The Perfect Theory (25 page)

Hermann Bondi made the most compelling case for gravitational waves at the Chapel Hill meeting in 1957. Bondi, then leading a relativity group at King's College London, presented a simple thought experiment: Take a rod and thread it through two rings a small distance apart from each other. Tighten the rings ever so slightly so that they can still move but rub against the rod. If a gravitational wave passes through, it will barely affect the rod itself. The rod will be too stiff to sense anything much. But the rings will be dragged up and down on the rod, like buoys in the sea being tossed about by the waves. They will move back and forth, coming close and moving apart as the wave flies through, and in doing so they will rub against the rod and heat it up, giving it energy. Given that the only place the energy could come from is the gravitational waves, the waves must carry energy. Bondi's argument was simple and effective. Richard Feynman, who was also attending the meeting, presented a similar line of reasoning, and the majority of the participants were convinced. Gravitational waves were out there, ready to be discovered. Joe Weber had been at Chapel Hill, mesmerized by the discussions. Bondi, Feynman, and all the other participants could sit around discussing the reality of gravitational waves, but he would actually go out and look for them.

Weber was just the sort of person who would attempt the impossible. An obsessive tinkerer, he had learned to fix radios to make money as teenager. An artistic visionary, constantly pushing technology beyond what was thought feasible, he would design and build experiments with the barest resources and then use them to probe the outer edges of the physical world. His drive infected all aspects of his life; he ran three miles every morning and worked a full day until he was in his late seventies.

Weber had trained at the United States Naval Academy as an electrical engineer and commanded a ship during the Second World War. Because of his expertise in electronics and radio he was asked to lead the navy's electronic countermeasures program. When he came out of the war, he became a professor of electrical engineering at the University of Maryland, where he decided to switch fields, studying for a PhD in physics.

In the mid-1950s, Weber became interested in gravity. John Wheeler had stepped in and encouraged Weber to take the plunge, bringing him to Europe for a year to think about the new frontier of general relativity. When Weber returned, he was ready to start designing and building an instrument. As he gradually immersed himself in the task of recording gravitational waves, he sketched out various possibilities, filling up notebooks with designs for contraptions. One method particularly took his fancy. The idea was simple: Build big, heavy cylinders of aluminum and suspend them from the ceiling. Strapped around the belly of each cylinder would be a set of incredibly sensitive detectors that would send an electrical pulse to a recorder if the cylinder vibrated. Anything could set it off—a phone ringing, a car trundling by, a slamming door. So Weber had to isolate the cylinders as much as possible, eliminating all possible sources of tremors and jerks.

When Weber finally turned on his cylinders, or Weber bars as they became known, he immediately began to pick up tremors. The bars vibrated, and once all the known disturbances had been eliminated, a few were left over: little blips of what just might be gravitational radiation. There was something odd about the blips, though. If they were truly gravitational radiation, they must have come from such an explosive event that it would have been observed through telescopes. The signal was too strong to be gravitational radiation. Weber had to improve his kit.

To be absolutely sure that any tremor in the cylinders came from a gravitational wave passing through, Weber placed one of his four bars at the Argonne National Laboratory, almost a thousand kilometers away from his laboratory at the University of Maryland. If cylinders at
both
places trembled at the same time, it would be a strong sign that they were being sprayed by gravitational waves coming from outer space. Weber would compare the readings of the detectors on each one of his bars. If a reading shot up on more than one bar
at the same time,
it would be more likely that the source of the disturbance was the same external thing—a gravitational wave—that had shaken both of the bars, and not just some randomly coordinated jiggle in each of the bars themselves. He would look for these “coincidences,” as he called them. Once again, Weber turned on his machine and waited.

By 1969, after working on his experiment for over a decade, Weber had something to show the world: a handful of coincident tremors not only between the ANL and the University of Maryland cylinders but between all
four
of his cylinders. It was too much of a coincidence to be random. They must have been sensing something in unison. There were no earthquakes, nor was there any strange electromagnetic storm to which he could attribute the phenomenon. Weber appeared to have discovered gravitational waves.

