The Fabric of the Cosmos, Dr. Brian Greene, Columbia University

[Music] [Music] [Music] so good evening ladies and gentlemen welcome to the science technology society lectures the 2004 2005 Linus Pauling memorial lectures sort of like tag that on there in that we're very much involved with promoting Linus Pauling as a role model citizen scientist my name is Jerry Bristol I'm the president of the Institute for science engineering and public policy and it's the Institute that organizes the series it's tonight's program which you probably already know is brian groot dr. brian green and the title of his talk is the fabric of the cosmos it's now my role here to thank the co-sponsors Mentor Graphics corporation has been our lead co-sponsor for a number of years and thank you very much to them all so yes [Music] [Applause] Oregon Episcopal school Morgan Stanley funds FBI company the Linus Pauling Institute down at Oregon State Oregon Public Broadcasting the Oregon University System and I'm very pleased with that the I want to mention I think Richard Jarvis is out here thank you Richard Jarvis who is the Chancellor of the system until recently and we're hopefully I wish you were back but there you go [Laughter] anyway Oregon State University's in Western Oregon University please we had that whatever that was but anyway Brian Brian was down at Western Oregon today for a session with some classes Oregon State University Portland Community College Clark College or Vancouver linn-benton Community College Mount Hood Community College and IDC architects and and a number of you are here because not only does Mentor Graphics corporation give us a grant to do this but also Mentor Graphics foundation we went to them and said we thought there were a whole lot more of the k-12 people who would like to come to these things and they agreed with us and so we they gave us a grant to subsidize these tickets in so how many of you here on these k12 tickets guy here at get a little hand [Applause] all righty so thank you to Mentor Graphics foundation for that there are most evening of programs there are question cards in the programs there's two mics and the aisles down below one up above so when dr. greens finished he'll field some questions and if you have those cards if you fill them out particularly emails because emails are cheap to send and I won't spam you too much and they're good spams anyway also anybody I just thought of anybody everybody check your cell phone if you haven't checked it so we and I like that going on make sure they're off so anyway if you turn in those cards either turn me to the question on them or even just leave them on a table as you go out and that and we you know have your email so we can let you know if there's what's coming up remind you of those and if there's any other special events that we want to let you know about I'm instead I was set aside but Stephen Hockey and we keep punching him in and he almost died in December apparently but Stephen comes back he's recovering in and I was talking to his assistant he said well Stephens looking for excuses to travel so we invited him I don't know Phil whether it be able to come apparently we'll see he's he has nine lives and I know how many he's already but he's there but anyway he's doing wonderful stuff you probably heard a lot of him he's in the news recently too so it's now my pleasure to introduce Greg Hinkley who is the president of Mentor Graphics corporation and since this is a guy to give a big hand to cuz he's a big player here [Applause] thanks Siri this evening I've been looking forward to with great anticipation because I was fortunate enough to years ago to be in the audience and listen to dr. Brian Greene dr. Greene is a full professor of both physics and mathematics at Columbia University he's co-director of Columbia's Institute of strings cosmology and astroparticle physics and you think of what a rough life it would be curing that title on your business card he is he's a symbol laude graduate from Harvard University he was a Rhodes Scholar to Oxford University he's acknowledged as one of the principal thinkers and contributors to the concept and study of string theory he's a best-selling author his the elegant universe was on the best-selling list for many many months in fact during much of that period outsold the then-current John Grisham thrill thriller novel so I encourage you to read it and the subject of tonight's talk is his latest best-selling work fabric of the cosmos I think the most important thing about dr. green is a comment that was made by the Washington Post where they said that dr. green was probably the best individual to take abstruse concepts and make them transparent to the ordinary lay person so it's going to be it's going to be a wonderful evening and I ask you to give it warm welcome to dr. Brian green [Applause] thank you very much and thanks for the kind introduction two quick things before we start can you bring those spots down a little bit because I just like to see who's out there and I'm completely blind to buy them at the moment and the other thing is I just wanted to quickly mention a statistic that I just read which I found particularly heartening maybe read a - that between 40 and 60 million people were watching the debates on television I mean I mean how many people here we're watching the debate yeah I find that I find that particularly gratifying for a couple of reasons I think it's good good for the country to have various issues discussed in a relatively open manner but from a more personal standpoint of relevance to tonight I find it gratifying because you see in this talk there's evening what I would like to do is describe a number of developments in theoretical physics that really if you will challenge conventional wisdom challenged conventional views of reality and there's a certain trepidation I have in doing that because look people typically believe what they see believe the ears and and aren't used to thinking that reality isn't what you see it is but the nice thing about you all having seen the debates is you've all been exposed to a tremendous amount of reasoning [Applause] and the thing is you know you've been exposed to an extreme form where not only is conventional reality challenge that reality itself so I mean one thing I hope is that by the end of the evening I really hope that I'll be able to lay out a chain of reasoning for you that even if you don't follow all the details you'll at least see that there really is a rationally motivated sequence of thought that leads us to believe that the universe not not the United States not Iraq but the universe is really quite different from what you would think that's really what the main point will be now as I mentioned a couple years ago I was here and gave a talk in this auditorium this theater and the topic there well that was dramatic I want to try that a couple more times maybe sort of halfway down would be good from yeah that's very good thank you and the the topic in that discussion was focused on the elegant universe my first book and the discussion was trying to lay out the search for the unified theory that's what that talk in that book were about tonight I'd like to take a different tack focus more on material that's in my second book fabric of the cosmos which really seeks to ask a very simple sounding question and that question is what is space and by association what is time in essence is space empty space if you will this space that fills out the universe is it a real substance its space a real substance or is space just a useful idea and it's time just a useful idea that this gray thing inside of our heads imposes on the world around us because it helps us organize our thinking about how events relate to one another that's the the basic thrust of the discussion and just to start things off it's worthwhile to reflect that it was about three hundred three hundred and fifty years ago or so that Isaac Newton first articulated a definition if you will took a stand on the meaning of space and the meaning of time and the reason is when Newton was trying to work out laws of motion laws that would describe how things move be it the motion of the moon be it the motion of the earth be the motion of objects on earth he found something very interesting he found that the equations that he had been fiddling around with and you don't need to know the equations but the equations that he was fiddling around with just didn't mean anything they failed to make sense unless he really took a stand and gave a definition of space in a definition of time so that's what he did he basically said space is time is he said space is an absolute unchanging arena extending throughout the cosmos eternal static it provides the background stage on which the events of the universe take place and similarly he gave a definition for time time according to Newton is universal it flows in equal intervals use word equably from moment to moment regardless of whether you're here or there on Mars Venus another galaxy time is if you will is ticked off by Universal cosmic clock that somewhere out there in the universe relentlessly ticking second after second after second absolute space absolute time that was the imagery that Newton used to make his laws of motion makes sense and I'd like to and I'll do this from time to time just show you a little simple video sequence that gives you a visual feel for what it is that Newton articulated so if we can kill all the lights if you will so here's a prototypical example of Newton where you see there's a arena if you will the background universe is just there and these objects these planets are moving within the static calm Placid unchanging background of absolute space and absolute time now this can bring the lights back up this simple imagery proved to be very powerful because the laws that Newton wrote down based upon this kind of visualization as if the universe is kind of a big box within which objects move the equations that followed from that way of thinking about space and time really work if you use the equations to plot the motions of the planets or the earth they really are borne out by your observations if you use these equations moreover in a more terrestrial setting to take you know if you gave Newton a baseball and oh I guess we're in baseball's magnet if you gave Newton a rock and he threw the rock into the air you could make use of his equations to predict where the rock will land and indeed if you do the mathematics correctly it works it does predict where the rock will and in fact even our space program even when we go more high-tech we try to launch a rocket to rendezvous with the moon or any of Mars or the other planets NASA makes use of the equations that are based on this framework now