Earth orbiter will try to determine whether gravity does indeed bend time, space
Tom Spears
Sun
Canadian and U.S. scientists will spend the next year testing whether Einstein was right or wrong in thinking that Earth — and other heavenly bodies — bend space and time with their gravity.
Today NASA plans to launch the experiment that astrophysicists have been planning since 1958. They’ll send a three-tonne Thermos bottle of liquid helium into Earth’s orbit, where it will fly at twice the altitude of most space shuttles.
Monday’s planned launch was postponed because of high winds.
Watching the magnetic field of the spinning gyroscopes inside the probe will test whether space and time actually curve under Earth’s gravity. It’s the latest in nearly a century of experiments to test different aspects of Einstein’s revolutionary theory of relativity.
So far, these tests have found he was bang on.
The current understanding of gravity works well enough to predict movements in the solar system, says Michael Bietenholz, a York University astronomer involved in the new Gravity Probe B project.
But the solar system isn’t that big. The universe is so much larger that even the tiniest flaw in the theory would cause errors on a huge scale.
“It would be nice to send spaceships a billion light years away to make measurements, but we can’t,” he said. “The alternative is to try and measure very, very precisely, close to Earth to see if the theory holds up . . . . If it doesn’t agree then that’s a sign that the theory is wrong and we need a different picture.”
Most of the betting is that Einstein’s theory was right, he adds, “because it has stood up very well so far.”
Gravity B contains four gyroscopes, each a sphere of quartz the size of a tennis ball, coated with a superconductor metal and able to spin 10,000 times a minute. They are probably as close to round as anything ever made.
As these spin they produce a magnetic field, which shows scientists on Earth the exact axis of the spin. If the axis shifts, they believe, this will show where space and time are bending under the influence of Earth’s gravity.
As well, the international science group led by Stanford University hopes to find evidence of “frame dragging.” This means that Earth’s rotation makes time and space rotate with it — as theory says time and space swirl around the dense centre of a black hole.
These effects “are fairly obscure by layman’s standards. But it’s our theory of gravity, which is fundamental to our understanding of the universe,” Bietenholz said.
But all this depends on the ability of the satellite and its gyroscopes to point themselves in exactly the right direction. And Canada‘s role is to give the satellite something to aim at, like a ballerina who focuses on one spot in the room to keep her turns precise.
Einstein proposed general relativity — that space and time are affected by gravity — in 1915. But he became a worldwide celebrity four years later, when the solar eclipse of November 1919 gave scientists a chance to test his revolutionary ideas.
When the sun disappeared behind the moon, observers were able to chart the position of distant stars on the far side of the sun.
Their positions appeared just a tiny bit out of place — because their light was being bent by gravity as it passed close to our sun.
As in 1919, today’s test of Einstein has to focus on a distant star.
A star called IM Pegasi (in the constellation Pegasus) will be a reference point for the satellite, just as stars serve for navigation on Earth.
The problem is that stars move, and even a slow motion across the sky will confuse the satellite.
So a team at York University will “fix” the star, plotting its exact location as it travels so that the satellite can compare space near Earth with the fixed star. If the picture wobbles, that will show where space and time are bending around Earth.
Launching the experiment and running it for 16 months will cost $700 million US.
The much smaller Gravity A probe flew for just two hours in 1976.
© The Vancouver Sun 2004