larger strategic missions especially missions with ambiguities, counterinsurgency is. >> i think it is an absolutely interesting parallel between vietnam and the current war in afghanistan, because you think about world war ii. my father, my uncle's they all fought. are we making progress? ian, we took guadalcanal and tarawa and hit the marianas. it is clear what we were doing. ..

>> you can watch this and other programs online at booktv.org. and now brian greene talks about the possibility of multiple universes and explains how this changes our understanding of reality. >> well, good evening. it's really a special pleasure and honor for me to welcome brian greene to our fair city, and before we start talking about other universes, let's talk about you. i know a lot of people would like to know some personal details about you. i understand you're a vegan? [laughter] >> yes, in this universe, i am. [laughter]

it's true. >> you're a mediator. >> disturbing to think so, but according to our understanding, that's quite possible. >> i was on an airplane a few days ago coming from london, and the woman next to me asked if i would be offended if i ate meat. i said i don't care what you eat. >> he doesn't sit next to me in the airplane, so it all worked out. [laughter] >> the kind i'm thinking both next on an paper. >> that's possible too. >> tell me something else. i understand you have a number called -- what is it? >> the air dose vacancy. >> explain us about that. >> yeah, there's this idea of how many degrees of separation you are from famous people. the original one is however -- how far away a person is from

kevin bacon and mathematicians wanted to compete and there's the question of how far are you away from having written a paper with airdosh and people said let's put it together and see how far away an individual is, and as you can imagine, there's not too many people that are sort of close, but there are a handful of us, so i'm one of them. >> how many are you? >> well, i used to be the world leader -- >> what's your number? >> number five, but i've been overtaken. >> five and what? >> five from airdosh and three from bacon. i think paltrow has taken over. there's definitely people who have taken over. >> it's another universe maybe

you're number one. >> that's probably the case, yes. [laughter] >> let me ask you, we all think that there's one universe. how could there be more? >> well, yeah, that is the essential question to start with because, you know, a long time ago, you know, two years ago -- [laughter] the word "universe" meant what you are saying, it meant everything, the totality, the stars, the galaxy, everything, the whole shabang and what we found it dates back a number of decades but 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 they can contain other realms that seem to rightly be called universe just as our realm has been called

universe which means there's many universes, multiple viewn verses calling them multiverse. >> that sounds like a brand of cereal to me. [laughter] so, tell me, i understand that civics is a science, an experimental science. >> yes. >> where does this come in? it sounds like a religion to me. there's this universe, how do we learn about them? >> yes, 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. let me give an answer in two parts. one is in two version of the multiverse, and there's not one proposal for how they might be many universes, but a number of proposals, and in some, there can be subtle connections between the universes that might

allow us to have come experiment or window on to them, but put that on the side for a 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 on to a reality that at the moment the math is being done, we can't actually see or observe that reality. i mean, einstein is the greatest example; right? he wrote down his equations to the -- and they found it seems to say the universe should be expanding. the math said the universe is expanding. einstein said, no, i don't believe that, but 12 years later, observations show the universe is expanding. the math was confirmed by observation.

einstein didn't believe it, observations now show there's black holes, so we're following in that tradition. we do mathematical equations, follow them, and as we discuss, they lead 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 officially compelling, that many physicists including me take a seriously and investigate is rigorously. >> the operative word here is can. mathematics is not physics. >> exactly. >> sometimes math mat ins works and sometimes it doesn't. you don't have to go back far, but the epicycles were invented by a greek mathematician and it was argued that the earth is the

center of the universe. here's mathematics that's valid as mathematics, not complicated, but mathematics nonetheless. you can go to later for example -- >> before you leave that example because 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, conclusions about how things were working. there were other physicists, mathematicians looking at that math and said this is so complicated, so con and the conclusion is the earth is not the center, so we were propelled by mathematical investigations 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 in

similar mathematical reasoning shows the galaxy is not the center, but one of many, many galaxies. we've gone through a series of motions by following the math confirming through observation. we may be on the thresh hole of the next demotion by following the same pattern. earth is not the center. sun is not the center. gal galaxy is not the center. the universe may not be the center following the same pattern. >> mathematics is simpler in a since. >> that's what we've found. >> but when you do complicated mathematics and trust your equations, often they are cumbersome. >> i wouldn't say so, but i understand where you come to that conclusion. getting into the details, the multiverse come from string theory which seems like a complicated subject when you hear about the features, but when you hear about it, the starting point is actually