you may be familiar with the unfortunate fact that although these equations do work well the user has to you correctly and there was this one instance where the NASA engineers one was using meters the other was using feet so much for that particular mission but that's a human failure it's not a failure of the equations now this means that there was a veritable mountain of experimental data that was supporting Newton's vision but even in Newton's age there were deep thinkers there were scientists there were philosophers who said Sir Isaac Newton it doesn't really make much sense to say that space is real that it's out there because well I can't literally see space I can't touch it I can't clutch it I can't grasp it I can't smell it I can't affect it and we're used to the fact that any object that's considered real like this video tape cover it's real and I know it because I can move it I can shake it I can bang it on the tabletop I can affect it so since that's not true with space how can you claim that it's real but here's the thing it's very hard to argue with success and Newton's laws worked so for 250 or so years people just sort of said okay Newton Newton got it Newton unraveled space and time that is until somebody else came on the scene in the early part of the 20th century a person for whom there was no such thing as received wisdom no such thing as a question that was beyond asking again someone for whom every issue was put back on the table and that person of course is Albert Einstein and Einstein was deeply disturbed by Newton's conception of space and time and it set him out to try to understand space and time more deeply and he felt in his gut that space and time must participate in the universe in a more intricate a more intertwined a deeper way if indeed they were real so Einstein thought about this for a long time and by 1915 he cracked it he realized the role of space and time in the universe because he realized that they are the medium that communicates the force of gravity they are the medium that communicates the force of gravity see Einstein studied intently Newton's works he for instance read a book that I know all the students here I know it's part of the Portland requirement that you all read Newton's Principia in Latin the original Latin I'm do so Einstein was a real student of this book and he noticed that if he looked under the letter G which had all of Newton's results about physics and math that began with G he noticed that there was gravity that Newton had discovered with his so-called universal law of gravity when he read Newton's description of gravity he was a little bit surprised part of the description was rather familiar Newton said you know every object the universe pulls on every other with a force that depends on how big they are and how far apart they are all that was old hat to Einstein but when Ison looked further under the subheading M the mechanism by which gravity works he found something that was unexpected because Newton said I have been unable to figure out how gravity actually works he wrote it is really odd that the Sun which is 93 million miles away is somehow able to reach across empty inert absolute space and somehow affect the motion of the earth we saw it in the video sequence Newton could predict how the earth would move but he didn't know how it was that the Sun was accomplishing this incredible feat of causing the earth to move in this orbit in fact in his own words he said to the answer of that important question the mechanism by which gravity works I leave it to the consideration of the reader now most readers would read that and read on Einstein was different and when he deeply thought about the force of gravity that is how he realized the true role of space and time in the universe now what's the basic idea it's one that I think many of you are probably familiar with let me first describe his discovery using a very familiar analogy then I'll show you a picture the analogy encourages you to forget about the universe forget about gravity and instead imagine I have a big huge rubber sheets stretched in front of me nice and taut good very simple picture take a little marble roll it on the surface of the rubber sheet we all know to go in a nice straight line very simple now change things take a big heavy rock put it in the middle of the rubber sheet what happens the sheet will now be curved because the rock is pushing down on it take that same little marble set it rolling along the surface no longer does it go in the same straight trajectory instead it goes into a curved trajectory a curved path because it's rolling on the curved surface of the rubber sheet Einstein says take that simple analogy apply to the universe in the following manner instead of the rubber sheet you've got space and in fact space and time and rather than thinking about a rock warping the rubber sheet imagine any object any big astronomical object merely by virtue of its presence warps the spatial arena around it and that way affects the motion of another object like the earth that's moving through the distorted environment that's the basic idea let me show you that visually just to make sure we're all on the same page so I'll always use a kind of grid like imagery like this for the fabric of space think of it as the substrate of the cosmos now this is 3d space a little hard to picture and work with let's go down to a two dimensional analogy which works well and here it is space is nice and flat if there's no matter present but when the Sun comes on the scene it warps space like the rock warp rubber sheets similarly the earth warp space now look here's the point look at the moon the moon is kept in orbit because it's rolling along a valley in the distorted spatial environment that the earth creates this is how gravity works and you see that the fabric of space the fabric of the cosmos is instrumental similarly the earth stays in orbit around the Sun because it rolls along a valley in the distorted environment that the Sun creates so this yes the stop button please work there you go now you're all one step ahead of me someone's going to come up and lecture in the next video sequence I suspect so there you have a fantastic insight think about this for 250 years space just was time just was Einstein comes on the scene it breaks the mold he breathes life if you will into space and also at a time because they participate in the evolution of the cosmos they play an intricate part in how the universe develops and evolves because they respond to the presence of mass and energy and and these ideas are not just true in the cosmos I mean right now I feel the the stage pushing up on my feet because gravity is pulling me down Einstein would say that the earth is creating chutes and valleys in the fabric of space and my body wants to slide down one of those valleys and the floor of the stage is getting in the way that's why I feel it pushing up on men you feel something pushing up on you somewhere else for exactly the same reason so these are critical steps in understanding the deep laws of the universe and understanding the role of space and time as you see space and also time become real because now they can influence and be influenced good but this sets up a very deep problem because if space is real and if it can respond just the way any more familiar object can be affected and respond then it is subject space is subject to the laws of the universe in particular a body of law known as quantum physics and when you apply quantum physics to the fabric of space you run into some very deep problems let me explain why so quantum physics is a very mysterious and complex subject that could easily take hours to describe so I'm just going to cut to the heart of the matter and it's a subject that was developed in the 1910 20s and 30s because scientists found that when they try to apply earlier ideas of physics that were developed in the 19th century to the realm of the small the realm of molecules the realm of atoms they found that the 19th century physics just gave wrong predictions for how molecules and atoms behave the biggest wrong prediction is that 19th century ideas say that every single atom in the universe should self-destruct in a fraction of a second it doesn't happen yeah we're kind of happy it doesn't happen but it alerts us to the fact that a new body of law needed to be developed to describe the small stuff and quantum mechanics is just that body of physical law now I'm sure many of you are familiar with various aspects of quantum physics things like particle wave duality or this idea of parallel universes a real puzzling idea of parallel universe and that's the idea that there are many copies of the universe as we know it each differing slightly from the one that we're directly aware of for instance in one of those universes you may have gotten caught in traffic and you didn't make it to tonight's lecture and you know it's difficult for me to say which universe you're happier at the moment in quantum physics doesn't give insight into questions like that but that's the kind of weird idea that emerges from this framework there's also the idea of quantum tunneling right that's the idea that were to walk into a solid barrier over and over again quantum physics says that indeed on most attempts I'll hit the barrier and bounce off imagine it's the other side of the stage that big solid piece of stone but quantum physics says that there is a small probability that in one of those attempts I'll actually pass right through the solid rock and emerge on the other side unscathed a small probability but not a zero probability and that's the key thing in fact the microscopic version of that experiment where rather than having a person walk into a wall if I have a little particle that I fire into a barrier that 19th century physics says no way the electron can't penetrate that little particle can't get through quantum physics says well actually there's a small probability that it can and every so often when you do the experiment it actually does so these ideas however strange have to be taken very seriously now here is the issue the only feature of quantum theory that I really need you to have a rough sense of in your mind to understand why there is an issue once space becomes real is something called Heisenberg's uncertainty principle now how many people are familiar with Heisenberg's uncertainty principle whew that's good it's sort of a difficult concept to explain and one way well I try this in the book but it really depends if if you have the same kind of Chinese restaurants that we have in Manhattan's Chinatown I don't know if you do I've been going to the vegetarian Chinese place downtown but they don't have the feature that I'm referring to which is a special order menu you