Brian Greene - The Hidden Reality

good evening everybody and welcome to the museum of science we are thrilled to present tonight's program and pleased that so many of you were interested in attending and we are happy to announce that c-span is here videotaping the program as part of their book TV series and you'll be able to catch the program on television sometime in the coming upcoming weeks not long ago the question of parallel universes was one of was wasn't one of science but one of science fiction now as I introduce our special guests I'm actually wondering whether there's another version of myself doing just that in another universe a parallel universe that's not too different but also not altogether the same as ours in fact an infinite number of versions of ourselves may be gathered at the Museum of Science to hear about the possibility of these other universe whether these other universes exist it's puzzling Brian Greene is widely recognized for a number of groundbreaking discoveries in super string theory the idea that minuscule strands of energy vibrating in at least 11 dimensions create every particle and force in the universe a math prodigy and a Rhodes Scholar Brian Greene currently is professor of physics and mathematics at Columbia University he has described his objective as enabling the general public to see science as a living breathing evolving undertaking and he has certainly accomplished that through his popular three-part nova series the elegant universe and his best-selling books brian speaks tonight with dr. Amir excel mathematician and author of a number of popular books on the history of mathematics and science including the New York Times bestseller Fermat's Last Theorem for his latest book president the creation the story of CERN and the Large Hadron Collider Amir interviewed the world's top physicists so please join me in welcoming Brian Greene and Omni axel well good evening it's really a special pleasure and honor for me to welcome grindr green to our fair city and before we start talking about other universes once we start talking about you I know a lot of people would like to know some personal details about you I understand you're vegan yes in this universe you stole my next question sorry whether your doppelganger is it mediator it's very scary to think so but uh according to our understanding that's quite possible I was an airplane just a few days ago actually coming from London and a woman next to me I ordered vegetarian she said would you be offended if I ate meat I said I don't care what you eat anyway I see you're offended by your doppelganger so uh but he doesn't sit next to me on airplanes oh good work Sheldon well the fifth of the kind I'm thinking you both disappear to sit next to you in an airplane that's possible too so um tell me something else I understand you have a number called what is it um are there something else for the Erdos bacon stuff yeah can you explain you about that um yeah you know there's this idea of how many degrees of separation you are from famous people so the original one was how far away a given actor was from Kevin Bacon and then mathematicians wanted to compete and have their own version of Kevin Bacon which is Paul Erdos who collaborated with many many mathematicians so the question is how far are you away from having written a paper with Erdos and then people said well let's put it all together and see how far away given individual is from Kevin Bacon and from Erdos and as you can imagine there aren't too many people that sort of are close to both but there are a handful of us so I'm one of how many are you uh well I used to be the world leader and soon number is number five but I've been overtaken you're five and one well five total I think it's so you from arid ocean three from bacon I see something like that but uh but I think like Gwyneth Paltrow is taken over the way it's ever she wrote a paper was a yes I know I I'm not sure but there are definitely people who've taken over I see but another University of number one that's that's always gonna be the case yeah so uh what is this let me ask you we all think that there's one universe how could they be more yeah well that that is the essential question to start with because you know a long time ago you know two years ago um the word universe meant just what you are saying it meant everything the totality every star every galaxy of the whole shebang so what sense could there possibly be in having more than one everything and what we have found in research that actually dates back a number of decades but most vigorously relatively recently is that our mathematical investigations are suggesting that what we have thought to be everything may actually be a tiny part of a much grander cosmos and that grander cosmos can contain other realms that seem to rightly be called universe just as our realm has been called universe which means that you have many universes multiple universes which we call the multiverse sounds like a brand of cereal to me Multi multi cereal Ori but you have a thing going on here doc you know don't we so tell me uh III I I understand that physics is a science experimentals yes so where does it come in I mean sounds more like a religion to me I mean there's this universe in another universe a how do we how do we learn about deciding universes yes so so how can you gain confidence in an idea that speaks of realms that we can't see that we can't touch we can't visit we can't observe directly so let me give the answer in two parts one is in some versions of the multiverse and I should emphasize there's not one proposal for how there might be many universes or number of bubbles and some there can be subtle connections between the universes that might allow us to have some experimental window on to them but hold that to the side for the moment let's think about the ones where you couldn't visit them well why do we think about these things well we have a belief founded upon really hundreds of years of experience that math can provide a gateway to reality it can provide a window onto a reality that at the moment the math is being done we can't actually see or observe that reality mean Einstein is the greatest example right he wrote down his equations of the general theory of relativity way back 1915 others looked at those equations and found that they seemed to say at the universe should be expanding the math said the universe is expanding Einstein himself said no I don't actually believe that but twelve years later observations show the universe is expanding the math was confirmed by observations other examples are black holes again Einstein's math gives rise to them Einstein didn't believe it observations now show that there are black holes so we're following in that tradition we are doing mathematical equations following them and as we can discuss in some specific cases they are leading us route by route to the possibility that ours is only one universe does that mean the math is right we don't know it has to be confirmed ultimately through some kind of observation or experiment but the possibility that the math is revealing this new picture of reality is sufficiently compelling that many physicists including me are taking it seriously and investigating it vigorously but I think the operational word here was can because mathematics is not physics exactly so sometimes the mathematics works and sometimes it doesn't you don't have to go very far but if we go back you can say the epicycles were invented by a mathematician a Greek mathematician and then Ptolemy used them to argue that you know the earth is the center of the solar system with the universe for him so here's mathematics that's valid this mathematics not very complicated mathematics with mathematic yes unless yes that doesn't describe reality and you can go to later on for example very before you leave that example sure because I think that is a great example where you had some individuals who were looking at the motion of the earth and the motion of the planets and coming to certain conclusions that we now know to be erroneous but conclusions about how things were working there were other physicists mathematicians who looked at that math and said this is so complicated this is so convoluted and if we look at the math this way it all simplifies but the conclusion is that the earth is not the center so we were propelled by mathematical investigation to imagine the earth is not the center and then others using similar kinds of reasoning noted that the Sun is actually not the center either and then similar mathematical reasoning showed us that our galaxy is not the center it's one of many many galaxies we've gone through a sequence of if you will cosmic demotions by following the math confirming it through observation we may be on the threshold of the next emotion by following exactly the same pattern earth is not the center Sun is not the center galaxy is not the center of our universe may not be the center it may be one of many universes following exactly the same pattern but I think the keys that the mathematics is always simpler in a sense for a Occam's razor or something that's certainly what we have found but when when you do very complicated mathematics and you trust your equations often these equations are cumbersome I would say so I mean I can understand where you might come to the conclusion because if we get into any of the details you know some of the multiverse ideas come from string theory which seems like a complicated subject when you hear about it's features but when you look at the equations of string theory the starting point it's actually pretty simple how many strengths