Nobel Lecture: Kip Thorne, Nobel Prize in Physics 2017

thank you can you hear me I'm so pleased to see so many of my like over goal colleagues here I just want to thank you for making me look so good I really think of myself as more of an icon for this collaboration and this nobel prize is really something that i accept as a representative of you who have made this great success in the end i would like to highlight the fact that the where we are and where we are going in gravitational wave astronomy and physics has relied on three different efforts each of which was roughly a half a century long in order to get where we are and where we're going the first was discussed in considerable detail by Ray Weiss and Barry bearish the experimental effort and a little bit along with that the data analysis effort I want to talk about the theoretical effort on understanding sources of gravitational waves the waveforms that are produced the shapes of the waves produced by the these sources and the information that is carried by those waveforms then I want to talk briefly very briefly about a third effort this has lasted for about a half a century I combined theoretical and experimental effort on what is called quantum non demolition that's a buzzword but I'll explain what that buzzword means then I will move into the future focusing on what we where we might be in the 2030s the four different frequency bands that Barry barish introduced you to and then beyond the twenty thirty so this is where I'm going in this talk let me just look at yeah okay just looking at the time here okay so so I want to begin however with some personal remarks I was a graduate student at Princeton in the period 1962 to 1965 my thesis advisor was John Archibald wheeler a fabulous man who had what seemed at the time wild ideas most of which have come to be out too to be true he was focusing and he taught me about neutron stars and black holes but I also as a hanger-on on the fringes of Bob Nikki's experimental gravity research group of which Ray Weiss at the time was a member a doesn't remember me in graduate school but I remember him because he was a real intellectual giant in Bob Nikki's group and I was sort of sitting back there as a mousy theorist trying to understand the experimental side of this subject but I'm so glad I did because I learned enough to in the end be able to collaborate with ray Weiss Ron dreamer very bearish right I was also much influenced by Joseph Weber whom Ray talked about Joe I met and spent a lot of time with in the French Alps at a summer school lasers in laser their shaman II we went hiking in the Alps and he told me all about his plans and the experimental work that he was already getting going on gravitational wave detection and so it was quite natural that when I went to Caltech in 1966 as a professor a young professor that I would build a theory group that worked in black holes neutron stars and the theory of gravitational waves by 1972 together with colleagues and students I'd begun to develop some amount of vision for the science that might be done with gravitational waves the information that might be extracted from gravitational waves and the key idea is this in a general form that there are only two kinds of waves that can propagate across the universe bringing us information about what's very far away electromagnetic waves and gravitational waves and that's it according to the laws of physics and there's an enormous difference between the two types of waves electromagnetic waves or oscillations of the electromagnetic field that propagate through space as time passes by contrast gravitational waves are actually oscillations of the fabric or shape of space and time extremely different kinds of phenomena electromagnetic waves are generally in a stir physics incoherent superpositions of emission from individual particles and atoms and molecules whereas the gravitational waves are produced by their coherent bulk motion of large amounts of mass or energy electromagnetic waves are all too easily absorbed and scattered as they travel through the universe so we only see a small portion of the universe because there's so much obscuration by gas and dust whereas gravitational waves are never significantly absorbed or scattered even if they're emitted near the Big Bang with those differences it became very quite clear and I think it was clear to my theorist colleagues and students by 1972 many sources of gravitational waves will never be seen electromagnetically and the colliding black holes that we have seen thus far there's been no electromagnetic signal that surprises then are likely and that there is a potential to revolutionize our understanding of the universe using this radically different kind of waves so that was what we had in mind already by the early 1970s and that was the same time 1972 Israeli Weiss having gone from Princeton back to MIT as a young professor he wrote a classic paper in which he described the design for a in her interferometric gravitational wave detector and he identified all the major noise sources these kinds of detectors might have to deal with and how you would deal with each of them and what kinds of sensitivity you could get as a result and he concluded that there was a real chance to be able to build detectors that could reach the sensitivities that were required by the sources that my colleagues and I were thinking about now I looked at Ray's ideas and I stated in a textbook a classic textbook that I wrote was John Wheeler my thesis advisor in Charles sir that these are not very promising he was telling us that you should build a detector that measures the motions of masses with ten to the minus twelve