The Warped Side of the Universe: Kip Thorne at Cardiff University

well I would like to say with regard to the Nobel Prize I got the call from Sweden at 2:15 in the morning on October 3rd of two years ago and the hit voice at the other end said it won't surprise you that this surprise is being awarded to you Rainer Weiss and Barry bearish and I said I'm not surprised I'm very disappointed I was disappointed because the prize should have gone to the entire team including as major contributors the people here at Cardiff who made huge contributions this could not have happened successfully without the combined efforts of a very large number of people and the Nobel Committee has not yet figured out that they have an obligation to educate the world about the power and the importance of collaborations on certain kinds of science and technology and that this can't just be done by a handful of people so anyway that's my attitude about it I'm happy to be an icon for the team but it really was a huge team effort with Cardiff playing a major role so what I want to do is tell you a bit audit biographically about my career I arrived at Princeton University in 1962 that's more than half a century ago it's if I count on my fingers it's 57 years ago and I went there to do PhD research to learn how to do research from John Wheeler was a very inspiring man who was the Guru in that era teaching us about black holes and about neutron stars gravitational waves Einstein's relativity theory and all the weird things that might happen due to warped space and time what I learned from John was and this is the way I describe you today didn't use these words at that time it's the basic idea there is a warped side of our the universe or that there probably was a warped side of the universe we weren't sure at that time by which I mean objects and phenomena that aren't made from matter like you and I instead are made from Warped space and work time and examples about which we speculated but we really had almost no observational data to say whether the speculations were correct or not for black holes that was totally speculative at the time gravitational waves totally speculative the Big Bang singularity in which the universe was born which is consist so was made from quantum mechanical warped space-time to use a buzzword phrase we did have observational data for that but it was far from clear whether there really was a big bang at the beginning or whether something else was going on at very beginning wormholes for rapid interstellar travel time travel these were all things that we speculated about that you could see in the equations that Einstein gave us called general relativity equations this lecture what I'd like to do is tell you what we have learned in these past 57 years about the warp side of the universe going from this being almost pure speculation to what has been found to be too absolutely true what is still speculative what is likely to be wrong so that's that's where I'm going and it the what I'm going to tell you is from the combined work of a large number of people again I have contributed and these are the things that I have been particularly interested in during my career but it really is again the work of a community of a large number of re great men and women who took upon themselves to study these kinds of phenomena so let me begin with black holes a black hole is the quintessential example of an object that is made from warped space-time there's an example if you have a black hole and it's sitting here it's absolutely black it's spherical or it is if it's spinning it's a flattened sphere and it's diameter is far larger than a circumference if you look at that you say well no way that diameter is currently smaller the circle for installation as one over pi it's in fact that's not true the diameter of a black hole really is huge compared to the circumference and the way that I like to explain this is by a little analogy if I take a rubber sheet a child's trampoline say put it up on tall poles and then put a very heavy rock at the center the sheet will bend down like that now pretend you're an ant you're a blind ants so you can't don't know what's going on you don't see the universe out here all you know is this rubber sheet this rubber sheet is your universe but you've studied physics to Cardiff University or engineering and so you know it's an interesting thing to measure the geometry of your universe and so you go walking around here and you measure the circumference and then you set out to measure the diameter and you walk and you walk in your walk in your walk and walk it well it's a very huge diameter that I haven't is huge compared to the circumference and you say to yourself well obviously I live in a warped space a universe or spaces world it's not like a flat sheet of paper and that it is precisely a precise analogue of a black hole all I do is change the labels so now I'm looking at an equatorial slice through a black hole something you would have thought was a flat plane through a black hole but going right through the equator cutting the black hole in half between top and bottom but in fact it is warped in just the same way as that rubber sheet was warped warped in what well not in our universe obviously if it is in our universe then then you would expect it to have the usual Euclidean geometry so it must be worked in some higher dimensional space which businesses sometimes call the bulk and so what I'm showing you then is a two-dimensional surface of our universe but you're looking at it as it has warped in the higher-dimensional space and then the diagram is just the same as what I showed you before now the thing that most people know about black holes is that if you fall into it you can't get out and you can't send signals out so here I am I'm a little two-dimensional Kip I'm falling into the black hole that means I'm on the surface of this sheet two-dimensional sheet and I'm sending microwave signals out to you to tell you what I am experiencing there's a surface of the black hole that we call the horizon and when I fall through the horizon after that I am pulled a inexorably down to something called a singularity of the center but also the microwaves that I'm trying to transmit to you they are also pulled down toward the center they cannot get out and so the horizon is a horizon in the same sense of the horizon we don't see beyond if we're sitting say out in the desert somewhere but this horizon is something that you can't see into you can't see from the outside in but if I'm in here I can see you I can look out and see like this coming down to myself now the black hole in is made from Warped space things can't get out of it but one way to understand that things can't get out of it it's because of warp time time slows as you near the horizon of a black hole and so if you're hovering here and not falling through the closer you get to the horizon the slower time is flowing compared to what you see very far away in the movie interstellar for those of you who saw it cooper goes down near the horizon of a black hole he's there for a few hours comes back and his daughter has aged from age 11 to becoming a great theoretical physicist of age 28 it was really nice to see Jessica Chastain playing a great theoretical physicist and in fact that the world premiere of the movie the only thing she talked about was the fun the joy of being at the article physicist so anyway so you see this in the movie if you fall through the her eyes and then time doesn't simply slow down time flows in a direction you would have thought was a space direction toward the singularity and so that's one reason you can't get out it's because you cannot move backward against the local flow of time you're just dragged by the for forward flow of time or the downward flow of time down to this singularity I'm not going to talk about the singularity in this lecture but if you want to ask me questions about it I can tell you about it about it in the question period I want to focus on things outside the black hole but first I want to tell you there's one other aspect to the warping of space and time around a black hole that's a whirling of space they closed if the black hole is spinning then it drags space into a Horla motion like the air in a tornado and that pouring emotion is absolutely inexorable if you're near the horizon of black holes there's no way you can remain remain at rest relative the distance stars you're dragged around and around a very high speed around the horizon of the black hole I should remark the horizon here is drawn as a circle but remember I've removed one dimension I'm showing you a two-dimensional slice of the black hole so that horizon is really a sphere that when I restore that dimension so you have a warping of space you have a warping of time and you have a horley motion of space this is a precise depiction of what general acuity says is the warping of space-time around a fast spinning black hole this is the precise shape of space you go out very far away and this becomes flat and you're out saying near Earth down here you have a very deep funnel down here the horizon is this black circle remember it's a sphere when I restore the other dimension the color coding is showing you the slowing of time where it's yellow time is flowing at 10% of the rate that it flows at back here on earth and where it's black time is slowed to a halt and the white arrows show their length is proportional of the angular velocity of dragging of space into motion and so