pretty simple. >> how many are there? >> only one now, but in the last decade, the math came together and we realize what we thought were different theories are just the same expressed in a different language. everything has been simplifying. you know, if you take even a good example of the dare darwin evolution. nevertheless, the principles 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, the string theory, extra dimensions, vibrating strings, it seems complicated, but that's like the richness of life coming from evolution, the starting point of evolution is pretty straightforward. >> i see. so, tell me what are some of the theories that lead to the

multiverse? in your book, you described several of them. i couldn't find the one where the anti-universe, my favorite actually where your anti-person and -- >> protons is there. >> do you favor that route to the multiverse? >> well, there's many ways to the multiverse. i consider the seven lest route of all which is to imagine the possibility that space goes on infin natalie far. if you get into a rocketship and head to the cosmos do you hit a brick wall? no, most think that's not the case. do you circle back to your starting point? that's possible, or do you simply keep ongoing on forever? we don't know. let's take the third possibility. if we do, there's a conclusion.

matter can only arrange itself in many different con configurations large number, but a fine number. if i take a deck of cards, shuffle the deck, the order of the cards differ. there's only so many different order of the cards, many different ore, but finite. if i should have the deck enough times infin nitly many times, the order has to repeat. similarly in space, the order of the particles have to repeat too. what's that mean? in the enter duction, it -- enter -- introduction, it means something strange. if the configuration of particles repeat someplace out there in the cosmos all we know is repeating. we are out there. that's a straightforward mathematical conclusion from a simple starting point. >> you leave out an important thing, the measure of that is

zero when you go to infinity. >> it doesn't matter. >> the probability of us speaking in another universe -- do you want to go to? >> absolutely. [laughter] i don't need to frame is in probably terms. if i have that deck of cards and shuffled it over and over again, do you agree sooner or later the cards repeat, not the probability. >> the deck is too large. >> 52 cards. >> that's the easy way out. we're talking about the universe, not cards. >> you're counting the power of infinity, but infinite space, 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 physicists have, that space goes on far, then you got -- you got a lot of room for this to happen. [laughter] that's the point. >> i have a problem with space going infin nitly far.

>> that's fine. >> gnatmatics go far, but the way i understand physics, these three dimensions in which we live and the time in which einstein taught us is related to the other three was created in the big bang, so i think if you think of the physicists and check me if i'm wrong, space here was created in the big bang. we are not expanding into another space, but creating space as we're going out, as the galaxies expand with their 13.7 billion years and so on. we're creating space. where's the other universe? as a mathematician, okay, this dimension goes on forever. call this x, y, and z, but in one of the universes here and there, and that's okay, but does it exist from a physical point of view when space and time were created in the big bang? >> right, so i do need to

correct you a little bit. >> sure, sure, sure. >> with all do respect. >> that's what i'm here for. [laughter] >> there's an incorrect image 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 cos you know mos were smaller and smaller and the universe we think of as very, very small and run that film forward, and as you say, space is created from a big bang, so how is it big if it was small in the past? if that was the right picture, you would be right, but that's not the picture compatible with an inmy gnat universe, the universe is still big. if you go back in time and the universe is half as large as today, half p infinity is still infinity. >> what does that mean here? >> the traditional one --

>> the universe is infinite? >> yes. >> what's the radius of 13.7 billion years? >> that's the observable universe. >> it goes beyond that? >> it does. the big bang is an event that gave rise to our realm, but if the universe is infinnitly being, this is just a piece of the spirity. >> the others expand as well? >> exactly. there's a distinction between the observable universe and the entirety. the observable is all we can see. we can't see past 13.7 billion lightyears 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. everybody believes it goes on at least a far distance beyond that, and the supposition of this particular example we're saying is that it goes on infin

nitly far. >> you pulled that out. what's infinity have to do here? what does infinite mean? is it the integers or space of function? to invoke infinity, you have to give me something. >> yes, and the most straightforward definition is it's the same coggalty of the real line. if expands in the way you know about from mathematics as a young age, goes on without balance. let me turn it around. if the universe is not big, what happens when you travel up? >> well, look, i interviewed steven weinberg a few months ago, and i asked him the big bang is believed to be a quantum fluxuation that created our universe. what was the quantum

fluxuation? what was the medium we were in to respond? that, we don't know. you're telling me something else. you're saying there's infititude of space. >> you build a spaceship, go out, and just keep ongoing, what happens? >> well, if i take physics the way physics has been done, here's the big bang. it started here. there's no location -- location has no meaning. you can't define that point as being located in space because space doesn't exist before the big bang from the universe we can see. i don't know about other universes. if you start here, this space was created with a big bang. >> if you go out in a rocket ship to space and you keep ongoing, what happens? >> you know this, you can't. >> what do you mean you can't. you have a space and go out. you hit an end, cycle back to