often find in Manhattan's Chinatown where you've got dishes arranged in column a oh they're dishes in column B and here's a thing the restaurant says if you order the first dish in colony you're not allowed to order the corresponding first dish in column B and vice versa that's basically the uncertainty principle I mean let me just amplify that to be a little bit more precise so the uncertainty principle says that knowledge knowledge of the microscopic realm is very much like that list divided into two columns and the uncertainty principle says knowledge of one feature of the microworld from the first list fundamentally compromises your ability to know a corresponding feature of the microworld from the second list and we're over here's the thing the better you know this feature the less you can know about its partner the more you know about its partner the less you can know about the first fundamental uncertainty let me give you an example to make that concrete I mentioned electrons little particles a moment ago if you apply the uncertainty principle to a single electron it says you can't know where the electron is and how fast it's moving you can't know where it is and how fast it's moving simultaneously with total precision can't be done in fact the better you know where it is the less you can know about its motion the more you know about its motion the less you know about its position this is not having some thing to do with your equipment how good it is how good measure or experiment you are there's a fundamental limitation on what you can know about the micro world and here's the thing that idea seems strange by everyday standards right I mean it seems like I can say where the glass is and how fast it's moving right it's right there and it's not moving but the key thing to bear in mind is that Heisenberg in 1927 didn't just declare uncertainty he declared uncertainty but also the minimal amount of uncertainty with total certainty and when you look at his formula in detail it shows you that the amount of uncertainty gets and smaller when objects get bigger and bigger so that for a relatively large everyday object the amount of uncertainty is very small so there is some uncertainty in the position and speed of the glass but it's so tiny that we don't even notice it we don't care about it but when you look at Heisenberg's equation and you follow its implications as you go smaller and smaller the realm of molecules and atoms there the amount of uncertainty grows larger and larger so that in the micro world uncertainty reigns now these ideas again have been experimentally tested for instance when I was at Cornell before I went to Columbia there's a guy down the hall named Tom Kinoshita did thousands and thousands of pages of calculations using quantum mechanics to describe particles like the electron and other ones like the muon and after these thousands of pages of calculations which he worked on for nearly 30 years he came up with a number that described a quantum mechanical feature of an electron people then went out and measured the electron and the answer they got agreed with the number he calculated to one part in ten billion to ten decimal places I mean can you imagine that you sit down and you do a calculation with a pen and paper a little bit of computer support and the number that you get tells you something about the real world to ten decimal places that convinces you that these ideas are correct now the issue is when you apply uncertainty to matter the glass electrons particles whatever as I said it works incredibly well but if space is real as seems to emerge from einstein's thinking about gravity then it must also be subject to uncertainty space must be subject to uncertainty and what does that mean well it means the following in the video sequence I'll be showing you space on law scales and Einstein said well space is kind of curved but it's very gently curved right the Sun appeared the fabric of space at a nice gentle shape to it quantum theory says that if you examine space on microscopic scales not astronomical scales it will be anything but gentle it'll be jittery it'll be turbulent it'll be frenetic because quantum uncertainty says that they're features of space that we can't nail down with total precision because that would violate the fundamental uncertainty that Heisenberg's principle injects into the physical world and that means that on tiny scales space will be sort of like the surface of a violently boiling pot of water an image of space that completely is at odds with the image of space that came from Einstein's theory let me show you that important idea visually so in this sequence will start on large scales where Einstein's theory works very well there it is space is nice and curved it's nice and gentle and what we're going to do is take this elevator which I hope you can see here it's the elevator of the imagination if you will allowing us to go smaller and smaller and smaller imagine every step of the way we're shrinking by a factor of 10 a factor of 10 again now you shrink small enough sooner or later you get to atoms but let's keep going let's go in fact a hundred billion billion times smaller than an atomic nucleus quantum uncertainty applied to space on these small scales says that this is what space will look like this foaming frenetic turbulent form for space and please note this imagery of space is totally different from the nice gentle image of space on which Einstein based his theory of gravity his general theory of relativity now if we take the elevator when we go up factors of ten larger and larger as I mentioned before the larger we go the smaller the amount of uncertainty is so at the scale of atoms there's a certain amount of uncertainty but it's getting let's keep going if we go factors of ten larger and larger we come say to the everyday scales of common experience let's keep on going if we go all the way back up to the scales of stars and galaxies we do recover the nice gentle Placid image of space on which Einstein basis theory and that's why Einstein theory of gravity works incredibly well on big scales where that imagery of space works but there's a real problem because when you apply this quantum uncertainty to space on small scales a completely different image quantum theory and general relativity lock horns now i briefly mentioned how small you have to get to encounter this problem I said a hundred billion billion times smaller than an atomic nucleus that's 10 to the minus 35 meters that's a decimal point 34 zeros and a one and there's really no denying it that is pretty damn small so small that I can imagine you're wondering who cares you know why should you worry about this issue Einstein's theory of the big stuff general relativity works stars and galaxies the whole universe quantum theory as I mentioned works fantastically well for molecules and atoms so maybe that's enough to say that we've pretty much nailed it we understand how the world works and for a couple of reasons thousands of scientists across many generations across continents would disagree with that reasoning and in fact have devoted their professional lives to trying to resolve this problem and let me just give you one concrete reason why this is such an important issue to come to terms with you see there are some questions about the world that we'll never be able to answer until we have laws of physics that can harmoniously be stitched together into one consistent framework you can't have for the big and laws for the small if they somehow clash which they do as we just saw because that will ensure that certain questions are forever beyond our ability to address and one such question which I'd like to give you as an example is how did the universe begin deep important question how did the universe begin well let me just show you a quick artist's sketch of current thinking on that idea so if you will in the beginning was kind of dark oh yes and there we go the universe somehow came into existence in what we often call a Big Bang like explosion in which matter and radiation in fact spacing time themselves are envisioned as being sprung forth from this primordial explosion and as the universe got larger it cooled down and as it cooled structures like stars and galaxies could begin to congeal giving rise to the familiar things that you can see on a nice clear dark night sky now of course we don't literally see that whole film when we turn telescopes skyward we just see the final few frames and what we try to do is make use of our understanding of the laws of physics to in essence turn that film this cosmic history in Reverse run it backwards using our minds and our equations to figure out what really happened at the beginning now I'm going to show you this run backwards and I will first show it to you in the context of conventional reasoning here's how it goes so if we run this backwards everything that today is rushing outwards in Reverse of course everything comes back together so the galaxies approach one another they merge together the stars within galaxies get very close together it's as if in Reverse the universe kind of implodes in on itself it falls in on itself and the point is this as we turn the cosmic film further and further back we can make use of the known laws of physics to go all the way back to a split second after the beginning that's coming up it's right around here but the known laws general relativity and quantum mechanics because of their conflict when you try to go further back breaks down and what we get is this noise static garbage and the reason is that the universe itself the universe itself as you run that film further and further back gets smaller and smaller and smaller at some point the entire universe is that tiny distance that I mentioned that hundred billion billion times smaller than a nucleus that 10 to the minus 35 meters when the whole universe is that tiny size the conflict between the laws of the small and the laws of the big rears up its head prevents us from turning the film further back prevents us from seeing what happened at the beginning so that's one concrete reason why you have to take this conflict very seriously so what do you do about this conflict well there are two approaches Einstein's first approach was to say well maybe quantum mechanics is wrong he didn't like quantum mechanics very much even though it was one of his papers that 1905 really set off the quantum revolution he thought his theory of gravity was so beautiful and so wonderful that if it was coming into conflict with this other theory quantum mechanics it probably meant that quantum mechanics was somehow wrong so he spent a lot of time trying to poke holes in quantum mechanics coming up with one idea after another that he would fire at the practitioners