it's a high angular velocity near the black and lower farther away they just like if in a tornado it's a faster speed near the core of the tornado and much slower farther away now what produces this warping of space and time well Einstein tells us that the warping of space and time is produced by huge amounts of energy or mass so where is the energy here there's no matter so there's no matter providing you energy no matter providing mass where is the enters the answer is the energy is contained in the warping itself if you think about that rubber sheet and you push this rubber sheet down you have to do work to push it down it may be very stiff you have to do a lot of work you're putting energy into the stretching of the rubber fabric in the same way there's an enormous amount of energy in the warping of space and time here and it's that energy that produces the warping so the black hole is held together in technical terms by what we call a nonlinear self interaction of the black hole black hole's energy of warping produces the warping that is what we sometimes we call a gravitational solids on to use a technical phrase there's another point of view to take on this dragging of space in a whirling motion if I have take my wife and I hang her just above the surface over black hole or if she falls through it doesn't matter either way this is a painting by a great artist named Lea Halloran who's good enough she has had one-woman shows that the Guggenheim in Spain she and I are doing a book together right now her paintings about these kinds of things and my attempts at poetry but that's what you do when you get to be 80 years old near our physicist you write hit write poetry okay so anyway her feet are dragged around faster than her head so she looks down she sees her feet whirling around counterclockwise and her feet look up at her head she her head she will see her feet will see her head going counterclockwise you can understand this my imaginary taking a wet towel and you wring the water out of it and to think about it if your left hand sees your right hand going counterclockwise your right hand will see your left hand going counterclockwise so there's a counterclockwise twist of space at the North Pole of the black hole and a clockwise twist of space we call these vortices counterclockwise vortex sticks out of the North Pole a clockwise vortex of twisting space sticks out of the South Pole now I probably won't have time to tell you in any detail about it but we have learned in recent years through computer simulations when black holes collide and merge these vortices fight with each other in behave in really weird ways so there's a great richness to the warping of space and time around a black hole they even it even has things sticking out of it like my arms that are made of strictly from twisting space which can behave in really weird ways when black holes collide black holes in our universe what do we know now after 57 years we know that there are roughly 10 million black holes in our Milky Way galaxy alone astronomers have been gun to make a census from their observations there are about a billion billion or 10 to the 18 black holes in the universe as a whole an unbelievably large number of black holes the mass of the black holes range from about 3 times the mass of the Sun that all that means when I talk about mass is the gravitational pull of the black hole if you're some fixed distance away from it it's the same as the gravitational pull of three suns and that's how we measure mass actually in astronomy you always measure the mass of a star by its gravitational pull the mass of the earth the mass of Jupiter by its gravitational pull so the masses of black holes range from three times the mass of the Sun to twenty billion times the mass of the Sun their diameters are proportion of their masses they range from 10 kilometers to a hundred billion kilometers so tiny black holes smaller than Cardiff the black holes that are as large as the solar system black hole look like to your eyes well suppose that I have here and I'm looking then and from the higher dimension from the boat I have a star here and it sends light to a camera there and the light rays can travel through this warped space around the black hole along this light ray that's one light ray that goes to the camera this is the closest thing you can have to a straight line that reaches from the start of the camera or along that right ray bar there's a light ray that goes down whirls around the black hole once and goes up to the camera and there are light rays that go down and whirl around several times and come up to the camera so there are a large amount of images the three images in this case are shown here here's the shadow of the black hole maybe you can see it better on the sides here this doesn't have as high a dynamic range in the central screen that what we have here so there's the black hole shadow and here are the three images carried by those three light rays now suppose that you have a huge number of stars and the black hole is just sitting here in front of the stars they're all very far away and it's creating a shadow just like this then what does it look like well this is from a computer simulation that was done by Oliver James is the chief science that double negative visual effects company in London that made and got the Academy Award for the visual effects in the movie interstellar and Oliver used equations that I gave to him fed to him to compute what this would look like if you're looking at this black hole in front of a large number of stars the camera is going to move around the black hole slowly and that so naturally the pattern of stars is going to change and it's quite interesting to see how it changes this place where the stars appear to move erat be moving rapidly is called an Einstein ring there's another Einstein ring down here in fact there's a whole range of and number of Einstein rings snuggling up to the edge of the black hole and if you look in here you see images two images of a star stay down here it's easier to see I'll back up and start over again you see images annihilate in pairs you see them created in pairs so you just have to look closely it's easier to see down in here but you see two images come toward each other and they can aisle eight each other you see there's no image and then suddenly a bright spot appears in the image and you have to stew images that go flying apart how does that come about well that's something that we explored that I explored together with the team that did the visual effects for the movie interstellar using this computer code and now I'm going to tell and say something for the benefit of the mathematicians and physicists in the audience the rest of you have to have to just let me indulge myself for a few minutes with some jargon okay there won't be much of it but each Einstein ring is the image of the intersection of the celestial sphere that the place where the imaginary celestial sphere very far away where all those stars are sitting with a caustic of the cameras past light cone so there is physics jargon but it means something to some mathematicians and physicists in the audience when a star on the celestial sphere passes through a caustic of the past light cone two images are created or destroyed the caustics on the celestial sphere looked like diamonds distorted diamonds and when the star moves into the diamond two images appear and when it moves out of the diamond two images annihilate and so it's really interesting mathematics underlying these weird patterns that you see okay let me indulge myself I'll move on if you want to read about the physicists or mathematicians the only paper I've ever published in the journal classical quantum gravity just look up my name and that jaren line you will find it there okay but that's not what the black hole looks like in the movie interstellar this is what it looks like and why is it so different well the answer is that the black hole in the movie interstellar is surrounded by a disc of thin disc of very hot gas that's really bright it's so bright that it outshines any of the stars so you can't see the stars and a light ray from the back face of the disc going to the camera is pulled by the warped space-time and but black hole's gravity down to the camera like that so the camera thinks that the upper back face is up here so that explains this piece of the image and the bottom of the back face a light ray gets bent as it travels to the camera and so the camera thinks the bottom back face is down here and so that explains this part of the image and then here is a light ray coming from the top face of the disc the camera is just above the plane of the disc and so that just comes directly out and that produces the crossbar so a very simple explanation but really quite startling to see it come out of the computer simulation so when we saw this so this was actually predicted several decades ago I think in the 1970s by Jean Pierre illuminae in France but I'd forgotten about the prediction and when I saw this coming out I was just amazed came out and when I was working on the movie with with my friends a double negative now in fact astronomers have recently just last April observed a disc around a black hole or hot gas around a black hole and observed the black hole shadow and they did this using something called the event horizon telescope they combined the data from many radio telescopes worldwide ranging from Greenland in the far north down to the South Pole and from