has mass energy think about all the stuff that fell in so that mass energy of the black hole is influencing the environment of the black hole and that's what Einstein tells us it's not that if I have an object gravity is escaping it it's not the gravity's escaping the earth in in in the sense that I think that you have in mind it's rather that the earth is impacting its environment in a manner dictated by the Einstein field equations so when you write down the Einstein field equations for the say Schwarzschild solution that solution solves the equations of Einstein outside a spherical body like the earth it doesn't you can go further and talk about the interior of the earth but to understand the gravitational field that the earth creates in its environment I mean you never talk about Einstein's equations inside the earth again not that you can you can and you can connect the solutions together and so forth but if you want to know what's happening outside the earth Einstein allows you to solve his equations outside the boundary of the earth similarly for a black hole if you want to understand the gravitational environment that a black hole creates exterior to itself usov Einstein's equations in the exterior realm you don't have to talk about anything crossing the event horizon of the black hole okay I hope that gives some insight in there so rigid and says by professor I got to go to sleep now take care and stay safe good night sweet dreams vision thanks for joining us josè as if gravity isn't a force yr gravitons necessary and what you're mixing in that question are two descriptions of gravity in the classical description of gravity of Newton the gravitational description involves something called the force of gravity F equals G m1 m2 over R squared the force of gravity Einstein comes along and changes the description a little bit gravity well not a little bit a lot of it gravity is associated to the geometry of the environment that a body creates so now it's even a slightly different language it's warps and curves and objects traveling along geodesics hey I never did the geodesic equation but the third description in terms of gravitons is a quantum mechanical description Newton and Einstein are both classical descriptions in the quantum mechanical description we do envision that gravity is communicated from place to place in much the same way that electromagnetism is communicated from place to place electromagnetism photons carry the electromagnetic force we believe but we've never detected but we believe a refined theory suggests that gravity quantum mechanically is communicated by gravitons spin to massless particles whereas a photon is a spin one massless particle and that's the natural quantum mechanical language and all of these languages are useful and you need to apply whatever language is most relevant to the kinds of questions that you are asking if you want to know about the bending of starlight by the Sun use the general theory of relativity the curved trajectory is the one that observations confirm if you want to launch a rocket ship to the moon use Newton's description of the force of gravity good enough and easier to use to plot the trajectory to the moon if you want to understand the gravitational interaction between two electrons as they scatter off of each other then you want to use the quantum mechanical description of gravity with gravitons going back and forth between the electrons that's something that string theory in principle provides us and that's controversial because not everyone believes it's drink there is the right quantum theory of gravity but that's the kind of question in which quantum theory of gravity would be a useful way of talking about the process also clearly talking about the big bang in the center of black holes those are extreme realms where you need quantum mechanics and you need gravity if we you need a quantum mechanical description okay hmm few more and then we will I guess wrap it up let's see t bald well people differ of a screen I hope you're doing okay I am I apologize for frequently asking the same question no problem I was joking but why is having a unified theory so important and tabled I would tell you that there are some people who do not think it's important to have a unified theory Freeman Dyson who I hope you know that name he is one of the influential physicists from the middle and late years of the middle you know 50 60 70 s 80s 19 20th century of course played a vital role in the development of quantum electrodynamics has a lot of creative ideas the Dyson Sphere you heard about that you know this way of captious of future civilization capturing all the energy coming out from its star Earth only captures a little part of the sun's energy but if you had the earth part of a sphere that would not allow any of the energy of the Sun to escape into space that would be a much more efficient way to go forward anyway so Freeman Dyson series guy does not think that a unified theory is really necessary he has suggested that maybe you used relativity when gravity is the dominant influence you know four stars and galaxies use quantum mechanics when you're way down at the small scale of particles electrons neutrinos and things of that sort and he says maybe the blending of quantum mechanics and general relativity into one unified whole is not only unnecessary it doesn't exist just wrong for instance he would even suggest that the notion of a graviton might be wrong you know and because that comes from blending quantum mechanics and general relativity and and Dyson may have been right in that perspective I don't agree with that I think most physicists do not when I think about the deep interior of a black hole or the moment of the Big Bang I know that our equations break down because they lack the ability to deal with those extremes of high energy high mass and small size and it would seem that a quantum mechanical theory of gravity would be