Over the next few years, Joseph Weber perfected his experiment, making sure that he was not simply finding what he wanted to find. The tremors in the bars were few and far between and were buried in the noise of the experiment. The bars would jiggle simply because of their own heat, as the atoms and molecules within them vibrated back and forth, and if you weren't careful, your eyes would pick up patterns where there were none. To get around this, Weber developed a computer program that would pick out the tremors and identify the coincidences automatically. He also decided to introduce a slight delay in recording the signal of one of the cylinders and then compare it with the other cylinders. If the coincidence were indeed true, the signal from one cylinder would arrive at the other time-delayed cylinder
after
the coincidence had actually happened—the number of coincidences would have to go down when comparing the records of the two cylinders. And, indeed, the number of coincidences fell.

By 1970, Weber had been running his experiment long enough that he was able to pinpoint the direction of the gravitational radiation that his instrument was picking up. It seemed to be emanating from the center of the galaxy, which he saw as a good thing. As he wrote in his paper,
“A good feature is the fact that [10 billion] solar masses are there and it is reasonable to find the source to be the region of the sky containing most of the mass of the galaxy.”

As Weber became more convinced that he was actually detecting gravitational waves with his experiment, the rest of the world began paying attention. His discovery had caught everyone by surprise. Such a straightforward detection of gravitational waves was unexpected, yet there was no reason, a priori, to doubt his findings. Weber's results were being brought up repeatedly by the relativists as they tried to figure out what they meant. Roger Penrose calculated what would happen if two gravitational waves collided with each other—could the final result be so explosive that it would trigger Weber's machine? Stephen Hawking worked out his own thought experiment of throwing black holes at each other, hoping that they would send out a burst of gravitational radiation that could explain Weber's detection. And throughout those early years, Weber's fame continued to spread. He was interviewed for
Time
magazine, and his work was featured in the
New York Times
and countless other newspapers in the United States and Europe. The results kept on pouring in.

 

Weber's results were amazing, and they seemed almost too good to be true. Weber appeared to have found an unbelievable source of gravitational radiation, far bigger than anyone had ever thought possible. For however sophisticated Weber's bars were and however refined the detectors he had glued to them, they weren't
that
sensitive. To actually get a detectable tremble, Weber's bars would have to be shaken by incredibly powerful gravitational waves, real behemoths traveling toward the Earth.

That was a problem, for even though the presumed gravitational waves came from the center of the galaxy, where there was a lot of stuff ready to implode, collide, and stir up spacetime, that was over twenty thousand light-years away from Earth. If indeed there was a beacon of gravitational waves lurking at the heart of the Milky Way, the waves it emitted would have been diluted in the intervening space into almost nothing by the time they reached the Earth. In fact, as Weber pointed out, the amount of energy in the gravitational waves he was detecting was equivalent to a thousand stars the size of the sun being destroyed at the center of the galaxy each year, a truly colossal amount.

Martin Rees at Cambridge was skeptical of Weber's results from the beginning. With his former PhD adviser, Dennis Sciama, and George Field from Harvard University, Rees worked out how much energy could be flooding out of the center of the galaxy in the form of gravitational waves. Rees and his collaborators found that, at most, two hundred stars the size of the sun could be destroyed each year to give rise to the gravitational waves. Any more than that, and the galaxy would have to be inflating, which they could verify was not the case by looking at the motion of nearby stars. Their calculation was approximate, so they were careful about their conclusions. In their paper they claimed,
“Since the high rate of mass loss indicated by Weber's experiments is not ruled out by direct astronomical considerations discussed here, it would be clearly desirable for these experiments to be repeated by other workers.” Weber was undaunted, for it was a
theoretical
argument that Rees, Field, and Sciama were putting forward. Maybe the theory was wrong, but his experiments were definitely right.