one trillionth of the amplitude of motion compared to the wavelength of the light you're using you move measure a detector that moves by an amount that is one one thousandth the diameter the nucleus of an atom and an atom nucleus is a hundred thousand times smaller than an atom I mean it just was crazy and then I studied his paper which he didn't publish in the regular literature he put in an internal report at MIT because his attitude was you don't publish something like this until you've detected gravitational waves but I he disseminated it's quite widely among his colleagues I read it and I began to think well maybe this will work I had this long night long all night discussion with him in Washington DC that he referred to I had discussions with Vladimir Brzezinski in Moscow and later with Ronald Reaver whom we brought to Caltech to start the Caltech effort I became convinced and it seemed to me that because the potential of this for human future understanding the universe is so great that I should do everything that I could as a theorist to help my experimental colleagues succeed and so here I am I and my students in the end draw to probably 70% of our effort research effort from then on July go let me now talk about sources of gravitational waves 1978 we had a workshop on sources of gravitational waves gathered together essentially all of the theorists and experimentalists not here because he hasn't joined into this field yet although he did play a crucial role and get helping us get Caltech into the field behind the scenes on a committee that commanded that we move forward in the field and at that workshop at the end there was a discussion of strengths of sources and this comes from the paper describing the workshop super novae where an upper limit was here that's ten to the minus twenty-one this is frequency this is the strain that we've been talking about compact binary mergers that's black hole binary to black holes two neutron stars a black hole neutron star estimated to be in this region and so it seemed clear to us that the taught goal had to be to reach a sensitivity of strain sensitivity of ten to the minus twenty one and so we even had t-shirts made up that said ten to the minus twenty one or bust there is the signal it came in the first thing that was seen one times ten to the minus twenty one that's obviously largely luck that we were right on the money but that was our gold beginning in nineteen seventy eight and that's where the first thing that came in 1983 when we were planning legal it seemed pretty clear to me the likely first detection was binary black holes and this is basically what I argued from then on though I think most of the community was expecting it to be two neutron stars but it seemed to me already then that the following would outweigh the neutron stars were versa for the black holes in favor of new truck black holes instead of neutron stars the distance to which you could see a signal for two objects going around each other they're approximately proportional to the masses of the objects we were thinking of the time the black holes we would be dealing with for maybe ten times heavier than neutron stars so you would see a volume of the universe there would be a thousand times greater than four neutron stars and that seemed to me that would outweigh the lower absolute numbers of black holes there are in the universe compared to neutron stars and that's how it did turn out to be but we were very uncertain as to how strong these waves were but we knew it was somewhere in the vicinity of that ten to the minus twenty one numerical simulations we're going to be needed it seemed very clear to me in that era in order to be able to extract the information from the colliding black holes that they carry because we could not with pencil and paper and analytical techniques we could not solve Einstein's equations to compute the shapes of the gravitational waves coming from colliding black holes so we had to do it by numerical relativity so let me go back a brief history of numerical simulations this begins in the 1950s motivated by Johnny wheeler my thesis advisor who told us already in the 1950s that we should try to study the veritable storms in the fabric of space and time that occur when space and time the geometry of space and time are highly excited in a nonlinear fashion and rapidly changing and we had and he said you go out and study this thing that I called geometric dynamics we tried we fell flat on our faces we didn't have the tools to do it but he recognized and they his students around him recognized that in order to really sort do this you had to do it numerically so you'd be had to begin to build the tools of solving Einstein's equations and numerically on a computer or computer simulations so the foundations were laid in the ferret period from 58 to 64 by Charles Messner Richard link whist who are associated with Johnny wheeler Susan Hahn who was a computer scientist at IBM who teamed up with Richard Lindquist to start this out this is the best photograph I can find a linguist in that era it was not however until 1978 the first successful collision a simulation was done of head-on collisions of two black holes by Larry Smarr and Kenneth F Lee building on foundations laid by Bryce to it and earlier foundations of Misner HANA Lindquist and there are a number of other contributors in this period I'm highlighting the people who were really the Giants in this early era so here 58 to 78 this is 20 years already struggling to get this started next was the problem of doing two black holes that circle around each other and spiral together collide and merge and the community began to work on that