of quantum mechanics trying to convince him that the theory was incorrect now one by one the quantum practice has shot down Einsteins thoughts about where quantum mechanics might somehow be wrong or incomplete but then something interesting happened in 1935 Einstein came up with a very very puzzling implication quantum theory I'd like to quickly describe it to you it's very very strange to do so let me just remind you of one fact about quantum theory quantum theory fundamentally tells us that you can never fully predict the outcome of an experiment you can only predict the likelihood or the probability that an experiment will turn out one way or another give an example so I mentioned electrons it turns out that electrons can spin around like a top they can spin clockwise we call that spin up they can spend counterclockwise we call that spin down they can spin up or they can spin down now because of this quantum weirdness of probabilities being fundamental it turns out that an electron can sort of be in a mixture of both spinning up and spinning down at the same time and only when you measure it when you look at it does it snap out of that quantum haze and definitely spin up or snap out of that haze and definitely spin down now look this absolutely is weird because we are unused to a reality that somehow is unambiguous until we look at it until we measure it we're used to were yata it seems to be solid but quantum theory says no things can be in a fuzzy mixture and only when you look does the reality really assert itself strange but I want you to accept it because I want to go even further and explain something that's even more bizarre than that and that is this Einstein and two colleagues Podolsky and Rosen showed that you could have two particles set up so that each is in this fuzzy mixture of both spinning up and both spinning down such that if you take one of the particles and put it in a box in New York take the other particle put it in a box in California they're both in this fuzzy mixture and then you go over to the box in New York you measure the electron and say it snaps out of the Heysen spins up they were able to show that the particle in California that very moment will snap out of the Heysen spin down or if you go over to the particle in California you measure it and say it snaps up then they were able to show that the one in New York immediately snaps out of the haze and spins down that's strange because you seem not to have anything to say the one in California when you measure the one in New York but somehow it's affected by something happening 3,000 miles away Einstein called this spooky spooky action at a distance you do something here and it seems to influence something over there now he was very happy when he found this implication of quantum mechanics because naturally he assumed that it was so crazy that when he showed it to the quantum stalwarts they would have to agree that their theory wasn't right how could any theory be accepted if it makes such a crazy prediction well Einstein showed it to the quantum practitioners and their reaction was at first strange but then they said well heck maybe that is how the world works who's right who's wrong well in the 1930s you couldn't actually do the experiment and the forties fifties sixties seventies you couldn't do the experiment but by the 1980s you could and when the experiment was done indeed when this particle snapped up this one snapped down and vice-versa it really is how the world works so you can't get rid of the problem between quantum mechanics and general relativity by trying to claim that quantum theory is somehow wrong because it always works its predictions are always borne out by experiment so you have to take another approach and the other approach that we believe is the right approach is called string theory and some of you know something about string theory and what I'd like to do in the remaining time that I have here is briefly describe string theory and indicate how it solves this problem and then in the remaining part of the talk I'm just going to lay out three fantastically strange implications that string theory has for this question that we've been asking the reality of space and the properties of space in our most cutting-edge approach to describing the universe so first off what is string theory well it's a theory that tries to answer a question that people thought about for thousands of years which is what is stuff made of what are the fundamental ingredients make up everything in the universe so if I take a piece of wood cut it in half keep on slicing into smaller pieces where does it stop what's the smallest uncuttable piece that you get to now we know in our age that if you cut far enough down you get to atoms we also know that atoms are not the end of the story because they have electrons going around the nucleus with neutrons and protons and even those particles sort of like a sequence of Russian dolls have particles inside of them so the neutron and proton each have quarks inside conventional theory and conventional experiments stop their electrons quarks a few other exotic particle species are the little dot particles that can't be cut any further that's where it all stops string theory suggests a different story and I say suggest because this is not a proven theory by any means but string theory suggests that there is one more layer to this progression namely inside electrons inside quarks inside any particle you've ever heard of is something else a little filament a little filament of energy it kind of looks string like that's where the name string theory comes from and the wonderful idea is that the different vibrational patterns of this different string just like the different vibrations of a violin string produce different musical notes the different vibrations of this little fundamental string and string theory produce different particles electrons or strings vibrating in one pattern quarks or simply strings vibrating in a different pattern everything emerges from the vibrations of these objects let me show you a visual and that one he so if we examine something quite familiar like a candle and a holder and examine its microscopic makeup so rather than examining the fabric of spaces we've done so far let's go on a journey right into the candle the smaller and smaller and smaller into it we knew we all know that we get to atoms you go small enough got the electrons as you see they're going around the neutrons and protons as I mentioned the neutrons and protons have quarks inside of them let's see those that's the old story these are the elementary constituents the new picture of string theory is that these objects are actually these vibrating filaments of energy these vibrating strings and the different vibrations as I mentioned give rise to the different particles so the richness of the world around us come from the rich spectrum the rich variation if you will of vibrations that these little tiny strings making up the microscopic landscape can actually execute it's as if you have a kind of cosmic symphony of strings vibrating matter and radiation into existence that in a nutshell is string theory and remarkably this relatively small change going from a little dot to a string resolves the conflict between quantum theory and general relativity let me just give you a one sentence explanation and I'll show you visual on that when you go from a point particle to a string you can think of it as if you're kind of spreading out the particle account of smearing it out now when you spread anything out at all imagine I take a drop of ink it goes into the glass of water as it spreads out it dilutes similarly when you spread a particle out you dilute it and it's not completely obvious but you also wanted to diluting the spatial fabric you in essence spread the spatial fabric out when you go from a dot to a string and when you spread the spatial fabric out those violent jitters that I showed you a couple of video sequences ago as space spreads they get spread out they get lessen they get diminished and they get two minutes just enough that there's no longer a conflict between the laws of the small and the laws of the big that's the basic explanation to show you an individual but this will go by a little bit quick so I'd like to just set it up for you what you'll see in this little sequence is we'll start by looking at the fabric of space and you'll see it doing those while it violent jitters that I showed you before that's the picture before strings we're thought of will then bring strings into the picture and you should note that they kind of push spaced apart they spread the spatial grid out and watch what happens watch what happens to the jitters of space as space spreads you'll watch them diminish diminish just enough for the theories to come together so let's do that here's the picture violent jitters in space look in that little white box focus your attention there now bring on strings strings are pushing the fabric apart notice that they're pushing the gridlines apart and then thereby diminishing the jitters the jitters are now really calmed down allowing quantum mechanics and general relativity finally to be put together in one coherent framework now there's a lot more to be said about the properties of string theory but as I mentioned my goal here tonight is not to talk about string theory as the unified theory rather I'd like to end with a brief discussion of three really stunning implications that string theory has for the fabric of space the fabric of the cosmos now what are those implications implication number one indeed string theory does for the first time put together quantum theory and general relativity the laws of the smaller the laws of the big but it only does so at a particular cost and that cost is the theory demands that our universe the spatial fabric of our universe have more than three dimensions have more than three dimensions that is in addition to left-right back-forth and up-down the mathematics of string theory says that our world has at least six and probably seven other spatial dimensions filling out the spatial fabric now when you first encounter that idea I can imagine you're thinking well hey that's pretty cool sort of sounds like Star Trek but then I wouldn't blame you for wondering how you can possibly take a theory seriously if it's making a prediction that seems to be grossly at odds with what we see in the world around us we're all familiar with left-right back-forth up-down the dimensions I mentioned that we all move through freely in day-to-day life there don't seem to be any others string theory says there are and let me just try to quickly convince you that that's a fairly sensible idea do it by analogy first and then I'll show you some visuals