The Nobel Prize in Physics was awarded today to Rainer Weiss, Barry C. Barish and Kip S. Thorne for their contributions to the LIGO detector and the observation of gravitational waves. Following the announcement and press conference, physicst Olga Botner explained the Nobel-winning research.

Steve Mirsky:    Welcome to Scientific American's Science Talk, posted on October 3rd, 2017. I'm Steve Mirsky.

Goran Hansson:         The Royal Swedish Academy of Sciences has decided to award the 2017 Nobel Prize in Physics with one half to Rainer Weiss and the other half, jointly, to Barry C. Barish and Kip S. Thorne, all of them members of the LIGO-Virgo collaboration. And the Academy citation runs: "For decisive contributions to the LIGO detector, and the observation of gravitational waves."

Mirsky:               Goran Hansson, secretary general of the Academy, at 5:52 this morning, Eastern time. What follows is an edited version of the announcement and press conference.

Hansson:           Rainer Weiss was born in 1932, in Berlin, in Germany. He received his Ph.D. at the Massachusetts Institute of Technology in the United States, and he is still affiliated with the MIT, as professor of physics. Dr. Weiss is, since many years, a US citizen. Barry Barish was born in 1936, in Nebraska, in the United States. He is a professor of physics at Cal Tech, the California Institute of Technology. And finally, Kip Thorne was born in 1940, in Utah, in the US, and he's currently professor of theoretical physics at Cal Tech. And as I mentioned, all three Nobel Laureates are members of the LIGO-Virgo collaboration, a large team of more than 1,000 scientists who built and ran the detector that was used to discover gravitational waves. And with that, I'll give the word to the chairman of the Nobel Committee, Nils Mårtensson, who will give us a brief summary of the research field and the discovery that has been awarded today.

Mårtensson:      On the 14th of September, 2015, the laser interferometer gravitational wave observatory, LIGO, succeeded, for the first time, to directly observe gravitational waves. These waves were predicted by Einstein 100 years ago, but until now, they have escaped direct detection. This is a truly remarkable achievement, which crowns almost 50 years of experimental efforts by hundreds of scientists and engineers. And today, the LIGO collaboration includes 1,000 members from 90 institutions in 5 continents, who have directly or indirectly contributed to this breakthrough. This year's Nobel Laureates represent, in an excellent way, the diverse competences needed for LIGO success. Rainer Weiss led the foundation for the detector design; he analyzed what performances had to be reached for the critical parts of the instrument, and what sources of background noise had to be mastered.

And Kip Thorne, also cofounder of LIGO, made predictions about what signals were expected from different astrophysical events of critical importance for the design. Barry Barish is a scientific leader who scaled the project up in a stepwise fashion, up to the advanced LIGO, thereby reaching the sensitivity which in the end allowed the successful detection. Without them, the discovery would not have happened. We now witness the dawn of a new field: gravitational wave astronomy. This will teach us about the most violent processes in the universe, and it will lead to new insights into the nature of extreme gravity.

Hansson:           And now, Olga Botner will give us some more insights into the discovery, the scientists, and the collaboration.

Mirsky:               Olga Botner is a physicist at Uppsala University, and a member of the Nobel Physics Committee.

Olga Botner:      Once upon a time, a long time ago, in a galaxy far, far away, two massive blackholes engaged in a deadly dance, revolving around each other, spiraling faster and faster, whirling. Finally, at half the velocity of light, they collided and merged, forming an even more massive blackhole. This momentous event reverberated through space and time, as gravitational waves sped outwards, carrying information on what had just happened. These events took place about 1.3 billion years ago, at a time when the first multicellular life emerged on earth. Ever since then have the gravitational waves sped through the universe, reaching our cosmic neighborhood, the Magellanic Clouds, about 200,000 years ago, when early homo sapiens walked in Africa. And finally swept through the earth on September 14, 2015, when the waves were recorded by perhaps the most sensitive instrument ever devised by man: the LIGO Interferometer Gravitational Wave Observatory.

This event caused a sensation worldwide. We knew that gravitational waves existed, indirectly, but this was the first time, ever, they had been directly observed, and this of course made the headlines of major newspapers like the New York Times. So what are the gravitational waves? Well, they were predicted by Einstein, within his general theory of relativity. Gravitational waves arise when heavy bodies accelerate, that is, when the velocity is changing with time. They are disturbances of space time, traveling through the universe at the speed of light, causing space to alternately stretch and shrink at right angles to the direction of motion. The effect, the gravitational strain, is tiny, even from a ponderous event like the collision and merger of two blackholes. If we imagine a ruler, the length of the earth diameter like 13,000 kilometers, a passing gravitational wave would make this ruler vibrate by 1 trillionth of a millimeter, which is about the size of an atomic nucleus.

Nevertheless, the team of scientists, led by this year's Nobel Laureates, succeeded in measuring this tiny vibrance. The key to their success is laser interferometry. The light from a laser is led towards a beam splitter, where the light is split along two detector arms at right angle to each other. In the case of LIGO, these detector arms are four kilometers long. Mirrors at the end of the arms reflect the light back towards the beam splitter, where the two waves are overlaid and channeled towards the light detector, where a fringe pattern is registered. Now, a passing gravitational wave will make one of the arms shrink when the other arm expands, and this makes the patterns shift very, very slightly, and this is what the scientists detect. Now, the effect is incredibly small, and the detector is amazingly sensitive: a passing truck or ocean waves beating against a far shore cause a disturbance, which must be monitored and offset.

