String Theory - Lawrence Krauss and Brian Greene

for those who arrived recently I'm Lawrence Krauss I'm director of the origins initiative here at ASU and it's my great pleasure in a minute to introduce my friend and colleague Brian Greene Brian needs little introduction he's probably known to many of you he's not only a distinguished theoretical physicist and one of the people driving a very exciting area of physics called string theory but he's one of the most successful and well-known popularizers of physics or in fact of science in this country and around the world now what we've decided to do something a little bit different because many of you may have seen his television show or read its books what we thought in order to provide a in some sense a break from the continuous lecture format is is we're going to have a dialogue and we're going to talk together about about some of the issues that of physics and and science education and communication and then and then we'll open up the questions from the audience so I'm very proud and pleased to welcome Brian Greene to the stage here today Brian thanks Brian this will be here's the experiment see how it goes I thought we'd begin by asking in some sense what what made you become a physicist what got you excited and and why did you choose the area physics that you ultimately decided to work in you know I've never I've never thought about that before no it's a great question I you know I think like many of us it's probably true for you too and I've never spoken to our community but I started in mathematics you know as a little kid my dad would set me the and I was just amazed at how with just a few little tools of knowledge you could actually calculate things you know multiplying numbers and do calculations that perhaps no one had done it before no one had done before because they weren't interesting but but it was still you know fun for a kid to do and then later on I must have been 12 or 13 or 14 you know I went through the kind of thing that most everyone goes through why am I here what's all about all that kind of the interesting questions those deep questions and it just occurred to me that if if people are still asking those questions there must not really be some fundamental answer so maybe the best you could do is try to understand the question and when I learned that math could help you learn about those questions you know how the universe began even what it means to ask that question I was pretty hooked so essentially you came in from math I think yeah what about your parents do they were they surprised disappointed my mother wanted me be a doctor for example and she was very disappointed when I became a yeah I've had exactly the same experience in fact I still have that that that experience yeah I got a job at Harvard my mother said my remember my first job at Harbor was a nice job and my mother said it's still not too late yeah absolutely um no my my dad was a composer okay and as with many composers very hard to make a living so he supported the family by playing bass fiddle at you know weddings and bar mitzvahs and things like that really and and it's a vocal coach as well a singer my mom was a secretary for a veterinarian so was not a very traditionally academic household what about I know one of these I write books I wonder if it's a reason for you what about did you read books by scientists for me that was very inspirational did that affect you at all it did a little bit later on you know I somehow didn't know about this whole area of science books without the technical details until I was at least or 13 or 14 but it was really two books it was it was a Carl Sagan you know cosmos but it was also the ascent of man yeah Bronowski and those two really just stuck with me as a very potent way of communicating information without having to go to a course without having to study it and so that certainly was with me all through my education is something I valued okay so why then physics and not mathematics although well it was really just a recognition that math you set yourself the problems whereas in physics nature sets see the problem so it felt like you had the capacity to in the most grandiose language sort of touch eternity you know if you were lucky if you were among the lucky few whose work actually was relevant to the world you'd be revealing something that could stand the test of time and that to me just had this this pole okay though now got to physics particle physics and ultimately string theory what was that what what about that well when I was in college I had a real obsession with grad I'm hesitating I think I think that's true pretty well I'll say yeah I'm hesitating a little bit because it was a little bit odd I mean you know I mean many of you may be familiar too but you know well Stephen Weinberg's book yeah gravitation and corollary principles and applications the general theory of relativity here it says and I bought that book I didn't understand it at all I think was a freshman or sophomore but I used to walk around wearing it carrying it help you meet women or caressing it sort of I just wanted to know what was inside that book and then when I began to understand it a little bit and learn that there was this big issue how do you incorporate quantum physics into gravity I became very very caught up with that notion and basically stayed in that area ever since now I'm trying to remember because I think I was at Harvard when you were still a student there uh but with string theory already I mean you were interested in gravity but string theory had you know it was an interesting timing so I will and went to Oxford and in the fall of that year following really the big breakthrough year so at Oxford there was this sense at first when I first got there have to say the older students had turned back yeah quantum gravity at that before string theory it was the dead end dead good students want to do it you never heard their name again and more over there even particle physics students who said this field is drawing up and it was a real kind of depressing couple of months hearing the older students with that perspective but then you know this big shot out of the blue these discoveries in string theory just changed everything maybe now it maybe now it's time to talk a little bit a little sign so so maybe want to fill in a little bit about what's what happened what was the range of breakthrough that that that made string theory of interest to people and and sure we can go on I mean maybe it may be 30 seconds back on string theory itself yeah so as many of you may be familiar well I you know I guess they already the audience already knows all the string theory that's what you forgot where I was yeah SAS you know come on by anybody want a little bit of background to me okay good so you know in the in the 20th century the two big developments that we all study intently where Einstein's breakthrough in understanding gravity the general theory of relativity and the other breakthrough in a field called quantum physics that focuses on the completely other realm of the spectrum in terms of size the small things general relativity big quantum mechanics small the weird thing was when you tried to put them together the math just wouldn't work so this was a big puzzle and string theory is an approach that tries to resolve that puzzle put gravity and quantum mechanics together into one theoretical package and the only feature of