Future Talk with guest Leonard Susskind

[Music] [Music] [Music] [Music] welcome to future talk on today's program we're going to talk about string theory it's a theory about the most basic units of matter and energy and it could potentially change our entire understanding of the physical universe in string theory all matter is composed of tiny vibrating strings that exist in ten dimensions at once and it appears to explain certain forces such as gravity better than more conventional theories my guest as Leonard Susskind he's the Felix Bloch professor of physics at Stanford University and director of the Stanford Institute for Theoretical Physics professor Susskind is considered one of the fathers of string theory he was the first to introduce the idea of the string theory landscape and was the author of the 2005 book the cosmic landscape which was one of the first attempts to bring string theory to a general audience leonard welcome to the program Thank You Martin glad to be here so tell me what exactly is string theory well it's what you said it's a theory of the most fundamental particles and the most fundamental forces in nature everything is made out of particles you're made out of particles I'm made out of particles and those particles interact with each other exert forces on each other electromagnetic forces magnets electric charges gravitational forces and string theory is a theory of all of this it's simultaneously a theory of matter that means the particles which make up matter and the forces that hold them together now why are they called strings I have an image of string is something you tie a package with is there a similarity yeah there is for whatever reason string theory is a theory of particles in which the particles are little one-dimensional threads of energy they vibrate they do everything that an elastic string a rubber band might do they can spin they can stretch they can vibrate and they are the particles of nature at least according to this theory now quantum theory all so attempts to explain the action of matter and energy the smallest scale how a string theory different from quantum theory string theory is not different from quantum theory quantum theory can describe many many things it can describe atoms it can describe the nucleus it can describe photons it's a way of thinking about objects string theory is just one of those objects which is susceptible to being thought about in quantum mechanics so string theory is a quantum mechanical theory it's a theory which makes use of quantum mechanics it's not different than quantum mechanics it's if you like a special case of quantum mechanics now what are the characteristics of a string what can a string do well it can vibrate just like a think of a rubber band think of a little rubber band they're actually two kinds of strings that string theory deals with they're closely related start with a rubber band take your scissor and cut it you'll have what is called an open string a string with two ends you can you of course can stretch it you're not there at those tiny tiny microscopic levels to be able to pull and push on a are more of these fundamental strings but they can hit each other they can vibrate they can spin around an axis they can do all the things that you would imagine that this cut rubber band can do and then there were closed strings closed strings are just like the rubber band before you cut it both those things are present in string theory and they both play a role for example the open strings in in many examples of string theory the open strings which have ends can represent photons the in order photon is a Florida like particle of light not a light particle in the sense that it's not heavy but a particle that makes up light in the same way that there are particles that make up light there are particles that make up gravity those are called gravitons gravitons in string theory are represented by these closed strings now people didn't just make this up this was not just a whim you know I think I'll make up a theory in which photons are open strings and gravitons are closed strings so the string theory explains something that quantum theory doesn't yes it explains why there's gravity quantum theory by itself has no explanation of gravity it's not inconsistent with gravity but it doesn't it doesn't produce gravity out of it gravity is something you would put in on top string theory is a theory which makes use of gravity but which automatically it can't help itself but have gravity so it explains gravity in that sense that's what makes it unique and different than other than other theories like atomic theory or nuclear theory string theory itself explains why there is gravity that's the special thing about it how can we visualize that without getting into long equations yeah I'm how do we explain that one object exerts a pull on another object that's a distance away from it is it there are particles going back and forth yes exactly there are particles going back and forth I don't know if my if I can do this with my hands properly but imagine a string here from one end to another end there's a string and now the string joins and splits it joins and splits and this piece of it could go over to another string be exchanged with another string that transfer of a closed string between some other strings is what accounts for gravity so gravity is the exchange or you sit going back and forth little gravitons going back and forth between other strings account for the for the for the gravitational force and also electromagnetic forces so Newton's theory that every particle in the universe attracts every other particle how far away does this mean they have to be close enough so gravitons can pass between them yes it doesn't mean exactly that on the other hand there's no limit to how far our graviton can travel there's also no limit to how far things can