Also, to exclude local disturbances, each LIGO detector cannot operate on its own, and this is why the LIGO observatory comprises two detectors, one in Hanford, in Washington State, and the other in Livingston, Louisiana, on opposite coasts of the American continent, separated by about 3,000 kilometers. The discovery, the first-ever observation of a gravitational wave, was a milestone, opening a new window to the universe. The prospects of observing blackholes hands-on are tremendously exciting, as are the prospects of being able to see the dark parts of the universe, the parts of the universe from which electromagnetic radiation light does not reach us. Since the first observation, three more discoveries of gravitational waves passing the earth have been made. The last one, announced less than a week ago, where the twin LIGO detectors operated in concert with the assistor detector, Virgo, in Italy. This is truly the dawn of gravitational waves astronomy. And I couldn't help but add with Einstein, who obviously was right again, even though back when, for a while, he didn't believe that gravitational waves existed.

Hansson:           And we may now have one of our Nobel Laureates with us on a phone line from the US. Dr. Weiss, are you there?

Rainer Weiss:    Oh, I'm here, yes.

Hansson:           So, I'm now sitting in the beautiful session hall of the Royal Swedish Academy of Sciences. We are in the midst of the press conference; here are journalists from Swedish and international media, and I'm sure they would like to ask you some questions.

Journalist:         My question is: Did you expect this or did you know that you have been nominated? And what was your reaction when you heard the news?

Weiss:                [Laughs] Yes, it's really wonderful. I mean, but I view this more as a thing that is recognized as the work of about 1,000 people [audio cuts out] and it's the work of, really, a dedicated effort [audio cuts out] been going on for – I hate to tell you, it's as long as 40 years of people thinking about this, trying to make a detection of [audio cuts out] sometimes failing in the early days. And then slowly but surely, getting the technology together to be able to do it.

Hansson:           There is slight problem with the phoneline, but I think you could hear.

Weiss:                And it's very, very exciting that it worked out in the end, that we are actually detecting [audio cuts out] and actually adding to the knowledge, through gravitational waves, _____ what goes on [audio cuts out] a wonderful experience, sort of begun [audio cuts out] and many of us who are in [audio cuts out] fully expect that we're gonna learn things that we didn't know about. I mean, at this moment, we do know about – we knew about blackholes other ways, and we knew about neutron stars. We've known about – well, those are the two things that ultimately are seen. But the thing is that, we hope that there are all sorts of phenomena that you can see mostly because of the gravitational waves they emit. That will open a new science and will add to the science that is already such a deep thing in terms of understanding the universe [audio cuts out]. So, I can't ask you any better than [audio cuts out].

Mirsky:               Following the announcement and press conference, Swedish journalist, Joanna Rose, spoke with Olga Botner about the Nobel-winning research.

Joanna Rose:     So, what was the main achievement of this year's laureates?

Botner:               Their competencies are quite complementary. Rainer Weiss is the founder of the whole project; he developed the concept starting in the beginning, or the middle, of the 1960s; he built the first prototype detectors, in 1967; and then, he demonstrated the principle. He charted the various noise sources which would influence the performance of the detector. And as I've been trying to mention, the detector is incredibly sensitive: a truck passing by will make the detector vibrate, ocean waves some distance away make also the detector vibrate, seismologic, other things. So, you have to know very, very well what kind of sources can give you signals which simulate gravitational wave, to be able to distinguish the true from the false. So, his main influence on the project is developing a prototype, chartering all the sources of disturbances, and finding means to offset these sources.

Thorne is this inspiring theorist, who figured out what kind of signals you can expect from astrophysical sources of these waves. So what to look for, how sensitive does the instrument have to be to be able to observe what the universe behaves like in terms of gravitational waves. And then we have Barry Barish, who is the person who joined the experiment late. He only arrived on the scene in 1994, however, he is the visionary behind upgrading the sensitivity of the instrument to the level where this detection was possible. The original LIGO could not have made the detection, which was possible thanks to the development initiated by Barry Barish.

Rose:                  So, the other two worked, like, for 50 years with this project – what did they say when they got the call from Stockholm, this morning?

Botner:               They were still humble and very, very gratified that they were awarded the prize. But also, all three of them mentioned, one, that they were happy that they were not alone, and, two, that we should make sure to stress the role of the collaboration, at the press conference and even at the award ceremony.

Rose:                  So, how was this collaboration, the LIGO collaboration [crosstalk]?

Botner:               Yes, the LIGO collaboration has grown over the last 40 years. In the beginning, it was small, it was just groups at MIT and at Cal Tech, at the universities in the United States. But then, as the detector grew in size and people started talking of kilometer-long arms, the collaboration also grew, and groups joined all across the United States, but also in Europe and in Australia. So today, the LIGO collaboration consists of scientists at 90 universities, all across the world.

Rose:                  So, now, when the gravitational waves are here, in some sense, what will they tell us about the universe?

Botner:               So, what we hope to learn from the gravitational waves is, one, about blackholes, and about gravity in its strong regime. You have to imagine gravity as the weakest force we know of – it's much weaker than electromagnetism. Just think of a kitchen magnet, a small magnet you put on the door of your fridge: it stays up; it doesn't fall to the ground. Which just shows you that the electromagnetism is much stronger than gravity. So, the gravity forces we know of from the earth are weak; gravitational forces close to blackholes are extremely strong. So, the discovery of gravitational waves carrying information from the surroundings of blackholes will teach us something about the strong regime of gravity, which is very, very exciting. We'll learn something about violent explosions like supernovae or gamma ray bursts. We might learn something about the Big Bang, because the Big Bang left imprint on the universe in terms of gravitational waves, which we've never seen before. They are even weaker than those which have been observe previously. But even more exciting, there are parts of the universe which are dark, which we've never seen before, because electromagnetic radiation doesn't reach us from there. Gravitational waves are unstoppable, so they will. So we hope to learn about this dark universe.

[Music playing]