the theory that really I think is worth keeping in mind because it's very visual string theory suggests a new way of thinking about the ultimate constituents of matter you know molecules atoms subatomic particles we view them as little tiny dots traditionally string theory suggests and i underscore suggests these are not proven ideas but inside of these little dots string theory suggests you'd find something else a little tiny filament a little tiny string-like entity that vibrates and it's called string theory it looks like a little piece of string and the idea is that the different vibrational patterns of this little tiny filament is what gives rise to the different particles the string vibrates one way it looks like a cork it vibrates a different way it looks like a photon so all the particles are the different musical notes if you don't mind that a metaphor that the little tiny strings can play that's the basic idea and and there's another important component of a very important component of it is that string theory to be to be mathematically consistent requires extra dimensions maybe it's very important they tent the strings vibrate not just in the dimensions we see but in principal dimension extra dimensions which is a major challenge of string theory because most of us usually most of us in the room usually or east of just four or three in fact us and you know and we rarely throw a baseball and have it disappear into an extra mention so maybe you want to talk about that little bit that's absolutely right that is one of the strangest implications of the theory so when I said that you put general tivity and quantum mechanics together in one mathematical package what I really should have said is there's a mathematical framework that when you study it you find that it fails if there are only three dimensions of space that is if you only have left-right back-forth and up-down these three dimensions that we all know about the math breaks and some people said well let's look at it even more intently what happens if there are four dimensions of space it still breaks five six seven eight still breaks but you get to a total of ten space-time dimensions and all of a sudden the math falls into place so that's where this strange idea that there may be more dimensions of space than the ones that we know about comes from and frankly I and many others have spent the most of my career trying to figure out where those extra dimensions are what their features look like and perhaps what implications they might have for physics that we can see in the world around us now in fact of course one of the big gum it's interesting this idea first came up the idea of x-ray mentioned early in the century in last century there was it was developed independently by mathematician and a physicist and the mathematician said well you know you can have these consistent extra dimensions that do interesting things when but the physicists rightly said okay if they're if they are there how come we don't see them and and the original idea was it that they were extremely small so they're so small you can't see that maybe you want elaborate on that sure so the gentleman you referring to Colusa way back in 1919 was basically studying einstein's general theory of relativity which had been so successful at describing the force of gravity and the language that einstein used was unfamiliar he used the language of curved space in fact curved space-time as the medium for mediating the force of gravity so right now according Einstein I'm sort of feeling myself being pulled down because my body wants to slide down an indentation in the curved space-time that the earth creates so it's an unfamiliar idea but a powerful one Colusa looked at it and said well that's interesting what if the other forces of nature namely the electromagnetic force also can be described in that language of curved space but the problem was Einstein had used up all of the known dimensions of space secludes had said maybe there's another dimension of space and maybe ripples and curves and that would describe the electromagnetic force and he did the math and lo and behold the equation for electricity and magnetism popped out by the simple assumption of one more dimension of space but then the question is where is it and you know I think it is interesting don't you think though that it's sort of an interesting differentiation between mathematics and physics he was just perfectly happy with that and it bothered asked the next question and I was it was Klein the physicists identity and it was Einstein - yeah you know so I mean at least as the story goes includes a sentence that Pedro Einstein and Einstein at first is very excited about this because he himself was fixated on unifying the description of all forces not just gravity so he loved this idea that by having one more dimension of space you could put together electricity magnetism and gravity in one frame er wow that was just what he was looking for but then like you say he said hold on this is crazy we only have three dimensions of space so this can't possibly be the right way to go he thinks about it for another year or two holding a publication of this paper yeah my the consternation of Colusa yeah and finally Einstein says yeah maybe this is possible but it was Oscar Klein who really then came along and said well here's how to think about it there can be more dimensions of space as long as they're really small the ones we know about are big we can really see all these dimensions because they're large but imagine there's a tiny curled up crumpled up dimension that's so small that we don't see it and in this particular case they imagined it had a little tiny additional circular dimension all around us the image that I like to use is imagine you're looking at a carpet from far away it looks flat but then you put your eye right down on it you see this little tiny loop's these little pieces of thread called the pile I guess so you see these little tiny circular pieces attached to the carpet extra dimensions curled up you don't see them far away the idea was maybe that's true of our universe extra curled up dimensions all around us so small that we don't see them okay so that's so that explains what we don't see them but of course the there it is over there the the job of physics is not to explain why we don't see things of course but to but to test the ideas and explain how we can see them or at least how we can tell that they might exist well maybe talk a little bit about the challenge and one of the one of the reasons that string theory uh is is is at this point has not yet sort of made touch with with experiments so maybe talk about that a little bit yes and I think you know jumping off from the historical line is not a bad way to go because after Kaluza and Klein suggested this idea of an extra dimension they did try to see if it could make contact with experiment and they found that for instance it was very hard almost impossible to get the electron a known particle of matter they couldn't incorporate it successfully into the theory and that was largely why this idea was ultimately dropped by the 1940s then string theory came along in the 80s and it didn't just allow for extra dimensions it required extra dimensions actually was i think it is interesting to point out that we actually really came along this early at least at 1660s yeah where it was first used to try and explain another force of nature