on it so the analogy is one that I'm quite fond of because it's so simple just look at a piece of paper flat on its surface you've got two dimensions right you got left and right you've got up and down two dimensions flat on the surface now let me take the piece of paper and roll it up into a tube certainly by rolling it up i've not destroyed any dimensions so it still has two dimensions on its surface but I have changed the character of one of the dimensions because we still have left and right as before but up-down has now been rolled up curled up into clockwise counterclockwise a tiny curled up dimension and in fact if I was to roll this tube up ever more tightly I can't really do it but the tighter I roll it the smaller the cross-section becomes and the more difficult it is for you to even see that there is a curled up clockwise counterclockwise direction so if I made this really tiny and I told you that there's a little ant living on it's life on the tube and I was to ask one of the people way in the back what kind of motion the ant could execute you probably say to me you know poor little antic well it assumes that I call in some it has a certain kind of empathy for ants but it's a poor little guy it can only move left and right because that's all you can see from your distant vantage point you don't have the visual acuity to even see that this has any thickness to it but then if way in the back you took a pair of binoculars and you zoomed in on the tube you'd say whoa it's not so bad for the ant it can move left and right but can also move clockwise counterclockwise because by enlarging the tube you can see that there's a curled up dimension that eluded the naked eye because there's too small maybe that idea is true for the universe that is we have the three big dimensions again left-right back-forth up-down those are the analog maybe of the big part of the tube just as the tube has curled up dimensions maybe our universe has curled up dimensions curled up so tiny that we don't see them with our eyes or even with our most powerful equipment that's the idea now let me show you that in a visual here so I'll amplify that analogy by looking at a traffic cable this is Central Park West 81st if you want orientation so there's a traffic cable notice that from this vantage point it looks one-dimensional the cable looks one-dimensional because you can't really see that it has thickness to it because it's too small but if we zoom in and look at the point of view of a little ant as I was mentioning and watch what this tiny ant can do notice that it can move and and and I do hope you appreciate this because it took forever to get these ants to do this notice that the the ant moves in a clockwise counterclockwise direction it has direct access to these curled up dimensions that you and I can't see because they're too small in everyday life now keep the lights down if you will let's apply this idea to the university here's the spatial fabric of the universe three dimensions I only show two on the screen let's go smaller and smaller and smaller into the spatial fabric string theory says you go small enough and you will encounter extra dimensions curled up dimensions of space so if we have our little ant walking around it can walk in the big dimensions that you and I know about but if it's a hyper hyper microscopic ant it will have access to these tiny curled up dimensions that you and I simply can't see and even our most powerful equipment can't see because they're just too small now string theory doesn't say that the extra dimensions look like this little circles it says actually that there are six or seven dimensional objects and they kind of look like this this is called the khalaby Yau shape if you want to know the technical name notice that it's a very richly intertwined curved object it has a really rich geometry associated with it and if these ideas are correct this is what the microscopic landscape of our universe actually looks like you have the big dimensions that we know about represented by the grid but at every point you have these extra dimensions that are curled up into these interesting complex shapes that fill out the extra dimensions that the mathematics of string theory demands are there so that's the first stunning implication of string theory the fabric of space more dimensions than we thought second implication I'll go through these sort of quickly as time is starting to run a little bit short second implication has to do with the way in which space can evolve so Einstein taught us that space can curve it can warp it can also stretch and in fact we believe it is we believe the universe is expanding and that expansion is coming from space stretching now take any familiar piece of material if you stretch it far enough what happens it rips thank you very much it'll rip the question is can that happen with the fabric of space or is that simply taking this analogy this fabric idea to an extreme where it misleads you well Einstein would have said that space can't rip because in Einstein's theory were space to rip it would cause a calamity a catastrophe that our well behaved universe just wouldn't allow to happen what about in string theory the answer is in string theory we found that space can rip let me show you how that goes so when a string moves and actually you can think about it as sweeping out a tube watch that string it sweeps out a tube and the tube itself can act as a barrier protecting us if space should rip so there you see a rip in space but the tube can surround it as you see up there as well in that way allowing space to rip but preventing any catastrophe from affecting us outside because the string unlike a particle can provide this important shield to us now let me show you what that can imply imagine the extra dimensions are like these little Donuts these are simplified versions of those calabria shapes that I mentioned a moment to go easier to picture here's what can happen if space can rip if the extra dimensions have that kind of shape focus on one of these extra dimensional don't donuts extra dimensional tore I in the more correct language here's the thing a string can wrap around the extra dimensions and it's kind of heavy if it it stretches all the way around the extra dimensions but if the extra dimensions should kind of shrink down in one component like you see here the strings wrapping around the shrinking part are much lighter and because of this decrease in their mass it turns out that they can begin to vibrate in lockstep they can begin to vibrate what we call a coherent manner and when many rap strings vibrate together here's what they can do they can force the fabric of space to rip apart and in that way transform its shape in this case from a doughnut to a ball from a to a sphere and there can be many more very very surprising and interesting evolutions of the spatial fabric that simply would not be possible in Einstein's theories lecture why strings and not sort of flying carpet or membranes like little frisbees or discs or why not little blobs what's special about strings and it turns out that we've learned that strings are not that special the theory actually has strings and blobs and so forth and moreover this is a stunning idea which I'll show you in just a moment there's a group of string theorists who have suggested that maybe our entire universe is just one large object in string theory one huge membrane the picture that you should have in mind is what if our universe is like a big loaf of bread and everything that we know about is just taking place on one slice of bread in this big cosmic loaf and there can be other slices which would be other universes living on other slices other membranes as we say it in more correct language let me show you what that means and what it implies so the progression that I just mentioned is prior to 1995 we thought the theory just had these little one-dimensional objects these strings after 1995 a variety of breakthroughs spearheaded by more understanding of the mathematics showed us that there can be these kind of flying carpets which can kind of roll up we call these membranes or two-brains or that can actually be 3-dimensional versions of this 3-dimensional blobs which can vibrate and undulate and in fact these three-dimensional blobs can be huge it turns out they can be big as an entire universe the universe as we know it so maybe we are living on one of these big blobs one of these slices now if one of the blobs that we see here is our universe notice what can happen the slices of bread that is the membranes can actually smash into each other they can come close together and bang in and some people have suggested that that smashing together of membranes might actually be the big or we now call it in this theory the big splat maybe the universe began when these big membranes slammed into each other and then perhaps a few trillion years later they slam into each other again igniting a new Big Bang and a new Big Bang maybe we have a cyclic universe these physicists suggest and what we are living through right now is merely one cycle of that now notice what this implies I started off this lecture by asking is space a thing is it a real thing if this idea is true then yeah it's a real thing because space that we know of is a membrane it's one ingredient in string theory it's as real as you can make it if these ideas are correct so I'd like to close with two more minutes if you will grant me two more minutes of your patience how would you test some of these ideas that have been describing here tonight well let me give you two possibilities one relies upon this idea that we might be living on a membrane and it goes is this if we're living on a membrane I'll show you this individual in a moment if you do a very high energy collision between particles you might be able to force some of those particles some of those strings to leave our slice of bread our membrane thereby carrying away energy and if that were to take place it would mean that if you compare the amount of energy before the collision and after the collision there'd be a little less after the collision because some would seep away we've never seen this but we're gonna look for it in the next few years what would that look like visually so if that is a little particle of gravity if you could bring the lights down graviton you can imagine that this particle might be created in a high energy collision this is our membrane this is happening in Geneva Switzerland the new Collider in a few years and it could force one of these particles to leave our dimensions taking away energy and if that energy goes away we'll notice it by a mismatch and the amount of energy after and before the collision perhaps giving us in direct evidence that these extra