Monday, September 26, 2016

The human side of gravity science

kw: book reviews, nonfiction, science, gravity, general theory of relativity, LIGO, scientists

Because I pay attention to the news, I knew the end from the beginning. So we'll start with the climax:

This is a screen clip from this YouTube video of the detection, just over a year ago, of gravitational waves, by the two facilities of the Laser Interferometer Gravity-wave Observatory, or LIGO. The video lasts just 12 seconds, and plays the sound as heard in each detector several times. The sonic spectra show that, when detected, the gravitational waves (GW's) indicate two black holes that are already very close to one another, revolving around one another about 30 times per second, and spiraling inward, in about one or two tenths of a second, whirling up to about 400 times per second before colliding and merging into a single black hole. So the subtle chirp is very quick. That's why those who made the video repeated the chirps so many times (4 times for each signal, in pairs).

As of this writing, three such black hole collisions have been detected, most recently this past June. You can read more about it here. What you will not find on that page, or hardly anywhere, is a chronicle of the LIGO project and the projects and people that led to it and its successes. For that, we must read Black Hole Blues and Other Songs From Outer Space by Janna Levin. While I find the technical accomplishment quite fascinating, the people are enlightening in their own right.

The stereotype of the white-coated, impassive mega-brain does severe injustice to actual scientists. Just like the rest of us, they have their tastes, quirks, habits, obsessions, relationships, and loves and hates. The kind of brain power needed to detect such extremely faint signals, just a few days short of 100 years after Albert Einstein proposed their existence, practically guarantees a collection of very unusual people. It has been said that reasonable people don't make changes, because they are satisfied with the status quo. Thus all change, for better or for worse, is made by unreasonable people. Gravitational "astronomy" attracted some of the least reasonable people of the past generation or two, with the proviso that they are able to carry out useful work.

The singular characteristic of the most unreasonable people is that they are predisposed to be bad team members. They have to work really, really hard to work together. Some never learn the knack. In Dr. Levin's chronicle, chief among these are two exceptionally talented experimentalists, Joe Weber and Ron Drever. Joe Weber came along first, inventing the suspended-mass GW detector, consisting of a ton or more of aluminum in the form of a solid bar, that would ring in response to space distortions of a certain frequency. It was designed to ring out the "song" of an end-stage black hole collision. Dr. Weber claimed he detected all kinds of GW signals with his device. Nobody else ever could get one to work.

Kip Thorne, a cheerfully unconventional man, as unreasonable yet as personable as they come, somehow shepherded a herd of "cats" over a period of four decades, to achieve LIGO. Scientists came and went. Directors of the project came and went. One early "cat" was Ron Drever, famed for inducing almost any detector to have almost supernaturally low levels of noise, so as to winkle out the signal. He was equally famous for insisting on his own autonomy and total authority.

But what kind of signal are we talking about? If two black holes collided somewhere "nearby", say, within a couple of light years, the resulting gravity waves would hurt, and hurt bad. You'd hear them, feel them, and possibly suffer brain death as a result. Since no such event is known to have happened in historic times (I suppose a latter-day Velikovsky could re-interpret some Biblical event thusly), Dr. Thorne and others were able to set a probable lower limit on the likelihood of such collisions per cubic megaparsec. The reality was even more sparse. At LIGO's present level of sensitivity, based on three detections to date, it can detect about one event per 2-3 months within a volume of about 700 trillion trillion parsecs. Such a volume has a radius of 2 billion light years.

At that kind of distance, the gravity signal is very weak. The "arms" of the two LIGO instruments are 4 km long. Over that distance, the gravity signals that were detected caused a fluctuation in the scale of spacetime that measured about a twentieth the width of a proton. The laser beams in LIGO don't just go down to a mirror and return. They bounce back and forth thousands of times (I didn't learn the precise figure) to amplify the motion such that the phase shift in light of wavelength around 600 nm becomes detectable and even measurable in magnitude.

Kip Thorne, Rai Weiss and others had to convince the National Science Foundation to spend, initially about $200 million, and eventually around a billion dollars. The first director of the project, "Robbie" Vogt, shepherded just the right mix of congressmen and scientists to obtain the early funding and keep it flowing. But he, being one of the "unreasonables", got fired after a few years, and for a while, directors of LIGO came and went almost with the seasons.

It seems miraculous that a physics project of this scope could actually be brought to completion, given the anti-science bias among American politicians. It was canny to tout LIGO as a physics endeavor rather than astronomy (in spite of the word "Observatory" in the title); supercolliders such as LHC set a high expectation for physics funding, while astronomers typically get stubborn resistance to spending more than a few percent of such amounts (LHC's budget is about $1 billion yearly).

By the time the author had completed her manuscript of the book, LIGO was just barely running in test mode, and simultaneous runs of the two facilities had yet to be performed. Fortunately, she held off publication long enough to "enjoy" learning of the first detection in September, 2015. This story really needed a happy ending, and her Epilogue describes it. I found it interesting, and comforting, to get to peek under the covers of a science project of this magnitude.

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