and and actually i'm and maybe it's interesting question neither you or I were practicing physicists then but at that time I don't think you were anyway at that time speaker yeah at that time it wasn't ten dimensions it was 26 yeah and I was amazed when I when I sort of gone back and looked at that stuff to think that people that the questions were so desperate that people would be willing to accept not not six or seven extra mentions but twenty two extra dimensions and and maybe you want to talk a little bit about about I it would be the physicists would sort of be willing to make that incredible leap yes so you're right the earlier the earliest version of strength here I should say did require twenty two extra dimensions for this total of twenty six if you include time and I think the reason people were willing to take it seriously is twofold one there had been so many attempts to put gravity and quantum mechanics together and they all failed they all just broke down so when a approach came along which seemed to work but required something weird and yet that weirdness was something that had already been contemplated in one form or another decades earlier and sometimes people said well you know whether it's one extra dimension or two or five or 22 it's the idea getting over the notion that this is all that there is once you allow for more dimensions the actual number doesn't seem to really sway you much one way or got a bunch X but I was actually thinking going back I think yeah it's interesting to me that even in the nineteen sixties where they weren't talking about gravity they were talking about another force which wasn't so profound at that time yeah yeah there was just a big problem accelerators kept coming up with our particles and if particles everywhere and then the zoo was growing and it appeared there was no order that that when people when when this when people came up with an idea that they thought might provide order they were willing to at least explore this idea that's exactly right and and I think it's it represents the fact that it's not and we'll ask you about one things I want to ask you if you really think there are those extra dimensions in a moment but but the idea of exploring them and using that hypothesis and seeing where it goes without becoming religiously devoted to it I think is interesting is that you're willing to try anything to see if it works and then and in the case of the 1980s what they discovered well it did they'd had the right solution but asked the wrong question at least they hope they had so that's exactly right so the earlier version of string theory was not trying to resolve this incompatibility between quantum mechanics and gravity strange enough the earlier version of string theory as you say was trying to describe data that was coming out of accelerators worldwide that we're finding this whole slew of particles a zoo that you mentioned Momentis whole slew of particles without any order and string theory and its earlier version seemed to supply an order all these particles now being thought of as different vibrations of the string gave an organizing principle for thinking about this wealth of data the problem was there is one pesky particle that came out of the mathematics of string theory that was not found in the accelerators it was a particle that people a few years later recognized as just the kind of particle that you would need if this was a theory embracing gravity a particle known as a graviton so people said let's take a big step back reevaluate this theory not just think of it as a theory that describes the particles and footnote another theory had come along which did a better job at that quantum chromodynamics two of the people who won the Nobel Prize for it at this data writing right now in fact so people said let's not try to answer that question which that other theory does better anyway let's take this vice of this graviton particle make it a virtue think of this now as a theory uniting gravity and quantum mechanics actually it's interesting you talked to this vice and virtue I it may not be a secret to many of you that Brian and I have appeared on stage a number of times and a different in a more combative form at a debating string theory which we're not going to do today because I want the other ones yeah but no but but I was Yogi's yet no anyway I'm the what do you talk about this the advice to virtue thing I mean in some sense the the difference for the in string theory of the 60s and the 80s and since the time is a huge leap that string theory in its modern form of trying to track this attack this fundamental problem of quantum mechanics and gravity and and let me make it clear it's that it's the I'll say it in public it's the it's the best bet at this point okay I'll come back to other things about it but but technical crew can you just cut out that snippet and send it to me just that little bit right Yeah right there no I wear it completely but it's completely different in the sense that it's really right now guided by mathematics for the most part and so I wonder whether you want to comment on this roll of aesthetics and mathematics versus experiment because it's all it's a very it's a new leap in a sense so it is a new leap in some ways but I think you would agree that if we look back at the history of physics say in the in the 20th century there are many moments where mathematics was playing a pivotal role in guiding the next step now was certainly the case for instance in quantum mechanics it was much more an interplay between data and mathematics because we were describing a realm that we could probe experimentally so we had the shining light of experimental data to help guide the math is wonderful back and forth between the theory and the experiment you know Einstein though was largely guided by just his powerful intuition and mathematics I mean the idea that gravity is associated with curved space-time I don't know about you but I've never gotten over the all that I initially felt that he came up with this idea it's just how in the world did he come up with this and it was just this powerful intuition that was working within the confines of mathematic oh yeah although I don't he did have pictorial experience he did have those Gedanken experiments the idea that light you know think of an elevator accelerating he tended to think pictorially and ultimately he he forced himself to learn the mathematics he needed and was almost beaten by a mathematician in his own game that's right but I think it's pretty clear that it was not just this unbridled pictorial sense this unbridled creativity it was working within the the context of a mathematical framework that really allowed him to go forward and I think the difference today is we're in realms that are beyond current abilities to probe experimentally or maybe not we'll see it the Large Hadron Collider there's a possibility so we have to be guided yet further by mathematics and could mathematics completely lead us astray yes it's certainly possible I don't think so but it's possible why don't you think so well it's just the experience that we've had and it's also this deep-seated sense that mathematics is this language it's almost tailor-made to describing the universe I mean we have as you say I don't know if they're in the audience right now but they'll be in the program later on you know there are our folks in our community who have been rightly lauded because they