theories are there there's one now I mean there was a time when we thought there were a handful of distinct string theories but wonderfully in the last decade the math has come together and we've realized that what we thought were different theories are actually all the same just expressed in a slightly different language so everything has been simplifying you know if you take even a good example Darwinian evolution the principles of evolution are pretty straightforward right but nevertheless those principles can yield the rich variety of life that we see on earth the outcome can be complicated even though the starting point is simple that is the way I would characterize our thinking about certain modern physical theories the outcome say string theory again if we get into it extra dimensions vibrating strings though it seems complicated but that's like the richness of life coming from evolution the starting point of string theory like the starting point of evolution pretty straightforward I see so um tell me what are some of these theories that lead to the multiverse in your book you describe several of them I couldn't find the one with the anti universe that's my favorite actually where your anti person you know as you know positrons in anti you know I trust our trackers right there so um did you favor that route to the multiverse well there are many ways to the multiverse may be a good place to start would be what I consider the simplest route of all which is to imagine the possibility that space goes on infinitely far right if you were to get into a rocket ship and head out into the cosmos would you at some point hit a brick wall no most of us don't think that's the case would you circle back to your starting point like what would happen on the Earth's surface if you took a similar journey that's possible or would you simply keep on going forever we don't know but let's take that third possibility seriously if we do there's a startling conclusion and it's simply this in any finite region of space matter can only arrange itself in finitely many different configurations particles very large large number but remember similarly like if I take a deck of cards sure if I shuffle the deck the order of the cards differ there are only finitely many different orders of the cards many different orders but still finitely many so if I shuffle the deck enough times infinitely many times the order of the cards has to repeat similarly in infinite space the order of the particles the configuration of particles has to repeat too now what would that mean was we heard the introduction it would mean something pretty strange you see you and I were just a configuration of particles everybody in this room is just a configuration of particles as is the earth and the Sun and so forth if the configuration of particles repeats someplace out there in the cosmos it means all that we know is repeating we are out there and that's a very straightforward mathematical conclusion not from a simple starting point space was uninformed and you go to infinity it doesn't matter no no the lady the probability of us speaking in another universe is do you want to go there oh oh absolutely in fact I don't need to frame it in probabilistic terms let me just do it in a more concrete setting if I had that deck of cards and I shuffled it over and over again do you agree that sooner or later the order of the cards will repeat not the probability yeah I'm not saying the deck is too large it's no it's fairly sorry deck no no $50 that's easy you're taking the easy way out I'm talking about the universe but you're you're discounting the power of infinity but infinite space this is the supposition that you can challenge that but let's not just to get to the end of the argument if you take on board this idea which I think most cosmologists and physicists have that space goes on infinitely far now then you've got you've got a lot of room for this to happen right that's the point I have a problem with space going infinitely okay that's fine enough that's a good place to try to poke a hole in mathematics dimensions go infinitely far but in physics the way I understand physics these three dimensions in which we live in the worth of time which Einstein taught yeah will is related to the other three was created in the Big Bang so I think if you think as a physicist and check me from wrong space here was create in a big bang we're not expanding into another space we're creating spaces we're going out as the galaxies are expanding with 13.7 billion years and so on we are creating free space or for space so where's the other universe when you as a mathematician okay there's this dimension it goes on forever call it X and yes Y and this Z but I think in one of your universities you got a universe here and one here and one here and one here and one here and intranet Li many of them that's okay yeah but does it really exist from a physical point of view when space was really create space and time yes we ate it in a Big Bang sorry so I do need to correct you a little bit with all due respect that's why um so there is an incorrect image okay that many people have in mind which is this when we think about the Big Bang typically we imagine that further and further back in time the entire cosmos was smaller and smaller and smaller and way back toward the beginning the universe we sort of intuitively think of is very very small and then run that film forward and as you're saying space is created from that Big Bang so how could it ever be infinitely big if it was very small in the past and if that were the right picture you would be right but that was not the picture that's compatible with an infinite universe in an infinite universe as you had ever further back in time we don't know universes the universe is still infinitely big if you go back in time and universe is half as large as it is today half of infinity is still infinity if you go back further one-third of infinity is still infinity well actually mean here it's the traditional one having the universe is infinite that simply big yes so what's the radius of 13.7 billion that's my observable universe so the universe goes beyond that so what solutely that's a big bang that's the key point is the Big Bang the Big Bang is an event that gave rise to our realm but if the universe is infinitely big then our part the part that we have access to is only as piece of the entirety so you need to make the others are expanding as well exactly so you need to make a distinction between the observable universe and the entirety the observable universe is the part that we can see and you're right we can't see further back than roughly 13.7 billion light years because that's the amount of distance that light can travel since the beginning but we almost nobody believes that the universe ends at that point most everyone believes it goes on at least a far distance beyond that and the supposition of this particular example that we're saying is that it goes on infinitely far uh Brian you're you're a magician too you pulled out infinity out of the Hat doesn't where I mean what does infinity have to do with anything everything we learn about physics is really finite what does infinite mean what cardinality does it have is that they have the cardinality of the integers or the continuum or the foot space of functions I mean to invoke infinity you have to give me something yes and the the most straightforward definition would be it's the same cardinality as the real line it's just the real line extended in exactly the way that you know about from when you took mathematics at a young age so just goes on without bound so let me ask you this let me turn it around okay if the universe is not inflated what happens when you travel out well look I interviewed Steven Weinberg a few months again about cosmology and I asked him the Big Bang is believed to be a quantum fluctuation that's what created our universe what was it a quantum fluctuation in what was a medium in which we were spawned if you will and he said that we don't know and we can't go there we know so but you're telling me something else you're telling you that there's an infinitude of space as mathematically I agree with you the real line exists but it exists platonically no mathematical the concrete question if you build a spaceship and you go out and you just keep on going what happens well if I take physics the way physics has been done here's the Big Bang it started here but it has no there's no location has no meaning you can't define that point as being located in space because place doesn't exist before the Big Bang the universe we can see I don't know about other universes so so if you start here this space was created with a big bang so if you go into a rocket ship and you head out into space you keep on going what happy no that you can't you can't what do you mean you can't you have a ship and you go out well you carry the possibilities you hit an end no cycle back to your starting point no right but you know you know pretty well if you aim a telescope in this direction at night and you aim a telescope in that direction tonight the two-part take the farthest galaxies you can see they're receding the receding at the speed faster than light because of the accelerating expansion but because of the expansion of the universe you don't even need acceleration so that part doesn't talk with this part how are you ever going to get from one part to another with a spaceship that travels less than C less than the speed of light so if you get in that ship what will happen I don't know what will happen I'd be lost in space right so so so you know it's a mathematical