Skip to comments.After 45 Years (and $700 Million), a Gravity Experiment Takes Flight
Posted on 04/13/2004 10:00:41 PM PDT by neverdem
Even its critics admit that it was a great idea in 1959.
It was then that three Stanford scientists, dangling their legs in a university swimming pool, agreed to team up on an ambitious effort to peer deep into the heart of the strangeness that is Albert Einstein's legacy.
Now 45 years and $700 million later, their dream has materialized as a van-size assemblage of plumbing, electronics and quartz, known unpoetically as Gravity Probe B, sitting atop a rocket at Vandenberg Air Force Base in California. It is to be launched into orbit next Monday on an 18-month mission.
When it goes up, the gravity probe will take with it the hearts of generations of scientists and engineers at Stanford and Lockheed Martin. Over the years, nearly 100 Ph.D.'s have been awarded at Stanford and elsewhere for work on the project. In pursuit of their goal, the engineers have built the roundest balls ever made and the largest thermos bottle ever to have been flown in space.
Beset by technical problems, glitches, ambitious goals, politics and management failures, the gravity probe has also been canceled again and again. How many times depends on "what you mean by canceled," said Dr. C. W. Francis Everitt, a Stanford physicist who joined the project in 1962 and is now its leader. "Seven is a good number," he added.
The experiment is organized to test one of the most esoteric predictions of Einstein's theory of gravity, the general theory of relativity, which predicted the expansion of the universe and the existence of light-swallowing black holes. The probe contains four gyroscopes to measure whether and how the spinning Earth twists space-time around itself like leaves in a tornado.
The answers, say Dr. Everitt, his colleagues and the National Aeronautics and Space Administration, will give physicists precise measurements on ways that matter warps space-time to produce the effect called gravity, allow them to calibrate the black hole dynamos that produce the monstrous energies of quasars, and perhaps find evidence of new forces in the universe.
"If it performs as well as we think, it will end up testing Einstein's theory 10 to 100 times better than any previous test," Dr. Everitt said.
Dr. Brad Parkinson, a Stanford engineer who is a project co-leader, called it "a testimony of perseverance at the least," in a recent NASA news conference.
But as the Stanford team heads for the finish line, other scientists say the ribbon has long been cut. Barring a surprise, they say, no new physics will come out of the gyroscope experiment. Increasingly precise observations of satellites, the Moon, planets and other bodies over the decades have already concluded that general relativity is correct, at least to the limits of the Stanford experiment's expected precision.
Dr. Kenneth Nordtvedt, a retired physics professor and relativity expert at Montana State University, said of the experiment: "When it was conceived, it could have added to our knowledge of gravity.
"Time passed it by."
Still, Dr. Kip Thorne, a physicist at the California Institute of Technology who is not part of the team, said that although there was no compelling reason to expect the probe's results to deviate from relativity, it was important to make a direct measurement that was free of astronomical uncertainties or theoretical frameworks.
If general relativity fails as most theorists believe it ultimately must it is likely to fail in some surprising way, he said.
Any deviation from general relativity would be "a profound result," Dr. Thorne said. But even if it agrees, he said, the measurement will be a landmark, in the books for years, "a significant legacy for future generations."
In for the Long Haul
The inspiration for the gravity experiment goes back to the 19th century and the Austrian physicist and philosopher Ernst Mach. He declared that all motion was relative, and speculated that therefore the inertia of any given object in the universe was somehow determined by its relation to everything else in the universe.
Einstein was taken by what he called Mach's principle, and it was part of the inspiration for general relativity. That theory described space-time as a kind of sagging mattress where matter and energy, like a heavy sleeper, cause planets, falling apples and beams of light to follow curved paths instead of straight ones.
But in a Machian twist that pleased Einstein, it seemed that rotating matter could not only make space sag but also cause it to spin. Just as stirring a thick milkshake with a spoon will cause the cup holding the drink to turn, a massive rotating object will slowly drag space-time around with it, according to calculations by Josef Lense and Hans Thirring, Austrian physicists, in 1918. That means that if you were orbiting, say, Earth, you would feel no force and think you were at rest, but you would find yourself spinning slowly with respect to the distant stars.
The effect, called frame dragging, is so tiny near Earth that for decades physicists despaired of being able to test it. In a year the twist would be about one hundred-thousandth of a degree about the thickness of a human hair as seen from a quarter of a mile away.
But in 1959, Dr. Leonard Schiff of Stanford (and independently Dr. George Pugh of the Defense Department), suggested that gyroscopes in space could do the trick. Shortly afterward, at the swimming pool, Dr. Schiff and Dr. William Fairbank, also of Stanford, recruited a colleague, Dr. Robert Cannon, an aeronautics professor who was also a gyroscope expert. They were joined in 1962 by Dr. Everitt, a young British postdoctor.
In 1964 NASA gave the Stanford group a contract to study the idea. While Stanford built the gyroscopes, Lockheed Martin constructed the spacecraft that would carry them. As the probe progressed, NASA sent men to the Moon and landed probes on Mars. The Vietnam War started and ended. The World Trade Center rose and fell. Gravity Probe A, which showed how gravity affects the rate of clock, flew in 1976.
