Brian Greene lecture "The elegant universe", 2000-09-22

I mean my name is Ruth house and I'm in the Department of physics and astronomy and on behalf of the department I'd like to say how glad we are to have so many friends in the University [Laughter] I like to make an introduction this is Rebecca behind who will be doing our interpretation tonight we also would like to thank Wayne Leonard who's CEO of energy power company Ruth Dudley Edwards who's a historian and a journalist and the many sponsors and participants in contributors to University in particular on this last plenary it's worthwhile I think for us all to really thank the steering committee who worked so hard to put this together and I should like to acknowledge the help support and particularly the money of our Provost Warren vanderhill [Music] following tonight's lecture please join the ball state architect students as they share their world 2000 student trip around the world through a slide presentation this will be in what is known as the ashtray now to the business at hand it's a real pleasure to welcome dr. Brian Greene as a keynote speaker he is a distinguished theoretical physicist he earned his bachelor's degree at Harvard universe at Harvard University and his doctorate to be HD at Oxford as a Rhodes Scholar he is well known as the author of The New York Times bestseller the elegant universe and I'm also informed unreliable authority that it made number 1 on amazon.com so it is with great pleasure that we welcome dr. gray [Applause] thank you for the opportunity to speak here tonight for a few thousand years poets philosophers mathematicians scientists have all struggled with some of the deepest questions that humanity has ever faced questions that really cut to the heart of what it means to be human and what it means to be part of this universe the Harvard universe as well as others and from the point of view of science the questions that I have in mind are let's get serious again questions such as what is space what is time where does it come from how does it begin will it ever end what are the basic ingredients that make up the universe the fundamental stuff out of which everything that we see around us is made and what are the forces by which those ingredients influence each other that as what are the fundamental forces at work that drive the evolution of the cosmos now I think it's fair to say that the last hundred years or so has seen the greatest strides towards gaining quantitative answers towards these deep and lofty questions and I think it's also fair to say that of the many people that have contributed significantly to the progress that's been made it's really the work of Albert Einstein that seems to be the the most lasting the most pivotal the most crucial to the understanding that has been achieved during the last century or so but even so even though Einstein contributed enormously to our understanding of the universe there was one goal that even eluded him and that goal was to find a unified theory of physics a unified theory as a theory that would be founded on principles of such depth such breadth that perhaps there'd be no question about the physical universe that would be beyond the theories ability to answer to address now Einstein spent the last thirty years or so of his life in real desperate pursuit of the unified theory but in the end even though at times he thought he had it in the end he really came up empty-handed and in retrospect it's not too hard to understand why there are many things about the universe that we've learned only in the last couple of decades that are crucial to trying to gain an understanding of the deep laws of physics things that Einstein only knew a little bit about or perhaps knew nothing at all about but the wonderful thing is that in the last 10 20 years we've been able to make use of this new knowledge to take dramatic steps toward finding the unified theory of physics toward finding the deepest laws governing the natural universe now there's a story I don't know if it's true but I think it really shows the tremendous importance that some people hold these questions with namely stories told that on his deathbed Einstein asked for a pad of paper on which he had his last equations scribbled out in the desperate hope that even in those final moments he might complete this journey complete the quest to find the deep laws of the universe and he didn't but the question is what is it that drives somebody so strongly to find answers to these kinds of questions and it's hard to really pinpoint exactly but it's certainly the case that without finding the unified theory without finding the deepest laws of physics there are some very crucial important questions that we will never ever be able to address and one of those questions has to do with for instance how the universe began and I'll do this from time to time show some video sequences that I think help get the ideas across so let's just start simply and begin with an example of the start of the universe which we usually describe as a big bang like explosion where all matter and radiation comes streaming out from some dense initial hot starting point and as universe expands it gets bigger and bigger it gets cooler and cooler things begin to spread out and as things cool down they begin to coalesce into structures that give rise to the Stars and the galaxies that we can witness if we look out on a dark starry night these are the kinds of structures that we see out in the heavens now we actually when we observe the universe can't really look back right to the beginning rather what we do is we seed the stuff that was in the last portion of that little animated sequence we see the stars and galaxies and what we as scientists want to do at least one question that we want to answer is what really happened at the beginning what really happened at time zero itself so what we do is we take that kind of cosmic film and we use our equations to run the film in Reverse and we try to run it back as far as we can hopefully right back to the beginning so in Reverse the kind of thing that we imagine happening is everything that's streaming apart starts to come together when you run the film backwards further further back in time things begin to collapse in on themselves then the universe gets denser hotter everything begins to implode and as we head back further further