question which in math language would be what's the topology what's the overall topology I don't that's where I disagree with you I think topology exists in a mathematicians mind as a platonic code of theta way varieties or motives or or thinks it may have nothing to do with the real world well this is a good way when you as a physicist take parts of mathematics you actually finessed my key point which is mac max is not physically a lot of mathematics here doesn't do anything for us I'll give you an example about the dos epicycles I'll give you when I'll take your glass I'll give you another example yeah so uh Verner Heisenberg whom I actually met fill it up good I want to filled up to the same level as that one right so we've got he Verna Heisenberg was one of the fathers of quantum mechanics and you know in the 20s he built this theory there you know everybody knows about the uncertainty principle and about maybe also about matrix mechanics and then you went a step further and he thought he's going to go into something else and he said here's a proton and I need three ice cubes here and he's right there anyway so you've got anyway so we've got the proton in a neutron it said there's a symmetry between them there's a proton a neutron I'm going to use the mathematics of symmetry to explain why these two are so similar and he called it su 2 which of course you know and then we won't go where it went from there but that assumption was wrong that was taking mathematics that makes a lot of sense in your mind as a mathematician but has nothing to do with the real world in the sense of the proton the electron they look very similar just because of an accident of nature because the quarks are so small so to speak one of them is a lot heavier than the other in absolute terms but we've compared to the to the mass of the two then you think they're really very very similar and he went into symmetries now of course you and I know that yang and Wilson went later and took su 2 and added V 1 and did all kinds of things and the mathematics sort of came back but at that moment what you have is mathematics is very powerful and absolutely useless yes but yes I rest my case no no it's a but but it's a case that I agree with I like today what I would say is mathematics opens up the realms of possibilities I thank you very much and what the art of physics is what the art of physics is being able to sniff out which mathematics is relevant for reality and which mathematics isn't now experiment and observation are a key part of that story and the one that you just mentioned ultimately it was observation and experiment that dictated that that math wasn't the right direction to go so what we need to do when what we spend our professional lives doing is trying to understand which body of mathematics is relevant for reality and which isn't now in this particular case that we were talking about the argument makes the assumption that a certain body of mathematics space can go on in far is relevant to reality if that's not right and it may not be I'm the first to say that it may not be but if it is you come to this startling conclusion if it's not then you don't and I think that's the mode of thinking about many of these multiverse proposals many of them start with a certain mathematical framework push the math as far as we can to the border of understanding and then use the math to look over the horizon and see what's there are we seeing reality or are we seeing mathematical ideas that's a question ultimately that has to be confirmed or disputed by observation now let me just give an example where that mode could help us here so people have asked himself if space doesn't go on infinitely far could we perhaps observation establish that that would be a nice thing to do well one way to do that is if it doesn't go infinitely far and if it does have the shape like the surface of the earth where it comes back on itself well then as you know there are structures in space that give off like galaxies the cosmic microwave background radiation and so forth if the universe has that shape light that comes from a distant source can hit our eyes but it can also pass by us circle around the universe and come back a second time or a third time so if you can see multiple copies of a given object that would be a nice piece of observational evidence showing that space is finite no such evidence yet that doesn't mean it's infinite could be big so big that it hasn't had time to cycle around but that's exactly what physics is about doing theoretical physics you know doing mathematical calculations pushing to the limit and then trying to find observational tests right so tell us about some of these specific theories let's start with the one I dislike the most yes how about there many worlds many or many world can't even say um many worlds is a so much different character of proposal for how we can be one of many universes and you may note that in the book it's actually one of the later chapters because worried about that why why why is it later because you write a lot of logic is your earliest that's right yeah because I think in thinking about this subject marching through the developments chronologically doesn't give you the most pedagogically sensible way of thinking about where we are today because in particular the many-worlds approach of quantum mechanics stands outside the chronological march that ends up with some of the ideas of string theory but it is an interesting proposal and that's why I have a chapter devoted to it we are don't you you're right it is weird and you'll note that in that chapter I basically come to the conclusion that I don't think it works but uh but but that doesn't mean it doesn't and if you're talking to other people like David Deutsch I'm Oxford or various other researchers David Wallace and so forth they would sit here and say it absolutely does work so I don't want to give the wrong impression that there's a consensus well here's the idea so the new idea of quantum mechanics in the early part of the 20th century was that whereas Newton said tell me how things are today and I will predict how they will be tomorrow the universe is like a giant clockwork I'll use my mathematics okay to turn the crank forward and predict how things will be and the observations establish that that way of thinking about things was very accurate when applied to everyday objects like glasses or to the moon's motion or to a rock that you throw Newton can tell you what will happen you do the observation and it does happen great when people began to probe the microscopic realm that whole structure began to fall apart universe they're completely different universe completely different realm I don't want to you know that's not you know use the word universe in too many different ways tonight but a completely different environment and in some ways you shouldn't be so surprised why should the laws that work on everyday skills also work on tiny scales and it turns out that they don't the new laws the laws of quantum physics and the new idea of quantum physic is that you can only predict the likelihood the probability of one outcome or another so if I'm not dealing with a rock or the moon but an electron and I want to know where it is the quantum laws say well there may be a 50% chance that it's over here and a 50% chance that it's over there or both or but well no no you know that's just just a bad situation fine you know there's a 50% chance of each and you can't do any better than that according to quantum physics now the weird thing is when you do an observation of the electron you always find it either here or there you never find it sort of half here or half there there's never sort of some melding of the two so the puzzle has been for 80 years even though the probabilities of quantum mechanics are confirmed by doing an experiment over and over again finding the electron 50% of the time here and 50% of the time here how do you go from the fuzzy hazy probabilistic mathematics of quantum theory to the single definite reality that we observe when we do an experiment nobody has answered this question yet shocking Leeds 2011 no one's answered this but the proposal that comes from Hugh Everett Wright in 1957 is this he says look if the math says there's a 50% chance the electron could be here or here he says when you study the math diligently and really follow it through and apply it to the experimenter as well the math seems to say that when you do the observation you find the electron here and you find the electron here just in two different universes in each universe there's a copy of you thinking incorrectly that there's a single definite outcome but from the bird's eye view there are two of you thinking that and that's just a single example with an electron the idea is that all of the possibilities allowed by the quantum laws are realized in one universe or another in this grand collection of possibilities that we call the quantum multiverse that's the idea but you believe in no I don't believe it I don't believe it because I don't think that we've established yet in any of the analyses and again this is controversial some people think we have I don't think we have established yet how this way of thinking about quantum mechanics actually describes our observations that link I don't think has been establish think we just don't understand quantum mechanics and well this is most people dismisses agree with that that's tantamount to exactly the same statement in to understand quantum mechanics is to say how does quantum mechanics link up with observation and I don't think we've answered that yet well it just doesn't appeal to our