Caltech, MIT Join in Project : Test of Einstein’s Theory on Gravity Waves Planned
In his general theory of relativity, Albert Einstein postulated that many major celestial events, such as exploding stars, should flood the universe with gravity waves, causing objects trillions of miles away to move ever so slightly.
Recognizing that Einstein had come up with yet another idea that could tell much about the dynamics of some of the universe’s most cataclysmic events, scientists around the world have spent the last few decades trying to prove that he was right.
As other elements in his astounding theories have been slowly confirmed, scientists have grown to believe that Einstein had to be right about gravity waves as well.
But all these years later, no one has been able to prove it.
Now, scientists at Caltech and the Massachusetts Institute of Technology, united in a shotgun marriage arranged by the National Science Foundation, plan to build two giant facilities to see if the great man was correct. If they are successful, they will open an entirely “new dimension” in astronomical research, according to Rochus (Robby) Vogt, former Caltech provost who is in charge of the project, which could cost as much as $150 million.
Gravity waves are not the same as the force of gravity that causes objects to attract each other. Instead, they are a very weak form of radiation beyond the range of the electromagnetic spectrum normally used in astronomy. The effort to prove that they exist, and thus open a new window on the universe, is extraordinarily challenging.
To succeed, the scientists will have to be able to measure movement so slight that it is almost unthinkable. A scale model of the two instruments that will be required for the project has been operating at Caltech for several years, and it is so sensitive that “it registers when a fly walks over it,” Vogt said.
The prototype, consisting of two tubes 130 feet long laid out in the shape of an L, is the largest gravity wave detector in the world and it can measure movement one-millionth the diameter of an atom.
‘Not Good Enough’
“But that’s not good enough,” Vogt said.
It, like other experimental detectors, has never detected a single gravity wave since it began operations in 1980. So Vogt and his colleagues hope to achieve sensitivities 100 times that great with two mammoth devices that will have tubes more than 2 1/2 miles long with suspended weights that the scientists hope will move either closer together or farther apart by a force that is so weak it defies imagination.
The idea behind the project is that a laser beam, bouncing back and forth between the suspended weights, will be thrown slightly out of phase in one tube compared to the other because the weights will move differently depending on the direction from which the wave enters the apparatus.
The concept is crudely analogous to two surfers riding a wave across an irregular shoreline. If rocks below the surface retard the wave beneath one of the surfers, the two will arrive on the beach at slightly different times because the crest of part of the wave will trail the other. In other words, the surfers will be out of phase.
The difference in the time of arrival of the two surfers would tell something about the nature of the obstruction.
Called Interferometry
That technique, called interferometry, has been used for years in radio astronomy to sharpen radio-wave images.
But applying that concept to the gravity wave search will take interferometry to new frontiers.
“Physics is the art of measurement,” Vogt said. “That’s what physics is all about. But this is the kind of thing that’s almost scary.”
To succeed, the scientists will have to break new ground in a number of fields.
But some of the best minds in physics, in this country as well as Japan and Europe, believe that it can be done even though all past efforts have failed.
‘It’s the Right Time’
“It’s the right time to do it,” said Ronald Drever, the wizard who is chiefly responsible for Caltech’s prototype, which has convinced others that the incredible levels of control needed for a machine 100 times larger are at least theoretically possible. It has taken a long time to reach this point, and Drever is clearly ready to seize the moment.
“It’s going to happen sometime,” he said recently. “One mustn’t die before then.”
It has also pitted two great institutions in a battle that has left scars and bitterness on both sides. MIT and Caltech have both been working in the field, each competing for funds from the National Science Foundation.
And although $150 million may not sound like much compared to projects funded by other agencies--like the $6 billion-plus for the super collider envisioned by the Department of Energy--it is a lot for the NSF, which has a total annual budget of only $1.5 billion.
The NSF had been financing research at both institutions at about $1 million a year, but a few years ago NSF officials grew uneasy with paying for competing projects. About four years ago, in what Vogt has described as a “shotgun” marriage, the NSF decided to finance one project involving both institutions, with Caltech in the lead role.
Asked to Head Project
Meanwhile, Vogt had grown disenchanted with his administrative role at Caltech, and in the summer of 1987 he handed in his resignation as provost of the Pasadena campus. Coincidentally, that same day Vogt’s colleagues at Caltech asked him to take the job of running the project.
“I think if I succeed here, I’m going to change the face of science,” he said.
Vogt’s excitement goes far beyond the challenge of simply being the first to prove the existence of gravity waves, which he said should be good enough to win a Nobel prize for Drever and Rainer Weiss, Drever’s counterpart at MIT. The excitement grows more out of the basis for Einstein’s prediction.
In his general theory of relativity, which is an extention of his earlier special theory of relativity, Einstein postulated that certain asymmetrical events would transmit gravity waves that should reveal much about the dynamics of those events. Gravity waves, he suggested, would be emitted whenever a star exploded and collapsed in an irregular form.