Hawaii to the Americas and all the way over to Europe and all the data from all telescopes were combined together to create something that was effectively a worldwide sized sized telescope by a team of 400 scientists and engineers at a hundred institutions led by chef toliman at Harvard and they succeeded after about 10 years of hard work in imaging the black hole at the center of a large galaxy narrow our own called m87 and this is where the image that they got and from the size of the shadow of the black hole and knowing how far away the black hole was how far away this galaxy is they can infer the size of the the mass of this black hole was six billion times the mass of the Sun a very very heavy black hole okay now let's look at this is the image and the movie interstellar this is the actual image that was actually made by the radio astronomers they're not quite the same I've had a number of people email me say gee you really got it right we didn't get it right at all there's no crossbar here and it's brighter on one side and we're not brighter on one side there so what's going on well here is one way to understand what's going on all over Jaynes my friend at double- made this little movie to explain one way this could happen so the camera for the movie interstellar is near the plane of the disc and so that's what it looks like an interstellar but we're going to move the camera up to the North Pole and see what happens it's pretty obvious you lose the crossbar and then you blur things out because the radio astronomers don't have very good angular resolution and so you get this but what you don't get that way is the bright edge so how come the bright edge and the answer is that in fact there should always be a right edge even the moon in the movie interstellar because the gas on one side of the black hole is moving toward you and there's a Doppler shift so shifted to become more blue but much more intense than the other way and so why isn't that there well I had discussions with Christopher Nolan he was the director of this movie he said look him you have to take account of the human eye and if a human is looking at a very very bright source of light they can't distinguish between whether how bright it is and what and it being somewhat dimmer on the other side and so we are going to make it the way it would look to a human eye including all of the failings of the human eye and also this was another important remark that goes into that image we are we are going to they did include the scattering of light in the lenses in the tail in the IMAX camera and so these a big glare around here because the light goes into the IMAX camera and gets scattered inside the IMAX camera and so what you see in the movie is the way it would appear to you if you were looking through an IMAX camera with the human limitations of the eye now there's another difference and that is that in fact the explanation for this is probably not simply that you're looking for the North Pole but in fact they flowing gas here is probably not even in a thin disc it's probably swirling around in something that is not a thin disc and it's what we call optically thin but that's the technical remark anyway that gives you some sense of what black holes look like and so I want to move now onto gravitational waves Albert Einstein in 1916 told us predicted gravitational waves but he said using his relativity equations which he had just formulated a few months earlier he said if a gravitational wave propagates into the screen here what it's going to do is stretch and squeeze space so space is stretched horizontally and squeezed vertically and then a moment later it's stretched vertically and squeezed horizontally and another way to say it more technically is that if you have a little inertial reference frame over here and a particle at rest in it the part will always mein at rest in it you have an inertial reference frame over here the particle will always rain rest in it but the inertial frames will move back and forth relative to each other and so the particles which behave inertially they have to move back and forth with respect to each other and that's the more precise meaning of a stretching and squeezing of space so let's watch space stretch and squeeze as depicted by a bunch of particles each of which is moving inertially as the gravitational wave passes they're all at rest with respect to each other before the wave arrives and they stretch and squeeze now Einstein when he predicted these gravitational waves he also said in effect it wasn't just as starkly stated as this but basically he said in this technical paper these waves are so weak that it's unlikely humans will ever be able to detect them but in fact we have but it took a hundred years and it took major changes in our understanding of the universe and in technology now there are only two types of waves according to the laws of physics as we understand the only two types of waves that can be created in the distant universe and propagate to earth bringing us information about what's far away electromagnetic waves that is oscillating electric and magnetic forces this includes light radio waves x-rays gamma rays these all just differ in the wavelength or equivalently the frequency of the ways but they all are electromagnetic oscillating electric and magnetic forces and the second and it was Galileo 400 years ago who built a small optical telescope and pointed at the Jupiter and discovered the four large moons of Jupiter and thereby he created electromagnetic astronomy as we know it astronomy done with instruments telescopes gravitational waves our goal in the project that Bernhard Shutts and I and a large number of people in this room who were in the gravity group here at cardiff it was our goal was to do with gravitational waves what Galileo did for electromagnetic waves that we wanted to create gravitational astronomy by building an instrument and pointing at the sky and seeing gravitational waves coming in from something now gravitational waves are made from the same thing as black holes they're made from Warped space and as a black hole is made from warp space also a black hole also has warp time but the gravitational wave is basically huh warp space but is there's a little more to it than that but but it is made from warp space-time just like black holes are and therefore gravitational waves are the ideal tool for exploring the warp side of the universe electromagnetic waves are produced by oscillating electric charges but gravitational waves are being made from warped space-time they are produced by things like colliding black holes that have no electric charge but that had that that they're made from warp space-time just like gravitational waves it was Ray Weiss at MIT a good friend of mine because we were at Princeton together he was a postdoc and I was a graduate student before this in 1972 who proposed the kind of gravitational wave detector that we have built and had success within like oh this was his original version I'll tell you about an improvement on it in a moment you're looking down on it so these are four mirrors that hang from overhead supports but overhead is pointy to you and so when your gravitational wave comes along these are pushed apart those are pushed together in the next half cycle these are pushed apart and these are pushed together what Ray said is to send laser beam in split it in half send the light through a small hole here and bounce it back and forth inside this cavity similarly bounce that back and forth and then recombine the light when the gravity wave shortens the separation between these mirrors that means that the light that went in this direction travels a shorter distance now than the light that went in that direction where the mirrors are pushed farther apart so when the light comes back and interferes it turns out through some physics that many of you will know about that the interference of that light causes a change in the intensity of the light going in this direction that's is this is where we read out the signal so that's what he said is how we should do go about building a gravity wave detector he called it a gravitational wave interferometer now I looked at some numbers because I had been thinking about gravitational waves quite seriously as a theorist and about their sources already for for a few years in 1972 and I together with my PhD mentor John Wheeler and an another former student of weeders named Charles Messner we were just finishing we were just sending to the publisher a textbook called gravitation at the time that I heard about Ray Rice's idea so I thought we need to include something about this idea in this book then there's the last minute as we were sending this to the publisher I looked at Ray wisest idea and I thought he'd gone crazy it didn't make sense and so I'm a gentle person I don't like to lay it on the line when a friend of mine seems to have gone crazy and so I just simply wrote in there this is ideas not promising and why did I think it wasn't promising well the key issue is that the strength of the waves that we were expecting was the change in separation of the mirrors divided by the actual separation about 10 to the minus 21 that's a tiny number if you multiply four kilometer separation here which was the separation that we have in LIGO by 10 to the minus 21 you get 10 to the minus 17 meters and so how big is that will you be in with one centimeter would you divide by a hundred you get the thickness of a human hair you divide by a hundred