came up with theoretical ideas took them seriously that yielded predictions for a particles that had never before been seen and then people look for those particles and found them I mean it's kind of breathtaking that you do this calculation and these symbols on a piece of paper that you got to by following some well-defined rules a language if you will yields a new insight it's and it's confirmed in fact you know maybe that's something we should spend a minute on it because it actually in some ways relates to to the talks we heard earlier and came up at our meeting it's more than breathtaking it's actually humbling and intimidating the notion I know Steve Weinberg who was here earlier has said that that the idea that you're sitting in your room working on a piece of paper the nature actually obeys the laws that nature you know listen not listens but obeys what you're writing down it it is almost incomprehensible when you're actually working on it's it's thrilling but intimidating at the same time and I think one often sees it's surprising to me that that physicists are more seemed to be more willing to sort of throw caution to the wind in that regard we talked about the fact that for example one of the reasons evolution isn't more lauded than it might it should be it's evolution is one of the most remarkable remarkable scientific ideas and in in that's ever coming to come up and and certainly Darwin we I'm Stein has gotten great press but but Darwin did more actually in my opinion but one of the reasons is that he didn't actually make predictions it's interesting he didn't say hey there's gaps in the fossil record we should we should look there and it's at estimating when you find that you could vindicate it but in physics we tend to say hey this theory will fall apart if you don't find X or Y yes but at the same time well let's ask what would fall apart I mean this is the problem with shrinking in some sense right now we don't have something that would fall apart if you didn't find X or Y that that's right and framing it that way and you using evolution as a backdrop I think is quite reasonable because in a way we're not using the right language right I mean for evolution as people who are describing earlier you know this notion of it just being a theory is sometimes used as a strange and really unjustifiable weapon against the theory because when we as scientists use the word theory means something very specific you know the best available explanation for the data that we have at hand and we're most happy with the theory when it makes predictions that are confirm or confirmable and string theory does not meet those criteria so in more precise language you know string theory should be string hypothesis you know David gross discussed as a string framework I use the language string hypothesis no I I think it so I've always said it's unfair to evolution to for string theory call today and then I'd have to agree with you actually I'd have to agree with you good week could we get that you know but there's you know it's just historical precedent that this is the language of going into but back to your question in particular we understand a lot about the means just use the language string theory and we have in my opinion achieve things in that structure that I when for instance I was a graduate student starting to work on this I never thought that we'd get this far in the length of time that we have been working on it but we've not yet gotten to the point where we can start with the equations and come up with some definitive prediction such that if it is not confirmed we give the theory up I mean vaguely we can come up with things like that but they're so Universal that it wouldn't really rule out strength II would almost wrote all physics if it weren't found and that's not a happy place to be and you know it's funny how you know not with you but I have encountered some people who almost interpret that as a situation that string theorists are happy with because it's some kind of I don't know job security or something like that people don't understand the tenure exists or something like that but the bottom line is I certainly feel and I'm sure all my colleagues agree that if string theory is wrong I really want to know right now right I'd like to know about ten years ago because I'm not in this game to prove one particular theory right or wrong in the game because I hope that I'm part of a generation that takes us one step further regardless of what that step happens to be so we're working very hard to try to come up with things that we might test and there are some circumstantial things that we could talk about that might happen at the Large Hadron Collider they're probably but um you know we cannot do what you asked namely say this falls apart unless you find that now in fact actually you know hit an important point people tend to think scientists are wedded to theories and in fact scientists most often want to be wrong more more importantly they want their colleagues to be wrong and okay and because because it gives you a chance a chance to discover something new and so so in a sense we want to be surprised by nature in fact it's fair to say that you know there's an interplay between theory and experiment and we try to talk about that a little bit and sometimes one leads the other and if string theory has any validity it'd certainly be an example of that usually it's the other way around usually experiment surprises us and and and derives us and and and so the other thing I want to want to get elaborate on is that so straight there's a problem that right now we haven't yet made contact with reality but there also is the mathematics of string theory have gotten you could either say more complex or more fascinating and and in fact if the theory has become much different in fact strings may not be the most it made me a not only made theory may not be the right word strings may not be the right word maybe you want to talk a little bit about that yeah so one of the big breakthroughs in the theoretical development of string theory happened in the mid 1990s where techniques were developed to go beyond the approximate methods that had almost universally been used in calculations up to that point and when people employed these more exact techniques they were able to reveal aspects of the theory that were completely hidden previously and one of the things that was revealed is that the description I gave in terms of the fundamental ingredients being these filaments the string like entities is incomplete the theory seems to also have within it objects that are two-dimensional looking more like membranes or 3-dimensional we call them three brains generalization of membrane four dimensional entities and so forth so there's kind of a democracy if you will of higher dimensional shapes that play a role in the theory strings were discovered first because they're the easiest part mathematically to reveal but if we had the exact techniques from the get-go we probably would not have singled out strings as the one entity by which we named the structure so yes that's one of the big developments and that has suggested a whole other way of thinking about the theory yeah it may it may if it may provide a slight hope about other than observational signature as well get to an assessment before we get to the possibilities what what do you say to people not me of course but what would you say to people who would say