able to handle those situations so that's why we're driven to find this unified theory this quantum mechanical description of gravity blending the large and the small because we really want to understand the moment of the Big Bang we really want to understand the singularities which I've discussed already today inside of a black hole but does that mean that such a unified description exists maybe not maybe there's another way to understand these extreme realms it doesn't unify gravity and quantum mechanics as Steven Weinberg has emphasized on number of occasions the universe is under no obligation to please theoretical physicists we theoretical physicists who imagine in the guise of Einstein using the same perspective that he had that there's got to be a single framework that blends all of the disparate disparate explanations of the world emerging from physics puts them all together into one unified whole we believe that that should exist we feel that it should exist we have an aesthetic drive to put it all together into a single unified package but just because we want it doesn't mean it's real and maybe one day we will recognize that this drive toward unity was misguided that there was another way of understanding these extreme realms of the Big Bang and black holes and it had nothing to do with unification is that possible yeah definitely possible are we ready to give up on unification no not at all so size says Weinberg is an atheist brilliant guy much more than Dyson well I don't want to compare Weinberg and Dyson Weinberg is an atheist may or is he an agnostic I don't know who cares it's a nice observation I'm not sure why you're telling us but thank you okay what else [Music] I am asks where do quantum and classical gravity need to be blended and that's basically what I was mentioning before you really do need to blend them in realms that are outside the domain of Newton's or Einstein's description and Newton's and Einstein's description are unable to accurately describe what happens when the masses are really big and the sizes are really small so any situation where the mass gets too big or the size gets too small is one in which quantum mechanics and general relativity need to be brought together and it's really the conjunction of the two a lot of mass in a small size a lot of mass gravity small size quantum if that's your situation you need them both gravity and the quantum you need quantum gravity that's the way to that's at least one way to think about it okay an almshouse could there be a fifth fundamental force absolutely absolutely in fact there has been chatter of late about data suggesting another force I don't know where that stands at the moment and in the past such chatter has gone away but even in a theory like string theory I should say in string theory there are many more than four fundamental forces the other forces in string theory often only emerge at very very high energies well beyond the reach of today's accelerators or even any conceivable accelerator that our species is going to build but you should know that fundamentally within the mathematical structure of certain approaches to string theory there are all sorts of other forces they just aren't relevant at the low energy environment that we inhabit but they're there in the equations so an emphatic yes to the possibility of a fifth force all right what 5:44 I'd like to break our previous right have we broken any previous records what was her what's the longest we've ever done on this Q&A I don't know the answer to that maybe someone maybe someone does but I'm gonna go a little bit longer as long as there's no tornadoes today nice day out here and you know when I when I finished this session I've got to immediately start cooking I don't I'm not in the mood to start cooking right now so I'm procrastinating on making tonight's dinner all right you're not all that interested in that nonsense so let me get back to physics Reverend Jonathan Barlow he asks Brian can tachyons faster-than-light particles actually be the force carrying particles of gravity the answer to that is no the force carrying particle for gravity really means to be a massless spin-2 particle if you look at tachyons they're particles that actually have imaginary mass traveling faster than the speed of light and they yield all sorts of issues of consistency that you know you can stand on your head and maybe make them work but most physicists do not take tachyons too seriously but most physicists do take the force of gravity mm-hmm and gravitons quite seriously all right um let's see multiplier fan is saying how are you and if that's to me or to the group I'm doing well I'm having a little bit of sore throat issues as you can tell but let's see I am says break some records all right I think we're on the verge of that Alexandra Kara Raymond ask is it tofu again I eat a lot of tofu yeah I'm pretty sure it's tofu tonight we are solo and are in our food stocks right now that tofu I think it's the only thing that is left what will it be it will be tofu and homemade black bean sauce a little bit of rice probably maybe a little bit of cold sesame noodles with it too and my son loves those so the record was 2 hours in 44 minutes we have now smashed that I think with 2 hours and 46 minutes but Farah asks what do you think of the serious genius and I've only I only saw the first episode we're not episode I guess by genius you mean that series I think that had Einstein like the 10 part series I only saw the first episode of that first incarnation of genius and I thought it was as a film really well done it was captivating it focused more obviously an Einstein the man you know the opening scene Wow Jesus Einstein the man as opposed to Einstein the scientist and I think people find that quite interesting I found it a nice contrast to the approach that we took in our PBS special the one that I've mentioned from time to time you know like Falls the live stage