back in time you never gets hotter and hotter and we can go right back right towards the beginning right back to a fraction of a second after the Big Bang but you see if we try to push all the way back to time zero we can't we see we get stopped right here the laws of physics as we know it don't allow us to go further back in time if we try to push further back that's what happens it all breaks down the laws make no sense and we can't actually figure out what occurred at time zero so what we want to do and what Einstein wanted to do in particular is to find laws of physics that never break down that really allow us to push back to the beginning of time to really understand how it is that there is a universe at all how it got started and then ultimately to figure out how it evolved to the form that we currently see so what I'd like to do here tonight is try to describe some of the hurdles that scientists have encountered in trying to formulate the unified theory deepest laws of the universe I'll try to describe then how a new approach that goes by the name of string theory we believe resolves the problems that scientists previously encountered and may well be the unified theory that Einstein was searching for and then I'll close by trying to describe how it is that if these ideas are true our universe has some incredibly bizarre properties properties that nobody would have anticipated before these modern ideas were brought to light now as was described in the introduction much of what I will be talking about here is in my book the elegant universe and since that book came out I received a lot of response both through ordinary mail and through email and I thought that before getting into the details of the subject I would share one particular letter that I got because it's my favorite it goes dear professor Greene I'm a high school student and wanted to thank you for writing the elegant universe I did want to tell you though about an experience I had reading your book one day during algebra class which I hate I was reading the book in the back of the room and I just got to the part about the fabric of space tearing and all of a sudden my nose started bleeding and I never get nosebleeds well that night I went back to reading and wouldn't you know it my nose starts to bleed again I struggled to finish the chapter turning pages with one hand and keeping pressure on my nose with the other slowly the bleeding stopped and I was able to finish the last chapters without further incident so when people say this stuff is mind-blowing maybe there's some literal truth there [Applause] I shared that letter with the organizers of the top tonight and well as you see they kindly place boxes of Kleenex at the end of every aisle in case anybody suffers a similar fate so the search for the unified theory can be picked up at many different places in the history of science I'm gonna start with the first attempt to understand gravity because as we will see gravity turns out to be the pivotal idea that one really must come to grips with if one hopes ever to find the deepest laws of the physical universe and to describe the first attempt to understand gravity we really need to cast our minds back late 1600s in England and this was a time when the Black Death was waging a winning war against mankind and to escape the scourge Isaac Newton retreated to the relative safety and comfort of his family home in the countryside of England and their thinking calculating wondering Newton was about to win a very different kind of battle for all of humanity because by the time the Great Fire of London lit up the sky as the fire that burned for about three days or so Newton was ready to return to Cambridge where he was thrown to dazzling relief a fundamental law about the universe a law that can simultaneously describe the motion of planets around the Sun and the descent of a ripe apple from tree to earth because he had discovered his universal law of gravity and in so doing he'd really took humanity on an incredibly important step forward because he showed the power of mathematics to describe the natural universe now the law of gravity that he found I think many people are familiar with it in one form or another but let's just all get on the same page by just looking visually what he encountered and basically Newton said that a body like the Sun can keep another body like the earth for example in orbit by in some sense reaching out and clutching hold of the earth with a gravitational tether that I try to illustrate here with these red gravitational lines of force now there of course are equations that go behind this little animated sequence and the equations describe the motion of the earth with incredible precision and those equations can equally well be applied in many other circumstances the other planets comets stars and galaxies all of these circumstances the equations that Newton wrote down described what happens experimentally with great precision in fact even today when we plot the course of rockets from the earth to rendezvous with other planets Mars and Beyond we still make use of the equations that Newton wrote down in the late 1600s so there really is a mountain of experimental support behind this approach to thinking about gravity but even so at the turn of the 20th century a young patent clerk who's working in Bern Switzerland realized that this view of gravity was wrong and of course the person I'm referring to is Albert Einstein and to understand how he came to this incredibly heretical conclusion that Newton's laws of gravity were not the full story we just need to remember that in 1905 Einstein discovered his so-called special theory of relativity and many people know something about special relativity in one form or another the only thing that we need here from special relativity is the idea that nothing can go faster than the speed of light and nothing really means nothing there no signal no disturbance no influence no information of any kind can go from one place in the universe to another at a speed greater than the speed of light now in day-to-day life that speed limit doesn't seem to matter all that much and the reason is well light travels really fast it travels at 186,000 miles per second and that's fast enough to go around the entire earth about seven times in one second so in day-to-day life that speed limit just doesn't really