that string theory has fallen on hard times whoever I have someone ask me that's that question you know it's a great question especially because no doubt some people here are aware that some books were written not too long ago which tried to make a case of that particular sort and what I would strongly emphasize is that the bread and butter of science and the exciting part about physics is you go forward into the unknown and sometimes there are very fertile periods when there are huge numbers of breakthroughs and your understanding is just leaping forward there are other times when the theory surprises you in ways that make you step back and really really and think about things now a theory falls on hard times when neither of those two things are happening when it stagnates yeah and we are nowhere near stagnation we are in a period we are reading and trying to take all the things that have been discovered and find how to best organize them so that we can gain the deepest understanding of this theory but because there is this progress this steady progress we feel the theory is quite healthy but perhaps going in directions that were unanticipated if you view it in that light I think the theory is not fallen on hard times per se if you view it has a theory achieved the goals that it has set for itself No yeah no yeah I mean that was part of problem there were some pretty lofty goals set at night like a is that as if made it seem as if by the time you know you had gray hair the the ah the and I was losing mine just make that but uh that the theory be solved we know everything I mean there were claim is made in the night in the nineteen eighties they were the important thing to know as you know those were not malicious claims yeah or were they claims coming from some sense of trying to hype yeah it was really coming from a place of excite excitement I think you know again you know during that period it was so wonderfully exciting in in in the 1980s early 90s there was this real sense that this is going to take us the final step to the deepest understanding and look the well seasoned researchers knew at that point calm down everybody you know this may be an interesting development but it's bound to be hard to get it to conclusion one of the ways when can this and I don't know the answer it's this particular question one of the ways you can try and judge how a theory is doing is where students are going and in fact we staged once when we were having a debate one of my colleagues the mode the fact that the the good students were going to strength Irina and you point out rightly I think that students vote with their feet and and what's exciting is what students go into and so it was a good sign that the good students were going to string theory is that changing at all is I mean are there more students doing other things that are harder to get students work on spring theory at all no certainly I mean my experience is no but I have certainly encountered students and maybe it's because my particular research focus of late has been more at the interface of string theory in cosmology I tend now to attract students that want to work in that domain that are not working on on pure pure string theory per se but trying to use the theory to gain some contact with observational data but I think that in terms of here to do a survey I think that it's quite similar to what it was years ago in terms of you know the most theoretically oriented students see this as an opportunity to make the biggest possible contribution which of course means the biggest possible risk that's how science works it's risk now I don't want to believe it it's the last question this guard but but what would what if anything would cause you to stop working on this and and working to direct direction if you started to work on it you know that you want that's right just you know something must be wrong well let's yeah what about nose in the Phoenix like that's what now what uh what would stop me from working at I guess I still working across mall jeans but by anyway it does matter which I'm Pro bucket if if if for instance two things I can imagine and this is quite possible some buddy comes along maybe it's some new student looks at the theory and says you guys have missed a fundamental inconsistency a fundamental mathematical flaw that is absolutely insurmountable that would be enough to say okay we have to let this go and I should say that has almost happened periodically in the history of the subject but people then looked harder and the math actually worked when you and by the way that I should say that's the kind of confidence that that's interesting because that's the kind of thing that drives you further when you think something's gonna be wrong and you find out boy the mathematics solves things I'm as a theoretical physicist that does give you more confidence that there's something right about the theory yeah you know absolutely I mean there was anomaly having to do with yang-mills degrees of freedom that trace F squared had to be equal to trace R squared which came to a total do I just want to see if they can type this out oh I say okay you can yeah that's close yeah that's not bad well it's pulling up a little bit here yeah actually I think out now are we going to get it to like some endless loop right here in factually read we are so good so I'm gonna yeah okay okay got you string loops but actually I think the way he wrote the equation down was right I think you may have discovered it but but the second thing back to your question is if a better theory came along I mean what we are constantly doing is we are looking at the landscape of possibilities and if somebody came along with a newer idea that we're like wow that that may be retained some of what we've done in string theory but takes it to a place that gets rid of a lot of the problems that we were encountering but that's the kind of thing that would make you drastically shift your focus okay now I hate when people ask me this question but I'm gonna frame it because you well the question is so where do you think then people often ask where is the next great breakthrough and and are we say if I knew I'd be working on it so let me just put it that way but where do you think the most fruitful direction in string theory is right now that may that may have the greatest payoff well I do think that the connection to cosmology has great potential I mean if you're going to test this theory there two ways either you tested in an accelerator you slam things together and we can talk about what yeah what might happen it's good before you test it through astronomical observations making use of the fact that the universe itself we like to say is itself a giant particle accelerator because the early universe was very energetic very hot things happen there that might be sensitive to the exotic physics that we're talking about so potentially the imprint of that exotic physics might still be with us in astronomical data so that's where my focus has been for a number of years and look we've done some calculations that suggest maybe in the microwave background radiation there could be a signal when we first did the work it seemed quite exciting to me as we looked further it began to feel a little bit fine-tuned and and unless an absolute consequence of string theory so who knows maybe they'll find something but again if they don't it won't rule the theory out so it doesn't quite reach the