understanding of the universe because we are living in a space where things don't happen the way they happen in the microwave but let me have let me ask let me give a small footnote to that yeah that's why mostly mostly except for bose-einstein condensate things like that sometimes you can see large objects behave in quantum mechanically but very very rare you know I wasn't going there I just want to emphasize that what you're saying explains why quantum mechanics is counterintuitive it's worse than that well that's crazy III never word you like I never wrote a Stein couldn't accept it um exactly right but why is that and there's two parts Laurie two part no I wasn't actually asking you a question by one answer yeah you know there's there's a part of quantum mechanics it feels very uncomfortable because so at odds with experience and that's the part which makes it hard to accept these crazy ideas but if these crazy ideas have been fully worked out mathematically and the link to observation has been made which it hasn't yet then we'd have to accept that our intuition has been built up from thousands of years of living in a world of this size and there's no evolutionary advantage to understanding the probabilistic motion of an electron when you're out on the Savannah trying to get your next meal it doesn't matter if you understand the probabilities of quantum physics it matters understand Newtonian dynamics of where that animal is going to be in five seconds so you can jump in and eat it and that's why our brains have developed to really be Newtonian if I took this glass okay and I take the water out and I threw it somebody could catch it they would be doing the Newtonian calculation because it's intuitive if I were to do the same thing with electron they wouldn't be able to catch it because they don't have that same intuition that's only part of the problem the real problem with quantum mechanics is not that it's counterintuitive or crazy it's that there's a real puzzle that we haven't answered yet how do you go from the probabilistic math to the definite reality that has not been solved let's Brian why do you have to are you a gambling man um why we talked about your food habits do you gamble uh everybody see that helps have you been to a casino now yes yeah Benji's okay so in a casino you have like a roulette wheel or something like that and it rolls around ball rolls around and falls it one number that's thirty six numbers and zero and double zero but it chooses one number yes oh do you have a problem with that uh I do have a problem yeah I got a problem no no okay why do you have a problem with their probabilities for the electron oh I don't have a problem with a description of the world that's based on probabilities I do have a problem with the theory that is incomplete and that's our einsteinium then you don't know you'll know Einstein's he said it's incomplete he said the theory is incomplete for a different reason oh well III I'm Stein's problem with quantum mechanics had to do with well I have to do it a lot of things nonlocality and the probabilistic and interpretation in all kinds of weather thinks even though he had the vision to actually understand you know something we call today entanglement and yes the EPR paradox and so on but but what I'm asking you something at the lower level you have no problem going to Las Vegas well maybe you do but gambling you have no conceptual problem as the guy in a prairie hunting Mastodon or whatever you if you have no problem with with the the wolf or whatever you're hunting going one way and in another time you're chasing an animal is going the other way that's Newtonian in a sense right what you're talking about would you really have a would you need to see a shrink if the wolf went one way and next time the other way it won't look like my mother father I might go to the train come but I'm healing no problem with it why not sure the point your okay here's my point you do an experiment and when you can observe it when you open the box the electron goes one way it can be to the right and in another universe so to speak another time you do it to the left you know when you don't the electron both goes both ways yeah right we know that because we can think quanta Klee we're not the under thoughts right may ever trained in court Raya yeah if we are it's okay for us like boxes close go both ways and interferes with itself typical young experiment with one one particle right you have no problem with that at all when you open the box you collapse the wave so to speak you toss the coin you roll the roulette wheel and it goes one way or another why is it and by the way a problem is not of mathematics and you know that Hilbert space does it all for us for mathematician Hilbert space operators and whatever yes you get a sense how many people are familiar with Hilbert spaces hi I was taught through you um but I think we're at they were going a little bit for a few so so let me just let me just be a little bit clear here my problem with quantum mechanics has nothing to do with the fact that involves probabilities oh so I'm happy with probabilities so there are no more many worlds you somehow we're well that's internal purposes that's the alternative to the probabilities no no no no absolutely not okay people who believe in many worlds also believe in probabilities they're just trying to make a link between the probabilistic predictions and the fact that when you make an observation you see a single definite reality okay and that link is a subtle one that has resisted solution now for about 50 years so if you were talking to a person who does believe that there are many universes in quantum mechanics you would ultimately find that they're trying to explain the very same probabilities that Niels Bohr was trying to explain back in the old day so it's not like Einstein where Einstein had in his mind that physics needed to make definite predictions no no that we've long since gone beyond that because observations do show that the probabilities were we're trying to close the gap in the actual quantum formalism but my suggestion is that we move on from this because this is simply one variation by a theme of multiverses what's your favorite multiverse ah you know it depends the way in which you judged favorite but I certainly have a leaning towards those that have a chance of being experimental II tested in the shortest time frame okay which is one way of thinking about the subject and from that there's it a multiverse it comes from string theory which I find particularly exciting along these lines which is called the brane multiverse not BR a impr a and E multiverse and it comes from the following idea so within string theory and I think many people have at least heard of what strength theory is it's this idea that the elementary constituents of matter little tiny particles in the old way of thinking of things that are little tiny dots the new idea of string theory is that within these little tiny particles there's something else which is a little tiny filament that vibrates in different patterns this little filament looks like a little piece of string so the idea is that deep in the heart of matter there's little tiny vibrating strings now as we've studied the math of this theory more and more we've come upon the following very interesting idea within this theory there are not only these little tiny filaments there can also be what we call membranes Johnny cheats if you will that can have two dimensions or even three dimensions and so forth and the math seems to suggest that at least it's possible that all that we know about every store every galaxy and so forth is living its life out on one of these membranes it would be a three-dimensional membrane that's very hard to picture so let me just do a two dimensional analogy imagine a big slice of bread where every star in every galaxy that we know about is on this slice of bread that is our universe now this proposal suggests there could be other slices of bread other membranes other universes that if you will are all part of some grand cosmic loaf to use the metaphor with our universe just being one slice of bread one universe in this grand collection now to your question why do I find this particularly exciting well at the Large Hadron Collider there's a chance that this proposal might be tested how would that be well the collider slams protons against protons at fantastically high speed and the math shows that in some of those collisions if there's enough energy if they're moving fast enough when the protons collide they can create some debris that will get ejected off of our universe off of our slice of bread how would we know that well the debris would take away some energy with it that means there'd be less energy left for our detectors to measure after the collision than before there'd be some missing energy people are looking for these missing energy signatures and if the energy is missing in the way that the math suggests that it should be this would be interesting evidence that this brain picture is correct but suggesting that there might be other universes out there have you been depressed recently uh why do you ask because you know that the LHC hasn't found anything at 70 V so maybe at 14 they'll find it but right now as a lot of people may have heard the results are negative and that and they're also negative on something else which I want to bring you let me just respond to that too so you know it's very very early in fact if they found anything at all it wouldn't announce it because it'll take years of analysis before they do but but the the importance not you're making a great point not depressed