Monday, April 5, 2004
Stanford ready to give Einstein big exam/Satellite experiment will test
whether General Theory of Relativity is correct
David Perlman, Chronicle Science Editor
After 40 years of effort, frustrating delays and budget battles between
NASA and Congress, Stanford scientists are finally ready to test whether
Albert Einstein got it right when he published his General Theory of
At stake in the Stanford experiment are many of the concepts that
modern theoretical physics. If the revered German-born scientist was
indeed right about space, time and gravity, then scientists can breathe a
sigh of relief and go on with their many discoveries about the
But if the experiment -- to be carried into space April 17 aboard a
high-precision satellite dubbed Gravity Probe-B -- reveals errors in
Einstein's theory, then many basic assumptions by today's physicists and
cosmologists about the state of the universe will be called into question.
At a NASA press briefing in Washington last week, the two Stanford
researchers who have worked on the experiment for virtually their entire
careers -- Francis Everitt and Bradford W. Parkinson -- described the
intricacies of their $700 million satellite project."It's hard to imagine
a simpler experiment ... yet we are hoping it will prove to be very
exciting," said Everitt, the project's principal investigator.
The guts of the three-ton Gravity Probe B satellite are four
of fused quartz, pure to within two parts per million and coated thinly
with the element niobium. Each is the size of a ping-pong ball and,
according to the scientists, each is the most perfectly rounded object
ever fabricated. The balls are actually gyroscopes, each cooled and
by jets of liquid helium at a temperature of 450 degrees below zero. They
can spin as fast as 10,000 revolutions per minute with total regularity
and total precision virtually forever, assuming they weren't disturbed by
some outside force.
The helium and the gyroscopes are carried aloft in an insulated
container known as a Dewar. The entire payload is contained in a vacuum
chamber where the pressure is ten times lower than the empty space where
the satellite will fly.
For the experiment, a small telescope aboard the satellite will aim
directly at a distant "guide star" known as IM Pegasi. The four spinning
gyroscopes will be aligned through the telescope with that same star for
the full 16 months that the satellite will be in orbit some 400 miles
above the earth.
The entire spacecraft was built, integrated and tested by engineers at
Lockheed Martin's Sunnyvale Space Systems factory.
In Einstein's theory, the mass of objects in space -- from fleas to
holes -- warps both space and time around the objects, or "spacetime," as
physicists perceive it. That warped spacetime causes all objects moving in
the vicinity of a more massive object to fall inward, as if they were
rolling down the slopes of a stretched-out fish net toward the most
massive object in the net's center. The Stanford experimenters call that
warping of spacetime the "geodetic effect."
Also in Einstein's theory, the very spinning of an object -- the way
spins on its axis -- would also drag spacetime the way a twirling apple
inside a bowl of syrup would drag the syrup around and around it.
To physicists, this effect is called "frame-dragging," and it too is a
consequence of Einstein's theory. The frame-dragging concept, in fact, was
proposed by Austrian physicists only two years after Einstein published
his first General Relativity paper. To determine whether both
frame-dragging and the geodetic effect are real, the four perfectly
symmetrical gyroscopes spinning aboard the Gravity Probe satellite should
slowly point away from the guide star by an infinitely tiny degree because
of the warping and dragging effects of our own spinning Earth on
The tiny movement of the gyroscopes would be so barely perceptible that
only the most sensitive instruments aboard the satellite would detect it.
That movement is measured in milli-arcseconds per year -- a predicted
6,614.4 milli-arcseconds a year if the geodetic effect is real, and 40.9
milli- arcseconds a year for frame dragging.
Those are mighty small shifts in direction. For example, the scientists
say, if you climbed a slope at an angle of 40.9 milli-arcseconds for a
hundred miles, you would rise only a single inch in altitude.
But that's the kind of measurements that Everitt and Parkinson will be
seeking during their satellite's 18 months in orbit. And if indeed the
geodetic and frame dragging effects on the gyroscopes fulfill their
predictions, then they will have proven Einstein's theory right.
And if not? Then it's back to the drawing boards and computers for all
world's theorists as they seek a new definition for what's known as the
Standard Model of the universe.
"This is all terribly important," said Kip Thorne, a California
of Technology cosmologist, on Friday. "It will enable us finally to
understand much of what's happening in the universe, like black holes and
neutron stars. And if General Relativity fails, it will have a tremendous
effect on all of cosmology and all of our studies of the universe
Whether or not more ordinary folks would care about validating
theory was a question that Everitt answered easily.
"I believe we should not underestimate the curiosity and alertness of
ordinary Americans," he said. "I was talking about life not long ago with
a policeman from Chico, and when I told him what I was doing and why, he
quickly got totally fascinated. So we shouldn't assume that people don't
have genuine curiosity about the universe we all live in."
A question ensued about the utility of validating Einstein, and here too
Everitt had a reply.
He recalled the fundamental equations of James Clark Maxwell in 1864
linked electricity and magnetism in a theory largely ignored at the time.
Yet, as both Everitt and Parkinson underscored, 40 to 50 years later those
equations proved fundamental to the electrification of the world, to
world- wide radio transmission, and to virtually all of modern
The idea of testing Einstein's theory came to the late Stanford
Leonard Schiff in 1960, and three years later the concept for Gravity
Probe B began developing.
NASA has funded the project for 40 years, despite its on-again-off-again
budgets, and Congress weighed in more than once to question the value of
the experiment. In recent years the project and the launch date have been
delayed by technical and budget problems eight times.
But finally, on April 17, at Vandenberg Air Force Base in Santa Barbara
County, the Gravity Probe B satellite will be launched, and after 40 to 60
days of checkout, tests and start-up in space, the Stanford experiment
E-mail David Perlman at firstname.lastname@example.org.