dimensions are real final point and then I'll be done is this I've described for you tonight some fairly strange ideas I started with the conventional approach of Newton which is very intuitive space is an absolute stage time is an absolute clock and that is the arena of reality the fabric of the cosmos we then moved on and described how that was very uncomfortable for Einstein after ten years of work it led him to general relativity where space and time are not absolute they could warp and curve in the service of the gravitational force space and time became part of the evolving cosmos we then noted in quantum mechanics that that created a problem because of space and time are real and participants in the universe they're subject to quantum uncertainty making them jitter violently conflict string theory comes along resolves the conflict by spreading out space diminishing the jitters but it requires yet further dramatic upheavals and our understanding of space requiring that we have extra dimensions requiring that the fabric of space be able to rip apart suggesting perhaps that we're living on a large object in a higher dimensional expanse and finally suggesting that these extra dimensions are not simply hidden away because we don't see them but that they may hold the answer to what many of us certainly I'm included in this list consider the deepest problem in science and this will be the final thing that I will tell you what is the deep problem of science well experimental physicists have over the last century measured about 20 numbers in a variety of experiments it seemed to really characterize our universe these numbers are things like what the electron waves its mass the mass of the quarks the strength of gravity the strength of the electromagnetic force the strength of nuclear forces on an on a list of twenty numbers that they have measured to extreme precision so we know the numerical values of those parameters with great confidence but the thing is nobody has any explanation for why the 20 numbers have the particular values that they do now you might wonder again should I really care about an explanation for those numbers I mean if the electron was like ten times heavy or ten times later who cares it's obeah that's just how the world would be should I really worry about that and the answer is you really should worry about it because if for instance I set up 20 dials up here and it lets you come up and fiddle with the twenty numbers by fiddling with the dials for almost any fiddling that you do you will destroy the universe and the reason is the universe has as its central feature stars stars rely upon nuclear processes in order to shine give off heat and light the nuclear processes demand intricate interrelationships between the twenty numbers you fiddle with the numbers you ruin the relationships nuclear processes don't happen stars don't light up universe is a completely different place so the deepest question in my mind that science faces is why did the 20 numbers have just the right values just the right values to allow nuclear processes to happen to allow stars to shine to allow planets to form and on at least one such planet life to exist and to evolve why why do those numbers have devised that they do now no theory has given an explanation for this string theory also has not given an explanation but for the first time in the history of science it gives the framework for an explanation and the framework the framework relies upon the extra dimensions of space and it goes like this those 20 numbers in string theory reflect the vibrational patterns of strings strings are so small that they don't just vibrate into the big dimensions that we see they also vibrate into these tiny curled up dimensions and their vibrations are affected by the geometry in these extra dimensions so if we knew exactly what the extra dimensions look like we might be able to calculate how strings vibrate and calculate those 20 numbers final video just to make that a little bit more clear so the idea is this with an analogy imagine you look at a wind instrument like a French horn notice that the vibrations of the air streams the vibrations of the air strings are affected by the twists and turns the geometry of the instrument now replace the instrument by this form for the extra dimensions of space as you can imagine if a little string is vibrating in this complicated environment the twists and turns in the geometry will have an impact on the vibrations just like the twists and turns of the French horn affect how the air vibrates let's bring a string in notice as it's vibrating it's affected by its environment and the point is if we knew exactly what the extra dimensions look like and we don't yet but if we did we might be able to calculate the allowed vibrational patterns of the strings we might be able to in that way calculate those 20 numbers and if the answers that we got agreed with the results that experimenters have found this would give us the first fundamental explanation of why the universe is the way it is and to my mind it's absolutely stunning that the explanation would rely on this rich texture this rich structure for the fabric of space the fabric of the cosmos that has emerged from this chain of reasoning stretching from Newton through Einstein through quantum theory and finally into string theory that's our hope that's our goal that's what we're shooting for thank you very much [Applause] so I'm happy to answer a few questions if anything wasn't completely clear is this on oh great doctor thanks for coming to Portland my question about the string itself is its infinitely one-dimensional does that mean that there's no matter or is is there matter to that string let me give people a moment to go and then when it's quieted down when I address your question well it's going to have a bit of a hum so we'll just go so the question is does the string have matter associated with it even though it in this incarnation is sort of infinitely thin and the answer is that strings have energy by virtue of their motion and from Einstein's equals mc-squared energy and mass are basically two sides of the same coin and therefore I'd really say that energy and mass don't really have any fundamental distinction at this fine resolution of understanding what makes up things in the universe so they're really the same thank you hello dr. green can hear me I can indeed in so far as you have a theory here in which you have a pretty much a single notion like a string which can be articulated in various ways to explain just about everything it's like a physical theory resembles other physical theories but it also resembles a notation system would you care to address the notion that that there's some overlap there and it may speak to an essential subjective nature of the universe I'd be happy to adjust the question if I understood it a notation system can you perhaps describe what do you mean by a notation system well insofar as you have a single articulated symbol which is the string itself which may be a closed loop or an open string right that if you can articulate in this in in various ways to come up with all the various physical laws that we're familiar with is that's not also resembling a notation system by which you can write down all the physical laws that we're familiar with and if there's some overlap here between a notation system and a physical theory does this not imply that there's a subjective dimension to the universe well I'm glad you repeated the question are you a philosopher but by NHS now let me you know I mean let me do my best and then perhaps we can carry on after when we describe string theory mathematically we certainly have a rigorous set of mathematical ideas represented by mathematical symbols that have been developed over the last few hundred years to have a rigorous foundation to everything that I've described here tonight so I've described things using metaphors and using pictures there's of course a rich and complex body of mathematics that supports everything that I just described now we can use that body of mathematics we hope to be able to describe essentially any physical system if string theory is correct so you give me a physical system a black hole the neutron star whatever in principle it has some description using the ideas that I presented tonight using the underlying mathematics which is the real language to talk about these ideas with precision so in that sense this does provide a notational system for describing things in the universe but that's not intrinsic to string theory any physical theory that anyone's ever taken seriously is founded on the same kind of mathematical system and thereby also would provide a notational system for describing the world so that's not intrinsic to string theory but certainly it's part of any well-defined physical theory in string theory is one of those under 20 parameters that you talked about can you tell me what's wrong with dr. Randall L Mills approach where and he claims to have calculated the masses of the fundamental particles by uniting the four forces in closed mathematical form from first principles I'd be happy to answer that question if I understood it I don't know the gentleman you're referring to I presume he's not someone who was published in any traditional journal because I presume I would be aware of it am i right and that who knows he's been a published in peer-reviewed journals but the catch is he's had to go to Europe to do it he's been banned in the US because he violates some quantum theory huh well I am all for people putting forward any ideas that strike them is relevant to describe in the universe I can assure you that every week I get alternative approaches to the one that I've described here I have a file that's that big filled with varieties of theories and who knows maybe one of those is right I am NOT trying to denigrate those theories and maybe the one you're referring to is right look let me just finish unfortunately can't comment on directly since I've not read it right but that's that's my point he's published the book it's right there in print and I was in hopes maybe you knew it was wrong with it thank you yeah I wish I wish I could be more specific let me just along those lines just mentioned one other thing you know Einstein when he discovered the special relativity was not in the Academy was not one who had followed the traditional trajectory that an academic physicist would he was this guy in a patent office who wrote a paper with effectively had no references and it looked like a completely crank paper and if I would have received that paper today I probably would have put it in that file and wouldn't have read it so that's not to say that just because something is following a non-traditional route that