I'd be thrilled if it weren't it wasn't because this is meant to be an experimental science right if we could rule out string theory let me just be on the record very clearly about this would I be depressed I would jump for joy because I'm not wedded to a particular theory I'm wedded to working toward truth I don't know how what you think I think you go around once and they go around once I don't want to do so much in this universe I don't want to spend my time working on a theory that's incorrect so if string theory is wrong I'd like to know today I'd like to know yesterday so it's not a matter of having a certain emotional investment in one outcome or another I have an emotional investment in contributing however minimally that may be to the ongoing human search for truth and finding that a given theory is wrong is progressing because you can throw that one away winnow down the possibilities so depression no excitement good so you'll always be excited whatever they find that's a nice of reality nature of the universe is incredibly exciting the LHC has been running for a full year now I think the end of March would be a 30th of March is when they started of course they stopped with a break but and they create so many collisions every second you know it's trillion zillions and the data accumulates they haven't found anything so the first thing they ruled out actually at this energy level is extra dimensions they they're not saying their nature exists but they haven't found it I want to lead in another direction in that at least for for for a short while they all I just heard from CERN that they haven't found any proof of supersymmetry either that's correct just happen now so as of now with all the data they've collected in a year at half the energy they can reach they haven't found any supersymmetry and I think supersymmetry is another place where the mathematics and the physics might diverge so let me add something I'm not here to play your psychologist but I'm a little bit worried how many people are really familiar with like is Anderson explaining things I'll explain it don't don't worry okay actually know it let me just let me just explain it for do a real fire you don't trust me I trust you I you know just you know I don't know you you live here they can come and visit you I just come here once a while fine so so the full name of string theory is super-strength you're in the super as you're Roger supersymmetry I'm not talking about straight finger and the full name of super string theory the super first to exactly what Amir is talking about which is supersymmetry now what is it well supersymmetry is a fantastically interesting mathematical symmetry that relates things that previously we thought were totally unrelated you know what is this imagery now if I take this glass and I begin to turn this glass around it's highly symmetric which means that no matter how I turn it it pretty much looks the same each point is related to every other point in a way that suggests that none is special each can be turned into the other point by simply rotating it similarly there are class of particles in the world that are very important to us that the particles that make us up electrons and quarks the things that make up protons and neutrons those particles seem to be very different from a class of other particles by virtue of the fact that they actually spin around differently those particles that we all know about turn out to have something called spin 1/2 that's the way these little particles spin but there are other particles that we know about that have spin 1 that's like the photon or the particles that communicate the nuclear forces and there are some hypothetical particles not yet seen that would have spin zero they wouldn't spin around at all supersymmetry is a mathematical symmetry that would relate all of those particles it would say that in some sense each of those particles can be rotated into the others now if that's the case for that to be true there will have to be a certain other class of particles not yet observed that the known particles we know about would turn into under this kind of symmetric rotation those are the super symmetric particles so for the electron its partner under this kind of symmetry is known as the super symmetric electron or this electron the quarks squarks neutrinos snute reno's i don't aim them for every every node for every known particle there's a cousin called ass particle so what Amir is talking about we're now looking for this particles if they're there it will confirm this idea if they're not it either means that we don't have sufficiently powerful accelerators to create these particles or it may mean that they don't exist that's the current state right it's a beautiful theory but we don't know if it has anything to do with the real world we don't the problem with mathematics and physics is goes back to Paul Dirac Paul Dirac was a person who is assistant English physicist who United quantum mechanics with a special theory of relativity and when he did that in 1928 I think something like that he looked at these equations now I'm going to sound like Brian maybe another universe I'm Brian so I'm talking at what Brian says is we trust the mathematics and that's what the rocky was let me finish I do not say we try I have to update your putting words my mouth okay I'm saying that Matt Braddock's hang a hand mathematics can be a potent guide for what we should consider interesting what we should investigate further but until observation until experiment confirms it no I don't trust I you so can trust observation and experiment fine so Paul Dirac was sitting in front of a fireplace at Cambridge and he looks and he realizes a way of uniting special relativity with with quantum theory creating quantum field theory relativistic quantum field theory when he does that he gets his mathematics and I'm not going to put words in his mouth and he looks at the mathematics and the mathematics tells him that there are negative energy levels for the electron and he says well maybe anybody else looking at it would have said this is just the math it's like when you solve an equation and you get two solutions one is imaginary and one is really Sam I'm going to ignore the imaginary it's only the real one that's good for me in this particular real-world example the Dirac didn't do that he said there must be a particle that has these negative energy levels and he called it well that turned out he first he thought it was the proton and then he realized it's another whole new particles so he was looking for new particles the way supersymmetry now looks for other particles and that particle deposit to honor the positive electron was actually discovered experimentally sometime later a few years later so the point is sometimes it works but it doesn't work all the time that's an example of Heisenberg so I'm glad you open-minded you're saying we want to follow the mathematics and we are an experimental science and we want to see where it leads us but the problem is and I think it's a it's a sort of disappoint there a lot of physicists because a lot of physicists today believe in supersymmetry more than or follow supersymmetry a lot more than other theories so if we don't find these particles that means here is a symmetry it's a beautiful mathematical construct that may have absolutely nothing to do with this universe or any other universe that's right so ultimately nature speaks and it speaks through experiment and observation but you're right there's a large segment of the theoretical community that takes this idea very seriously we have been working on it in one way or another the 1970s so if these particles are found scientists around the world will be popping the champagne corks this will be an exciting moment where the example you just gave of Dirac would be recapitulate in a very big way if these particles are not found we will accept that as the way the world works and go back to the drawing board and that to me is throwing good fair enough so how about the other theories Oh that's about some of some of the other ways that you can get to multiple series well another simple one is one that comes out of thinking very carefully about the Big Bang so again we touched on the Big Bang earlier which is this idea that the universe underwent this rapid expansion early on but one of the things that perhaps we don't emphasize enough when talking in general context is that the Big Bang Theory actually leaves out something pretty important which is the bank The Big Bang Theory tells us how the universe evolved from a split second after whatever started the outward swelling to happen in the first place but it doesn't tell us what caused that swelling to actually occur now people have been working very hard to fill in this gap and the reason I bring this particular gap up is because there is a proposal now for what caused the outward swelling it's called inflationary cosmology it's basically the recognition that goes back to Einstein that gravity on certain circumstances can be repulsive we're used to gravity being attractive you drop the glass it falls because the earth attracts it you drop the ball it falls again because the earth pulls things together that's what gravity does but actually Einstein showed surprisingly that under exotic circumstances gravity can actually push things apart the belief is that the possibility is that the early universe that exotic environment was realized there was an energy fusing space that gave rise to repulsive gravity that pushed everything apart that's why the universe started swelling in the first place the thing is when you study this theory