crop up but nevertheless Einstein realized that this notion of nothing going faster than light spelled the end of thinking about Newton's view of gravity as the be-all and end-all of trying to describe this force that permeates the cosmos and the reason is in Newton's approach to gravity the gravitational force gravitational influences are transmitted from place to place in no time at all instantaneously much faster than the speed of light that is the origin of Einstein's realization that Newton's approach couldn't be the end of the story now let me just make that a little bit more concrete imagine that you're outside and it's a nice bright sunny day and the Sun explodes how long will it take for us to learn that the Sun has exploded by virtue of seeing light from the explosion that was actually a rhetorical question but you know feel free to jump in at any point that's right the answer is a little more than eight minutes let's call it eight minutes the idea is that the Sun is 93 million miles away and like going at 186,000 miles per second still takes about eight minutes to travel that enormous distance so if the Sun explodes at one moment around eight minutes later light from the explosion will have traveled all that distance enter our eyes and let us see that the Sun has blown up but how long will it take for us to learn that the Sun is exploded by virtue of feeling it after on that little video sequence we were illustrating that the Sun keeps the earth in orbit so if the Sun goes away our motion through space will change will no longer go in orbit and we should feel that change in our motion but how long will it take before we feel it well according to Newton his approach to describing gravity according to him we would feel it instantaneously the moment the Sun explodes we would feel it by virtue of a change in our motion in other words we would feel it by virtue of the influence of gravity before we see it before light has a chance to alert us that the Sun has exploded so in Newton's approach gravity goes faster than light and that is what Einstein realized just can't be true so this said Einstein out on a journey to try to formulate a new theory of gravity one that would be as accurate as Newton's or who knows maybe even more accurate than Newton's but one that would not suffer this defect of gravitational disturbances going faster than the speed of light and it really was a long obsessive tortuous task to try to figure out this new theory of gravity in fact in about 1912 this is midway through the ten year quest Einstein wrote to a friend of his and said something like compared with understanding gravity the special theory of relativity which he discovered earlier 1905 that was mere child's play that's how much more difficult Einstein found understanding gravity to be but nevertheless by nine 18:15 the genius of Einstein really blazed through the final equations and he gave the world a new theory of gravity it's called the general theory of relativity now describe that here in a moment but to lead up to it it's really worthwhile thinking about what Einstein was struggling with what were his main concerns during that 10 year journey to find this new theory of gravity and the answer well the answer really highlights what it is that distinguishes Einstein from every other scientists well you know beyond the fact that it's kind of a smart guy the thing that the thing that really distinguishes him is the willingness to ask the simplest seemingly childlike questions about the universe take them very seriously think them through to their logical conclusion oftentimes resulting in a complete revolution in the way that we think about things now in this particular case the question that Einstein asked is how does gravity work what is the mechanism by which it gets the job done after all the Sun 93 million miles away somehow affects our motion through space how in the world does it do that when it's so far away and to try to get a handle for instance on what Newton was thinking about the mechanism of gravity because I thought well if I only understood what Newton was thinking microscopically how gravity works maybe I'll see that Newton got it a little wrong gravity doesn't go instantaneously or or maybe they'll be way to patch it up in a way that gravity will no longer conflict with special relativity so an Einstein did he he went to a book it's called the Principia many people know data familiar with it it's a book that has all of the results about mathematics and physics that Newton found during his lifetime so Einstein went to that book and he you know went to GE opened it up found the universal law of gravity and then he went to the subheading M no for the mechanism of gravity and there he found something very very surprising because Newton basically says I don't know how gravity works I can write down equations that govern its influence with great accuracy but I really can't figure out how it literally works in fact in his own words he said for the answer to that important question the mechanism by which gravity works I leave it to the consideration of the reader now the reader at that moment was Albert Einstein and he was one of the rare individuals in the history of science who was up to the challenge of trying to fill in this gap in Newton's view of gravity and that's what he was struggling with for 10 years and by 1915 the answer he came up with for the mechanism the medium by which gravity is transmitted is an idea which is subtle it's powerful it's beautiful and it's also quite elusive he found that the medium for transmitting gravity is the fabric of space I know it's frightening but just hang on a little bit with that the fabric of space in fact a little more precisely the fabric of space and time now it's a tough idea if you haven't encountered it before so I'll show it to you visually in a moment but let me just try to give an analogy it's an analogy that physicists love to use in this context to try to get the rough idea across first so for this forget about the universe forget about gravity for the moment let's just focus attention on a huge flat rubber sheet that stretched out nice and flat before me now if I take a little marble and I set it rolling along the surface of the rubber sheet it's going to go in a nice straight path nothing nothing too complicated about that but now imagine that I take a bowling