In the April 1981 issue of Popular Science, we explored the many initiatives and techniques used in the exciting hunt for sensing gravity waves, then out of reach.
In his story, Fisher describes the far-out wilds of space responsible for shaking space-time, including starquakes, gamma-ray bursts, and ticking neutron stars . But it was Weiss, shortly after his device detected its first gravity wave in 2015,
Even though gravity waves have never been directly detected, virtually the entire scientific community is convinced they exist. This assurance stems, in part, from the bedrock on which gravity-wave notions are founded: Albert Einstein’s theory of general relativity, which, though still being tested, remains untoppled [PS, Dec. ‘79]. Says Caltech astrophysicist Kip Thorne, “I don’t know of any respectable expert in gravitational theory who has any doubt that gravity waves exist.
To find out, l visited experimenters who are building gravity-wave detectors and theoreticians whose esoteric calculations guide them. In the process, I learned about the problems, and how the attempts to solve them are already producing useful spinoffs. And I learned about the ultimate payoff if the quest is successful: a new and potent tool for penetrating, for the first time, what one physicist has called “the most overwhelming events in the universe.
Probably the prime candidate for detection is what William Fairbank, professor of physics at Stanford University, calls “the most dramatic event in the history of the universe”—a supernova. As a star such as our sun ages, it converts parts of its mass into nuclear energy, perhaps one percent in five billion years.
But first, as the cookbooks say, you must catch your gravity wave. Until the 1950’s, no one presumed that the task was even feasible. Then Joseph Weber, a physicist at the University of Maryland, began to ponder the problem of building a gravity-wave detector, and proceeded to do so. It is no exaggeration to say that he fathered the entire field.
Fairbank told me why the low-temperature route was essential: “At room temperature, the random thermal motion of the atoms in a bar is 300 times as big as the displacement we’re trying to detect. The only way to approach the sensitivities we’re after is to get rid of that thermal noise by cooling the bar.”
Superconductivity is also the key to one of the most perplexing of all engineering problems: designing a transducer capable of sensing the tiny displacements of these antennas and converting them to a useful voltage that can be amplified and measured. “You can’t buy such things,” says David Douglass, “you have to make them, and go beyond the state of the art.
Of course, laser interferometers have engineering problems, too, problems that become exacerbated as they grow larger. The laser beams must travel through vacuum pipes, and isolating pipes a kilometer long will not be simple. But Drever is convinced it can be done. “Maybe we’ll put it in a mine, or in the desert,” he says. This device may be ready by 1986, and has, Drever thinks, a chance of eventually detecting supernovas in the Virgo cluster.
A gravity-wave experiment had been planned for the International Solar Polar Mission. But, according to MIT’s Irwin Shapiro, who chaired the Committee on Gravitational Physics of the National Academy of Science’s Space Science Board, the experiment was dropped by NASA because of budget cuts. Einstein’s theory of general relativity predicts that this binary system should produce a considerable quantity of gravity waves, and that the energy radiated should be slowly extracted from the orbit of the system, gradually decreasing its period as the superdense stars spiral closer to one another. Einstein’s equations predict a decrease of one ten-thousandth of a second per year for a pulsar like PSR 1913+ 16.
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