in detail it seems to show that this outward swelling would not have been a unique one-time event it says that there could be many of these big bang like beginnings at various and distinct locations in a much larger cosmos each giving rise to a swelling realm each giving rise to an observable universe and a universe that people like us could inhabit but the universe's upon universes upon universe this is the inflationary multiverse and the nice thing about this approach is that the idea that space underwent this rapid swelling early on from this repulsive gravity that has been subjected to some very interesting observational tests if the universe went through this rapid swelling early on here's what would happen little tiny quantum jitters quantum fluctuations in the young universe would be stretched out by the rapid swelling and smeared out across the sky and analogy as if I had up a little balloon with a fine tip pen imagine I wrote a little message on the surface of the balloon you couldn't actually see it it's too small if I blow air into the balloon as the balloon stretches my message gets smeared out across the surface of a balloon now you can see it now the tiny quantum jitters in the early universe may behave similarly they're like the little message and as space when Derwent this rapid expansion that message gets smeared out across the sky as tiny temperature differences in the heat left over from the Big Bang is called the cosmic microwave background radiation and we have measured this heat left over from the Big Bang and the way the temperature varies from point to point is exactly in line with the mathematical calculations but that is a very convincing piece of evidence for at least taking this theory quite seriously I think the theory is taken very seriously but most not only cosmologists believe in astronomers all young physicists your question is does it really imply the existence of something that's unobserved in ways of now which is a multiverse I think that those microwave you know fluctuations and as they expand I think they're these there are galaxies that are spawned from them as well sure does that really imply other than the mathematics oh you keep going back to the mathematics doesn't mathematics really tell you that if you see this picture of the microwave background radiation in space you must have no no okay not must and that's why I'm not here saying that these ideas are you may recall when we started out this conversation I emphasize that these are speculative ideas that come from our investigations and until we have observation of them we can't believe that it's real let me ask you but let me let me just take a little bit further but what happens in the subject is when you have a theory that is able to describe things that you can see it bolt is your confidence to follow the theory further that's where the confidence comes from to follow the math further now does the math uniquely imply that there have to be these other realms no there are versions of the inflationary theory where they'd only be one room they're very hard to come by they're very cumbersome they feel very contrived from a mathematical standpoint that doesn't mean they're wrong it could be right but the ones that don't have that contrived quality are the ones that do give rise to these other universes so do we note that that there absolutely not but does this suggest this as a compelling possibility that's worthy of further study yes and how would you know it what sort of experiment might give you some insight well here's again rhetorical so if you had these um if you had these expanding realms I'd shut up it no I don't know about you know if you have these expanding realms imagine it you know as a big cosmic bubble bath of different universes with our universe being one of those bubbles now in a bubble bath the bubbles can collide similarly these universes as they expand can't collide - if they form close enough together they can smash into each other how would we know that if our universe had a kind of fender-bender with another universe in the past well that collision can send ripples through this heat left over from the Big Bang this cosmic microwave background radiation once again so scientists are looking in that background radiation to try to find finer patterns in the temperature variations in space that might indicate that we got hit by another universe is there any positive evidence yet no not yet the collisions could yield a signature that's too small for our current level of technology to access or maybe it never happened but that's the way in which in principle you could have observational evidence of a universe that you can't live really see you see its effect in our universe SP the please so how would you know there there been several generations of satellites looking at the microwave back circulation and we know a lot about the microwave background radiation in fact it's it's uniform to one in 10 to the 6 or something like that they're they fluctuate yes very very small right how would you be able to tell you got to give us something concrete say here's a universe and here's another universe and they collide I yes you know you lost me at the beginning because I don't think another universe can exist on this axis it just because of the fact that we created this space what is this space I you haven't answered my question on that but let's leave that out so below you hold on let me finish so you crash this you given the impression that there's something missing and the missing part is actually you're not fully comprehending the idea because we're talking about a very title I know what you're feeling there's the the hyperspace there in the space calabi-yau manifolds knowledge could be a dangerous thing um you sort of know too much right applied you know um this has nothing to do with hyperspace nothing to do with expectations bread and butter cosmology that takes place in the ordinary dimensions so I have this possibly so let me just describe it so the wider cosmos that you're having trouble grasping think of it as a big song us 18 are three it's informational artery yes dimensions let's just stay simple so three dimensions that's filled with this dark energy that causes the outward repulsive gravity that was referring to what happens is region by region in this big cosmos the energy can degrade and as the energy degrees holes open up in this wider cosmos where the energy turns into particles that make stars and galaxies so our universe is simply one of these regions where the energy has degraded the in photon energy has degraded the image that works pretty well as think of a block of Swiss cheese imagine that the cheesy part of the Swiss cheese is where this energy exists and it's forcing things to experience gravitational repulsion the holes in the cheese or places where the energy is degraded where stars and galaxies can form so the different universes that I'm talking about are just the different holes in this big so they're on with G so they're really one universe whatever language you'd like hi and as I said early on that was my machine as I said early on the language is confused fine yeah let's leave it up yeah let me ask you we're talking about experimentally detecting the evidence of the multiverse yes whatever the multiverse may mean yes exactly you have a cheese all right so you've got these two universes colliding yes and here's the background radiation yes it's fluctuating yes how do you know it's from that and that's from something else that's a question you face with all experimental data when you look at data you say what's the best explanation for it and you try to rule out all other competing proposals and the proposal that stands up and is the best explanation is the one that you gain confidence in so we've done calculations and actually I've not done these little calculations myself others should get the credit for it but other physicists have done calculations of what would happen to the microwave background radiation under this process and they have very explicit predictions for what would happen to the radiation plots of how the temperature would vary from place to place and if you find temperature variations in line with those predictions and there's no other competing explanation then indeed your confidence and this possibility would rightly grow that it's way science works fine let's assume it will happen someday and then we'll have proof of it but until then of course we don't know I agree so tell us about some of the other multiverse theories well let me ask you what time is it because I think we be around 8:10 are well you know only because I don't want to make sure that people get a chance to interact if they want to I don't know what the format here is but you tell me I'm happy to keep on going I got no place to go tonight but uh whatever you whatever you want to do I guess you got your answer um so so yep carry on no actually no any anybody have a question want to throw anything out ace tired of my question if we'll take some time for some questions now we have two museum staff members with microphones will be walking up and down the aisles will select you and when you when we do select you please stand up and don't begin talking until you have a microphone so we're ready for some questions now first question down here I know this field moves very quickly but in 2006 Lee Smolin theoretical physicist at the brita Institute in Canada yes I wrote a book entitled the problem with physics the trouble with the trouble excuse me yeah and it seems to be that he has basically abandoned a string theory so because chiefly because of lack of experimental