again you get the wavelength of the light that Ray said he wanted to use to measure the motions of the mirrors divided by 10,000 you get the size of the atoms in the mirrors that are reflecting the so that's the size of the minimum roughness in the mirrors they they're rough certainly at that scale if not at a bigger scale divided by a hundred thousand you get the diameter the nucleus of an atom a hundred thousand times smaller than the atom divided by a hundred you get the magnitude of the motions that I was expecting the the Ray would have to deal with in these instruments it was obvious there's no way this could work therefore I called it not promising and then I spent two years not full-time I think you were this is while you were a student the beginning of this or you were just finishing your PhD and you're starting here you started here in 74 No so this was basically when you were when Bernie was starting here on the faculty I spent some time during those two years thinking about this studying right raised a technical paper and being impressed by how he identified all the major noise sources you would have to deal with in these instruments and proposed ways to deal with them and made estimates of what kind of sensitivity you could achieve and he seemed to have an argument that maybe this could succeed that I had long discussions with Ray including one all-night session in Washington DC when we were there for a committee meeting we weren't very clear headed for the committee meeting the next day but we set up in his hotel room all night long talking about this and then Vladimir Berg insky a brilliant physicist friend of mine in Moscow Russia again law extensive discussions with him and I finally became convinced and so I decided that this was so important in terms of the payoff that we might have that I and my research group would do everything we could to help the experimenters pull this off and Bernie made the same kind of decision here at Cardiff as we started to move forward as did some of our other colleagues at other institutions the some of the key experimental work developing this was occurring at Glasgow and at Glasgow Ronald Reaver conceived an improvement ray ysus design it would be much harder to make it work but if it can be made to work it would be make these interferometers much simpler and more versatile he said let's have all of those light beams and be on top of each other there's no hole in the mirror but you separate the mirror by a distance such that when light goes down and comes back it travels an integral number of wavelengths and so it's super poses coherently on itself and it goes down and back so the light can be trapped between the mirrors but can leak out and so the light goes in it gets trapped and then gradually leaks out this is what's called a fabry-perot cavity I don't want to go into the technical details but it was a very clever but difficult to make work improvement and I decided that we and convinced my colleagues at Caltech that we should build a research group doing experimental work in this area and so we imported Ron dreamer to Caltech initially half time so he's going back and forth between Glasgow and Caltech as we began to work on this experiment at Caltech now I'm going to jump over a very long period of time this talk is about more than gravity waves okay and I could I could give happily give you a lecture for fifteen hours about the history of gravity waves but I'm going to jump over 40 years of intense work from 1975 to 2015 experimental work initially at MIT Glasgow Caltech and I didn't talk about it but the Max Planck Institute for quantum optics and then as time passed other Max Planck Institute's including including the Albert Einstein Institute that Bernie was the founding director of the university of hannover and then groups in Italy and France Japan Australia and then extending on elsewhere so a huge amount of experimental effort over that time data analysis pioneered here at Cardiff burning claimed that that I convinced him it should be done it was doable no he convinced it was doable I may have told him it need to be done but he convinced me it was doable and he really he and his group really laid the foundations and showed us how how to go about doing the data analysis here here at Cardiff computer simulations of sources Bernie's group here at Cardiff did some of the earliest work on simulations of sources and there now is back here another a group within the gravity center that is continuing to do computer simulations of sources led by mark hanim and then like oh we finally when things were sufficiently mature we put together a LIGO collaboration laser interferometer gravitational-wave Observatory led by Barry barish who was a superb ly skilled leader of large projects who knew how to organize things and make everything come together successfully and he put together then alaya collaboration of a thousand scientists and engineers at 80 institutions 14 nations it's larger than that now but this was what it was by i think by 2015 so 2015 what happened I'm going to tell you what happened by talking about the source of gravitational waves that we saw 1.3 billion years ago in a galaxy far far away to a black hole circle around and around each other and you can see them better on the side screens for the resolution is better I'm going to turn the lights down also because I if I can do this right okay so the the two black holes circled around around each other they made these patterns just like the patterns I showed you before but now with them going around is more interesting patterns to Einstein rings that are more complex and as the black holes circled around and around each other they gradually lost energy to the gravitational waves and so they aspired closer and closer together with gravitational waves getting stronger and stronger as they spiraled together those black holes as they near each NER each other they collided and merged in a gigantic Cataclysm the gravitational waves they emitted traveled out of the galaxy in which the black holes lived they traveled into the great reaches of intergalactic space across intergalactic space they arrived at the outer edge of our Milky Way galaxy 50,000 years ago when our ancestor who are sharing the earth with the Neanderthals they travel 50,000 years through our galaxy and arrived at earth on the 14th of September 2015 three days before our first gravitational wave search with what we called our advanced interferometers it was scheduled to start these interferometers that by then had been built they were very complex and they had to be tuned in many many ways and so the tuning was nearly finished and this signal came in and David writes he who was very bearish his successor his director at that time he declared the first search has begun because we saw something and so the first search was often running the signal when it came in it went up through let's go back it arrived at the down at the Antarctic Peninsula traveled up through the earth unscathed oh where am I going ok up through the earth unscathed and came out of the earth at the LIGO gravity wave detector or interferometer in Livingston Louisiana and seven milliseconds later it came up out of the earth at the LIGO detector in Hanford Washington this signal stretched and squeezed the mirrors pushed them closer together and farther apart at the ends of these long arms so the laser beams are inside pipes and bouncing back and forth in the mirrors that are the ends and the corner of these arms so the mirrors are pushed back and forth by the gravitational waves and then the light recombined as ray wise had originally described and that recombined light then when had a city had an intensity that went up and down and that it was fed into a computer that analyzed the data and the computer compared the oscillations with computer predictions from computer simulations or colliding black holes the LIGO collaboration together with one something called the Virgo collaboration which was a primarily at the time a French Italian collaboration which had be also built interferometers of this sort but their interferometer was not yet working they participated in our data analysis and so the two teams together participated in the data analysis together took five months to analyze the data and become totally convinced that this was really real there were so many things that could go wrong that was necessary to go in and study the signal and study the output for many auxiliary output channels a hundred thousand there are a hundred thousand zero output channels to tell you what's going on inside these complicated instruments in the environment they studied the young members of the collaboration who really understood how these things work and understood the data channels they were in and they studied key ones among these many data challenge channels be absolutely sure there was nothing wrong and this really was I've just caused by a gravitational wave and then we announced the discovery when we announced the discovery we by comparing the signal cleaned up in some sense this is the cleaned up signal is the gray read grace oscillation I'm applauding the stretching of the separation between mirrors up and the squeezing down in units of ten to the minus twenty-one for this fractional stretching and squeezing and the red is from numerical relativity simulations of colliding black holes and by comparing with simulations for black holes of different sizes different masses it was possible then to determine