and it became a very concerted effort by 1983 when we were and I started when we were co-founding LIGO and we were telling our colleagues doing these simulations we really need these simulations in order to extract information from the way so you'll see by the 1990s there was a something called the binary black hole grand challenge alliance led by Richard Matzner at the University of Texas all of the world's experts in this getting together and working in a concerted sort of a way and I became a little concerned that was going more slowly than it should be so I made a bet I like to make bets and I made a bet that I hereby wager that LIGO will discover convincing gravitational waves from black hole coalescence or merger before the numerical relativity community has a code capable of computing waveforms I wanted to lose this bet and the worst possible way I wanted to lose this bet by the early two thousands I paint came alarmed the progress really was slower than the experimental progress why was it slow it's been really hard you're trying to simulate not two things that collide in space and time you're simulating things they're made out of warp space in time that are colliding so you don't have an arena in which this is going on you're simulating the arena itself a warped arena and it says this is going on and so by the early two-thousands I became alarmed and so I started in collaboration with Salter Kolski at Cornell what we call the sxs collaboration to work in this field Saul had been working on this already for a few years and 2004 the first successful simulations were done my friends Pretorius a postdoc in our group joan central emanuelle at compa nelly and their research groups by 2014 the simulations were mature enough for the first leg of observations and I conceded the bet with great happiness and when the Smurfs signal came in in September 14 2015 the numerical relativity gravitational wave form is the red here the observed wave form is the gray and that matched beautifully and by comparing those waves the theoretical and the observational with each other we inferred the properties of the black holes and the distance to the sources this is a you can then go back knowing from the observations of the comparison of the theoretical waveforms of the observational waveforms you can go back and look at the simulations and see what was happening during those simulations and this is a simulation of the colliding black holes has seen from outside our universe looking in on the warped shape of space and time around the black hole the red is the slowing of time the arrows are the dragging of space and emotion is a gigantic splash in the shape of space and the slowing of time and then an oscillation the gravitational waves go propagating out you can also compute what it would have looked like to your eyes if you had seen the two black holes go around each other collide and merge creating what's called gravitational lensing distorting the star field that's behind the two black holes and this is a movie that was played extensively at the time of the first discovery that came again from this xs/s collaboration it was essential that we not only had numerical relativity simulations but for the earlier parts of the waveforms they were computed by a different technique called post-newtonian expansion which I won't go into detail but that was another 40-year effort led primarily by Luc Blanchette tiro no more and then the matching the two together by a different technique led by tiro de Moura and Alessandra Bruin so that was the way we had the wave farms that we needed quantum not in demolition I just want to mention very briefly because I'm also running out of time the challenge is to monitor the motions of 40 kilogram mirrors to a precision that is 10 to the minus 17 centimeters which turns out to be approximately the half width of the quantum mechanical wave function of the center of mass degrees of freedom of these mirrors so the challenge in advanced LIGO is to deal with quantum flexural and fluctuations of the motions of the mirrors themselves to circumvent the Heisenberg uncertainty principle and this means that for the first time in advanced LIGO humans see human sized objects behave quantum mechanically and that has required developing a field of technology called quantum don demolition technology to deal with this this is a branch of modern quantum information science it was Vladimir Brzezinski in 1968 that told us we need to do to do this no matter what kind of gravity wave detectors rebuilt I didn't understand what he was saying for 10 years and then I finally understood and then I had my research group work as closely as possible with his research group to work out the techniques for this i've running out of time I'm going to skip over my discussion of the techniques for this except to say that the key idea which comes primarily from carlton caves and from bill unruhe is that use take the vacuum of quantum electrodynamics the vacuum fluctuations of light and you modify that vacuum by what is called squeezing and you inject the squeezed vacuum into the back end of the interferometer it's it sounds just crazy but this turns out to be absolutely crucial for the future of this field when we go beyond advanced LIGO I want to wind up by briefly talking about gravitational wave astronomy in the 2030s there are four different frequency bands that Barry barish talked about the low frequency band minutes to hours to be studied by Lisa these four three spacecraft attract each other with laser beams it's a ISA mission we hope that it launches by about twenty thirty and Lisa is capable of monitoring the gravitational waves from giant black