ball and I set it right in the middle of the rubber sheet well the bowling ball is going to cause the sheet to warp to deform to curve and now if I take that little marble again and I said it rolling along the surface it's not gonna go in that same straight line that it did a moment to go rather it's going to go in some curved path due to the curvature of the rubber sheet because the bowling ball is sitting on top of it Einstein wants us to take that idea and apply to the universe in the following way instead of having a rubber sheet imagine it's the fabric of space this stuff all around us and rather than having a bowling ball that curves the rubber sheet imagine that any heavenly body like the Sun for instance by virtue of its presence causes the fabric around it to warp and now the earth for instance as it moves through the Warped space will go in a nice curved orbital trajectory much like that marble when it was going along the curved surface of the rubber sheet that is the rough idea let me show you that visually so what we'll do here is look at the fabric of space which I'll always illustrate by this grid like icon think of it as a substrate of the cosmos extending throughout the universe now Einstein says the fabric is nice and flat if there's no matter present but the presence of mass like the Sun causes the fabric to warp much like what happened when you put a bowling ball on a rubber sheet now look at the earth the earth is kept in orbit around the Sun because it's rolling along a valley in the distorted spatial environment caused by the presence of the Sun so here the mechanism of gravity is laid out very clearly it's warps and curves in the fabric of space that are responsible for transmitting gravity from one place to another that is einstein's idea for how gravity works and it really is something which we are all actually experiencing right now so we're all feeling gravity right now I'm sort of feeling it on my feet you're feeling it someplace else and and the idea is that the earth is also warping space around it and we are all attempting to slide down an indentation in the warp space caused by the presence of the earth and for instance the floor is getting in our way and that's why we feel the floor pushing on us it's not allowing us to slide along the indentation that the earth is causing in the spatial fabric so it's a very nice way of thinking about grabs it's very visual but the two quick two key questions are this first does this describe experiments well and the answer is it does anytime Newton's approach to gravity goes head-to-head with Einsteins approach Einsteins is a little more accurate so not only is it a theory that lays out the mechanism something Newton's approach didn't do at all it actually is more accurate but the second question which is really the most important one is does this new approach to gravity resolve the conflict that set Einstein out on his tenured journey in the first place namely how fast is gravity transmitted in Einsteins approach is it instantaneous or not and the answer can be gleaned again by forgetting about the universe and gravity and again going back to that rubber sheet so imagine again the rubber sheet is flat in front of me no bowling ball on it and imagine I start just to tap to poke the rubber sheet well as I poke it I'm gonna send ripple like disturbances heading outwards on the surface much like what happens if you throw a pebble into a pond and if you know enough about the composition of the rubber sheet you can actually figure out how quickly those ripples will go now Einstein was able to do a similar calculation not for a rubber sheet but for the fabric of space he was able to figure out how quickly warps and ripples to the fabric of space will travel in essence how quickly gravity will travel from place to place and at the end of the calculation Einstein was quite gratified because in this approach to describing gravity he found that the gravitational force is not transmitted instantaneously rather it is transmitted at exactly the speed of light so no longer is there a conflict between our understanding of gravity and the central dictum of special relativity that nothing goes faster than the speed of light because gravity and light go at exactly the same speed in this new approach so anytime you ever hear the phrase speed of light you can substitute the phrase the speed of gravity because they really are one and the same so just to go back to that little example with the Sun exploding we mentioned or actually you told me it takes about eight minutes for light from the exploding Sun to reach us that's how long it takes for us to learn about the sun's demise now in the context of general relativity's description of gravity we learned that we will feel that the Sun has exploded by that change in our motion through space at exactly the same moment eight minutes later so this was a very pivotal moment in the search for the deep laws of nature because now our understanding of gravity the grand force that really governs everything that we see out there in the heavens is described in a manner that's consistent with Einstein's special theory of relativity but you know how these things go by giving the world the general theory of relativity this wonderful theory of gravity it turns out that Einstein opened up a whole nother can of worms because it turns out that the general theory of relativity is in conflict with another theory and that theory is called quantum mechanics so what I'd like to do now is just describe a little bit of quantum mechanics and how it is that Einstein's theory is in conflict with it and then I'll go on to describe how string theory resolves this problem now quantum mechanics itself is a very bizarre weird mysterious subject it's easily a subject which can occupy an entire lecture in its own right or even a sequence of lectures and well the organizers asked me to wrap it up within five hours tonight so I'll sort of have to cut to the heart of the matter pretty quickly just discuss the bare-bones essentials of quantum mechanics quantum mechanics was developed in about the 1920s 1930s or so because scientists found that when they tried to use older 19th century ideas about physics and apply those ideas to the newly emerging microscopic realm molecules and atoms they found a whole host of completely inaccurate predictions for instance one