confirmation so my question is as he has he abandoned it too early because of this if evidence can or can't carry on to future it's a good question and you know Lee's a good friend of mine and when I speak to him he says largely things his book has been somewhat misinterpreted what what he claims that he was really meaning to say in that book was that string theory is not the only approach to putting together quantum mechanics and general relativity there are other approaches in fact he's a champion and has been one of the founders of a competing approach called loop quantum gravity and part of what he was saying was he feels that too many people work on string theory not enough people work on loop quantum gravity and the health of the field would be advanced if there was a more balanced approach where more people worked on these other approaches and string theory wasn't sort of the primary one that was looked upon as the solution in the physics community you know I agree with that I feel that health of a field is evidence by all sorts of different ideas the reason why more students work on string theory frankly is I think it's a more attractive and more appealing a more promising approach I think that's how graduate students make their decisions but you know I full well agree that it would be great to have active centers of research in all these approaches and he helped found the Perimeter Institute that you mentioned and there are a lot of people there working on loop quantum gravity so the idea that he abandoned string to he's not really string theorists and he's worked on it from time to time because he's one of the folks who really tried to cross over maybe there's a way of doing loop quantum gravity and string theory melding them together he and I have discussed this that would be great if that happened but his main point is that there are other approaches and they deserve attention on that point I would agree we have a question over here hi yeah my question is related to the many worlds theory uh basically about the fact that like right now in another world like I don't know I could be asking a question to someone else but whose world is it like if we're making these choices like a week creating these worlds and like so whose world is this whose world is the other world so yours as mine is it someone else is here yeah well according to the bread and butter many worlds approach as Hugh Everett wrote down as others have developed it since the 1950s if you're in a situation where quantum mechanics says there's a possibility of this possibly of that a possibly of this and so forth all of those possibilities happen it's not really a matter of you choosing which happens the mathematics doesn't allow any possibility to go unreal eyes all roads are traveled in the quantum multiverse you know it's funny I'm teaching this right now I'm teaching undergraduate quantum mechanics and I'm literally this week we're talking about in the many-worlds approach and you know we set it up last week and it is if you actually go through the mathematics of it which very few people I found actually do few people actually go back to the 1957 paper and read it few people go back to the thesis that you ever wrote down back in the 50s and read you know if you actually read his thesis I mean his thesis is a mathematical Jim where he makes a very potent case for this idea from a modern perspective as we were discussing I don't want to sort of open it up again I think there's still things missing but when I read his thesis I'm taken along and I'm very critical of it because sort of like a mirror it's an idea that I don't I don't think is right but I'm taken along by the mathematical argument to sort of the last step and the last step he didn't quite get right I don't think anyone in my opinion has yet filled it in but others disagree with me and say that the last up has been filled in but if it's correct all possibilities allowed by quantum physics actually happy now sometimes I'm asked by this one described about does that mean that like there's one universe where like Sarah Palin is president you know and I have to tell them you know it has to be compatible with the laws of physics next question over here so you mentioned on some of the other potential quantum gravity unifications like at ojos theory and look at mountain gravity up do any of them have any implications as far as a the multiverse goes uh you know it's a good question I don't know enough about them I have to say to answer that with any degree of confidence in all of them quantum mechanics is part of the story so if the quantum multiverse is true then I think all of them will likely embrace it in the manner that we've been discussing so from that perspective yes in terms of the other multiverse ideas that we've discussed here today I'm actually not sure what they have to say about it question over here in your many bubbles world we know that after the Big Bang certain specific criteria had to be met or the universe would have flown apart and the particles so in the other worlds do they had to follow our laws in order to succeed or did some of them die or or what what how does that work yes so one of the deep questions that we have faced over the last 15 20 years is aligned with exactly what you're asking we have gone out and measured certain features of our universe certain numbers certain parameters like the electrons mass the strength of the electromagnetic force the strength of the gravitational fourth is the masses of the quarks and so forth and what we found is that we understand the numerical values that the experiments are revealing but we haven't been able to explain why those particular values have been found now you might say should we care if the electron was a little heavier or a little light maybe that's just one of those details you shouldn't really worry about it but you should for exactly the reason that you asked if those numbers had been somewhat different than the universe as we observe it and know it wouldn't exist if I had a machine up here with 20 dials I calling someone randomly to come up and you make gravity stronger or you make the electromagnetic force weaker phone was only fiddling that you do the universe does not evolve in the way that we Noah stars don't form planets don't form and it's hard to imagine how life would exist in such a universe so the deep question has been why do those numbers have just the right values to give rise to the universe that we are familiar with we have hit a dead end so far in trying to answer that question the multiverse casts a very different way of thinking about that question it's really along the lines of what you suggest the idea is maybe there are many many many universes in which those numbers vary from universe to universe to universe and in most of those universes we couldn't exist because the stars wouldn't be there the planets wouldn't be there and so forth and the answer for why the numbers have the values that we observe is we couldn't observe any other values we couldn't exist in those other realms and that is an approach that may ultimately hold water now let me just give you a little analogy on this that that happened to me - two years ago with my four-year-old which I think helps one to understand this a little bit more you know my son is six years old now he was about three and a half or so we went to a shoe store and we got two shoe stores before but this is the first time he was really old enough to begin to think about what was happening but going to the shoe store the guy measures his shoe goes in the back comes out with a shoe put some on it fits we leave everything's happy my son turns to me in the street he says wasn't it lucky that they had my shoe size and as I probe further I realized that what he had in mind was that shoe store had a single shoe size and it just so happened that it fit his foot what a mystery that would be but when I explained to him that back in the stockroom there were many many many different shoe sizes and the guy just picked out the one that he'd measured the mystery went away what's the moral the moral is if you think there's a unique object that you're trying to explain that can be mysterious but if you then realize that it's not a unique object it's one of a vast collection the mystery can evaporate that may be true with these parameters just as we found the shoe size that fit his foot we find a universe where the parameters fit our existence and that may be the answer all right I guess preface this question I guess I'm going to ask if you're familiar with I think his name is Ronald Mallett and his a time time machine experiment sorry I don't it was I guess he's a theoretical physicist out of Stanford University on diversity and Ironmen in Connecticut right yeah I guess he postulates that if you twist light enough that you can twist space-time sufficiently to create like a centrally upon my curves we can go back and try right well yeah at least or at least something like a subatomic particle stream back through time to when the machine was turned on okay can't go back before washing out turn right but if such a machine were actually built could something like that possibly be used to maybe test some of these series oh boy oh well you know you talk about speculation we're now in speculation squared or something here um you know uh you know how would time travel interface with some of these ideas let me just turn it in that direction and I'll simply say this one of the big puzzles with time-travel of course is you go back in time and you affect things in a way that maybe prevents your own existence you go back and you kill your parents