Following Weber's lead, in Moscow, Glasgow, Munich, Bell Labs, Stanford, and Tokyo new sets of experiments were being built. Some were exact copies of Weber's, and all of them were in one way or another inspired by Weber's original raft of designs. As they were gradually switched on, results started to trickle in, and a common pattern began to emerge; apart from a few events in the detector at Munich, none of them seemed to find the copious amounts of coincidences that Weber was finding with his apparatus. They simply weren't there. Weber was unfazed. He had a ten-year head start thinking about these experiments, and it was clear to him that all the other experiments were much less sensitive than his, so there was no surprise that there was no signal. If they wanted to criticize his results, they should build a detector
exactly
like the one he had built, a “carbon copy.” Then they could talk. Several of the experimenters, including those in Glasgow and at Bell Labs in Holmdel, rebutted that the experiments they had built
were
carbon copies, and they still weren't seeing anything like what Weber was finding. Again Weber had an excuse: their copies simply weren't good enough.

But there was something troubling about Weber's own experiment. For a start, his bars weren't necessarily more sensitive than all the others. In such a nascent field, it wasn't yet clear how to determine the sensitivity of the experiments. But more worrying was the fact that Weber was prone to making mistakes but
still
found coincidences. For a start, he had claimed that the gravitational waves he was measuring came from the center of the galaxy. He concluded this by realizing that the tremors were mostly happening in clusters of events every twenty-four hours, when the bars were oriented toward the center of the galaxy. But Weber had missed an important point: gravitational waves would have no problem passing
through
Earth. So if the bars were aligned with the center of the galaxy but on the opposite side of the Earth, he should expect to find the same amount of coincidences. The clusters should happen every twelve hours, not every twenty-four hours as Weber had found. When Weber realized he had made a mistake, he went away and reanalyzed the data to find that, indeed, there was a twelve-hour cycle of coincidence that he hadn't picked up in his initial analysis. He seemed to find what he wanted to, once he knew what he was looking for. Bernard Schutz, a young relativist at the time, recalls that
“people were very suspicious. He wasn't releasing his data so we could all have a look at it, yet he seemed to find whatever he wanted.”

An even more glaring problem came up when Weber joined forces with another experimental team at the University of Rochester. As with his own cylinders, when Weber compared the tremors from the Maryland cylinders with the Rochester ones, he found a bundle of coincidences, vibrations that seemed to happen at exactly the same time in both places, a sure sign of gravitational waves. It turns out that Weber had misunderstood the way that the Rochester team had logged the time of each event, and the coincidences that Weber found in fact occurred with a four-hour time difference. Once the time delay was corrected, Weber analyzed the data again, and, again, he found coincidences.

Weber's discovery seemed to be impervious to mistakes and miscalculations. He could find coincidences anywhere. And coincidences meant gravitational waves. Weber's unwavering ability to bypass errors had a devastating impact on his reputation. He wasn't helped by the fact that no one else could reproduce his results. One respected experimentalist, Richard Garwin, wrote an article in
Physics Today
with the title “Detection of Gravity Waves Challenged” that systematically tore apart Weber's own data analysis and experiment, stating categorically that Weber's coincidences
“
did
not
result from gravity waves and furthermore
could not
have resulted from gravity waves.” The community of relativists, en masse, turned their backs on Weber. Though he had once produced a stream of high-profile papers, Weber's publication rate plummeted. His funding dried up as more and more of his colleagues refused to support his prolific experiments. By the late 1970s, Weber had been cast out from the physics establishment.

 

Weber's experiments may have been discredited, but his results had set something much, much greater into motion. A new field was born out of the turmoil. Astronomers had realized that instead of capturing electromagnetic waves, such as light waves, radio waves, or x-rays, they could use gravitational waves as a new way of looking at the universe. Better, they could see
with
gravitational waves and look at things out in the farther recesses of spacetime that they couldn't see when they used conventional telescopes. Optical, radio, and x-ray astronomy would be joined by gravitational wave astronomy.