the level that we want but I should say that when I came in started being a research physicist if just a few years earlier than you it was a similar idea that's one of the reasons I got involved in cosmology the time it was something called grand unification unification of the non-gravitational forces required a great leap not quite as great leaper string theory but still a very great leap from where the experiments were and it seems to me that the universe and that's what makes the universe exciting one of the things is that because it's growing at early times was smaller hotter much more energetic and so at early early times there were energies that you could never achieve on earth in a trés drole accelerator that we're there and so the universe is a big big particle physics device in a sense and that's really what got me interested in cosmology early on too so if you don't mind another analogy just to amplify that idea because I think it's a very potent one if you if you have a balloon with no air inside of it and you have a really fine tip any write a little message on the surface of a balloon you know it'll be too small for you to see but then if I blow air into the balloon it stretches out my little scribble into something that perhaps you can clearly read so the idea is that the early universe might be affected by these little tiny strings if string theory is correct or even the physics of grand unification in some way and that little imprint of the exotic physics is too small to be seen and there was presumably nobody there to see it anyway but then through 14 billion years of cosmic expansion the message of string theory if you will gets smeared out across the sky like my little scribble on the balloon gets smeared out across the expanding surface so if you know what to look for or so this approach suggests you could see the imprints of exotic physics out there and after nautical data and let me say I mean well while that may or may not be the case that that tradition has worked and probably I'll show some pictures later today but we use that one of the reasons that actually one of the people who recently won the Nobel Prize for discovering small hot spots and cold spots the microwave background is that we think we definitely think they do provide a signature of of another process that happened very early in the history the universe so so and and you'll see pictures of it so it's a it's a tradition that's a noble one and whether we'll get to the level you want we no one knows that that's right but let's talk about that we mentioned it a few times the Inklings of the of potentially being able to detect some of this stuff it's because of I think and you'll correct me I'm sure if I'm wrong that the that the that the discovery of brains in some sense has driven the to an interesting idea that maybe originally the whole idea of string string theories these extra dimensions were very very small and that's the reason you couldn't see them but a very another interesting possibility has arisen and that is that they might not be so small and they could be invisible because only gravity can detect them and gravity is very weak but that large the fact that they can be larger leads to something interesting so why don't you go on yes so you're you're absolutely right one of the developments from the mid-1990s that we alluded to before that it's not just strings it's also membranes and three-dimensional blob-like entities people came up with the idea that perhaps we actually might be living on one of those entities and it's hard to picture in the actual three dimensions so a two dimensional analogy I think is pretty good if you imagine for instance a loaf of bread Mabel just stop stop right there with a loaf of bread we did give you breakfast as we know so you have to have this loaf of bread and imagine that what we have long thought to be the entire universe is just one slice of bread so a two-dimensional version of the real three-dimensional story and the idea is that there may be other slices other brains that we don't see because all of the ways that we access the world except for gravity mentioned a moment are kind of trapped on our slice of bread the strings can freely move along our slice but they can't get off of it so photons that's how we usually see things the photons can freely move along our slice but they can't get off that's why we're unable to see the other dimensions but these theories also show that since gravity it turns out is associated with a snippet of string in which the ends are tied together into a loop it's not stuck to the brain the open strings of which we are made are stuck by their endpoints but when the end points come together and yield a little particle of gravity it can escape and it can probe into the other dimensions so the idea is maybe at the Large Hadron Collider now imagine there's a Collider on this piece of bread so you've got protons going opposite directions around this Collider they slam into each other and it's possible the calculation shows it's possible that some of the debris from the collision would be these graviton particles that could fly off of the piece of bread and we'd notice that by having a little less energy after the collision on our slice than before because the graviton would carry away energy with them so that's one of the exciting possibilities that might happen at the large it's a remote source citing remote possibility there's also something else that's got a lot of press you may be because it changes the nature of gravity and these extra dimensions gravity acts a little bit differently in order for these theories to work you might be able to create kind of black holes that might do something interesting and and and that's fascinating people but it's also caused a lot of public press and concern so maybe you want to talk about that per second yeah you know when large hadron collider was doing its initial runs some months ago I'm sure it was the case with you too I got so many phone calls all the time to be on this or that program and I was like wow physics is really you know it's statues risen but they only cared about this idea of black holes that might be formed in Geneva and sort of eat up Switzerland and then yeah which wouldn't be so bad per se but then if it went on actually you know it would have helped the whole financial knowledge it's always a reasonably good metaphor um but the idea is a serious one yeah and scientists in our community have done calculations I mean you if you create this little black hole what would happen could it eat up the world around and the answers is no and the calculations number one they show based on fairly well-established physics that these little tiny black holes would disintegrate in a tiny fraction of a second before they could cause you know any trouble at all but even more so if you don't think that's a convincing argument these collisions that we can create at the Large Hadron Collider however powerful they may seem to us are very weak compared to collisions that are happening in our atmosphere right now cosmic ray particles are slamming into our atmosphere with energies far in excess of anything that we'll be able to achieve the Large Hadron Collider so little black holes if they were going to be created in Geneva would be created there and if they're created up in space and they're not causing any problems here but we should be fine some will come back and say oh hang on a