prediction if you apply 19th century ideas to atoms is it turns out that every atom in the universe according to those ideas should self-destruct in a fraction of a second doesn't happen thankfully and their force therefore scientists knew that another theory of the microscopic realm was called for and that new theory is quantum mechanics now some features of quantum mechanics that you may have heard about things like particle wave duality or interference phenomenon or multiple universes or quantum tunneling that's the idea that if for instance I were to walk into a solid wall over and over and over again most the time I'll bounce off but quantum theory says that there's a small chance that if I do it long enough I will pass through the wall and appear intact on the other side it's a very small chance that though that that will happen but nevertheless if you apply the same idea to the microscopic realm where rather than a person bouncing into wall little particles bouncing into barriers which classical physics says they simply cannot pass through they do pass through in a manner that's well described by these laws and in fact in a manner that helps to run the computers and various other electronic devices that we are all familiar with so these ideas are experimentally tested and they're quite accurate but the only real feature of quantum theory that we will need for tonight's discussion to understand how it is that quantum mechanics and Einstein's theory of gravity are in conflict the only thing that we will need is something called the uncertainty principle this is a principle that was developed in 1927 by Werner Heisenberg and well I don't know if you have these kinds of Chinese restaurants that that we have in Manhattan where you go in and sometimes there's a special order menu with dishes and column a and other dishes in column B and if for instance you order the first dish in column E you're not allowed to order the corresponding dish in column B and vice versa well that's basically the uncertainty principle maybe I'll be a touch more precise than that the uncertainty principle says that knowledge knowledge of the microscopic realm is much like that list divided into two columns and knowledge of one element from the first list fundamentally compromises your ability to know a similar complementary characteristic from the second list and vice versa and moreover the better you understand the first characteristic the less you can possibly know about the corresponding characteristic in the second list and vice versa let me just make that concrete with an example electrons among the elementary particles that make up matter when you apply the uncertainty principle to electrons it says that you cannot know where an electron is and how fast an electron is moving simultaneously with total precision nothing to do with how good an experimenter you are nothing to do with how good your equipment is it's a fundamental limitation from the laws of quantum physics now I'd like to summarize the uncertainty principle is basically telling us that on microscopic scales the universe is fundamentally jittery turbulent frenetic frenzied because there are fee years of the microscopic realm that we can never ever nail down with total precision due to this uncertainty principle and therefore in a sense they're free to roam among all men our possibility consistent with our limited knowledge of what's actually taking place now let me try to make that idea of visual but before I do that let me illustrate in words first and then in an animated sequence why it is that this idea of uncertainty in quantum mechanics gives a conflict with Einstein's general relativity his theory of gravity and the idea basically is this in the previous animated sequence I was trying to illustrate how Einstein encouraged us to think about gravity in terms of curves in the fabric of space the thing about those warps and curves though is they're kind of gentle nice sloping gentle geometry to the shape of space when it becomes warped but quantum theory is anything but gentle it's got this jittery character from the uncertainty principle and it's a jitteriness of quantum theory that conflicts with the gentleness of Einstein's general theory of relativity that's the origin of the conflict between the laws of the small quantum physics and the laws of the big and massive general relativity let me spell that out in words a little bit more than I'll show you a sequence so when we looked at general relativity we saw that the Sun appear in the fabric of space warped but you see we were looking in that sequence at the fabric of space on astronomical scales scales on the order of stars and beyond and on those large scales the fabric is nice and gently curving quantum theory says that if we examine the fabric of space not on big huge scales but on microscopic scales tiny microscopic scales the fabric will not be gentle rather it'll be turbulent sort of like the surface of a violently boiling pot of water and it's that feature of the spatial fabric on small scales that general relativity cannot hand let me show you that visually so what we'll do here is again focus our attention on the fabric of space grid like image here again is meant to give you a sense of scale so the large set of grid lines you should think about them as being for instance a meter apart and the sequence of ever-closer grid lines is meant to draw your eye to ever shorter distance scales now from the overview it looks like space has the same properties on all scales but if we go on a journey if we probe into the microscopic structure of the spatial fabric the quantum jitters of space itself get bigger and bigger and bigger such that way down here space takes on this wildly undulating frenetic frenzied form and it's on these tiny tiny distance scales this is around a billionth of a billionth of a billionth of a billionth of a meter that the jitters of quantum uncertainty obliterate the gentleness of Einstein's general relativity and that's why the two theories come into conflict but you see if we recede back to ordinary everyday scales the jitters are too small to directly affect us on everyday scales and we do recover the nice image nice gentle image of the spatial fabric and that's why Einstein's theory works incredibly well when you apply it on big scales everyday scales and beyond but it breaks down completely if