Steve Mirsky:    Hi. Steve Mirsky here for Scientific American's Science Talk. It's February 11, 2016. When hundreds of reporters and a throng of TV cameras jostle one another to get a good view in the National Press Club in Washington, D.C., you figure maybe the president is talking. But today, it was astrophysicists, and the throng had gathered because the researchers were announcing that they finally had evidence for gravitational waves, the first observation of ripples in the fabric of space and time, thus confirming Einstein's prediction of their existence a century ago. The gravitational waves in question emanated from the collision of two black holes some 1.3 billion light years away, which means the collision took place 1.3 billion years ago but the waves only arrived at our planet a few months back. They were noticed by an experiment called LIGO, for Laser Interferometer Gravitational-Wave Observatory. There are actually two separate facilities that make up LIGO, one in Louisiana and one in Washington State. Both had to spot the same phenomenon to make the observation meaningful.

Our Web site, www.scientificamerican.com, has a batch of fresh articles about LIGO and this finding. One of the astrophysicists at the National Press Club this morning was Kip Thorne. He is the Feynman Professor of Theoretical Physics Emeritus at Caltech. He co-authored the standard text on general relativity titled Gravitation, and he wrote the popular book, Black Holes and Time Warps: Einstein's Outrageous Legacy. He was also one of the founders of the LIGO project. Following the announcement, Thorne talked with Scientific American's Washington, D.C., bureau chief, Josh Fischman, about the discovery. You'll hear Thorne explain that what the experimenters observed was definitely not a blind injection. As Davide Castelvecchi noted in a recent article in Nature, a blind injection is a false signal deliberately injected into the detectors to train LIGO's data analysis team, and that's exactly what the signal that they saw was not. It was the real thing. The first voice you'll hear is Kip Thorne followed by Josh Fischman. Enjoy.

Kip Thorne: The first gravitational wave ever observed, the first observation of colliding black holes ever, the first observation of non-linear dynamics _____ space time, there are a number of firsts.

Josh Fischman: Now, you, in one of your concluding remarks, compared the technology that enabled this to the art of the Renaissance, and I wonder if you could just repeat that for me, because I thought it was an interesting observation.

Thorne:It's not so much the technology but what we learn from this, so when we look back on the era of the Renaissance and we ask ourselves, "What did we as human beings get from our ancestors of the Renaissance that's important to us?" the answer I think will almost universally be great art, great architecture, great music. Similarly, when our descendants look back on this era and ask, "What that's important to us did we get from that era of the late 20th century and 21st century?" I believe it's going to be an understanding of the universe around us and the laws that govern the universe, an understanding that comes from LIGO and gravitational waves, and from electromagnetic observations with electromagnetic telescopes.

Fischman:         Okay, that's a great answer and it's a great segue to my next question. What is this telling us about black holes? What do these observations tell us about black holes?

Thorne:The observations by themselves tell us, or when we have a few more of these, they're going to tell us how many black holes there are in the universe, they're going to tell us something about what kinds of mass ranges and spin ranges occur, the demography of black holes, but more interesting to me is that by comparing the waveforms we get observationally with the waveforms from computer simulations of colliding black holes, we are able then to deduce what was happening to the black holes when they collided. For the first time in that way see through this combination of observation and simulation, see how warped space time behaves in a storm when it's wildly excited, when the rate of flow of time is oscillating wildly, when the shape of space is oscillating wildly, the combination of the observations and the simulations. This is a dream that I got from my Ph.D. advisor back in the early 1960s, John Wheeler. He called it geometrodynamics, understand how warped space time behaves under these circumstances. Geometrodynamics has become a reality.

Fischman:         Now, you, along with Ray Weiss and Ron Drever, you proposed this experiment, LIGO, in the 1980s as a way to detect gravitational waves, and following up on what you just said about this being a dream for a long time, how does it now feel to look at what LIGO has achieved today?

Thorne:So, interestingly, when I first saw the waves and became convinced they were real, I would have expected I would feel great excitement. I didn't feel any excitement at all. What I felt was a sense of profound satisfaction. I knew with high probability the day would come, and it finally did come, and the dreams that we had had became a reality.

Fischman:         Now, what form, in that moment, when you first saw the waves, or heard the waves, was it a sound? Was it a plot?

Thorne:I had an e-mail from Christian Ott, a young colleague at Caltech, who is much closer to the experiment and the data analysis than I am. He e-mailed me and said, "What is likely a detection of gravitational waves has happened. Go look at a certain internal Web site." That internal Web site, there were plots of what we call the time frequency plots, time frequency plots that actually appear in the published paper and that were shown today, showing how much power there is in oscillations of particular frequencies as time passes, and that shows the chirp, and those are produced automatically. The signal comes in, it is detected in the two sides, it goes through computer programs that have been pre-written, and then they write this to the Web page that _____ can go look at. So this was just a few hours after it came in. I looked at these chirp signals that were shown today, and you had me on the screen in a film saying, "Oh my god, this may be it."

Fischman:         Now, "This may be it." What convinced you that it was it?