it's wrong and I don't mean to imply that it is at all the problem is were I to read all of the papers that I get I'd never have time for anything else so it's a very difficult thing to know what to do with these variety of proposals oh that's so let's do one up there yeah Kandee transformation of one extra dimensional shape into another happened to a three dimensional gob you'll that you mentioned our universe being inside of I'd be happy to answer the question now that one that one I did understand pretty well thank you you say the question is you know I discuss the fabric of space being able to rip apart and the question is I also said that the fabric of space that we know about might be one of these three dimensional blobs sort of stretched out very huge so it fills what we traditionally call the fabric of space three-dimensional space could three-dimensional space to rip apart and go through the transformations that I mentioned I'm not completely sure I certainly mathematically in fact is ripping a space you know very satisfying his work that I was involved in and we were able to show that the fabric of space in the extra six dimensional component can rip apart we have not really been able to find the mathematics to fully address it in the three-dimensional big part my gut feeling is that space is kind of space and if the six dimensional part of space can ripped in the three-dimensional part can - because they're fundamentally the same kind of entity but I can't really make that precise yet oh one of these sure back to the cosmic loaf of bread actually can I do one of these written questions that I was handed here questions about the fabric of the cosmos and the nature of the universe seemed almost theological how do you feel string theory informs your theology yeah that's a it's a good question it really depends on what one means by theology I personally don't subscribe to traditional organized religions in any traditional sense so I've given lectures of this sort mostly on the elegant universe and sometimes people come up at the end and said well you know do you believe in God and well I believe in order I believe in harmony I believe that there's some fundamental organizing principle that makes the universe and I hope that strength theory is part of that set of organizing principles but if you are willing to consider that belief in faith if you will in order and harmony if you are willing to consider that a kind of theology a kind of religious belief then I would say an answer to this question that stream theory thoroughly informs my theology because string theory has thoroughly and dramatically affected my belief that there is an explanation for it all as we have gone from the mid 80s until today huh as we've gone from the mid 80s until today I have been impressed all along the way with how string theory has pieces that just seemed to fall together and fit together in a really coherent and an elegant and beautiful manner if however the questioner by theology meant the traditional notion of theology then I would say the string theory hasn't had much impact on it also it's partly a matter of how you define the word theology back to the cosmic loaf of bread yeah the cosmic law for bread sure if there is a graviton that can escape from one brain to another and there are black holes on another brain yep wouldn't we see large wells or disturbances where gravity would just be an immense concentration for no apparent reason yes absolutely but it does depend on how close the other slice of bread is how close the other membrane is so people have suggested you probably have heard of something called the missing matter the dark matter the dark matter is matter that we hypothesize to be out there in space because we see the gravity that we believe that matter exerts but we don't actually see the matter itself because it's not giving off light so we believe it's there gravitationally even though we don't see it some have suggested something much along the lines of your question maybe the dark matter lives on one of these other membranes one of these other slices so it supplies gravity because the gravitons can exchange but we don't see it not because it's dark but simply because it's on the other slice people have tried to make sense of that idea and it's hard to make it work completely but it's an interesting thought you were talking about the whole idea with the particle accelerator and that the super high energy collision perhaps allowing energy to leave the universe well and so if you were to do that experiments and and you were to to find that's that mad that some of the energy that had gone into that collision was what was now missing from your your instruments is there some sort of a test to determine whether the energy Hatton has actually left our our particular local universe or earth or has merely been transduced into another form of energy that your sensors are not calibrated to detect yeah so that's a good question because when I said that you compare the amount of energy at the beginning with the amount at the end and I said if there's a mismatch that means some of it must have gone away seeped away but you could say maybe your detector simply wasn't able to measure some of the energy because it was of a form that somehow the detector wasn't set up to be sensitive to and it's conceivable that's that's not impossible but the detectors are very carefully set up to measure any kind of matter or radiation that we have any evidence exists so while in principle you're right it could be in some form that the sensor somehow is insensitive to it's very very unlikely but it's a possible explanation as well so if indeed there is missing energy that will be one of the things that people will try to rule out first they will try to rule out the possibility that the sensor somehow just missed it I think that there will be a high degree of confidence if indeed the standard tests that they use to determine whether the sensors may have missed it if those turn out to be negative I think they'll then be a fairly high degree of confidence that this energy really has seeped away thank you earlier you mentioned that that there were different forms of dimensions to have the strings vibrate but in your Nova program you said there could be other than just six other ones I was wondering how much how many dimensions you believe there are well that's a more subtle question than perhaps you might think it is before 1995 if you would have asked me that question I would have said there's a grand total of ten dimensions nine of space one of time three of the space dimensions are big and we see them six are small and we don't making up the total of nine after 1995 something quite shocking happened in the development of the field part of which I showed you in one of the final sequences but I didn't emphasize it and that is we realize that the calculations done before 1995 were done in a fairly crude manner and in 1995 new methods were developed that are far more precise and when those methods were used to calculate the number of dimensions we realized that one had been overlooked so now the perhaps best way of describing is that there are a total of eleven dimensions ten of space one of time seven of which are small spatial dimensions three of which are big spatial dimensions do you believe that there could be more than just seven dimensions of space well I presume that your confidence in my answer may be slightly diminished by virtue of my being thoroughly honest and telling you that we miss one and prior to 1995 however we so fully understand how we missed it and we so fully understand the new mathematics that reveal the missing one that to my mind it would be very hard to believe that there's any more that will turn up but who knows thank you one of these here's your order did that one good question Mike qualia but too hard I feel like what was that guy's name second debate yeah Charles yeah his time travel possible at all could you explain the Big Bang Theory more extensively well Wendy it's time travel possible by that oh of course you mean time travel beyond the ordinary even we're all traveling through time right now of course second after second after second but the question of course is can you travel through time at a different rate and the answer to that question is absolutely yes you can definitely travel through time at a different towards the future I'll come back to towards the past in a moment and this is an implication of special relativity that should be more widely appreciated than it is see when Einstein studied space and time in 1905 before the discoveries of the general theory on which I focused attention he realized that if you and I are moving relative to one another our clocks will tick at a different rate literally if you and I synchronize our watches and then we move relative to each other and we come back together at some later time our watches won't agree anymore in fact if I am the one who's doing the bulk of the motion when I come back my watch will have ticked off less time than your watch will have ticked off now take that to the extreme if you move really fast in everyday life if we move too slowly for these effects to manifest themselves but if you move really fast near the speed of light and so you go off in a spaceship for six months near the speed of light turn around and you come back if you go fast enough when you return you of course will be one year older six months out six months back but because your watch is ticking slow relative to the one on earth or equivalently because the one on earth is ticking fast compared to yours when you return one year older people on earth will be perhaps ten years old or a hundred years older or a thousand years old or a million years old or depending on how fast you go so if for instance you want to see what the earth will look like a million years into the future you can do it you can leapfrog into Earth's temporal future by going off in a rocket ship and coming back going fast enough the obstacle of course is we can't build ships that would go that fast yet but to my mind that's a technological obstacle and they set up one of these prizes not ten million dollars you know I don't know what it should be trillion dollars is the suggestion from the man behind the curtain and he raises this kind of money so you know maybe he'll be able to do it you know it's just a technological issue so yes time travel to the future is possible within the laws of physics now travel to the past harder question because of course if you travel to the past you have to come to grips with all the paradoxes that we've all seen in in Hollywood films you know you travel to the past you hold some grudge against your grandfather you see your grandfather as a young