that the source really was from colliding black holes the initial black holes weighed 29 and thirty-six times as much as the Sun so that's a total of 65 solar masses that just means that the gravitational pull was the same as that from a star that weighed 65 times as much as the Sun and the final black hole was 62 solar masses and so three solar masses had been turned in to gravitational wave energies as though you had annihilated three suns and turned all of their mass into gravitational waves and that happened in about a tenth of a second so the power output the amount of energy three solar masses worth in a unit time in a time of a tenth of a second turned out to be 50 times larger than the power output from all of the stars in the universe put together 50 universe powers from two little black holes colliding for a short time just a tenth of a second but it was the most powerful explosion that we ever had any evidence of except for the Big Bang birth of the universe and we also by comparing with the computer simulations deduce that the distance of the source was 1.3 billion light years and they when the result was announced it made front-page headlines in all the major newspapers around the world well it's now several years later and we had were in the midst of our third gravitational wave search between each search that's carried out each search last for some months the instruments were improved there's shut down and they're improved for some months and then it searches again by now more than 30 gravitational wave signals have come in and I'm just going and there's a app you can get for a smartphone that's called G W events it's on my smartphone and wherever I am in the world and whether it's the middle of the night of the daytime when a gravitational wave event comes in within less than an hour of when it arrives a signal goes off and my smartphone app it goes whoop it's a chirp that's what what a single gravity wave signals would look like if you put them on a sound like if you put them on a loudspeaker and so there's a chirp and then I can go in and I can see oh there's a new gravitational wave signal in this list of recent gravitational wave signals I want to go in and see what the details are so I click on this to see what the details of this particular one were what were this this is one that came in September 30th of this year so what's that's a couple of weeks ago these detectors the interferometer is shut down for the month of October for some small minor improvements what I'm showing you here the events that came in in the two months from late July to late September there were 10 events you're look at these and and this is what you yourself can see this is not me going and talking to my Lyle colleagues who are pulling this off I'm not involved hardly at all anymore it's this team of younger people who are superb that they're pulling this off and it been responsible for the discoveries but I can just go on my iPhone I can see like you can there were five collisions of black holes in that two month period one collision of neutron stars the first collision of neutron stars that was seen what is that two years ago was spectacular with electromagnetic emission this one was not seen electromagnetically partly perhaps because only two of the gravity wave the three gravity wave detectors that we had at the time we by then we had a Virgo gravity wave detector operating and so we had three of them at the time but and when it was three of them operating you can determine very fairly accurately where the source is on the sky with one of them down you don't get a good location on the sky so it was harder to see it on the sky and this thing was quite a bit farther away than the one that was spectacular there were two cases in those two months of a black hole swallowing a neutron star hole each neutron stars about 30 kilometers across what of almost pure nuclear matter massive about one-and-a-half times the mass of the Sun and no electromagnetic emission and reason to believe that the neutron stars were swallowed whole by the black holes and there are two black holes as follows something that we're not 100% sure what what it was they were swallowed and they're actually up here they they were both in late September it's labeled mass gap the point is that we think that neutron stars don't get heavier than three solar masses and we've never ever seen a black hole despite huge amounts of all astronomical observations never seen a black hole smaller than five solar masses so that's a mass cap where and there were two signals one with a hundred percent confidence that it was a object in the mass gap there's one hundred percent confidence there's an object in the mass gap and the other 95 percent confidence and so this is sort of a breakthrough there really are compact objects like black holes they probably are black holes but nobody ever seen a black hole this small and so so no paint no technical papers written yet on any of these things and there's a lot of really exciting science in here but you can go onto your ion to your app and just see the basics of what what is likely to come out in these exciting technical papers that are being worked on at the present time by the late 2030s twenty years from now the successors to LIGO and Virgo which are called Einstein telescope pair in Europe a large new much larger interferometer from than what has been operating at the present time and a similar a much larger interferometer called cosmic Explorer in North America will likely see gravitational waves that are maybe twenty times weaker than what is seen today and that's really impressive that means if the universe were infinite and flat you'd be seeing out twenty times farther that we'd be seeing a volume twenty cubed times bigger twenty times twenty is four hundred that's eight thousand is that right so eight thousand times more frequent events instead of one event a week that's 8,000 events a week the universe is not flat and it doesn't extend forever so it's going to be a little lower than that but nevertheless an enormous number of events every blackhole collision in our universe with mass is less than about a hundred solar masses is likely going to be seen at that time a variety of other phenomena on the Warped side of the universe and also by the 2030s will be seeing gravitational waves in four different frequency bands like oh and Virgo and their successors operate with fun for gravity wave signals that have frequency have wavelengths of oscillation of milliseconds Lisa a European Space Agency mission that you don't see so well here let's go up here consists of three spacecraft that track each other with laser beams and we'll look at gravitational waves with periods of minutes to hours there's a technique called pulsar timing arrays that I won't talk about in at all but that will see gravitational waves with periods of years to decades and then a technique called CMB polarization I'll talk about very briefly seeing gravitational waves with periods of a hundreds of millions of years of course that's a little longer than a graduate student lifetime and so you don't sit there as a graduate student waiting for the singular oscillate so you need your thesis on it instead you look at a pattern on the sky of what is called polarization of causing microwaves a pattern that has been produced by gravitational ways from the very early universe as I'll describe very briefly in a minute let me talk about this Lisa mission it's a really exciting mission it's a I think the science that it's going to do is more exciting than anything that has been done as yet with the ground-based interferometers I have been hoping it would be launched by 2030 but burners says it's so such a challenging thing that 2030 for what it is more likely for when it will be launched and it's a as I say a European Space Agency mission it will look for gravitational waves from giant colliding black holes masses of millions of Suns also particularly interesting in me is that a small black hole going around a large black hole will obviously create ripples in the shape of space and those just become gravitational waves to go propagating out and as was shown by a student of mine Fenton Ryan back in the 1990s the gravitational waves from essentially from the small black hole as it's exploring space around the big black hole should carry a full map of the warped space-time the big black hole encoded in these emitted gravitational waves and you might ask well how can it possibly carry a full map the warping of time the warping of space the dragging of space and in motion if it's just going around and around like that how is it going to get enough information to make a full map well let me get rid of the warping of space here and just pretend the space is flat around the big black hole and then let's again look over here where we have more dynamic range on the screen so the black hole is here maybe I'll turn the lights down also it's a little hard to see so the orbit of the small black hole around the big black hole is very complicated it's nothing like these nice elliptical orbits of the planets around the Sun why is it complicated because gravity is so weird in there gravity includes a warping of space a warping of time a whirling motion of space around the big black hole and the gravitational pull and even the gravitational pull is different than it is here on earth it's not an inverse-square law if you know that the meaning of that jargon it's more complicated and so that gives rise to an