work that we had it was broadcast nationally in the United States I don't think it's been broadcast anywhere else in the world we have to work on that I'd like it to be broadcast elsewhere but that focus much more on Einstein the scientist and that's the story look I think all the stories are interesting but the one that really captures me obviously as a physicist is how radically changed the world one one guy in the span of a single lifetime change so much of our thinking and to me that's the inspirational story and yeah I'd love to know more about Einstein the person and that's good but for my taste it's really Einstein the scientist that really gets me gets me fired up so junus yo you nice ask did Einstein's wife wife helped him with the math that was that was something that was said by people during a period of time that Mileva Maric I'm not sure how to pronounce her last name so it correct me on that that's how it's spelled that maleva helplines dying with the mathematics now I believe it was she was good apparently she was a fine physicist did well in school there's no evidence that she had the genius capacity of Einstein and I'm pretty sure that subsequent research has debunked the idea that she was really the force behind Einsteins discovery in special relativity there's really no evidence as far as I know for that story obviously it's a would be an interesting story it would be a romantic story it'd be like that film was it called the wife was that the film in which the wife of the the writer who won the Nobel laureate Nobel Prize in Literature she actually wrote all the books it was it called the wife Helena may have been or maybe I'm talking about the wrong film somebody tell me if I've got that right but that would be the story of course in this case maybe that rumor of malaya was the inspiration for that film I don't know but there's no evidence as far as I know that malade was behind the mask that allowed Einstein to come forward with special theory of relativity marriage someone to expect 11 marriage thank you I don't know okay thank you I trust you more than I trust me diem are there any theories about what the singularity that may have existed before the Big Bang was and there are many theories we've discussed some of them here on various occasions there are bouncing cosmologies where we are living in the aftermath of one cycle in what might be an infinitely long progression of cycle after cycle expansion contraction bounce expansion contraction so the Big Bang singularity may have just been a moment between the previous period of contraction and the subsequent period of expansion that's one possibility there are other theories even in string theory there's an idea that people worked on one of the founders of string theory Gabriele Veneziano worked on a pre Big Bang scenario for a number of years in which the universe would have in some sense begun big in the infinite past and then it in some sense the right frame of reference it would have collapsed down and then not bouncing in the sense of going over and over again but it would have had a prehistory our development would have had a prehistory in the far past so so people do write down theories they develop these ideas they try to analyze the singularity try to make sense of the Big Bang and some theories claim that they have there's no consensus though that any of these description are the right one Pryor goes to the freewill question I'm gonna put that off prior if you don't mind I've answered it before it's in chapter 5 of my book again I'm not asking you to buy it get a bootleg copy read it that really captures with precision my perspective on freewill and again as I mentioned before anybody wants to take my class I wish I could offer it for free maybe there's a way to audit it for free some are taking it for credit it starts next Tuesday Tuesdays and Thursdays from 6 p.m. to 9 p.m. and maybe too late for some of you guys who are in other countries but I'll be talking about that in detail there as well and again it's not that I don't want to talk about here it's just that it's it's 8 to 6 it's almost 6 o'clock and I think it'll take us too far down that rabbit hole that's the only this is a good question to end on it just went by where'd it go I don't know there's some question about an ultimate truth I liked it but now it went by too fast see if I can find it again trying to find it I can't seem to find it whatever I guess I'll move on looking for the question this isn't the final one do I know Robert Lawrence kun kun I do he I've been at conferences with him he's a good guy I'm really curious about deep questions I like him on what his m-theory sort of already did the hem theory so string theory on steroids string theory done with a greater degree of mathematical precision that's really what it is sir Brian just a bunked the board good for Lincoln theorem no no no no no that's not the board Guth of Lincoln theorem tells us that if you if you're gonna follow any trajectory far back you're going to encounter a singularity but but it's not that every trajectory it's that singularity on the same singular surface so you can have trajectories that go farther and farther back and again that's only in the context of the assumptions made in that theorem so no that is not my point let's see oh here's one so Sameer cut cut cut cut cut car sorry is there one single ultimate truth what is your opinion I think I'll be my final question for today cuz nice and philosophical and um I don't think there's a single ultimate truth I think there are many truths I think the notion that truth is a singular essence or quality has led to much strife in the world much dissension much unnecessary bloodshed I think that there are qualities of the world that are objectively accessible and what I mean by that is not that we can get outside of our heads we already discussed that earlier everything that we know about the world is subjective in