the starting point -- >> brian, brian, you know well if you aim a telescope in this direction at night and aim a telescope in that direction at night, the two parts, the furthest galaxies you can see, they recede at speeds faster than light because of the expansion of the universe. how are you going to get from one part to another with a spaceship traveling less than the speed of light? >> if you get in that ship, what happens? >> i don't know, i'd be lost in space. [laughter] >> so, you know, it's a mathematical question which in math language is what's the overall -- >> well, that's where i disagree with you. i think it exists in a mathematician's mind as a platonic current state of varieties or motives or things that may have nothing to do with the real world. >> well, yes. when you as a fizzist take

mathematics, you finesse my key point. a lot of mathematics here doesn't do anything for us. an example. we talked about the ep icycles. brenda whom i met -- >> [inaudible] >> i want it filled up to the same level. [laughter] he was one of the father's of quantum mechanics, and you know, in the 20s built the theory that everybody knows about the uncertainty principle and the matrix and mechanics and then he went a step further and thought he's going to go into something else and said here's a proton and i need three ice cubes there and here. anyway, you got the proton and the neutron. there's a symmetry between them. i'm going to use the mathematics of symmetry to explain why they

are similar. he calls it -- which, of course, you know, and then we don't know where it went from there, but that assumption was wrong. that was taken mathematics that makes a lot of sense in your mind as a mathematician, but has nothing to do with the real world with protones and neutrons. they look similar. one of them is heavier than the other in absolute terms, but when compared to the mass of the two, then you think they are really very, very similar, and he went into symmetries and we know later they took u1 and did all kinds of things and the math came back, but at that moment, what you have as mathematics is a very powerful, absolutely useless -- [laughter] >> yes. >> i rest my case. [laughter] >> but it's a case i agree with. what i would say is mathematics

opens up the realm of possibility -- thank you very much. what the art of physics is is being able to sniff out what mathematics is relevant for reality and what isn't. now, experiments in observations is a key part of the story, and what you just mentioned ultimately it was observation speerpt that kick dated that math was not the right way to go. what we need to do and 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 we're talking about, the argument makes the assumption that a certain body of mathematics, space goes on forever, is reality. if that's not right, and 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 is the mode of thinking about many of the 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 hoer rye zone and see what's there. are we seeing reality or are we seeing mathematical ideas? that's the question ultimately that has to be confirmed or disputed by observation. now, let me give you an example where that mode could help us here. >> uh-huh. >> people asked themselves if space doesn't go on forever, can we observationally establish that? that would be a nice thing to do. well, one way to do that if it doesn't go on far and if it does have the shape like the surface of the earth coming back on itself, well, then, as you know, there's structures in space that give off light, galaxies, background radiation and so forth, if the universe has that shape, light hits our eyes, but it can pass by us, circle around the universe and come back a second or third time. if there's multiple copies of a

given october, that's a nice piece of evidence. no such evidence yet. it could be big, so big there's no time to cycle around, but that's what physics is about. doing mathematical calculations pushing to the limit, and finding observational paths. >> right. tell us about some of these specific theories. let's start with the one i dislike the most. [laughter] yes. >> the many worlds. >> i can't even say. [laughter] many worlds is a somewhat different character of proposals 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 -- >> yeah, i was worried # about that. why? >> why is it later, chronologically, it's the earliest, right, but marching through cron chronologically dent give you the best sensible way of where we are today. in particular, the many worlds

of quantum mechanics stands outside the margins that has the idea of the string theory. it's an interesting proposal and that's why there's a chapter devoted to it. >> it's weird though. >> you're right, it is weird. you'll notice in the chapter i come to the conclusion, i don't think it works. >> phew. [laughter] >> that doesn't mean it doesn't. if you talk to other people and various others they would sit here and say it does work. i don't want to give the wrong impression. here's the idea. the new idea of quantum mechanics in the early part of the 20th century where newton said tell me how things are today, and i will predict how they will be tomorrow. the universe is like a giant clock work. i'll use mathematics to turn the crank forward and predict things how they will be and that's the way of thinking about things was

accurate when applied to every day octobers like glasses or to the moon's motion or a rock you throw. newton can tell you what happens, you do the observation, and it happens, great. when people probed the microscopic reel, that fell apart. >> a different universe there. >> it's a different environment. let's not use the word universe too much tonight. [laughter] why should the laws not work on tiny scales. they don't. the new laws, the laws p quantum physics and the idea is 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 there's a 50% chance it's over here and a 50% chance it's over there. >> or both. >> no, no -- >> fine.

