Yesterday the Royal Swedish Academy announced that the 2017 Nobel Prize in Physics would recognize the discovery of gravitational waves; the recipients would be Barry Barish, Kip Thorne, and Rainer Weiss, three of the visionaries who shepherded the Laser Interferometer Gravitational-Wave Observatory (LIGO) through four decades of technological and bureaucratic innovations. (Another founder of the project, Ronald Drever, died earlier this year and was therefore ineligible for the Prize.) LWON has twice published essays based on discussions with the new Nobel laureates. The first, in December 2014, explained the physics behind the black hole in Interstellar, a movie that Thorne helped conceive and produce. The second post, republished below, addresses the LIGO experiment itself; the post originally appeared in June 2016.
A few weeks ago I was talking to one of the founders of the Laser Interferometer Gravitational-Wave Observatory (LIGO), the collaboration that last September made the first detection of gravitational waves. Even if you’re not science-savvy, you will almost certainly recall the worldwide breathless news coverage following the February announcement of that detection. Now Rainer Weiss, MIT professor emeritus, had further news. He told me that the LIGO collaboration would soon announce another detection of a gravitational-wave-producing event.
That announcement came yesterday [Ed: June 15, 2016]. As was the case with the earlier, initial detection—the one that so far has garnered for the three founders of the project, as well as for the rest of the collaboration in some cases, a Gruber Prize, a Kavli Prize, a Shaw Prize, and a Breakthrough Prize in Physics (stay tuned for news from Stockholm on October 4) [Ed: off by a year!]—this second detection documents the collision of two orbiting black holes.
The discovery of gravitational waves last September didn’t especially surprise the collaboration. Discovering gravitational waves was what they’d designed LIGO to do; if gravitational waves were out there, this latest iteration of LIGO’s instruments, which had just come on-line, would find them. What surprised the LIGO collaboration instead was the nature of what they’d detected. Of the various gravitational-wave-producers that LIGO might observe—the kind that disturb space-time to such an extent that LIGO could register the aftershock—the collision of binary black holes was perhaps the least likely. Supernovae, neutron stars, colliding neutron stars: These were what the LIGO collaboration foresaw as far more common candidates.
And now LIGO has detected a second pair of colliding black holes. Well, not now, exactly; the new detection actually came in December. That’s only three months after the first detection. Again, it was a surprise: the detection of a relatively uncommon example, among one species of phenomena. Again, it was not a surprise: the detection, among one species of phenomena that the LIGO team had designed the experiment to discover, of an example.
Within the next couple of years, discoveries of gravitational-wave-producing phenomena will be routine, part of the common cosmological discourse. Weiss told me we could expect one detection a month, maybe more. As exciting as yesterday’s announcement of the discovery of a second source of gravitational waves is, what’s more exciting from a historical perspective is the promise that there will be more detections to come—many more.
We’ve seen this pattern over and over in the history of astronomy (as well as in other sciences). Satellites around other planets were practically unthinkable until Galileo discovered the moons of Jupiter in 1610. The existence of known galaxies outside our own was a subject of debate as late as the early 1920s; now we number them at 100 billion, at least. Last month NASA announced the discovery of more than a thousand planets within our galaxy: What was unique and stunning just 17 years ago has become routine, and along the way the discussion has shifted from the very existence of extra-solar planets to their frequency, to a revision of the Drake equation (the statistical possibility of the existence of alien civilizations), to a deeper understanding of planetary formation and the dynamics of planetary systems, and on and on.
And that’s how science at its best proceeds: The outlandish becomes commonplace, the impossible predictable. An experiment begins with a question: Does this thing exist? It provides an answer: Yes, and then some. And then that “then some” leads to a new question: