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NASA Probe Proves Einstein Right

Research leads to groundbreaking technologies

Artist concept of Gravity Probe B orbiting the Earth to measure space-time, a four-dimensional description of the universe including height, width, length, and time.
Artist concept of Gravity Probe B orbiting the Earth to measure space-time, a four-dimensional description of the universe including height, width, length, and time.

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Rosanne Skirble

Albert Einstein was right. The U.S. Space Agency (NASA) released data this week from its Gravity Probe B spacecraft, whose primary mission while in Earth's orbit was to test Einstein’s 1916 Theory of Relativity. While the experiment evolved over decades, the results confirm Einstein’s work on the physical laws of the universe.

A Stanford University scientist first proposed an experiment to test Einstein’s theory in 1959 by rotating gyroscopes in space. Beset by launch delays, budget woes, faulty data and several federal investigations, Gravity Probe B was finally approved and was launched in 1984. The onboard experiment tested two of Einstein’s theories.

The first, explains lead investigator and Stanford University professor Francis Everitt, is the "geodetic effect." "In Einstein’s universe, space and time are warped by gravity. And what happens is the earth distorts the space around it very slightly by its gravity. And it’s 1.1 inches in 25,000 miles (2.75 centimeters in 40,000 kilometers). So it’s a rather modest distortion."

Gravity Probe B prior to launch in 2004
Gravity Probe B prior to launch in 2004
The second of Einstein’s theories that was put to the test is "frame dragging," which is the tendency of a spinning object to pull the fabric of space and time with it as it rotates, a phenomenon Everitt likens to the Earth immersed in a sea of honey.

"You can imagine that the honey would be dragged around with it, hence your pointer in the honey would be dragged around and that’s what happens to a gyroscope.So the earth actually drags space and time around with it."

Gravity Probe B housed several state-of-the-art technologies that did not exist when the Stanford group first conceived their gravity experiments. Among them, Everitt says, were four precision gyroscopes one million times more sensitive than any available back in the 1960s.

"Spheres the size of a Ping-Pong balls go in a quartz housing. We electrically suspend it. We spin it up by means of gas. (We) get it spinning to 5,000 rpm (revolutions per minute), pump out the gas to an extremely high vacuum and there we’ve got our gyroscope."

Once in orbit, the gyroscopes - spinning like a child’s top - were designed to keep Gravity Probe B perfectly aligned with a distant reference star. In confirmation of Einstein’s theories they experienced minute but measurable changes in the direction of their spin as they were pulled by earth’s gravity. 

Over the years, insights gained from Gravity Probe B have spawned a wave of new technologies, including the Global Positioning System, or GPS, a network of earth-orbiting satellites that have become essential for precise navigation on land and sea.

Former NASA manager Rex Geveden says despite the odds that the Gravity Probe B mission would fail, its success is a triumph of the human spirit - and intellect. "It’s a reminder of the sort of greatness that humans can get to when they put their hearts and minds on an objective like this."

Albert Einstein, who died in 1955, never dreamed that his Theory of Relativity would or even could be proved. In his book, The Meaning of Relativity, the famed physicist wrote: "...confirmation of them by laboratory experiments is not to be thought of."

Gravity Probe B lead investigator Francis Everitt adds, "Thanks to NASA we’ve done more than think about them. We’ve measured them."

The findings will appear in a forthcoming issue of the journal Physical Review Letters.

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