you try to push Einsteins ideas into the microscopic realm now I quickly mentioned how microscopic you have to go to encounter this problem it was that billionth of a billionth of a billionth of a billionth of a meter more precisely it's about 10 to the minus 35 meters and well there's really no denying it it's pretty small in fact it's so small that you could well wonder who cares is it really worth worrying about I mean we have Einstein's theory of gravity that works out to the farthest reaches of the cosmos we have quantum mechanics that works incredibly well in describing the microscopic structure of the universe so long as you don't push way down into the ultra ultra microscopic realm so maybe that's enough to call it a success just pack up and go home you know phrase that way it's kind of convincing so maybe I'll just end the lecture and right here okay I'll go on there are a number of reasons why why many of us think that this is a problem that needs to be taken very seriously let me give you two reasons the first is absolutely not one that all scientists agree with it's really one that I personally feel but many others disagree with I think that what we as scientists are trying to do is not merely model how the universe works I think perhaps naively but I think that what we are trying to do is find the truth of how the universe works and no matter how extreme or esoteric the realm that you need to push into to recognize that our current ways of thinking about things break down they break down at all it's a pretty good sign that there's something deeper there's a deeper truth that we have not yet discovered and that to me is enough reason to take this problem seriously and try to find a solution a second perhaps a little bit more concrete reason really reflects back on the opening animated sequence that I showed you where we were talking about the origin of the universe if you ever really want to understand how the universe began you're going to have to come to grips with this problem and the reason is basically as we saw in that sequence as you go back to the beginning of time the universe gets smaller and smaller and smaller and in fact there comes a point in time when the entire universe is roughly the same size at which the conflict between quantum theory and general relativity emerges so if you don't have a theory that can overcome that conflict there's no way in the world that you're ever going to be able to push further back in time to be able to push back to time zero itself you know many times popular counts lead us to believe that the Big Bang is the theory about how the universe began and that is completely not true the Big Bang is a theory about how the universe evolved from a split second after what ever occurred to bring it into existence and any attempt to push further back has met with this problem the conflict between quantum theory and general relativity and that has prevented people from truly understanding how things began so that's two reasons for wanting to take this conflict very seriously and what I'd like to do now is describe how a new approach string theory we believe resolves the problem so let me let me first start with briefly saying what string theory is then I'll indicate how it gives insight and we believe solves this conflict and then I'll finish up with just one piece of string theory that is quite bizarre quite compelling and quite interesting and if these ideas are true one that's going to dominate our understanding of the physical universe for time to come so first off what is string theory well string theory is a theory that attempts to answer a question that has been bandied about for at least 2,500 years and that question is what is the basic most fundamental uncuttable constituent making up the universe so in concrete terms for instance if we take any piece of matter like this piece of wood right here and we slice it in half slice that piece and again keep on cutting into ever smaller pieces what is the final uncuttable thing that we will come to now we certainly have learned in our age that sooner or later will come to atoms but we've also learned sometimes through disastrous consequences that atoms are not the end of the story because they can be split they're made up of smaller ingredients you have little electrons that swarm around a central nucleus which itself has smaller particles known as neutrons and protons and even those particles neutrons and protons have yet smaller particles inside of them we learned in late 60s particles known as quarks it's sort of like a sequence of Russian dolls going to ever smaller ingredients now string theory comes along and strongly suggests that there's at least one more layer to that progression to ever smaller ingredients it says deep inside an electron deep inside a quark deep inside any particle that was previously thought to be uncuttable there is something else it's a little filament a vibrating energy kind of looks like a string looks like a vibrating string that's why we call it string theory and the wonderful idea is that just like the string on a violin or a cello can vibrate in different patterns which our ear sense as different musical notes these little filaments of energy these little strings in strength e also can vibrate in different patterns and we don't hear them as different tones rather we see them as different particles so the electron is a string vibrating one way a cork a string vibrating a different way in a different pattern let me show you that visually so we'll take a look in this sequence at matter down on atomic scales where you have electrons orbiting the nucleus and those of you who know recognize that ordinarily the number of electrons equals the number of protons but well my animator got a little bit confused but anyway it's just it's just kind of schematic anyway so we want to do is examine these particles with great precision so we reach into the nucleus for instance pull out a proton as I mentioned it has these quarks inside of it if we bring in for instance a neutrino just to fill out the particles that you're familiar with these were thought to be the fundamental uncuttable ingredients making up the universe now here is the new picture of string theory inside each of these particles is this little dancing thread this little dancing string and note that the electron on the left for instance and