orbit basically samples the entire space around the big black hole and is capable of providing the data for a map now it's a huge challenge with this Lisa mission to extract the map from the data and it's going to be a but efforts are underway to develop algorithms permit that to be done so what does the central body is not a black hole for example what if it said that inside a black hole there is something called a singularity it's a place where gravity becomes infinitely strong and really weird in its properties and the laws of general relativity get replaced presumably by something called the laws of quantum gravity its conventional wisdom that singularities today exists only inside black holes but what if you had a naked singularity well here's a particularly good singularity in here and in orbit of a small objects a small black hole going around that naked singularity and the orbit is not at all like what we saw before it's chaotic sort of has little jumps and jiggles and it is chaotic in the mathematical sense of chaos and quite remarkable and obviously the map that you would try that you would manage to extract from this if you can extract the map will be wildly different so we have the possibility to search for naked singularities this is one example of weird things that might be done I'm particularly interested in the dynamics of the space-time geometry around colliding black holes and we explore this by computer simulations and then we we compare the shapes of the waves that are come off in our simulations with what is seen by LIGO and Vercoe and in order to see whether or not the shape the this dynamics of warped space-time that we are predicting is correct and we get very good agreements between the predicted wave shapes and what is observed and so we believe that the true warping of space is what is predicted by the computer simulations so this is a simulation showing the warping of space around than two black holes that are spiraling together the each black hole is like a funnel in terms of the warping of space the color coding is the slowing of time and I have to tell you tell for the mathematicians and physicists there's a slight cheat here what we have is a two-dimensional surface in the orbital plane the two black holes any two-dimensional surface can be embedded in a three-dimensional flat space so that's what's being done here the bulk that you're looking in from is a three-dimensional flat space but that embedding can only be done locally and so if you try to do it and you go around the black hole and you come back the shape does not match up smoothly and so there has been a kludge down here I won't tell you what the Cluj is but there's been a clearance done here but you should can still take this seriously is representing and some fairly accurate since the warping of space around the black holes as they collide now we're going to slow the movie down as the collision begins you see there's a huge splash in the shape of space forming like the splashing of the surface of the ocean and a giant storm at sea and the color coding is the slowing of time it oscillates wildly settles down and the gravitational waves go away so this is what we call Geo Metro dynamics the dynamics of the highly warped space-time around two colliding black holes and we've been learning about this from computer simulations and particularly interesting but I won't take the time to describe it is what we have learned about how these vortices and stick out of black holes behave when the black holes collide I want to wind up gravitational waves by briefly saying that one of the things that the thing that I think is going to be most interesting with gravitational waves in the coming few decades is to observe the birth of the universe and the birth of the fundamental forces that govern the universe as an example when the universe was a trillionth of a second old the electromagnetic force and the weak force came apart gaining their own identities and in what is called the electroweak phase transition and so inside this bubble if this was as it could have been if what's called a first order phase transition inside of this bubble the electromagnetic force exists outside it does not exist in here it exists outside it doesn't exist the electromagnetic force was born and the words no such a thing as electromagnetic force before then and these are bubbles then predicted to expand very fast and collide producing a burst of gravitational waves as the universe subsequently expands those gravitational waves are shifted to longer wavelengths and today they're in Lisa's frequency domain so at Lisa we hope to see the gravitational waves from the birth of the electromagnetic force when the universe was very young we expect to see gravitational waves from the Big Bang I'm going to go through this very quickly because I want to wind up with a few words about time travel and wormholes but the basic idea is that something came off the Big Bang and whatever it was was in terms of gravitational waves was amplified by a process called inflation at the beginning of the universe that some of you are aware of and these gravitational waves then a very rich spectrum of gravitational waves that have then been amplified by inflation they interact with a hot gas when the universe was about 380,000 years old and they put this polarization pattern on the hot gas which then astronomers have searched for they have found this a polarization pattern but there is noise in the data and they're not sure that they've whether what they've actually seen is due to the noise or whether it's really due to these primordial gravitational waste that will get sorted out I'm sure within the next 10 years and we then will have the today we will have then indirectly through this pattern of polarization on the sky we will have then detailed information about the Big Bang singularity in which the universe was born but mixed together with information about inflation the very rapid early expansion of the universe can evolve together I look forward to seeing this there are predictions for what the result should be and I expect the predictions will turn out to be wrong and it will force the theoretical physicists to go back to the drawing boards do and then in the middle of this century there is likely to be a successor the Lisa mission called the Big Bang observer which will see these primordial gravitational waves with periods instead of hundreds of millions of years periods of a few seconds radically different periods and again I'm just from past experience I'd be surprised to the theorist habit right when they predict what is seen okay I want to conclude with a few words about wormholes and time travel I think it electron what we have learned during my career would not be complete without saying something about this and I think many in the audience are probably eager to hear what we have learned so wormhole suppose that our universe in the bulk is Bend around like this this is a two-dimensional slice through the universe like I was doing for the equatorial slice through a black hole it's bend around so that our solar system over here and in particular Saturn there's only a distance of a few kilometers away from some galaxies in the very distant universe so if we travel out through the universe it may be ten billion light years the solar system from there but across the bulk it may only be a few kilometers if we could travel across the bulk but we are three dimensional beings we have three space dimensions - if I have removed one like this and we can't live in the bulk the electromagnetic force is crucial to our existence in our life can't even exist in the Vulcan it can only exist in three space dimensions - if I've suppressed one like this and so in order to go across the bulk we need to have a structure a wormhole it's called like that where that you could travel then along the surface of that the surface selects two-dimensional it's really three dimensional to get from our galaxy to this distant from our solar system to this distant galaxy in the movie interstellar this is what happens both beings that live in the bulk have provided to the human beings in this movie that I worked on have provided two human beings a wormhole of this sort you Jenny van Tunsil Minh double- in London and a set of painters associated with her made paintings of the center of this galaxy that is on the other side of the wormhole I worked out the equations for the propagation of light beams from that galaxy through the wormhole up to the camera I fed them to Jane Oliver James whom I have mentioned before who was the chief scientist at double negative and he then programmed those to make a movie that I'm going to show you of the what it looks like to go through a wormhole so this is what the wormhole looks like in the movie interstellar for those of you who have seen the movie interstellar and I I for the movie I'm going to move the the wormhole almost in front of Saturn so Saturn is very far away the wormhole is only a few kilometers across and Saturn is very very far away and so it looks about the same size as the wormhole light rays from the Saturn bend around the wormhole to produce this image and Bend around the wormhole on the other side to produce that image and if I now start to travel into the wormhole the images of Saturn or pushed apart as I go into the wormhole I'm entering the wormhole now I'm traveling through the wormhole and I've come out the other side that's what it really looks like for the wormhole in the