Kip Stephen Thorne is a noted astrophysicist and a central figure in the legacy of gravitational physics research. He is the Richard P. Feynman Professor of Theoretical Physics, Emeritus, at the California Institute of Technology. He has made seminal contributions to theories underpinning the origin, characteristics and properties of blackholes, and theorised about the existence and behaviour of wormholes. Thorne is also famously interested in communicating ideas in advanced physics to the general public. He has written many popular books, notably Black Holes and Time Warps (1994), and helped helped Carl Sagan ideate on wormhole travel for the latter’s novel Contact (1985). The science behind the 2014 film Interstellar was defined by Thorne.
Even more recently, he has been in the limelight for the LIGO experiment’s discovery of gravitational waves. Thorne was instrumental in developing the idea of the instrument (alongside Rai Weiss and Ronald Drever), securing its funding, evolving a thrumming community of researchers around it, and getting it going. Karan Jani, a doctoral researcher at the Centre for Relativistic Astrophysics, Georgia Institute of Technology, and a member of the team that discovered the gravitational waves, spoke to Thorne on behalf of The Wire (from the lab of Laura Cadonati, Chair of the LIGO Data Analysis Council). The full interview (edited for clarity) follows.
The ball that you rolled has allowed hundreds of young scientists, like me, to be part of Einstein’s legacy – thank you so much for that.
Well, thank you, thank you. I was much influenced by a guy named by George Gamow who was a cosmologist in the early 20th century. It was his writing that I’ve been able to pass on to the next generation.
So, hundred years of Einstein’s general relativity, a hundred years of solution of blackholes and gravitational waves. A hundred years of waiting for the first discovery. And now you are [among] TIME’s 100 Most Influential People. Does this make you believe in numerology?
Oh no, not particularly. We just happen to use base-10. If we used base-9, it wouldn’t work. Maybe I have faith in our choice of the base.
What was your first reaction when you saw the gravitational-wave event on September 14, 2015 and the whole process which followed until the historic announcement?
I think it was just one of deep satisfaction, that a dream that Rai Weiss, Ron Drever and Joseph Weber and Vladimir Braginsky and Stan Whitcomb and others had developed and shared so many decades ago that was finally reaching fruition.
In fact, nature turned out to be giving us just what I had expected – I’d expected since the early 1980s that the first thing we would see would be merging blackholes because the distance you can see goes up roughly proportionally with the mass of the binary, and so the volumes are cubed, and that factor would overwhelm the absolute lower event rate for blackhole binaries compared to neutron star binaries. It seemed very likely to me so that’s just what I thought would happen. It’s a big part of how I hoped to sell this project.
To have that come out right was pleasing, to have the strength of the waves be 10-21 – that’s a number we started targeting in 1978. So it all came to pass the way we expected it to, thanks to enormous work by your generation of experimenters. You were the ones who really pulled it off. The way I like to say it is that it’s your generation of experimenters that makes me look good!
There had been science runs of LIGO before the detector went through upgrade. Was it that prior to every science run, you anticipated the discovery of gravitational wave signals? Or was it particularly during [the operation of] Advanced LIGO that you had the bet that this would be the time?
Well, so, Barry Barish [then the principal investigator] and I did the presentation to the National Science Board in 1994, which led to the final approval to go forward with construction. In that presentation, we explained that LIGO would have to be done in two steps – that there would be initial detectors and then there would be advanced detectors. And that the probability of initial detectors to find gravitational waves was small, and the advanced detectors would likely see lots of gravitational waves. That’s what our expectations was, that basically what we said in our proposal and that’s the way it turned out. It would’ve been nice if the initial detectors had seen waves but we didn’t really expect it. We did expect the advanced detectors to see waves. So, no, I was not expecting it [to happen] in any previous run.
I was actually not expecting this quickly with the advanced detectors. Then, two things happened: nature was kinder than my expectations – not kinder than my hope – and, second, the commissioning went extremely well, so the detectors were more sensitive than I expected in 2015. Those two things came together. Instead I was expecting [a signal to be detected in] 2017.
When this experiment was being conceived and a lot of relativists were involved, what was it that made you feel you had to take a leadership role in LIGO? It was going to be a long and uncertain journey. Did you believe that this is something you had to do?
When I started my career, I had a PhD in [Einstein’s] relativity but I had already done research in astrophysics as an undergraduate – I was planning to combine them. I started building a research group at Caltech in 1966, working on what we now call ‘blackholes’; the name wasn’t invented yet.
The relativistic stars and gravitational-waves – we’d been working on these things from the theoretical side, but I’d had experience… doing nuclear physics experiments I’d done as a graduate student at Princeton University. I’d published several papers on it. I’d worked with John Wheeler at Princeton on my PhD thesis but I’d met and had been a member also of Robert Dickie’s experimental group which played a major role in the discovery of the cosmic microwave background. They didn’t make the discovery but they told me they were on the verge of making it when it got discovered at Bell Labs.