be and still feel some degree of gravitation as a graviton I'm limited by the speed of light it is yes a graviton is limited by the speed of light and in fact what that means in practice is if you have two objects which are attracting each other gravitationally for example strings going back and forth and back and forth and you suddenly come and give this one a pole it doesn't affect the other one until light could have gotten across them it doesn't affect the other one until that graviton has a chance to get over to the other side so yes it does take time for gravitation to the travel now can this information be useful with this understanding of gravity could we maybe reverse gravity we know no way to reverse gravity unfortunately cancel it out as I get older and older I wish more and more I could figure out a way to reverse gravity but no gravity is universal it's as universal as Newton thought that it was now we actually have some pictures of strings we see that image please it's actually a computer rendition of a string we see that graphic please oh there it is okay I recognize it I think I made it yes oh okay what those are actually those are very complicated strings there are strings which have undergone a process in fact a falling toward a black hole the one way over on the left is a string after it's gotten close to a black hole as it gets closer and closer to the black hole it begins to stretch and begin to make itself more and more complicated and so the one on the far right is just before the blood of the string lands in on the horizon of the black hole and disappears altogether forever what happens is it gets mixed up with a bunch of string on the horizon of the black hole what's not shown in that picture is a sort of background of string that represents the horizon of the black hole so what happens is it falls into this mess of string and the horizon and gets mixed up with it so thoroughly that you can't you it loses memory of which piece of the string was the one falling in and which one was the thing that made up the black hole but I've separated them so that you could see them there's like different levels of excitation of the string exactly different levels of excitation as the string falls through the hirato at the horizon it gets more and more excited more and more stretched more and more curly more and more like a complex ball of wool you know that your cat is played with now here that strings exist in ten dimensions at once what do we mean by dimensions in this case we usually think of the three spatial dimensions and time as a fourth dimension although it's very different it's a very different one you measure it with a watch instead of a ruler but when we say the number of dimensions were always including time as one of them so there are three space directions one time direction okay of the ten dimensions you're talking about one of them is time and the other is like having nine perpendicular axes instead of just three so they're all spatial dimension they're all spread they're all but one and so what imply that what we think of as our three-dimensional space has the capability or the potential to actually be a nine dimensional so yes it does yes it does but why don't we see those nine dimensions in other why can't I move around in them and stuff it's because they're very very small at least everything I'm saying of course is subject to the disclaimer that this is true if string theory is the correct theory of the world I don't think we know that with utter certainty so from now on I won't say if string theory is the Right theory you can assume that I mean that is there any way to test it string theory yeah a lot of much of it is already tested in many ways as I said the most important and most central prediction of string theory which no other theory really predicts is the existence of gravity so when I drop something in some sense I'm testing string theory now most people would say oh come on you're not really testing string theory just testing gravity and I sort of agree with that well we know that gravity exists the question is the string theory the explanation of it that's right that's right so what I would say right now is it's the only theory that we have that gives an explanation does that mean it's the only theory that will ever be that gives an explanation it does not mean that but right now it's the only theory that we have that implies the existence of gravity and that to me is a serious serious business that the string theory under development or new things happening is the theory being filled out or is it has it reached a point where it's stopped developing no it has not it's been around 40 years almost almost 40 years the it keeps giving new insights new insights into all kinds of things cosmology particle physics gravitation and to ignore it to say well you haven't proved it therefore you shouldn't be thinking about it or there's no way to prove it therefore you shouldn't be thinking about it that strikes me as silly we have this mathematical theory which does a number of things it has particles in it it has photons in it that has electromagnetic forces it has gravitation but because all of these particles are so tiny and so remote from our senses that we don't have a good way to directly test it does that mean we shouldn't be thinking about it because it's too hard to confirm well you could take that view well every theory is ridiculed before it's finally accepted as being valid indeed so the question is the string theory seemed to have enough potential that physicists are willing to devote their careers to working on it well I think the best answer to that is that young physicists coming into the field flock to the string theory of course it not the only thing that's interesting there's lots of areas of physics which are very exciting quantum computing all sorts of things but in some