>> it's a 50% chance of each, and you can't do better than that according to quantum physics. when you do an observation of the electrons, you find it either here or there. you never find it half here and half there. there's never the 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 electrons 50% of the time here and 50% of the time here, how do you go from the fuzzy mathematics to the single definite reality that we observe when we do an experiment? nobody answered that question yet. shockingly, it's 2011, and nobody answered this. the proposal who comes from hugh ererett says this. if there's a chance it could be here or there, when you study the math diligently and follow this through and apply it to the

experiment 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, and 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's two of you thinking that, and that's just the single example within an electron, the idea is that all of the possibilities allowed by the quantum laws are realized in one universe or another, and in this grand collection of possibilities, that we call the qawn tule multiverse, that's the idea. >> but you believe it? >> no, i don't believe it. i don't believe it because i don't think we've established yet in any of the analysis, and, again, this is controversial. some people think we have. i don't think we've established yet how this way of thinking about quantum mechanics describes our observations. that link has not been

established. >> i don't think we understand quantum mechanics. >> no, but that is the same statement. to understand quantum mechanics 5e7b how it links up with observations, a went have not answered that yet. >> it 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 microworld. let me -- >> a small point to that -- >> mostly. sometimes there's large objects -- >> i just want to emphasize that what you're saying explains why quantum mechanics is counterintuitive. >> it's worse than that. [laughter] >> well, maybe. whatever word you like, whatever word you like. >> einstein couldn't accept it. >> exactly right, but why is that? there's two parts of the story. >> why? >> i was not asking you a question. >> let me answer it.

>> there's a part of mechanics that feels uncomfortable because it's at odds with experience. that makes it hard to accept the crazy ideas. >> right. >> but if the crazy ideas have been fully worked out mathematically and the link to observation has been made, which is hasn't yet, then we 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 problem lissic motion of an electron. when you are trying to get your next meal in the desert, it doesn't matter if you understand quantum physics but understand where the animal will be in five seconds so you can jump in and eat it. that's why our brains have developed to really be newtonian. the fact of this and i take the water out and through it, somebody could catch it. that's the newtonian calculation

because it's intuitive. if i throw an electron, they can't catch it because they don't have the intuition. it's not counter intuitive other crazy, but there's a puzzle we have not answered. how do you get to the reality? that's not been solved. >> brian, are you a gambling man? talk about your truth habits, but do you gamble? >> i've been to a casino. >> there's roulette and the ball rolls around and falls at one number, there's 36 numbers and 0 and 00, but chooses one number -- >> yes. >> do you have a problem with that? >> doo i have a problem with that? >> yes, do you have a problem with that? >> no. >> why do you have a problem with the protocol of the electron? >> i don't have a problem with probabilities, but a problem with the theory that's incomplete. >> [inaudible]

>> einstein -- >> einstein said the theory is indeplete. >> for a different reason. >> it had to do with a lot of things and the interpretation and all kinds of other things but he had the vision to understand something we call today entank lment and things like that and the epr paradox and so on. i'm asking something at the lower level. you have no problem going to las vegas, well, maybe you do -- [laughter] gambling, no problem as the guy on the prairie hunting or whatever, you have no problem with the wolves or whatever you are hunting going one way and another time you chase an animal going the other i way. that's newtonian in a sense. would you need a see a shrink if the wolf went one way and another way the next? >> if it looked like my mother or father. [laughter] >> here's the point.

you do an spearmint, and when you observe it and open the backseat, the electron goes one way. it can go to the right, and in another universe, it goes to the left. when they don't, they go both ways; right? we know that. we can think. we're not the underthoughts. >> we're trained. >> yeah, it's okay for us. goes both ways and interferes with itself. typical youngest experiment with one particle; right? you have no problem with that at all. when you open the box, you toss the coin, you roll the roulette wheel, and it goes one way or another. why is it, and by the way, the problem is not of mathematics, and you know that. from mathematician, operates and -- >> just to get a sense, how many people are familiar with -- >> i was referring to you. [laughter] >> but i think there's only a little bit -- >> let me just be clear her.