So I was tied into that group. Rai Weiss was in that group. He was a postdoc when I was graduate student, so we met there. And I had a real interest in, rather an appreciation for, experiments as a graduate student. And so, it was with eagerness that I developed a close collaboration with Vladimir Braginsky, a leading experimenter in this field in Moscow. It was beginning in the early 1970s that I had long discussions with Rai Weiss about gravitational wave detection by [the] technique he had invented, I think it was 1975 or 1974. I became convinced from my discussions with Ray and Vladimir that the experimental side was going to succeed. So, I then decided we should build a group at Caltech to work on the experimental side, because I believed it was so important. I talked Caltech into doing that and we brought Ron Drever to Caltech to lead the group and Stan Whitcomb to work with him. And Stan was chief scientist [at] the LIGO Laboratories.
That’s how I came to be involved very early on. It was also, I think, what I had that the experimenters didn’t have a deep understanding of the science LIGO could do, so I tried to play a very major role in formulating the science vision for LIGO – both initial LIGO and then Advanced LIGO in the 2000s. I also built a group that worked at the interface with the experimental group, did some design work on aspects of the experiment like noise analysis and developing ideas to deal with noise. So, that’s been my tie to it. But it’s really Rai Weiss first and Ron Drever second who are the major inventors of the technique – Ray who’s been the intellectual leader on the experimental side of the project.
As you said, alongside the experiment, the astrophysical modelling and gravitational wave data analysis also came through quite a substantial leap to be ready. My adviser, Deirdre Shoemaker, says the reason we do numerical relativity is because of Kip Thorne. And on the day of the discovery, we had hundreds of high-performance simulations of binary blackholes ready to compare with the data. How did you feel that the community was just so ready for the first detection?
I was afraid the community would not be ready! In 2001, at the same time I was putting together the science case for the proposal for Advanced LIGO, I was making a decision that we at Caltech should get into the business of numerical relativity. I was quite worried. As the chair of the advisory committee of what was called the Grand Challenge Alliance of the numerical relativity groups in 90s, I watched in great details the struggles to get binary blackhole simulations for generic binary blackhole mergers. I was becoming more and more dismayed that the whole community was hung up and was not succeeding.
That’s when I basically left day to day involvement in LIGO not in order to work on the simulations myself but rather to put together a collaboration to work on it. We started a group at Caltech in tight collaboration with Saul Teukolsky’s group in Cornell which had already been working on the problem for about 15 years. My secondary motivation for this was I wanted to begin to see and understand the nonlinear dynamics of curved spacetime, which is triggered when blackholes collide. So my principal role in terms of the science connected to numerical relativity was trying to use simulations to understand this nonlinear dynamics.
But I think I played a significant role in getting a large enough collaboration together to make major contributions to numerical relativity, and I think that was very, very important. I was sure that we would not be able to understand the most interesting of the sources of gravitational waves that LIGO would see without numerical relativity. That’s why I made that move from being involved in LIGO in a hands-on way, which I was up until about 2001, to helping in numerical relativity work, which I’ve been doing from 2001 up until recently.
Over these years, you’ve had to wear multiple hats – of starting a collaboration, getting NSF interested, work on astrophysics and nonlinear dynamics of general relativity. Did you at any point feel you just wanted to be a conventional physicist, just have a pipe and smoke, and just do pen-and-paper physics?
[Laughs] Not really! I mean, another aspect of this is that I’ve a personality such that I do not like to work in large projects while LIGO had to become a large project. So I was happy to get out after it had become a large project. I had trained many people in to do the things I could do on LIGO but probably do them better, and data analysis, theoretical analysis of quantum nondemolition analyses, and so forth. And numerical relativity was still small and there was hardly anybody who was really thinking about nonlinear dynamics in curved spacetime. So for me it was really a pleasure to move out of day to day involvement with LIGO and do something in which there was less competition and more opportunity to do something unique.
The hats one wears just depends on the opportunities that come along… plus personality.
One of the questions I’ve really wanted to ask you is about your time with John Wheeler. Was there some particular learning that you got from him that you feel a need for passing on to your students and other scientists?
There are a number of things. John Wheeler was a very great teacher and mentor for young scientists. I think from the communication, which he was superb at and I tried to emulate him and learn from him, to strategies – he used to say that the most effective people are those who make the most mistakes fastest, so you don’t be afraid of making mistakes – to the importance of going to others for advice, who are better experts than you are, and to helping everybody maintain self-respect and build a community in which there’s a huge amount of mutual respect, a community that works together and gives credit to other people for work done… a variety of things in terms of research strategies and sociology of science that I try to pass on to future generations.