Thorne:Well, the first issue was that I wanted to see more precisely in comparison with the numeric relativity waveforms to make sure that the agreement was good, and that came very quickly, and the agreement was really very beautiful. So the first detection was made by a particular group within the LIGO collaboration, young people. This triumph belongs to the young experimenters and data analysts. But there was a group that had developed the data analysis, algorithms and pipelines for what's called an unmodeled search, no assumption about what's going on, you just go in and you look to see if you see anything, and that's what showed the chirp, the same chirp at both sides. But then, I wanted to see what do you get from a different data analysis group called the compact binary group, and what they do is they compare with templates. They're based on numeric relativity waveforms and on analytic calculations in the machines where you can do analytic calculations.

So it was only a matter of a few days, as I recall, until they had their analysis done, maybe less than that, and we saw this fabulously beautiful agreement between the theoretical waveforms based on solving Einstein's equation of _____ _____ precision and the observed waveforms. At that point, I was fully convinced, unless somehow this was something that had been injected blindly by an experimenter. But then, there was a deep, internal study of whether that could be possible, and blind injections are done, this is well know, but the blind injection process leaves, I am told, lots of fingerprints all over the data. So the experts on this, again this team of young people, went in and they couldn't see any fingerprints, but every blind injection that anyone has ever done leaves lots and lots of fingerprints.

Fischman:         How long did it take between that first phone call or e-mail you got from your grad student, to that point that you just described –

Thorne:It was a colleague who is a professor.

Fischman:         A colleague, yeah.

Thorne:Yeah, a young professor.

Fischman:         He contacted you when?

Thorne:Well, so he contacted me on September 14th. It was a matter of a few weeks. It may have been sooner than that. But to be quite sure that it was not a blind injection, my impression was a matter of a few weeks. I need to emphasize that I have not been intimately involved with LIGO for some years. I still have ties to LIGO, but I left day-to-day involvement in the early 2000s in order to initiate a numeric relativity effort at Caltech in order to do these simulations, and so we did this jointly with Saul _____'s group at Cornell, so that's where I've been is I'm tied to the simulation side. So I'm describing stuff that's outside both my involvement, and really my expertise.

Fischman:         Do you want to call out any particular by name? I know there are 1,005 people on the paper.

Thorne:Yeah, there are a lot of people, but Patrick Brady is here, for example, one of the lead data analysts. Bruce Allen. Bruce Allen and Patrick Brady are two who are here and played a big role in the data analysis.

Fischman:         Talk about sort of the big breakthrough technologies that allowed us to get to this point.

Thorne:Again, I'm not the expert—

Fischman:         You're not the expert.

Thorne:—but a very crucial piece was mirrors with extremely high reflectivities, far higher than anybody thought was likely, which were developed in the 1980s in industry for other purposes, and that was absolutely essential. Another thing that was absolutely essential was to be able to stabilize the lasers so that the frequency of the light that comes out is very, very stable over time. There were theorems, published theorems that said you could never stabilize lasers good enough to do this, but they were based on the assumption you stabilize them by locking them to the frequency of ticking of some atomic transition. So Ron Drever, he invented a way based on earlier work by Bob Pound at Harvard, taking some ideas of Bob Pound's from the microwave into the ______ of doing this stabilization.

He proved it experimentally with Jan Hall at the University of Colorado. It's now called Drever, or Pound-Drever-Hall locking. The basic idea is you lock the laser's frequency to a highly stable physical cavity, to the _____ frequencies of a physical cavity, and that technique now of stabilizing lasers is the standard technique that's used if you want highly, highly stable _____, but it came out of this project. It was invented for the use of this project. So those are a couple of—

Fischman:         That's really remarkable. Let me just round out by asking you what does the long-term future hold for gravitational wave astronomy?

Thorne:I think the long-term future is largely going to be working hand-in-hand with electromagnetic astronomy. There will be areas where you see only the gravitational waves, and this was one, our first detection. But most of the things we do will be looking at different aspects of the same thing, such as super nova explosions or neutron star collisions, or black holes tearing neutron stars apart. With gravitational waves being able to bring a completely different set of information about these phenomenon, what you're getting from x-rays, from light, from radio waves, from infrared, from ultraviolet, and so we like to call this multi-messenger astronomy, and I think multi-messenger –

Fischman:         Why multi-messenger?

Thorne:Each messenger is a different type of radiation—

Fischman:         Oh, okay.

Thorne:—so a different window, x-rays, light, radio waves, high-frequency gravitational waves, which is this band. Low-frequency, which is the _____ band. Very low-frequency, which is _____ timing, extremely low-frequency. So all the windows focusing in on every window that brings in information about a source, those data being brought together to get a really complete picture. But then there will be those things that can only be seen gravitationally, and those are also going to be tremendously important, and this is our first example.

Fischman:         That's terrific. Last question, which I'm going to ask for my mother, who is a smart English teacher but doesn't know from gravitational waves. Why, today, should she be excited when she reads about this?

Thorne:She must be interested in the universe.

Fischman:         Yeah, she is.

Thorne:She lives in it. She must be interested in the universe. We're born with a curiosity about the universe. Those people who don't have a curiosity don't have it because it gotten beaten out of them in some way. But we all are born with that curiosity, and this is revealing aspects of the universe we have never seen before that we have no other way to see, and it's just opening our eyes to marvelous things in the universe that will become part of everyday lore in the coming years but that are brand new today.