my problem with quantum mechanics has nothing to do with the fact is involves probabilities. >> oh. >> i'm happy with probabilities. >> no more many worlds. >> somehow -- >> well, that's the al ternivetive -- alternative to the probabilities. >> no, absolutely no. the people who believe in many worlds believe in probabilities, they are just trying to make a link between the probability predictions and the fact that when you make an observation there's a single definite reality, and that link is a subtle one that has resisted solution now for about 50 years. if you were talking about a person who does believe there's many universes in quantum mechanics, you would ultimately find they are trying to explain the very same probabilities that neil was trying to explain in the old days. it's not like einstein where einstein had in his mind that fizz -- physics needed definite

predictions. no, no, long sense beyond that because obvious vaixes show the probabilities work. we are trying to close the gap in the actual quantum form. my suggestion is we move on from this because this is simply one variation of the multiverses. >> what's your favorite multiverse? >> you know, it depends the way in which you judge favorite, but i certainly have a leaning towards those that have a chance of being experimentally tested in the shortest time frame, one way of thinking about the subject, and from that, there's a multiverse coming from string theory which i find particularly exciting along these lines which is called the brain multiverse, and it comes from the following idea. within string theory, and i think many people have at least heard what it is, the idea that the elementary constituents of

little tiny particles and the old way of thinking of things, little tiny dots, the new idea of string theory within the particles there's something else which is a tiny filament that vibrates in different patterns and it looks like a little piece of string. the idea that deep in the heart of matter there's little vibrating strings. as we study the math of the 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, giant sheets with two dimensions or three dimensions on so forth, and the math suggests at least it's possible that all that we know about every star, every galaxy and so forth is living its life out on one of these membranes. it's a 3-d membrane. that's hard to imagine. imagine a big slice of bread where every star and every galaxy 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 we will are part of the grand cosmic loaf, to use the metaphor, with our universe one slice of bread, one university verse in the grand clerks. why is this exciting? well, there's a chance that this proposal might be tested. how would that be? well, the colliders slam protons against protons at high speeds and the math shows in the collisions if there's enough energy and moving fast enough, when the protons collide, they create some debris that get injected off of our universe, off of our slice of bread. how do we know that? well, the debris would take away energy with it. that means there's less energy left for our detesters to measure after the collision than before. there's some missing energy. people are working for the

missing energy signatures, and if the energy is missing in the way the math suggested it would be, this is evidence that the brain picture is correct suggesting there's other universes out there. >> have you been depressed recently? >> why do you ask? >> because you know the lac has not found anything, so maybe at 14 they'll find it, but right now, the results are negative on that, and they are negative on something else. >> it's early. if they found anything, they will not announce it because it takes year of analysis before they do. you make a great point. not depressed. i'd be thrilled. >> if it wasn't? >> if it wasn't because this is an experimental science. if we ruled out string theory, i'll be on the record, would i be depressed? i'd jump for joy because i'm not wedded to a theory but towards working towards --

on working towards truth. you go around once -- >> in this universe. [laughter] >> i don't want to work on a theory that's incorrect, so if it's wrong, i want to know today or yesterday, so it's not a matter of having a certain emotional investment in one outcome or another, but 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 throe that one away. depression, no, excitement. >> good. you're always exciting at whatever they find? >> that's the nature of reality, the nature of the universe. it's exciting. >> the lac ran for a full year now, the end of march is when they started. of course, they had a break, but they create so many collisions every second. you know, it's trillions and trillions and the data accumulates, and that have not found anything. the first thing they ruled out is extra dimensions.

they have not found them. i want to lead in another direction in that at least for a short while. i just heard from stern that they have not found any proof of supersymmetry either. >> that's correct. >> just happened now. as of now with the data they collected in a year, they have not found supersimilar fry. -- supersymmetry. that's another place where the math and physics might diverge. let me add something. i'm not here to play your psychologist. >> how many people are familiar with supersymmetry? >> i'll explain it, don't worry. >> okay. >> let me just explain it first. [laughter] >> you don't trust me? >> you know, just, i don't know, you live here. they can come and visit you. i come here once in awhile. >> fine. [laughter] >> the full name of string theory is superstring theory.