the cork in the middle differ only by virtue of the pattern of vibration that the string is executing it's the same ingredient it's the same kind of thing it's the same stuff it's just vibrating in different ways giving rise to different particles so in fanciful language it's like the electron is a G and a cork as a si different notes that a string can play give rise to the different particles and thereby the richness of the world around us so it's a very nice way of thinking about how everything in the universe is created but the real question is does this way of thinking about matter resolve the conflict between quantum theory and general relativity that's really what we're after and the answer is yes and let me just try to give you a real quick description of how that goes when you take a point particle and you replace it by one of these strings in essence what you're doing is you're smearing out the particle into a string you're spreading it out into a string you're kind of extruding it now whenever you spread something out you wind up diluting it for instance you take a drop of ink and you drop it into a vat of water as the ink spreads out of course it dilutes now similarly when you spread a point particle out into a string you wind up diluting it and although it's not completely obvious you also wind up diluting those violent jitters in the spatial fabric on microscopic scales the origin of the conflict between quantum theory and general relativity as we saw in a video sequence now the jitters don't go away but by spreading them out you make them less violent and it turns out that you make them just gentle enough that quantum theory and general relativity can fit together harmoniously and in fact it's actually better than that in the context of string theory it turns out general relativity needs quantum mechanics and quantum mechanics needs general relativity for the theory to make sense so it's not even a forced Union in the context of string theory rather gratifyingly it's an inevitable union between the laws of the small quantum mechanics and the laws of the big general relativity in the framework of string theory and that's why so many people in fundamental physics are very excited about this new approach to describing the universe what I'd like to do now is turn in the last section here to one of the strangest features of this new approach to describing the universe and that feature is this string theory does indeed put together the laws of the small and the big in one package but it does so at a particular cost and that cost is the theory only makes sense if the universe has more than three space dimensions in fact the theory must have at least six and probably seven more space dimensions that is yet nobody has ever seen so first off what what does that mean when we talk about the universe having three space dimensions we mean say left-right back-forth and up-down the three dimensions in which we're all immersed fully and moved through easily in day to day life string theory literally is saying that there are more dimensions than those other directions that is yet nobody has seen now when you first encounter that idea you might say hey cool Star Trek but then you think about a little bit more and you're like well why in the world our serious scientists still thinking about this theory if it's making a prediction which is obviously wrong there obviously are only three space dimensions and what I'd like to do in the remaining minutes of the talk here is at least try to convince you of the mere possibility that our universe really does have more than the familiar three space dimensions that we see in the world around us and to do that again it's worthwhile to work by analogy so again forget about the universe forget about space and all that stuff just focus your attention on something simple like a flat piece of paper so a flat piece of paper on its surface has two dimensions you can think about them as left right and up down two dimensions right on the surface of the piece of paper now if I take the piece of paper and I roll it up into a tube it still has two dimensions on its surface because I haven't done away with a dimension but by rolling it up into a tube I certainly have changed the characteristics of one of those dimensions you see you still have left right as before but up down the up down dimension is now curled up turned into a circular dimension the circular cross section of the tube of paper and in fact I can't really do this but you could imagine if I was able to twist this tube of paper up into a tighter tighter tube making this circular cross-section smaller and smaller if I make it small enough you won't even be able to see that it has a circular cross-section at all for instance imagine that you're looking at that tightly wound tube of paper from the back of the tent or even from a farther distance from that distant vantage point this tube of paper is just going to look like a one-dimensional line because from far away you don't have the visual acuity to see that it has thickness so for instance if if I told you that a little amped is living out its life on the tube of paper you'd say poor little guy can only move left right that's the only dimension available to the ant living at its life on the tube of paper but of course if you take a pair of binoculars and you zoom in on the tube of paper then by magnifying it you can in fact see that there is a circular dimension a second curled up dimension and now you realize that the little ant can not only move left right it can also move clockwise counterclockwise around the tube of paper a second direction in which the ant can move that you wouldn't be aware of if you didn't magnify the tube of paper sufficiently large now what string theory is suggesting is that that idea perhaps applies not just to a tube of paper but maybe to the entire universe so our universe has big three dimensions left-right back-forth up-down and perhaps they are the analog of the big extended dimension on the tube of paper but just like there's a tiny curled up dimension in the tube maybe the fabric of space itself also has tiny curled up dimensions curled up so tightly that we at the moment do not have sufficiently powerful magnifying equipment to actually reveal that they are there that is the rough idea let me show you a final sequence on that so what we'll start with