here but what I'm saying is their qualities of the world that if we attempt to access them we will access the same thing like as I said before the mass of the electron the electromagnetic charge on the electron and so but those truths are only one kind of truth in the world and the patterns that we develop to explain those qualities of the world via the standard model of particle physics be general relativity be at whatever those are accessing one kind of truth which is that objective third-party accessible qualities and patterns of the world the inner kinds of truth the subjective kinds of truth that we as individuals have access to through whatever meditation through introspection through self-awareness through inner experience through the experience of music or art or theater or reading literature or poetry those truths are equally real they're not truths that are third-party accessible they're not truths that are available to everybody in the same way because they are deeply dependent on the specific icon equalities of our own particle arrangement the way our brains are configured the experiences that we've had the genetic makeup that we acquired from our parents so those truths are real those truths are valuable those truths are a vital part of a complete understanding of what it means to be a human being living in this universe and those truths are different for each of us and so in that sense the totality of truths needs to be forefront in people's minds so it's not that your God is better than my god it's not that your theory about consciousness is better than my theory it's not that your art is better than my art it's the recognition that we are all on a journey to better understand ourselves to better understand the world and we get that better understanding through a variety of sources physics is one source it answers the kinds of questions that we have been primarily focusing upon here today but if somebody else was in this chair and they were talking about the truths that emerge at higher levels of understanding the truths say of biology chemistry the truths of psychology or philosophy the truths of art the truths of anything else that we use as a tool of investigation into the nature of reality those are vital truths those are not truths that physics directly provides to us and the truths that also come from religious exploration from conscious introspection vital part of the story - and those are the stories that we as individuals tell those are not stories that we have objective descriptions that we can all agree on because they're accessing qualities of the world that we all are able to touch in one way or another so an answer to your question I do not think there's one single truth you have to recognize that there are many truths many valuable truths and the beauty of life is that we are equipped to experience those truth to pursue those truths and in all their wonderful very expect from a possibilities that doesn't mean that their qualities of the world that aren't amenable to factual discussion are their qualities out there that absolutely science can give us insight into like climate or viruses or things of that sort yes not open to opinion or discussion at this stage of understanding but are there other truths that are much more fluid and flexible and much more sensitive to the individual yeah and they're equally important all right with that I think I'm just about done we're at 5:59 so I don't know it's close to three hours of conversation maybe I hope you've enjoyed the time that we've had together again as I mentioned at the outset your daily equation will be a little bit less frequent I'm going to still try to create some episodes so look out for those and I'll try to do this next week these sessions are fun again I may be doing a reddit our Reddit public access network discussion next Friday at 2:00 so if you want to join us at 2 o'clock for that and then we can segue into this one at 3 o'clock that will be a possibility to again follow me on Twitter if you sort of want to keep up to date on the things that I'm doing I have no means of connecting with you except during these sessions it'd be really useful if I had a confidence that if I wrote down something on Twitter like I'm not going to do a daily equation today or I'm not gonna do a live session that thought I would reach you so follow me on Twitter it's at be green follow me on Facebook if you'd like a lot of stuff I post there I think it's be green I don't know what I am on Facebook sorry but easy to find and and also subscribe to the world science festival I think this is their right hand it's always confusing I think this is pointing at this subscribe button I hope it's there on the screen so sign up and and we will connect again sometime during this week hopefully with new episodes of your daily equation if I can get to it I will try against my first week of teaching I may not but certainly by next Friday we can join up here again alright thanks for your questions enjoyed it see you guys later

Channel: World Science Festival

Views: 238,317

Rating: 4.6772332 out of 5

Keywords: brian greene, Live stream, #livestreaming, #livestream, #live, #streaming, Albert Einstein, daily math lesson, Your Daily Equation, brian greene interview, brian greene until the end of time, professor brian greene, astrophysicist brian greene, professor brian greene interview, physicist brian greene, brian greene book, professor brian greene until the end of time, brian greene physics, brian greene joe rogan, brian greene string theory, number theory, daily series, math series

Id: 9gAcHKraVWE

Length: 177min 38sec (10658 seconds)

Published: Fri May 22 2020

Reddit Comments

[u/divyesh2005]

Bonjour

[u/InspectorLevin]

Strange to now have a moderator on the live stream, a few people were put on timeout and there were rather useless banners with the questions on now, I don't know how to feel about it

[u/MiserableCat8]

Hello?