sense the a certain class of people with a certain bent of mind who were always the ones who were most curious about the fundamental laws of physics those young people still flocked the matter still maybe more than ever are coming into the field and finding all sorts of new and exciting discoveries and also the people who fund the research have to decide that it's worthwhile so they must be finding it so yes well if they fund it don't ask me I I don't fund it myself so how can we really visualize the basic facts of existence is there some way of looking at it that gives an intuitive glance and what's really happening at that subatomic level strings are banging against other strings colliding being exchanged with other strings and in the process creating forces which bind things together from nuclei to atoms through galaxies so can one string express itself as one proton the full of its attributes were set correctly one string as the one proton that's where string theory began as a theory of the proton that's where it began in the first place yes so the answer is yes a proton is a stringy like thing now protons we do do experiments with and we can collide protons with other things and we do see that they behave like strings so it's not completely right to say that string theory has never been confirmed the places where it's not been confirmed or directly confirmed is basically when it comes to gravitational for a tiny tiny tiny elements of gravity which means the gravitons which are vastly vastly smaller than protons and there it has proved very very difficult too now the graviton be one string that's figured a certain way yes it would be one string that's configured in a particular special way it is much much smaller many many orders of magnitude smaller than the strings that make up protons and the result is it is simply very very much harder to get direct confirmation now in a physicists does research and string theory what does he do and does he work what do I do all day long yeah is it working out mathematical formulas or well you do well let's see I get in to work around 10 o'clock I find my colleagues and we sit down and have coffee after coffee the coffee lasts for about an hour all of that time we are debating discussing latest thoughts the thoughts we might have had the night before and we are plotting largely in our own heads what we're going to spend the next seven hours doing and then we tend to go into our offices some of us stay at the blackboard and sometimes I go in my office I work out equations I think about how these things are supposed to work and then later in the day I'll get together with my colleagues again my students my postdocs our faculty and we'll talk more about sewing the people who are providing the funding say what did you do in the past year we're smooth all right well you know the word yes so that's how scientific progress takes place yes I don't know about all areas of science I know about my own area of science and it is a very social enterprise in a sense people exchanging ideas left and right it's almost a Wild West of ideas being thrown back and forth some fraction of them stick some fraction of them stick and then you work out the consequences of it that can be extremely intense that's when the intense part of it happened so it's the main thing visualizing how things work and then attempting to explain it in the language of mathematics yes for me for me it is some of my colleagues tend to I think visually I do think visually I close my eyes and try to see the phenomena some of my colleagues think in a different way they think more algebraically they tend to rely more on algebraic symbols and equations and so forth so there's a variety of different types let's call it that's what makes a theory that's what makes the whole thing work that there are different people coming at it from different directions but yes for me it's a process of visualization and then trying to convert that to mathematical formulas and that's largely what I spend the day doing now let's say that string theory turned out to be true what would we get from that so early atomic theory resulted in the atomic bomb for example where my string theory lead us it's very hard to say but I think one of the places we hope that it will lead us to is a better theory of the creation of the universe a better theory of how the universe began and why its properties all what they are why the universe is expanding the way it is we also want to know why the particular particles that we see why the electron is so much lighter for example than the proton the electron is about 2,000 times lighter than the proton why who where did that come from the hope is and it is not a it has not been established but the hope is that the equations of string theory will have answers to these questions and will understand where we came from at least in so far as the Big Bang and those things now this is a dream this is a dream it's not a reality at the moment reality story at his dreams right or we all know I've heard the word multiverses or multi universes in relation to string theory you know so what does that mean there's more than one universe it's a matter of linguistics that they can only be one universe yuuna means one by definition by definition but the universe we know now this is a matter of a Pyrrhic all evidence we know from astronomy from cosmology from I'm talking about now observational cosmology we know the universe is very much bigger than the portion we can see the portion we can see is a tiny tiny tiny fragment of the whole thing the string theory permits many many different kinds of environments many many different kinds of spaces times particle content and so forth and there's no reason to believe that the little piece that we see is characteristic of the whole thing and it's much much bigger let's call it a multiverse there may be