movie interstellar I had a telephone call from Christopher Nolan the director of interstellar when he first saw this trip through the wormhole they were in the process of starting to integrate the computer graphics into the film he had just finished shooting all the human action he said we've got a problem would you come over to my house I want to talk about it and so I went over and he said look this is not exciting enough and we had agreed I'd happily agree with him that and he'd agreed with me that we would do everything we could to make all of the movie be scientifically accurate to the extend it did not get in a way of making a great movie and this is the one place where we compromised or where we had it had a significant compromise so what what what did I say - I said you use artistic license and so that's not the trip you see though it resembles this but there's a lot of artistic things stuck on top of it but this was the real trip through the wormhole now the problem with wormholes is that as John Wheeler my PhD adviser showed back even before I was his student went together with a young colleague Martin Kruskal and wormhole will pinch off if you don't do something to hold it open so if I have a particle of light a photon trying to travel through the wormhole to bring me an image and the wormhole is just empty sitting there with nothing except say a bunch of light traveling through it then as the light travels through just at the moment that the light that the photon reaches the center of the wormhole it pinches off and you're left with two naked singularities and the light has been destroyed so you can't get the light through and you can't get humans through so there's the issue of how can you hold a wormhole open well various people have worked on it and we now know that what you have to do is stick inside it's something that repels gravitationally that's pretty obvious the walls need to repel each other gravitationally and that means you have to have something with negative mass or negative energy and in fact and so you just say gaint you would say games over how can you have negative energy and the answer is you can have it and just for physicists the Casimir vacuum and the squeezed vacuum they you have some squeezed vacuum do you have squeezed vacuum here in your new lab now or you're just going to have it is so it's so that there's a plan to have squeezed vacuum in the lab if they don't have it already and so they're going to be making negative energy matter here exotic matter but the problem is as well I can tell you what the problem is in a moment so Kenwright wormholes occur naturally in the real universe the answer is almost certainly no these are answers that a number of people have struggled to understand and this this is the bottom line after several decades of trying to understand it and wormholes be made by an advanced civilization possibly it's possible quite possible as John Wheeler told us that down on very very tiny scales of 10 to the minus 33 centimeters called the Planck length there is a form of tiny tiny wormholes there's just bubbling and bubbling and bubbling quantum mechanically and so you can imagine a very advanced civilization reaching down and grabbing one of these wormholes and enlarging and making it big so you can travel through it this is pure imagination it's something you would do and if you're a physicist when you're very very drunk to speculate about this but that doesn't I don't think it's totally out of the question if you do have such a wormhole can it be held open the answer is probably not and this is where the a lot of work has been done because it appears to require two large amounts of exotic matter of gravitationally repelling matter negative energy but when speculating beyond the frontiers of firm knowledge I've been proved wrong many times sometimes spectacularly so you don't take my pronouncements that you can't have wormholes too seriously and I was willing to use that in the movie interstellar finally a few words about time travel this is from a technical paper that I wrote with two students of mine Mike Morrison all VRC were in 1988 suppose that I my wife Carolee Winston has one mouth of a wormhole and she's in this rocket ship and I'm back home with the other mouth of the wormhole and she goes out she has a very advanced technology she travels out close to the speed of light turns around and comes back now there's something called the twins paradox which says that she will age much less than I do she may have a aged a few hours or a few months and I may have aged a few years when she goes out and comes back and so I'm an old man and she's still quite young as we see each other looking through the external universe but if we're holding hands and I look at her wristwatch and she looks at my wristwatch inside the wormhole they have to take it the same rate inside the wormhole this is what the prediction is and so looking through of the wormhole she sees me young as she's young and our watches have been ticking in the same rate but looking out through outer through the external space she sees me old so she returns back to earth and so these wormhole mouths are here almost side by side and so all I need to do is an old man is go and the end of that wormhole and go back and meet my younger self because I can see my younger self through that wormhole mouth so so it's easy to turn a wormhole into a time machine if you have a wormhole well not yet not technologically easy but relativity seems to allow it the problem is that relativity which seems to allow it is not the only set of laws of physics that we have to deal with we also have to deal with the quantum mechanical laws of physics and quantum mechanical laws of physics when you look at them they say they seem to say that whenever any advanced civilization tries to build a time machine the time machine will have it a gigantic explosion at the moment it's turned on and in this case of this particular time machine the key issue is that if you imagine she's travelling back toward me and there's a first moment when something could when something could go down through the wormhole out my wormhole travel back and return at the very moment that it started out and so you have two of them so these might be photons particles of light go through the wormhole and then back out the exterior region VPN with one photon you now have two they're the same photons but they're side-by-side then the trip ins made again you now for photons are the same photon they're side-by-side you have a huge amount a huge burst of energy going through the wormhole at the moment that this wormhole turns into a time machine well you can shield out photons but you cannot shield out something called vacuum fluctuations and these things which are also called virtual photons these things which play a huge role in modern physics and experimentally manipulating this vacuum and I'm not going to go into is the key to making this squeezed stuff that is going to be made in the laboratory here that has negative energies so these vacuum fluctuations can do this and you can't shield them and so there will inevitably be an explosion and so I found this with a postdoc of mine and a calculation and then some colleagues of mine and here's the technical paper did a far more rigorous calculation that showed the same kind of a thing but not showing any details of the explosion so I think this is incontrovertible that there is some sort of something really goes wrong at the moment you make a time machine try to make a time machine but what we don't know is whether the explosion then is strong enough to destroy the wormhole and Stephen Hawking was working on this at the same time as I was Stephen is one of my closest friends and we never collaborated together but we worked at the same time on this problem and we argued back and forth and older when we came to agree that we can't tell whether the explosion is strong enough to destroy the wormhole only the loss of quantum gravity which we don't understand know of whether lestrade the wormhole the loss of quantum gravity governed the birth of the universe they governed what goes on inside black holes and they seem to have govern whether or not címon time machines self-destruct Stephen then proposed the chronology protection conjecture because he was so sure that the explosion is going to be totally destructive that the time machines will always self-destruct when you turn them on keeping the universe they for historians and that that's his phrase in this technical paper whose title is the chronology protection conjecture so I was working on this at a period just before we got approval to construct LIGO and when we got the computer to construct LIGO I left this all behind because Lyle got very exciting and I've not had a chance to return to it but it's quite interesting that you see these weird kinds of things coming out of warp space-time just like gravitational waves in black holes so conclusions when I was a student there were speculations about the warp side of the universe today 57 years later we know a lot more we have observed black holes we have observed gravitational waves we have a lot of observational evidence about the Big Bang we doubt that wormholes exist and doubt that backward time travel is possible but we're not absolutely sure and in the future I believe gravitational waves will reveal a great deal about the Warped side of the universe there will be enormous surprises of which we can't even dream today thank you [Applause]

