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.

A force most familiar

kw: book reviews, nonfiction, gravity, science

In my musing about the Higgs particle on Monday, I considered the odd case of the graviton. If there is such a thing, it has proved mighty hard to find. Particle accelerators of higher and higher energy don't seem the right approach, because it would have no mass anyway. I recall a science fiction novel from many years ago (50 or more) in which control of gravity was attained, and forces were developed called "electrogravitic" and "gravitomagnetic" and so forth. All kinds of magical effects were found.

So far, though, the only way to produce gravity waves, if they do exist, is to shake something very massive, and the only way to detect them is with a long, massive "antenna". The longest "antenna" yet produced has yet to detect anything, even though we expect things like the collision of two neutron stars, or of two black holes, to occur from time to time. Such events ought to radiate copious amounts of gravity waves. We have only indirect evidence that gravity waves might exist: A pair of neutron stars that orbit one another with a period of about 8 hours. The period is getting shorter, which indicates that the orbit is getting smaller. It is inferred that gravity waves are leaking away some amount of energy. But who knows? Maybe there is a thin gas dragging on them.

So what is gravity? If you put the question to Brian Clegg, author of Gravity: How the Weakest Force in the Universe Shaped our Lives, he'll most likely quote Richard Feynman, who urged us not to fear not knowing. In other words, we have mathematical descriptions of how gravity acts, but what it is? Nobody knows. Fortunately for the full employment of physicists, not knowing is a spur towards finding out!

Gravity as a concept seems to have begun with Galileo, and was first described mathematically by Newton. In earlier times, at least in the West, people thought things moved because angels pushed them, and heavy stuff moved downward because it was their purpose to do so, a completely teleological explanation. The "elements" were understood to be earth, air, fire and water. Earth received heavy, "earthy" things, and water, having a lesser downward purpose, stayed upon the earth but above it. Fire's purpose was to rise, and air's was to rest upon water or earth, having a neutral purpose (It didn't occur to people that they needed air to breathe. The function of the lungs was discerned quite late).

The focus of the book is the development of the general theory of relativity by Albert Einstein. He first thought of the equivalence principle, that acceleration and gravity mimic one another, in 1907, but it took him until 1915 to learn and apply the mathematics needed to describe the warping of space that is its most useful feature. Having this theory, which has been verified to great accuracy by a number of methods in the following century, it drive physicists crazy that it cannot be reconciled with quantum physics, which describes everything else!

Thus the hunt for gravity waves and the graviton. The ideas getting the most attention all relate to "string theory", which has been sardonically called, "a theory of everything, because everything can happen". I read in another book that there are at least 10⁵⁰⁰ versions of string theory that are possible, and so far there is no way to determine if any of them is more correct than any other. It sounds like it'll be a long search. But string theories are not the only choice. A number of alternative theories are being studied, including some that would sever time from space, thus scrapping relativity altogether. Both theories of relativity rely on unified spacetime. It is thought that the effects of special and general relativity might be better described by a better meta-theory.

This is not as far-fetched as it might sound. Theories based on strings, for example, get complicated fast, and they remind me of the epicycles used prior to Kepler's work to describe planetary orbits. Even Copernicus needed epicycles to make his earth-centered cosmology work, because he thought the orbits were based on circles. Kepler showed they are ellipses, and later work showed that the ellipses are "perturbed" by the gravitational effects of all the other planets. Maybe someday an über-Kepler will discover the hyper-elliptical math required to reconcile gravity and quantum mechanics, or maybe it will be a different approach entirely.

I was hoping for an extended discussion of the graviton. I puzzle over whether it will itself feel gravitational effects. I tentatively conclude, probably not—or not very much—or they could never escape from black holes. Instead, in the discussion of general relativity I learned that one term describes the self-energy of gravitation, which amounts to the same thing. It is an enfeebled effect, lest gravity's self-energy cause it to collapse into itself (and stay inside black holes). It is kind of like the self-energy of the electron, which classically becomes infinite at zero radius. Thus, the electron cannot be a point particle (and this might be a hint that space is actually quantized, in support of one of the alternative theories).

I have also wondered whether gravity's effects, or gravitons, necessarily move at the speed of light. Gravity is not light. The common understanding that information cannot travel faster than c (repeated on p 224), may have a spurious basis. We derive c from Maxwell's equations, based on the strength of interaction between electrical and magnetic energy. Gravity seems to stand alone. Why should it be subject to Maxwell? Besides, g may be less than c! If so, could that explain the seeming orbital anomalies in galaxies that led to the theory of dark matter?

The book entire is a masterful and accessible survey of the field. I find that I have read another book by Brian Clegg, and that another one is near the bottom of my current pile of reading material, so I'll get to it in a week or two. This book's frontispiece lists ten books, so this is his eleventh. It looks like he has caught the bug to explain everything. I like that.

I do have to point out a few signs of hurried production. In general, I find numerous indications that publishers tend to scrimp on proofreading. This book is much better than most. However:

• At the bottom of p 130, concerning a star that appears near the limb of the sun during an eclipse, we find, "…the star should appear shifted slightly toward the Sun…"; the bending of the light is toward the sun, so the star should appear shifted away from the Sun. Draw a picture to see what I mean.
• On p 143 the GPS satellites are described as moving "around 87,000 miles (14,000 kilometers) per hour". The actual mph speed is 8,700. A good item to remember is that escape velocity from Earth is about 25,000 mph or 40,000 kph.
• This is a more picky point: In the middle of p 215 the term "vast difference" ought to be "vast distance", describing whether light is refracted by the quantum nature of empty space. It takes a lot of distance to see a difference. An easy slip by a fast typist.