second you create the black hole up there in space and it has a speed from the incoming particles maybe just rushes through the earth before it can create any problems so the final way to answer that is these kinds of collisions also would happen near neutron stars neutron stars are sufficiently powerful that they'd hold on to this little tiny black hole so if black holes eat things up we should see neutron stars disappearing and we don't so the stability of the universe around us pretty much shows us that there's not a problem yeah and the other example has been used the moon because it doesn't even have an atmosphere I am the fact that right into and you look up at night there's a moon it gives you good confidence that they're probably not there but what do you do during new moon yeah well that's true so half the time you have to tell you exactly you sleep half the month of the well let me ask you before we move on to last thing because I want to leave time for questions from other people uh this this oddity of extra mentions I mean it is kind of sexy the idea that we might create them and I I'm excited about one of my actually one of my students was one of the people who proposed it as you know Rob when I taught at Yale and I like to say I was really happy about it cuz it got him tenure but I think it's pretty ugly what do you think I don't find those theories from a mathematical standpoint compelling yeah okay so what we're talking about earlier you know you get your guided by mathematical aesthetic at times and I don't find that these fit into that they don't fit into string theory very easily do they I mean we don't talk about I mean it's just they seem contrived to me and I just wonder whether you agree I agree with that the only hesitation I have is you know when something's right we somehow have the ability to go back and modify our aesthetic yeah that so I that's what I'm unsure but now that's you know actually that leads it to the nice segue to the last thing I want to talk about briefly because one of the things that I wish more people understood especially I was down in Texas recently talking of the school board there that the universe is the way it is whether we like it or not and and and and if more people could just get used to that idea that that its nature that tells us how to behave not us telling nature it'd be interesting things so it is absolute true many things have seemed ugly black holes seemed ugly so but then once you realize that might happen you Rhianna mechanics all these things seem weird and we have to adjust our minds to understand because like it or not that's the way nature works and so maybe in the last two minutes because I want to leave six or seven minutes at least for questions you know both you and I spent a lot of time trying to communicate and and I want maybe and we just did a little TV program the other day talking about that maybe you want to elaborate why you think that's so important well I think there are there are a number of reasons that I give when I'm asked questions like that and sort of depending on the setting one or another answer I think is is most powerful on the one hand I truly believe and I know you do too that all of the issues in opera that we face going forward the fundamental ones are scientific at their core right I mean the opportunities with stem cells the challenges with climate change the possibilities with nanotechnology and and you know human space travel I mean all of these things are fundamentally scientific an alternate energy so you need to have a public that's at least willing to engage with the ideas so that we are making the decision it's not a decision that's being made on high and basically being presented to us so I think it's so the fact I would argue that a healthy democracy depends on not just the public but the legislators as well we have to make if you make decisions in the absence of data then they're generally not good decisions yeah absolutely eight years so I mean I agree with that fully but if you were to really ask me why I do what I do why I take time out of research to spend time popularizing science and and it is there is a huge opportunity cost right yeah I used to think that there wasn't but that was one eye I wasn't married and I had no kids Yeah right so so what I would do is I would do the writing at night and I do physics during the day and it simply meant I was watching less television or or reading less books or things like that but that's no longer the case so there's a real opportunity cost and the reason in my heart of hearts why I do it is not because of the issue that we just yeah it's important but I do it because when I see a kid open up his or her eyes and say oh my god this is spectacular it feels great I agree that's why I did no in fact you know that and for me it's precisely comes down to the same thing it was a gift given to me I read Isaac Asimov I read I read George gamma I read Albert Einstein because he used to read popular books too and it and for me that's what turned me on and so when I read a book and and I see a kid you know and and enough they're old now enough now some of them say I became a physicist because that it's just yeah okay well enough of that let's let's go to the audience and and and feel free to come and ask the questions oh I can't thank you oh good lighthouse lights are up so I can see now any questions I guess are you at the microphone why do you begin yes hello gyro yeah we can hear you yes I'm with the Large Hadron Collider being able to possibly create energy densities that will be in the range that the Higgs boson is predicted to be in would it be more exciting for you to for the Higgs boson to be detected or not detected well I think it's a great question just to amplify it so one of the reasons for building the Large Hadron Collider was and is to find a particle that we in the community of physicists have assumed exists for the last I don't know 2530 years if not longer but as yet we have not found it it's the one missing piece of the so-called standard model of particle physics so you know if it is found it will be kind of bittersweet I think because it will show us that these mathematical ideas led to a correct insight about nature and it will complete one particular chapter in our exploration of the fundamental constituents of matter on the other hand it will be kind of sad because when you close a chapter and you move on you know there's this sense of of departure the sense of you know it almost would be more exciting if we don't find it because there'll be the wonderful challenge to figure out what is going don't you think for a lot of physicists the biggest nightmare in some senses that we find it and nothing else yes for the Large Hadron Collider absolutely if you find exactly what you were looking for and nothing else it's hard for you to use that as a springboard for the next step it's a we don't - right I mean we need the guide tell us whether any of these ideas that are coming up in theoretical physics are actually fruitful yeah I mean the biggest nightmares to find absolutely nothing because we would find that exciting but it'd be hard to convince the powers-that-be hey we found we found nothing is that great you know but some of the biggest experiments the history of physics have found nothing it had been very significant yeah although they weren't funded by the government at the time yeah yes so I have a third grader and a