here again is the fabric of space and by direct observation as I've emphasized we all know that there are three dimensions three big dimensions and I can only show two of them on the surface of the screen so everything that you see on the screen is meant to be everything that we know about in day-to-day life and what we want to do is probe into the microscopic structure of the spatial fabric and see how there might be more dimensions curled up so we go way down deep into the microscopic structure and indeed we can find extra curled up dimensions tiny curled up dimensions here I just illustrate to in the shape of a ball so for instance if we have that little ant walking around it can not only move in the familiar extended dimensions it can walk in these curled up tiny directions that the ant Oh has access to because it's ultra microscopic in size because again if we go back to day to day life the extra dimensions the curled up ones are too tiny for us to see them they were seeded into the microscopic distance and you might be fooled into thinking that this is all there is the big stuff in fact string theory says we have been fooled deeply tucked in the spatial fabric there are more dimensions they're just so small that nobody has been able to magnify them to a scale that reveals them directly so that's the idea for how we can make sense of a theory that predicts that there are more dimensions than meet the eye you might say well okay if they're small enough perhaps they're there and we haven't seen them but you know you could retort by saying perhaps there's a little microscopic civilization of green people walking around down there because if they're small enough we would not have seen them either and that's true that's one of the other predictions of string theory yeah I have to thank you for laughing at that particular line because I used it a couple weeks ago in another talk and nobody laughed that was frightening but let me close by by noting that the idea of extra dimensions is not only more rationally motivated than the idea of little civilization of green people walking around but it actually is more than just a matter of hiding the dimensions away it turns out that we believe string theory seems to tell us that there are many important questions about the physical universe whose answers in a sense are bound up in those extra curled up dimensions let me just describe this final point that I'll make there are about 20 numbers that over the course of the last 50 years or so scientists have measured with great precision numbers like the mass of the electron how much it weighs the mass of any of the quarks the strength of gravity the strength of the electromagnetic force a whole list as it mentioned about 20 of these numbers that we know with exquisite precision the numerical values but nobody at all understands why it is that those particular numerical values are the ones that characterize those physical properties now you could say you know does that really matter you know if the electrum wait a little bit more if it weighed a little bit less so be it should we really care and the answers we really should care because it turns out that if you were to change any of those 20 numbers by even a small percent the universe as we know it would disappear for instance if I gave you 20 dials put them right here and allowed you to just dial those 20 numbers to any values that you want if you dial in two values that differ from the ones that they actually have in the world around us the universe goes away the reason for that one way of thinking about it is a central feature of our you grocer stars and stars rely upon nuclear processes and nuclear processes it turns out demand delicate and intricate relationships between those twenty numbers you change those relationships nuclear processes don't happen without nuclear process these stars don't light up without stars the universe is a very different place so perhaps the deepest question that science faces is why is it that those 20 numbers have the values they do allowing stars to shine allowing planets to form on at least one planet also allowing life intelligent life to emerge now no theory has given any insight into why those 20 numbers have the values that they do string theory has not given any insight either but it has for the first time in the history of science set up a framework that has the potential to address this important question and the potential simply put is this those 20 numbers in string theory are a reflection of the ways in which strings can vibrate the mass of electron for instance is a reflection of the energy of its vibrating string from Einsteins e equals mc-squared energy equals mass times the speed of light squared the mass of an electron comes from the energy of its vibrating string if the string vibrates more energetically the electron would have weighed more if it's string vibrated less energetically the electron would have weighed less so if we could figure out exactly the patterns of vibrations that strings can execute the the note so to speak that they can play we would have a chance of calculating those numbers now the key thing is as the string vibrates it doesn't just vibrate into the familiar extended dimensions that we know about it also vibrates into tiny curled up dimensions it sits so small it can vibrate into those other directions now just as for instance the vibrational patterns of forced air streams that are going through a French horn are affected by the twists and turns of the instrument the vibrational patterns of strings are influenced by the twists and turns in the geometry of those extra curled up dimensions so if we knew exactly what the extra dimensions look like we perhaps would be able to calculate the allowed of string vibrations perhaps calculate those 20 numbers now we don't know exactly what the extra dimensions look like that's what we're heading towards but if we did those calculations perhaps would give us an explanation for why the 20 numbers have the values they do in essence giving us an explanation for why the universe is as it is that's where we are headed thank you very much [Applause]

Channel: Ball State University Libraries

Views: 5,045

Rating: 4.9175258 out of 5

Keywords: Unified field theories, Superstring theories, Cosmology

Id: K4vrRlURCYA

Length: 61min 13sec (3673 seconds)

Published: Mon Aug 19 2019