>> i'm not talk k string theory. >> the first is what he's talking about is supersymmetry. what is it? well, supersymmetry is a fan tassicly -- fantastically interesting symmetry that relates things we previously thought were unrelated. if i take this glass and turn this glass around, it's highly sigh membranes rick -- sigh met trick. each point is related to every other point that suggests none is special. each can be turned into the other point by simply row rsh rotating it. there's a class of parols in the -- particles that are important to us, electrons, protons, and neutrons. those particles seem to be different from a class of other particles by vur chew of the fact they spin around differently. those particles have something

called spin hats, but there's other particles we know about with spin one, that's like the foton, and there's hypothetical particles not yet seen with spine zero. supersymmetry is a mat mat call symmetry relating all those particles and they can be rotated into the others. now, if that's the case, for that to be true, there has to be a certain other class of particles not yet observed that the known particles we know about turn into under this kind of rotation. those are the supersymmetric particles. for the electrons, it's partner under this semitry. the cork and neutrons, neutron. i don't name them. for every known particle there's a cousin called a sparticle.

we are looking for the sparticle. if they are there, it confirms the idea. if not, we don't either have sufficient accelerators or it means they do not 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 math mathematics and physic is goes back to an english fizzist who united quantum mechanics with relativity, and when he did that in 1928, something like that, he looked at the equations. now, i'm going to sound like brian, maybe in another universe i'm brian. what brian says is we trust the mathematics -- >> let me finish. you're putting words in my mouth. 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 it. i trust observation and experiment. >> fine. [laughter] paul was sitting in front of the fireplace at cam bridge and looks and realizes a way of units special relativity with quantum theory creating quantum field theory. when he does that, he gets his mathematics, and i will not put words in his mouth, and he looks at the mathematics and it tells them there's negative energy levels for the electron. well, maybe anybody else looking at it says this is just the math. it's like when you solve an equation and there's two solutions, one is imaginary and one is real. ..

>> that's right. >> so there is so large

segment that will take this idea seriously. working on it one way or another since 1970. says scientists around the world of the campaign course. this could be an exciting moment that could be capitulated in a very big way. and they could go back to the drawing board. >> some other ways? >> and other simple one is to think very carefully about the big bang. we touched on that earlier which is the idea the universe went rapid expansion early on but one of the things that we don't talk enough is that the big bang theory is the bang.

it tells us how the good universe evolved from the split second afterwards but it doesn't tell us what caused the swelling to occur. people have been working very hard to fill in the gap. the reason i bring this gap up is because there is a poem for what caused it called inflationary cosmology the recognition going back to einstein that gravity and the ripples of. if you drop the glass it falls. the earth pulls things together. that is what it does but einstein shows under exotic circumstances it can push things apart. the belief or the possibility the early universe that exotic environment was realized through the energy of space and they gave rise to

ripples of gravity pushing everything apart which is why it swelled in the first place. but if you study this in detail, it seems to show the award swelling was not the unique one time event. there could be many big bang beginnings at this thing to locations and a much larger cosmos each giving rise to the observable universe that we couldn't have been put it could be a universal upon universe in pot datapoint universe that is inflationary. but what is nice is the idea that it underwent the rapid swelling early on, that has been subjected to interesting observations. if it went through the rapid swelling early on, here's what would happen. quantum jitters or fluctuations and the young universe would be stretched

out by the rapid flow and smeared out across the sky. if i had a little balloon and wrote to a little message on the surface you could not see it but if i blow air into the balloon as it stretches my message is smeared out over the surface and you can see your -- see it. that is like a message with the jitters has space underground the rapid expansion the message is spread out as tiny temperature differences in the heat left over called the microwave background radiation. we have mentioned that he leftover and the way the temperature varies from point to point* is exactly in line with a mathematical calculation. that is a very convincing piece of evidence to take the theory quite seriously. >> host: i think it is taken seriously but even

astronomers and physicists question doesn't that imply the existence of something? to think that those microwaves fluctuations fluctuations, there are galaxies that are spawned from them as well. does that really imply other than the mathematics, does that really tell you that if you see this picture? >> no, no, no. that is why i am not saying these ideas are proven. you may recall when we started the conversation i emphasize these are ideas that come from our investigations. until we have observation of them we cannot believe that it is real. let me take a further. what happens is when you have a theory that can

describe things you can see if bolsters your confidence to follow further. that is where the confidence comes from. that doesn't mean there has to be of the realms. there are other versions there is only one role. varo -- they're very hard to come by and feel very can try too mathematically. they could be right to put those that don't have that quality are the ones that do give rise to the other universe. do we know they are there? absolutely not but the possibility it is worth further study. what sort of experiment would give you an insight? it is rhetorical. [laughter] if you have the expanding wells imagine as a big cosmic bubble bath. we are one of those baubles.