man and certain instincts well up that you're unable to control and you might knock him off but if you knock him off before he helps your father come into existence how were you even born in the first place and thereby there to carry out that particular act now does that paradox mean that time travel to the past is impossible no in fact one of the chapters in the fabric of the cosmos like carefully go through that paradox and suggest a way to avoid it just as a matter of principle to show that merely because there's an apparent paradox it doesn't rule out time travel to the past and in fact in that book I also go into real proposals for time machines to the Past and I try to describe the physics behind them and to emphasize how while they're not ruled out yet by the laws of physics as we understand them they all brush right up against the edge of physics as we understand it and it's my belief and many others agree that when our understanding of physics gets even deeper we'll probably be able to rule out time travel to the past but we have not done it yet just a question you you described the idea that once you know the characteristics of the shape of that thing yeah that you would be able to calculate or determine as a result why the 20 different numbers are the numbers they are will at that point also be possible to know why the shape is the shape it is in other words one ended up that way as opposed to some other shape yeah and in essence your question is will we have simply sort of shifted the burden of the question from explaining the 20 numbers to explaining the shape of these extra dimensions and the answer is certainly it'll require an explanation for why the extra dimensions have a particular form to be satisfying can we do that we can't do it yet but the idea is that because of that ripping in space that I described to you that ripping of space means that every possible form for the extra dimensions can mutate can transmute into every other form by suitable rippings and tearing Xandra pairings so in essence all of the possible shapes are connected to each other through these rips and tears which means in principle we may be able to define some notion of a an energy on the space of all possible shapes and our hope is that when we can do that maybe by minimizing the energy things always like to go to lowest energy States by minimizing the energy it may select one shape from the many and that's the kind of explanation for the form of the extra dimensions that we're seeking and then once we have that if we can then do the calculation figure out the 20 numbers then that would really be a first principles calculation where everything was emerging from the theory as opposed to being put in by hand dr. greens thank you so much for tonight's magic show and for your candor and patience in dealing with a sillier questions that coming along if you'd like to stay reuters the spot for the next hour I have about 68 idolised like to us but maybe I limit myself to a single 7 word question in just a moment but I'd like to make an observation that science for the longest time was based on the use of words that could be understood we can talk about Galileo dropping LED balls we can talk about electrons acting like ripples on a pond or like billiard balls we were using everyday words and it seems to me that many of the things you've said tonight and we've read about so often before are doing the same thing it's the kind of a smoke and mirrors you talk about a membrane that can be stretched to explain gravity but where are the anchor points for the membrane why how can we translate that simple two-dimensional image into a multi-dimensional space and still see how it works the question is is scientific explanation up against a semantic roadblock no I don't think so [Applause] let me just amplify that a little bit further so you're absolutely right the challenge to somebody explaining Galilean physics and Newtonian physics is not as severe as the challenge is someone to explain quantum physics and string theory and the reason is obvious that it's rooted in your question the way you phrased it when you're dealing with physical ideas physical laws that operate on everyday scales LED balls dropping people running and throwing objects you can use those everyday examples to describe the theory because after all that's where the theory truly operates if you're describing a physical theory that operates in a realm that's very distant from human perception such as quantum mechanics which deals with things that are billions and billions of times smaller than anything that we can see when you're dealing with a theory like string theory that describing things that are billions and billions of times yet smaller the challenge to describe those theories and everyday words is definitely more significant but you know perhaps you don't like my books or other books but the attempt in those books is to do exactly what you're asking to try to describe the science not using smoke and mirrors but using language and using analogies that maintain scientific integrity but nevertheless are phrased in the language that anyone can understand even without any technical background now you raise an issue for instance I gave an analogy for gravity with the stretching membrane and so on and you have certainly raised a couple of issues that you have with that analogy if you read chapter three of the elegant universe you will see those issues raised and discussed in order to avoid some one feeling that the description somehow was smoke and mirrors so many science writers have different approaches my approaches when an analogy has an obvious failing I don't try to sweep it under the and hide it away I bring it out I can't bring it out in an hour lecture because we wouldn't get anywhere but in a textual form I bring it out I show you the failing in the analogy I described how to deal with that scientifically and then we can all move on could I just add I probably came across less sympathetic that I intended to I didn't mean that books of your kind are doing some kind of a you know a blindfolding job I didn't mean that at all what I meant was that fundamentally it seems to me that the ways that were used in the past to cope with scientific ideas making use of everyday words are now no longer capable of doing that and so we're left with mathematics principally as our medium of expression and therefore when we talk about strings we cannot visualize what that means and when we talk about that singularity that we call the Big Bang where all the laws of physics suddenly started or stopped or don't apply we're out of words that's my point that even the most adept scientific commentator cannot find words to talk about these things because there aren't words that no words were ever made to do that job that's what I mean uh well well at the risk of sounding defensive let me let me just try one one more response to that it's certainly the case that any words that you use describe any physical theory are always going to fall short and ultimately even Newtonian physics you really need the equations if you want to be able to understand the theory at a certain level of rigor and a certain level of precision but my feeling is that in perhaps you are mathematician I don't know but even were you to learn the mathematics underlying everything that I described here tonight the mental imagery that you'd use would be very similar to the mental imagery that I've used to try to describe these ideas not mathematically because frankly these images are the ones that I have in my head when I'm actually doing my own research so these are not somehow watered down or baby versions of the ideas these are as close as I think we can get using ordinary language and ordinary pictures of course I have the advantage and maybe you do too again as I said I don't know maybe our mathematician or physicist I have the advantage that with every picture I have a body of mathematics that I sort of lean on and it gives me confidence in showing a picture of strings or of gravity and so forth because I know that if you push me I can always turn to my mathematical crutch examine it and say ah that's really what's going on but even without the mathematical approach my imagery is very similar to what I showed you here tonight so I think it does capture the heart of the ideas fairly well Thanks in your book the fabric of the cosmos you state that you describe in therapy entropy by giving an example of unbinding the book war and peace and then tossing the pages up in the air and you say that by a little calculation you get the answer of possible states of disorder is 10 to the 1787 power I was wondering which little calculation you used [Applause] well it's actually a complicated number that emerges from a fairly simple calculation so for instance if I had three pieces of paper and I threw them up into the air you could pretty directly calculate how many ways they could land right the good land like this this this they could land like that that that big event like this this this and so forth and there's a certain mathematical operation many of you may be familiar with called a factorial may are you familiar with the idea of a factorial by any chance yes you got great so roughly speaking the answer is you just take the number of pages factorial now that's a little wrong because you see pages have two sides right so you have to be a little bit careful so you have to take the number of pages divide it by two and you see I chose an edition of warm piece where there were an even number of pages I'm careful man I searched around for that particular edition of of war and peace so you take the number of pages divided by 2 you then factorial it and then that's actually not completely the answer either because any given page could land up or down so then you have to multiply that answer by 2 to the number of pages divided by 2 and that's not quite the answer yet almost there because there's one order where they all land in order I was calculating the number that land out of order so you have to subtract 1 from the answer I just got now the only way you do this calculation is on a computer you use a program called Mathematica have you ever heard of Mathematica yeah okay so when you go home tonight make sure your parents buy you a copy and then if you plug in the calculation that I just quickly summarized you will get that one thousand seven hundred and eighty seven digit number that I spent a page and a half recording on the pages in the book thank you very much [Applause] [Applause]

Channel: Linus Pauling Memorial Lecture Series

Views: 15,768

Rating: 4.6959066 out of 5

Keywords: Space, Time, Space-time, Brian Greene

Id: 3ZNTVNeSWKI

Length: 105min 7sec (6307 seconds)

Published: Sat Sep 29 2018