sixth grader and they're going through some standardized testing now but it doesn't include anything on science this wondering as you talk to legislators and others in the government what is the feedback you're hearing it's you know science is really important but I really don't see a whole lot of educational emphasis on it you will you'll be well it is it is a problem it is a huge problem I think and they're they're two sides the problem there are a lot of educators or at least school board members who are who are really afraid that our kids who learn science I really mean that we're afraid that our kids learn science and somehow lose their faith and it's it's written and and in fact I one of the great things that's happened in in this year politically is that is that at a federal level we now have the present ministration has said we believe in scientific integrity and and we're only appoint peoples to to boards who have the proper credentials and I've recently argued although to deaf ears I think that that we should do the same in school boards that people should actually have some credentials who are going to who are going to make the decisions but but but but the other issue that I know Brian have talked and I've talked about this and I know Brian feel strongly about too is it is that we tend to the other problem is we tend to turn off a lot of kids from science because for a number of reasons one of the big problems at least at the at the public school level and it's terrifying to realize is that in this country in public schools most of the middle school science teachers in this country don't certainly don't have degrees in science and if you're not comfortable in teaching science you tend to teach a bunch of facts but it's Brian and you've talked eloquently about this I know it's not the facts that make science interesting it's the process that's the excitement you know when when we're talking about this or string theory or whatever get that's what gets kids excited and it's kind of sad that we we instill this wrote facts or or require kids to learn these things and not at the same time introduce some of the exciting things that are happening in the forefront but I think you can only do that if you have some comfort level if you have some comfort level to the part for the quick Libyan or at least included it in the curriculum and I so I think that's a problem we have and that's why the National Academy of Sciences is arguably and I firmly believe we should be not only paying teachers more but but recruiting a lot more teachers to teach science who are comfortable with teaching science and it's only that way that will overcome the problem but it's going to be very hard I don't know whether you want anything else yeah that captures it well I think ok ok it's alright hi you um you described this theory as requiring extra dimensions and there's also been a radical effort to to reconcile quantum and relativity by removing a dimension specifically the dimension of time are any of these timeless models compatible with string theory and is this an active area of researchers it kind of been abandoned well the approach that you're referring to is one that is not as exotic as string theory it really starts with the basic principles of quantum mechanics and applies them to Einstein's equations as best we can without really introducing anything new and one of the features that emerges is that time does disappear from the equation so-called wheeler do it equation and you know string theory has enough flexibility of their current understanding that it can embrace these ideas but in no way would I say that string theory leads us to this particular way of thinking about quantum gravity or the early universe so I'd say it's really up in the air as to how these quantum theories that involve gravity deal with time in fact if you were to ask me what the next major breakthrough would be I would say it's coming to a firmer understanding of what time is in these theories where it comes from is it fundamental is it built up from something more basic and what does that tell us about the fundamental ingredients of the world so that I think is a big frontier area ok well I think actually given the time that forgive the pun that that's a that's probably a good time to to to stop and and before I think I just want to say I know a lot of you there are books being sold outside we're not actually having book signings and we will hope that many of the people here have written books and we will try and get a number of them signed pre signed for you for you to buy we meant to do that this morning but things didn't work but we want to really break because we want to have some time for people to have a relaxation before the exciting afternoon session I want to thank all the speakers - morning was morning you made it so great but I I I'm screwed they were all great I I do want to particularly thank Brian not only for having the guts to or to trust that's coming out to be interviewed by me but also out there very few people I think I would feel comfortable enough to know that we could have such a conversation and it would be I hope of interest to you so thanks a lot thank you okay you

Channel: Muon Ray

Views: 305,830

Rating: 4.8747554 out of 5

Keywords: Brian Greene (Physicist), Lawrence Kruass, String Theory, Physics, Science, Education, Extra Dimensions, M-Theory

Id: jtgLYXBC1z0

Length: 57min 0sec (3420 seconds)

Published: Sat Nov 24 2012

Reddit Comments

[u/BlackBrane]

This isn't a debate. If anything its an interview. There isn't any point here where the two really attempt to contradict each other in the slightest.

It seems like a decent enough choice if somebody wants to hear a very general discussion. Still there are some points I wish Brian could have made better. In particular, no discussion of the problems of general predictions from string theory could be complete without alluding to the analogous situation in quantum field theory. This is described well by Matt Strassler in Quantum Field Theory, String Theory, and Predictions, as well as in the David Gross talks that Brian alludes to. The essential point is that the only reason we talk about the 'great mystery' of quantum gravity at all is because it doesn't fit in to the otherwise highly successful framework of quantum field theory – which in itself is neither a 'theory' nor predictive. So if we take seriously what is established by experiments we have little basis to hope for a totally unique theory, as opposed to a general framework like quantum field theory that needs various ingredients and parameters specified before any predictions can be made. In many ways string theory is better labeled as a framework, because in practice thats what it is: all kinds of predictions can and are made by postulating a configuration (a vastly more constrained a process than the analogous one in field theory). The fact that all of these possible configurations are related by dynamical transitions (at least within a given superselection sector) has almost no significance for the kinds of predictions that can be made. Its impact is really only positive, in that it hints at a fulfilment of Einstein's dream of having a unique theory totally fixed by consistency with no choices whatsoever.

Of course it would be ideal to find a way to test all of string theory definitively, but the present situation could hardly be surprising to any student of quantum field theory.