they can collide. similar they the universe as eight expand could collide and smash into each other. having a fender bender that collision ripples through the heat so scientists look for the background radiation with the temperature variations that may indicate we are hit by another universe. is there any positive evidence yet? and no. it could be too small for the current levels of technology to access but that is the way to have observational evidence of the universe you cannot see. if it is the best in our universe. >> host: there have been several generations looking

at that microwave radiation. we know all lot that it is uniform? it is very, very small. give us something concrete. here is a universe and they collide. i don't think they could exist on the access. what is the space? let me finish. [laughter] so you crash t when you give the impression there is something missing but not fully comprehending the idea. >> host: i know what you are saying. the hyperspace. >> guest: no, no, no. knowledge could be a dangerous thing. [laughter] it has nothing to do with hyperspace. it takes place in the

ordinary dimensions. the wider cosmos that you have trouble grasping, think of that has a big sauna. think and three dimensions that is filled with energy that causes the outward gravity. what happens is region by region the energy could degrade and holes open up where the energy turns into particles. our universe is one of the regions where that energy has degraded. think of a block of swiss cheese. unimagined where the energy exist forcing things do experience gravitational pollution. where it is degraded is first tarzan galaxies are formed. it is just a different holes

>> so it is really one at universe. >> languages confusing. >> host: fine. love me ask you talked about the multi verse whatever that may be. of wheat have these two universes' colliding here is the back -- background radiation fluctuating how you know, it is not from that 10 not anything else? >> guest: you ask that for everything what is the best explanation? you try to rule out all of bir -- and all other ones that you try to get to calculations. other businesses have done calculations to the but

background radiation? what would happen? it would vary from place to place and did you find temperature variations and no other competing explanation then your confidence would grow. >> host: let's assume that it will happen some day than we have proof but until then agreed don't know. talk about the other multi first theories. >> guest: what time is it? only because it wants to make sure people have a chance to interact if they want to. i am not sure of the format. i have no place to go. [applause] >> anybody have a question? >> we have to museum staff

members with microphones flocking up and down the aisle. >> i know the field moves quickly, but in 2006, one theoretical physicist from canada wrote the book entitled the problem with this six. >> the trouble with physics. >> excuse me. it seems he has abandoned that theory chiefly because of lack of experimental corporation in. has he abandoned too early?

and is carry on to the future? >> he is a good friend of mine. he thinks it is misinterpreted. he said what he was trying to say is that it is not the only approach to put together quantum mechanics. there are other approaches. he is the founder of a competing approach. part of what he said was too many people work on strings period not enough on quantum gravity and the field would be at advanced if there was a more balanced approach and a string theory was sent their primary one looked upon as the solution. i agree with that. i feel that is evidenced by a different idea is.

the reason why more students work on the string theory frankly it is a more attractive and appealing and promising approach. that is how they make their decisions but i full well i agree it is great and to help found the premier institute to work on a quantum gravity. so there is a way to do this string theory and building it to gather but the main point* is there are other approaches. >> my question is related to the many world's theory. basically about the fact right now in another world like to be asking the question of someone else.

whose world is it? do we create the world's? whose world is a of the world? >> guest: according to the bread and butter been a world approach as others have developed, if you're in a situation where quantum mechanics says there is a possibility of this, all of those possibilities happen. it is not a matter of shoot -- and choosing. it does not allow any possibility to go and realize. i am teaching this right now. this week as me said it up last week if you go through the mathematics we go

through the 1957 paper if you read the thesis? it is a mathematical gem where they make of potent case. there is still thing is missing but when i read the thesis i am taking a long and i am very critical because it is but idea i don't think it is ripe i and taken along for the argument as the last up. i don't think he quite got that right but nobody has filled it and but others disagree say it has but if it is correct, all possibilities, sometimes i am asked, does that mean there is on universe where sarah palin is president? [laughter] i have to tell them have it

has to be compatible with the laws of physics. [laughter] [applause] >> you mentioned quantum gravity unifications, do any of those seven implications as far as the multi bourse? >> i don't know enough about them. not without any degree of confidence. with all of them, quantum mechanics is part of the story. if the quantum multi vs. truth and they will likely embrace it in the matter we have been discussing. but in terms of the other most diverse ideas, i am not sure what they have to say about that. >> in your may baubles world's come a we know after the big bang certain

criteria had to be met or the universe would have blown apart. in the other world do they have to follow our laws to succeed lowered to some of them die or how does that work? >> one of the depressions to have faced over the last 20 years is exactly what you are asking. we have measured features of the universe, and dume -- members and the strength of a gravitational force and what we have found is we understand the numerical values the experiments are revealing but we cannot explain why they have been found. you may say should we care if it is heavier or lighter maybe we should not worry. but you should because of that. if the numbers for different then the universe as we