before you were born and there's a logical paradox you know we've seen this played out and back to the future you know Hollywood loves this idea you know you know uh there's a variation on the paradox you know which comes from the following idea I mean imagine you know that you you you you travel the lamenting you can travel to the future you know imagine I travel to the future let's just say and I and I want to see what's happened in string theory you know has it been proven or not and so forth oh I go to the library or the floating Internet station whatever and I see that surprisingly the theory has made a major advance and the author of that paper is my mom and I'm like that's weird because my mom doesn't like physics just know wants me to be a doctor you know not this kind of doctor I am a doctor you know all this sort of stuff you know so so um and I look in the acknowledgments to the paper in the future and she thanks me for teaching her all this physics and I'm like holy crap I better get back I got a lot of work to do she doesn't not very much you know so I use your little machine I travel back and I start to tutor my mother and man it's not going well you know she's not getting at a year goes by two years I'm like how in the world is she ever gonna write that paper you know and then I said to myself I know it was in that paper I read it let me just tell her what to write so I tell her what to write and she writes the paper and everything turns out in the future as I had it now the question is who gets the credit now you know it's not a question of credit really it's question of where did the information come from did she think of it no she got it for me did I think of it no I got it from her paper so information ideas seem to just sort of pop in from thin air if these things are possible now how does this relate to multiple universes coming back to that here's the possible fanciful idea that people floated imagine that when you travel to the past for instance you never come back to your own universe you come back say in the quantum multiverse let's use that as an explicit example you come back to one of those other copies of our universe so for instance if I go back in time and kill my parents before I'm born I wouldn't be born in that universe but so what my origin would still be unaffected because my parents would be unaffected the universe which I started so that's sort of but again it's a little far afield but at least that's some interaction with time travel question over here I just had a question about something I read aware of the bose-einstein condensate yes theory and it's something that physicists now we are so lucky to live in a time when people can produce a bose-einstein condensate and a certain elements now if they can hypothetically if they could create that instant in a room assuming that let's assume they can't is that to all the basic theories of quantum mechanics break down if you have a situation do you want to get one of you people sure I don't think it does that Brian will be the final arbiter but I think that bose-einstein condensate was created right here at MIT it was also created in Colorado yeah so that around the same time at bose-einstein condensate is just you you cool something you cool some atoms to a very very low temperature and what happens is the wave the very particle is a wave also so the waves overlap so you're really creating quantum mechanics for a large object in this case a collection of atoms I don't think it relates to anything else we've been talking about that yeah and and it really comes out of basic quantum mechanics oh it's not incompatible with it pardon me if you actually reach a bose-einstein condensate all of those waves become one point they jump - well that's what that's what the physicist at MIT say I wouldn't I person wouldn't describe it that way so I'm not sure what MIT described it okay yeah I'm not sure exactly what they had in mind sighs well they describe it that way okay we have time for one last question over here yes excuse me I should preface this by saying I'm a die-hard mini-worlds er and so the question most sense if you like that I was impressed by an observation in your first book where you noted a duality between length and one over length time one over time which seemed to have a special meaning if I understand this correctly at about one Fermi time after the Big Bang when the energy for a wound and unwound string are about the same and there was something I I don't recall the details now but something that you said there and then the notes prompted this idea and I'd like to know if anyone's pursuing anything like this okay and that is that if you imagine that there is a moment perhaps it's this one Fermi time after the Big Bang of perfect symmetry and I mean it's a zero microscopic entropy at that point also a finitely describable universe that is now mini-world style going to evolve perhaps 10 to the 500 the vacuum states or every whatever it takes to get us forward to all the different versions of us here now and shortener with this dead cat extraordinaire with his live cat we could look at the same thing you'd expect the same thing to be happening in that one over-interpretation going back towards the moment of the so-called Big Bang now that singularity turns into an illusion it's like the singularity at the North Pole it's an accident of using an appropriate set of axes to describe what happens that first little thing so here's this image of us and we have another double ganger now which is the whole multiverse repeated back in that first little moment of time yes so curious anyone's pursuing ideas anything like that um so it is one of the most surprising features of string theory which shows that under the circumstances largely that you're recounting a universe that's bigger than let me call the Planck length not the firm's got the Planck length bigger than the Planck length and expanding is actually equivalent to a universe that's smaller than the Planck length and contracting that's the R and one over our worlds that you're talking about I wouldn't use the word doppelganger or image to describe these two realms they're really distinct mathematical descriptions of the same reality so it's really just two different ways of looking at the same thing even though they've seemed vastly different but ask your question how would cosmology look and how would the singularity look in this picture yes in fact right here at Harvard Herman Vasa and another cosmologists named Robert Brandenburger they studied cosmology in the context of this universe that had that one R goes to one of our symmetry and they did find something along the lines of what you're suggesting so what is the singularity so if you run the universe back and back in time because denser and denser and denser way back at the beginning the density soars to infinity they found that in this setup when the universe gets smaller than a Planck length that's about 10 to the minus 35 meters when it gets smaller than the Planck length the temperature levels out and as you never get smaller the temperature starts to turn down because of this very symmetry that you're talking about it never spikes excuse me it never spikes to infinity there's never a time when the density grows infinitely big so this is a cosmological model that has been proposed based on that symmetry it there are the things that it doesn't describe yet so there's much work that would need to be done to take it fully seriously but as a toy test case of a cosmology where there wouldn't be a singularity yes it's one of the most potent ones that's come out of string theory do we have time for another brief comment question I just wanted to point out that if you're taking that kind of a model seriously then our current event horizon would be represented by all of the possibilities in the many worlds that could have happened to to this point over this space and now if we want to get in our imaginary spaceship and go out much farther everything that's happening there is just the same set of things and what we're doing is are kind of getting an outer product of all these combinations when we go out there and and wait long enough to see what's out there if that were allowed we're really just sampling what's happening in another brand the universal wavefunction here and so now this gives you another way to wrap that infinity so that it's not incident we've described one with vectorizing you've described everything and it will look like an evolving infinity to an embedded observer but you don't have this problem of what we mean by infinite yeah and that's rooted in the fact that we're talking about the radius of a circle which is of course a finite size so this is an example we have a finite universe not an infinite one so indeed you're right you would not have this problem that we were tussling with earlier on absolutely it can yes absolutely more questions oh that I'm sorry we done well I was gonna say I think our time is up but thank you so much for that wonderful lively and very mind expanding conversation right you

Channel: BostonMOS

Views: 789,007

Rating: 4.7769837 out of 5

Keywords: Brian Green, Greene, Amir Aczel, Aczel, physics, The Hidden Reality, string theory, superstring, Museum of Science, Boston Museum of Science, lecture

Id: fJqpNudIss4

Length: 78min 26sec (4706 seconds)

Published: Tue Mar 22 2011

Reddit Comments

[u/salmon10]

I've read a few of dr. greene's books, and they certainly are amazing...however he comes off as a giant douche in this interview

[u/mathent]

ITT: people who couldn't understand the speakers, and blamed them for it.

Thanks for this OP.