Because of its irregularity, Einstein said, that event would create a disturbance in the distribution of matter in the universe. That disturbance, he concluded, should release energy that would propagate through space at the speed of light in the form of gravity waves. Those waves, in turn, should distort the shape of any region of space through which they pass.
The waves should result whenever matter is redistributed, usually in a violent, sudden event. But the waves are so weak that a 500-ton steel bar rotating so fast that it is almost torn apart would generate gravitational waves far too small to be detected.
But the concept is exciting to space physicists because it could help decipher such things as the supernova that exploded in the Large Magellanic Cloud in 1987 and that was largely hidden from view by the gas and dust resulting from the explosion.
Gravity waves should begin deep within the object as the mass is redistributed, and travel through the envelope around the star. If they can be detected and analyzed on Earth, they should tell much about the earliest moments of the event when the most dynamic processes were shielded from view by debris from the explosion.
The same would hold true for rapidly spinning binary systems--two stars that orbit around their center of mass--because such systems are constantly redistributing their mass as they rotate around each other. About half the stars in the universe are members of binary systems.
Gravity waves from such events should cause objects to deform slightly as the waves pass through them. The waves should cause weights suspended in one tube to expand in one direction and contract in the other, somewhat like squeezing a basketball into the shape of a football and pointing it first in one direction, and then in another. If a second tube is placed perpendicular to the first, similar distortions should occur there but in opposite phase to the weights in the first tube.
Shorter Travel Distance
Thus, light traveling between the weights in one tube will have a shorter distance to travel than light in the second tube, “and that gives you a phase shift,” Vogt said.
But there is a catch. Gravity waves would be dampened and deflected by the medium through which they travel, so to be accurate the space between the weights must be nearly a perfect vacuum.
Each tube, measuring 4 feet in diameter and more than 2 1/2 miles long, must be maintained in a vacuum that is better than anyone else has been able to achieve anywhere on Earth on that large of a scale.
“When you have gas in there--like when you drive down the highway in the summer and the road flickers--the air is turbulent, and that gives you a phase shift, which simulates a gravity wave,” Vogt said. “So the only way to eliminate it is to remove enough air out of the beam tube that the fluctuations don’t matter.”
Vogt said the vacuum in the beam tubes will have to be 1,000 times purer than the vacuum tubes used in fusion research at Lawrence Livermore Laboratory.
When he told scientists at Livermore of the levels he would have to achieve, “they said you can’t do it,” Vogt said.
Would Ruin Vacuum
At that level, molecules of hydrogen break out of steel, “and that would ruin our vacuum,” he added.
So an effort is under way to develop steel that is as free as possible of the hydrogen that normally becomes trapped in the manufacturing process.
In addition, such things as tiny earthquakes and a pounding surf would be recorded by the system as gravity waves, so Vogt wants to build two separate facilities many miles apart. One would likely be at Edwards Air Force Base in the Mojave Desert, and the other would be in a completely different geological setting to separate the two from any local disturbances, possibly even on the East Coast. That way the results of one part of the “Laser Interferometer Gravitational Wave Observatory” could be compared with the other for confirmation.
That, of course, adds substantially to the cost of the project, causing some scientists to question it.
Richard Garwin, an IBM physicist who is best known for his blistering criticism of the Strategic Defense Initiative (“Star Wars”), was an early pioneer in gravity wave research and built one detector that proved that earlier detections were in error.
Might Be Premature
But he fears that building an expensive observatory at this time might be premature.
At the request of the National Science Foundation, Garwin participated in a study of the proposal in 1986. Although the study resulted in a report that endorsed the idea, Garwin remains personally skeptical.
It may be, he suggested in an interview, that gravity waves are just too weak to be detected with present technology, and that would make the effort “a waste of money.” “The likelihood (of success) is not sufficiently high to justify doing that right now. My recommendation is that people continue to get money to improve the technology, so that when we do build something we will have something that will run.”
Vogt, however, believes that time has come. Japan and Europe are also leaning in that direction with proposals for large gravity wave detectors in each of those areas.
International cooperation is essential if the program is to succeed. Two gravity wave detectors would tell which direction any waves came from, three would narrow the region down to two points in the sky, and a fourth would pinpoint the position of the source.
Essential for Astronomers
That is essential for other astronomers to point their instruments at the source for a multidisciplined study.
The NSF has allocated $10 million to plan and design the detectors, and Vogt expects financing for construction of the facilities in this country in about two years.
That, he said, would give scientists a chance to study the universe “with something which is radically different,” he said.
“It’s a new dimension.”
TESTING FOR CHANGES IN GRAVITATIONAL WAVES Caltech and MIT plan to build a device that would detect gravity waves predicted by Einstein but never proved. The device, which would be one of the most sensitive instruments ever built, would detect a tiny change in the distance between weights suspended in two steel tubes, each 2.6 miles long. Such a change caused by gravity waves would be measured by laser beams. Because seismic activity would also cause such a change, the institutions want to build two devices, one in the East as well as at Edwards Air Force Base.