observe it would not exist. by have a machine with 20 dials and grab -- randomly make the magnetic force recur everything you do the universe is not eve of the way that we know and the stars and planets do not form and how would like to exist? the question is why do those numbers have just the right value to give rise to the universe of what we are familiar with? we have hit us dead-end. the multi first task is a different way to think of a question and along the lines of what you suggest. maybe there are many men universes' were the numbers vary from universe to universe and most of those could not exist because the whatnot the there. the answer for why is. >> we could not observe any

other. that is an approach that may ultimately hold water. let me give you an analogy. it happened to be two years ago with my four year old helps you to understand. [laughter] he is six now and we went to a shoe store. this was the first time he was old enough to think about what was happening. thank god measures his foot and puts on the issue then he turns to me and says wasn't it lucky they had my shoes size? [laughter] as i probe further i realized that shoe store had flensing goes to size and it just so happen that it fit his book. what a mystery that would be but when i explained in the stock room there are many, many different shoe sizes

the mystery went away. if you think there is a unique object to try to explain that can be mysterious but if you realize it is not unique though one of the vast collection it evaporates and that could be true. just as we have found the issue size that fit his foot we could find a universe that fits our parameters that could be the answer. >> 82 preface the question are you familiar with ronald and in that time machine experiment? >> guest: i am sorry. i don't. >> a theoretical physicist at the university of connecticut. right. i guess that you could twist space times sufficiently.

>> go back in time? >> course of the atomic critical time. you cannot go back before but couldn't something like that be used to test of the theories? >> guest: now we are in and speculation squared. [laughter] how would time travel interface with these ideas? one of the big puzzles of time travel is to go back in time than you a fact the way that may affect your own existence. if you kill your parents than you do not exist we see this with back to the future. is a variation on the paradox can you imagine that you could travel to the future.

unimagined that i did and i want to who have been-- want to see what happens with string theory i go to the library and ic surprisingly the theory and the author of the paper is my mom. that is weird because my mother once made to be a doctor so i am a doctor. [laughter] i look in the acknowledgments of the paper and she thinks may for teaching purposes six. wholly crap. i have a lot of work to do. use her little machine and i start to tutor my mother and it is it going well. [laughter] of them after two years out and the world will she writes that paper? then i a say i know what was then the paper let me tell her what to write. she writes a paper and

everything turns out. know who gets the credit? [laughter] is not the question of credit but where did the information come from? she did not think of it she got it from me but i got from her paper. now how does this relate to the multiple universe? here is the fans of all idea. imagine when you travel to the past, you never come back to your own universe. you come back as the quantum universe to the other copy. if i go back in time and kill my parents before i am born i would not be born in that universe but so what? i am still unaffected because my parents are unaffected that is a little far afield but that is some

interaction with a time travel. >> something i recently aware of his the einstein theory that this is now that we're so lucky to live in a time when people can produce with these elements. hypothetically if they could create that in a room room, assuming they can do all the basic theories of quantum mechanics breakdown? if you have a situation? >> guest. >> host: brian is the final arbiter but that was created write here at m.i.t. also and colorado at the same time. b.a.t is to cool some adams to a very low temperature and what happens and is the wave of particles, they

overlap so you create quantum mechanics for a large section of objects that of think that relates to what we're talking about. >> it comes out of basic quantum mechanics. >> if you have the bows einstein all of those waves become a one point*. >> guest: i would not describe it that way. >> that is out m.i.t. describes it. >> i am not sure what they have in mind. >> they describe it that way. >> we have time for one last question. >> i should preface this by saying i am a die-hard. i was impressed by an observation interfirst book

where you noted the duality one overtime that seem to have a special meeting there is something i don't recall the details to prompt the idea and to pursue anything like this? if you imagine there is a moment this is zero microscopic into a free. ticket to all the different versions we could look at the same thing to be happening in that one over interpretation and going

back to the moment of the big bang now the singularity turns into an illusion. looking at the inappropriate said of access. so here is that an age of us now the whole ball tiber's repeated back in that first moment of time so is anybody pursuing those ideas? >> one of the surprising strength series is you are recounting as it universe bigger beyond expanding if is equivalent to the universe. that is the one over your talking about. i would use the word amateur doppelganger. but the distinct

mathematical description of the same reality is two different ways to look at the same thing. but how would cosmology are singularity look? right here at harvard another cosmologist studied cosmology in the context to have the cemetery and they did find you are suggesting. what is the singularity? to run the universe back in time to infinity? when the universe gets more than one planks length or smaller, the temperature levels out and starts due to an turndown because of the summit tree -- asymmetry talk aboutea