Dr. Schiff died in 1971; Dr. Fairbank, in 1989. After stints as an assistant secretary of transportation and at Caltech, Dr. Cannon returned to Stanford in 1979. Dr. Everitt, born in England, is now 69. His long hair is gray. He admits that he didn't know what he was getting into when he joined Stanford and the gyroscope team at age 28.
"I knew I was getting into something that might waste two or three years and get nowhere," he recalled. But he was young. "It's good to spend a couple years on a far-out idea and then move on," he said.
Gyros and Squids
By all accounts the experiment now at Vandenberg is a technical tour de force. At its heart, isolated as much as possible from the universe, are the gyroscopes: four quartz spheres slightly larger than golf balls. They are said to be the most perfectly spherical objects ever made by humans out of round by only 40 layers of atoms. If the Earth were this perfect, the tallest mountain would rise just six and a half feet.
In space, they will be suspended by electrical fields and spin at 10,000 revolutions per minute inside a quartz telescope trained assiduously at the star IM Pegasi.
To make sure that no outside influence imparts a stray wobble to the spinning balls, the telescope floats freely inside an external spacecraft equipped with jets to sense and counter any drag from stray wisps of atmosphere. It is also surrounded by a superconducting lead bag that shields it from magnetic fields. And the whole assembly is cooled by liquid helium to less than 2 degrees above absolute zero, or about minus 456 degrees Fahrenheit.
But that's only the beginning. After having isolated the gyroscopes from the rest of the universe and aligned them with IM Pegasi, the scientists have to monitor which way they are spinning.
To this end, the quartz balls are coated with niobium, which loses all resistance to electrical current at these temperatures. As a result, when the balls rotate, some of the electrons in the niobium slip behind their atoms. Their relative motion creates a small current that generates a tiny magnetic field, located by detectors known as squids superconducting quantum interference devices built into the gyroscope.
The squids have two missions. One is to measure the frame dragging, which would cause the gyros to turn in the direction of the Earth's rotation. The other is to measure a parameter called gamma, or how much matter causes the geometry of space to deviate from the "flat" Euclidean geometry familiar from high school. Because the Earth makes space-time sag, a circular orbit around the Earth should turn out to have a circumference ever so slightly less than pi times the orbit's diameter.
This "missing inch," as Dr. Everitt calls it, should cause the gyros to turn in a direction perpendicular to the Earth's rotational axis. Some physicists regard gamma as a more interesting measurement than frame dragging, because many of their more exotic speculations, like hidden extra dimensions and undiscovered forces permeating space, could cause its value to deviate from the Einsteinian prediction of exactly 1.0.
Up and Away, at Last
The gravity probe's technological legacy is already secure. Many of its advances have been incorporated into other projects. Its scheme for cooling by liquid helium, for example, was used on the Iras infrared astronomy satellite back in 1983.
But its scientific legacy is less clear.
Although frame dragging has not been detected directly, astronomers say it has been measured indirectly. Last year a group of Italian physicists claimed to have measured it within a margin of error of about 20 percent by analyzing data from the two Lageos satellites, spherical objects pocked with reflectors that were launched to serve as sort of geodetic markers in the sky. More satellites in coming years could reduce the margin of error to 1 percent, the precision that Gravity Probe B is aimed at.
Meanwhile, last September, astronomers claimed that they had measured the parameter gamma by timing radio signals on their way to Earth from the Cassini spacecraft, which is approaching Saturn. The signals were delayed as they passed the Sun, dipping into its gravitational warp. The scientists found that gamma was equal to the Einsteinian value of 1.0 to a precision of about one part in 40,000.
That is better than the designed precision of the gravity probe, said Dr. Nordtvedt, though Dr. Everitt replied in an interview that final tests indicated that the experiment could exceed that level.
Dr. Nordtvedt said that Dr. Everitt was a good friend and that he would be at the launching on Monday. Nevertheless, he said, "I'm critical of the fact that the program has been allowed to drag on for 40 years and to consume so much money."
Such doubts came to a climax a year ago when the spacecraft failed an important test, portending yet another postponement and more expense. NASA convened panels of engineers and physicists to determine whether to go on with the mission.
The panelists concluded that there had indeed been "erosion" in the gravity probe's mission, particularly in regard to the measurement of gamma. Nevertheless, they wrote, Gravity Probe B "is still a precedent-breaking mission for the space program in that it will perform a precision physics experiment in space."
In November, a month before the probe was to be launched, electrical problems sent it back to the clean room for four months. After all that time and money, NASA was playing it safe.
Dr. Michael Turner, a cosmologist at the University of Chicago and chairman of the review panel, said, "I think all of us Francis included just want to see this remarkable experiment in space get done."
Dr. Everitt agreed. "We could have done it better and quicker, but not enormously quicker," he said, adding:
"The medieval cathedral builders took longer."
Or at least 18 months? :)
Or hyperspace (i.e. faster than light travel). More likely IMHO. While both are supposedly theoretically possible, FTL doesn't open nearly the can of worms that time travel does. Both also beg the question that if FTL travel or time travel is possible, where are all the travels from distant stars or the future?
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