Your former doctoral student and my former adviser, Lee Samuel Finn, once showed me a draft of his PhD thesis and all I could see were red markings by you on every second paragraph with comments. Do you think that the skill of scientific writing and communication is still somewhat neglected in the physical sciences? Should we have focused more on it?
Oh, I think it is, I think it is. It’s a very important skill. And I should say this: Sam wrote a lot better than a lot of my other students did. There was a lot less red on his manuscripts than on most of my students’. [Laughs]
I think communication is tremendously important. Science is in fact a communal process. Even when you’re trying to work alone or in a small group, like I prefer to do, your impact is what you’re communicating in your results to others. Exchanging ideas with others is one of the things that enables science to move forward; it cannot be done entirely when there aren’t other people. You want other people to build on what you do and you’ll do much better work if you know what other people have done and if you can integrate that into your own work. Communication is crucial. It is, I think, very undervalued – I think as a community, we’ve failed to teach communication effectively.
When you were a doctoral student, it was this period when experiments on gravity had not assumed priority, and the work was more mathematical – unlike in particle physics. I heard a story that Richard Feynman was very upset with gravitational physics at the time because there was no one really targeting experiments. Do you perceive [what Feynman felt] now, in this period when the next generations of theories are being built, that there is a need to always to have an observational aspect in mind?
I think there is a need for that but for general relativity the technology was not there to actually do really interesting experiments until the second half of the 20th century. In the first half of the 20th century, you just didn’t have the technology. That’s a big part of why there was no experimental pursuit and it became more the domain of theorists and mathematicians. I think we’re in a similar situation in the current time of string theory, M theory and loop quantum gravity, and various approaches to quantum gravity. I think this is a tremendously important area of work. I am confident that good experiments will come but the technology just is not there. Either that or people have not yet succeeded in finding adequate low-energy shadows, or imprints, of ultra-high-energy physics.
I think the quest to find such imprints is very important for us. The search for cosmic strings by LIGO I think is an important piece of the prediction that some fundamental strings may have been expanded in the early inflation of the universe to cosmic scale. The prediction by Joseph Polchinski and others are very important if those gravitational waves can be seen by LIGO. We know from the cusp and individual parts of strings on what the gravitational waveform should be. Those might seem now to be tremendously important but the search for things like that could show up with current technology – that I think is very important. And string theorists are searching for such things. I am confident that those kinds of connections will be made experimentally, but it’s hard with current technology and there may be key ideas still missing – but I believe that the community is searching hard for experimental connections, and ultimately they will come.
There’s a 300-year legacy of understanding gravity. What advice would you give to us young LIGO scientists to carry this legacy forward for at least another half century?
[Laughs] I don’t think I have any one piece of advice. I have a general piece of advice: that to have a big impact on science requires a lot of intense work. You need to love work or you should be doing something else. It’s been a great joy to be involved in this quest but it’s not so much a joy of the ultimate success, which we have thanks to your generation, but it is the joy of the process.
To be successful both in science and in life, I think, in the modern era where technology is as advanced as it is, daily life is as comfortable as it is (for at least most people in the US), I think one should be doing something one is enthusiastic about but that also has some significant impact on others.
As a kid when you saw the night sky and today, post the discovery of gravitational waves, when you see the night sky, do you indulge in existential ramblings of how far the human species has come?
I’ve always thought and indulged in that… I think that was part of what got me enthusiastic about astronomy already at age eight. I learnt physics at 13. It was amazing to me that we could understand, and we do understand, the things we do understand.
I could talk to you for eternity but…
Let me just emphasise one more thing. Although I personally don’t enjoy working on a large project, that’s the way this had to go, and I’m so grateful to huge numbers of people who have made this a success. I think the credit really does go to the whole team and I’ve ended up getting a lot, lot more than my share. I think somebody who has been much overlooked has been Barry Barish, who was the director of LIGO [1997-2011] who carried us from a small scale experiment into the current structure of LIGO, who designed the current structure of LIGO, the LIGO scientific collaboration, the multiple institutions and it’s that kind of leadership that brought together the contributions of many, many, many scientists.
LIGO is a wonderful thing. It’s a wonderful community. I’m so grateful to have been tied to it.
And we are very grateful to have had initial impetus from you. Thank you, Kip, thank you so much for this discussion.
It was a pleasure to talk to you.
Karan Jani is a doctoral researcher at the Georgia Institute of Technology, a member of the team that discovered gravitational waves at LIGO in September 2015, and part of the LIGO-India project. He currently holds the Senator Nunn Fellowship in National Security and International Relations and serves as vice-president of the Student Government.