places over here where one set of solutions of string theory which means some collection of particles some collection of forces might hold sway some other place things may be different it could well be that somewheres out there there's a place where the electron is 2,000 times more massive than the proton so the model of the protons being in the nucleus and the electrons Sikora sister Mary doesn't have to be there it does that we know we know that the equations of string theory have many many different solutions that means that they have many many different kinds of possibilities that they can describe the experience can express themselves in many different ways right the extremes can express themselves in many many different kinds of ways and that's what makes it so hard incidentally that there are so many possibilities more possibilities probably than the possibilities for living organisms and so we're stuck with a theory which is so rich that we have trouble finding our way through it and finding the particular version of it that describes our world the string multiverse is sort of the collection of all of these worlds all of the various possibility things that can happen and may actually happen in different places now do not see these other worlds because they're just too far away or yeah but too far away that's a simple way that's probably a slight oversimplification but without the equations and without blackboards I think it's close enough that they're too far away now another area you've also done a lot of work in is black holes I have which I have a vague understanding that that's a collapsed star that exerts so much gravitation that nothing can leave it yeah yeah so one question about black holes is once the black hole was there does it last forever as a permanent hazard to space navigation or does eventually disappear on very very long timescales many many many times the age of the universe black holes will evaporate just like a puddle of water you may watch it for an hour and you say that puddle isn't going anywhere but if you watch it for six hours you might discover that it evaporates evaporates doesn't that mean that some of its particles are leaving yeah some of its particles are sort of boiling off the horizon boiling off the horizon is I think a good picture and the timescale for this is very long but at the present time now most black holes are not evaporating and shrinking they're growing and the reason they're growing is because there are so many particles out there photons and other kinds of particles that it keeps absorbing them a black hole that's out there has much more likelihood of catching something and absorbing it than it does of giving off its mass so today black holes are growing in time the universe will expand as it expands it will cool it would become more and more empty and sooner or later the black holes will start to evaporate there won't be anything out there for them to absorb anymore and they will start to evaporate and then in some length of time which is so long that it's inconceivable timescales the black holes will themselves evaporate do we know that the universe keeps expanding and if it does what is it expanding into is it in a larger medium that it expands into that's the wrong way to think about it it's not expanding into something like that it is all there is and it's expanding so the picture that people often imagine that described things is a balloon being blown up well you say well the balloon is being blown up and it's bring blown up into the rest of the room it's that's a two-dimensional thing expanding into three dimensions but don't think that way think that all there is is the surface of the balloon that's all there is it has nothing to expand into it itself just grows and the material is getting thinner on the surface okay that's rubber for you rubber that's where rubber fails to be a good model of the universe because it's as if the rubber kept replenishing itself as it expanded so more space is being created more space which is almost analogous to saying that as the rubber balloon expands more and more rubber comes to fill in the holes between the that's left by the expansion well most stores become black holes eventually well that's just that's a different question I don't know what the ratio is of stars that will and won't if the star is like our Sun it won't it's not heavy enough to form a black hole it'll form I think a white dwarf a white dwarf is a thing which isn't heavy enough to collapse under its own weight and form a black hole a star which was let's say ten times heavier and there are plenty of such stars out there they will collapse under their own weight and form black holes so some fraction of them will form black holes some fraction of them will form neutron stars pulsars some fraction of them will form these white dwarfs we just have about a minute left so okay you wrap your explanation of the theory up and you know 30 seconds or so leave us with something optimistic well I'm very optimistic but I'm always optimistic look I think the best thing to say now is it's a work in progress it is the best idea that we have out there for explaining the basic laws of physics in fact I would almost say it's the only good idea out there but that in itself doesn't mean it's right okay and we're gonna have to leave it at that cuz I've gotten this signal like to thank my guest our Leonard guy in physics professor at Stanford thanks for being here thank you for watching visit our website www.jfn.co.jp/toho [Music] [Music]

Channel: Midpen Media Center

Views: 45,831

Rating: 4.9041395 out of 5

Keywords: future talk, marty wasserman, leonard susskind, midpen, media center, stanford, big bang theory, sheldon cooper, theoretical physics, string theory, black holes, cosomology, palo alto

Id: Hk4qFxenT-A

Length: 28min 12sec (1692 seconds)

Published: Tue Oct 30 2018