Channel: Cardiff University

Views: 283,317

Rating: 4.8117852 out of 5

Keywords: Gravitational Waves, Einstein, Astronomy, LIGO, Interstellar, Cardiff

Id: GlmMxmWHEfg

Length: 76min 39sec (4599 seconds)

Published: Tue Oct 22 2019

Reddit Comments

[u/easilypersuadedsquid]

Professor Kip Thorne is a theoretical physicist and Nobel laureate. In this talk he discusses "My Romance with the Warped Side of the Universe: from Black Holes and Wormholes to Time Travel and Gravitational Waves".

Kip is a world-leading expert on the implications of Einstein's theory of General Relativity, from time travel to wormholes, and from black holes to gravitational waves. Until 2009 he was the Feynman Professor of Theoretical Physics at Caltech, but has since retired to take up a new career in writing, and collaborations between science and art. He was executive producer and scientific adviser on Interstellar, the 2014 blockbuster film. One of Kip's key contributions was the visualisation of black holes and their surroundings, which contributed to the film winning an Oscar for "Best Visual Effects". Kip explained the science in the film in his 2014 book The Science of Interstellar. His many other multimedia projects have cemented his reputation to be able to explain complex concepts in ways that everyone can understand.

As one of the founders of LIGO (Laser Interferometer Gravitational Wave Observatory), Kip was awarded the 2017 Nobel Prize in Physics for "decisive contributions to the LIGO detector and the observation of gravitational waves, along with Rainer Weiss and Barry C. Barish. The first detection of gravitational waves by LIGO (of which Cardiff University is a member) in 2015 confirmed a key part of Einstein's theory of General Relativity, and observations have continued to test one of science's most famous theories.

[u/TilleroftheFields]

I saw him give a similar lecture at Cornell. Very well spoken.