holes millions of Suns that spiral around each other collide and merge with sigla noise ratios of ten thousand or more and thereby capable of studying geometry dynamics with unbelievably high precision pulsar timing arrays a gravitational wave sweeps across the earth and it speeds up or slows down all the clocks on the earth and so naturally if you time the radio time pulsars at different locations on the sky they will all slow down and speed up our pair to slow down to speed up in synchrony because it's the clocks on the earth that are being screwed up and that technique will look at great supergiant black holes billions of Suns in mass so we cover the whole range some solar mass scale of black holes and millions of solar masses to billions of solar masses and a small black hole going orbiting around a large black hole generates gravitational waves that carry a full map of the large black hole that is being explored by this small black hole as the small black hole goes around it in orbits and here's the small black hole going around the large black hole the orbit is wildly crazy because of the dragging of space into motion by the big black hole as well as other relativistic effects and it's samples essentially the entire space around the big black hole and gives us then the information to do exquisitely accurate mapping of the geometry of space and time around big black holes what are the central bodies not a black hole for example the naked singularity the orbits will be wildly different and the maps will be wildly different so we have the capabilities search for unexpected kinds of massive central bodies I want to wind up by saying that we have a potential to study the moments of the universe by the 2030s when the universe was at an age of 10 to the minus 12 seconds there is predicted to have been a electroweak phase transmission where the electromagnetic force and the weak force come apart and gain their own individual identities the birth of the laws of electromagnetism and this may have occurred in what's called a first order phase transition inside bubbles the bubbles of the new phase where electromagnetic force does exist in the bulk of the old face where it doesn't exist collide produce gravitational waves which today have been redshift into Lisa's frequency band and like who could see similar phase transitions that would have occurred when the universe was 10 to the minus 22 seconds so we have no idea what was going on in the universe at age twenty ten to minus twenty two seconds primordial gravitational waves coming off of the Big Bang itself are predicted to have been amplified whatever came off the Big Bang amplified by inflation in the first ten to the minus thirty three seconds of the universe theoretical prediction that is pretty from strongly believed by the theoretical physicists and what is speculated to come off the Big Bang is vacuum fluctuations the minimum amount of fluctuation of the gravitational field that are possible they would get amplified to make a rather rich spectrum of real gravitational waves that would propagate out interact with a hot plasma and the universe was 383 380,000 years old and put out polarization on the Cosmic Microwave Background produced by the hot electrons at that age which would be seen today and so they challenged the people who work with the Cosmic Microwave Background is to measure definitively that polarization thereby infer the gravitational waves that came off the Big Bang can volved with the effects of inflation so the spectrum that would be seen is a convolution a combination of the effects of inflation and what came off the Big Bang we also have the by 2050 to fly a successor to the Lisa mission which be capable of seeing these gravitational waves from the earliest moments of the universe independently at periods of a few seconds so imagine if you had the gravitational wave with periods of a few seconds you have their primordial gravitational waves with periods of hundred million years seen by polarization on this guy polarization pattern on the sky both of them are produced by whatever came off the Big Bang can volved with the effects of inflation and I envisioned that by the 2050s those will not agree there will not be an agreement between what's coming off at periods of one of a few seconds at periods of 100 million years and there will be a huge mystery what really came off the Big Bang why was it not vacuum fluctuation so that's my dream of the future and that at that point those observations may really feed into understanding the laws of quantum gravity that govern the birth of the universe so let me just conclude by saying it was 400 years ago that Galileo created modern electromagnetic astronomy by turning a small optic telescope on the sky and discovering the moons of Jupiter it was two years ago that this wonderful Lyell Virgo collaboration turned on the advance detectors the advanced LIGO detectors and saw the gravitational waves from collisions of two black holes in those four hundred years since Galileo we have learned so much about the universe with optical Astronomy our understanding of the universe is so different today than it was 400 years ago thanks to optical Astronomy what might be the future 400 years from now when we have 400 years in our pockets of gravitational astronomy together with electromagnetic astronomy I think the future is really very very exciting thank you [Applause] so I I would not cost professor vice and mr. Barrett so if you go over to the bar in the front of the stage so you you can advance selected [Applause] okay

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Length: 27min 36sec (1656 seconds)

Published: Fri Dec 08 2017