Test of Einstein's Theory of Gravity Hits a Snag
It has been more than 90 years since Einstein put forward his theory of relativity. Physicists agree it is basically right, but they also suspect there is something deeper behind it.
Since the 1960s, scientists funded by NASA have been working on a project to precisely test Einstein's theory. The experiment, called Gravity Probe B, finally made it to orbit a few years ago, at a total cost of $750 million. The researchers gave a progress report at a conference in Florida last weekend, and said they have run into some snags.
Back in 1959, physicist George Pugh published a paper outlining a way to test Einstein's theory of general relativity of gravity. It said that gravity was not just some magical, invisible tugging: Gravity was the result of objects actually warping the space around them — imagine a bowling ball sitting on a trampoline.
Heavy objects could also drag space around with them, and Pugh suggested looking for this effect around the Earth as it spins.
To test this, Pugh decided to send gyroscopes into orbit. A spinning gyroscope always points in the same direction. So if a gyroscope moves, that means space itself is shifting. Einstein's theory predicted a very small shift. Any deviation could mean a crack in relativity — a clue to something beyond it. For the experiment to work, the gyroscopes would have to be extraordinarily sensitive.
Scientists began to work on Pugh's idea but ran into a string of difficulties. The project was killed, resurrected and killed again. Finally after 40 years of work, the satellite was launched in 2004. On board were four super-precise gyroscopes — each with a spinning sphere the size of a ping-pong ball.
Over a year, the team hoped to be able to detect tiny shifts in the gyroscopes. For the experiment to be counted as a success, it had to make very precise measurements — less than one-millionth of a degree.
The team had planned to release its results around now. But there have been problems: The results so far are 1,000 times less precise than what the team had expected. Much of the trouble came from the gyroscopes. The spheres inside carried small patches of electric charge, which subtly disturbed their motion.
Physicist Francis Everitt at Stanford University is the project's leader. He says the team will be able to subtract the disturbance and correct the data.
In recent years, scientists have found other ways to observe the subtle warpings of space predicted by Einstein. NASA recently gave the Gravity Probe B team several million more dollars to continue their work. The team hopes to have better results by the end of the year.
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It's been over 90 years since Einstein set out his theory of relativity. Physicists agree it's basically right, but they also suspect there is something deeper behind it. Since the 1960s, scientists funded by NASA have been working on a project to precisely test Einstein's theory. The experiment, called Gravity Probe B, finally made it into orbit a few years ago at a total cost of $750 million. The researchers gave a progress report at a conference in Florida this weekend, and they said they have run into some snags.
NPR's David Kestenbaum was there.
DAVID KESTENBAUM: Testing Einstein is notoriously difficult, and this experiment has been in the works for so long that some of the scientists involved aren't alive anymore. Others are eligible for social security, like George Pugh. He's how old?
Mr. GEORGE PUGH (Physicist): Let's see if I can figure it out. Well, I can tell you when I was born. I was born in January 1926.
KESTENBAUM: Which makes him 81 years old. Back in 1959, Pugh published a paper outlining an ingenious way to test Einstein's Theory of General Relativity, of gravity. The theory said that gravity wasn't just some magical, invisible tugging; gravity was the result of objects actually warping the space around them. Imagine a bowling ball sitting on a trampoline, or a fat man on a bed. Heavy objects could also drag space around with them as if it were honey. Pugh suggested looking for this effect around the earth as it spins.
A weird thought - to think of space being dragged.
Mr. PUGH: Absolutely. And if you wanted to measure whether space was rotating or not, how on earth could you do it? Nothing to grab on to, how would you know it was rotating?
KESTENBAUM: Pugh's clever solution? Send gyroscopes into orbit. A spinning gyroscope always points in the same direction, so if a gyroscope moves that means space itself is shifting. Einstein's theory predicted a very small shift; any deviation could mean a crack in relativity, a clue to something beyond it. Scientists began to work on Pugh's idea but ran into a string of difficulties. The project was killed, resurrected, killed again. Finally, after 40 years of work, in 2004, the satellite was launched.
On board, four super-precise gyroscopes, each with a spinning sphere the size of a ping-pong ball. The Guinness Book of World Records lists them as the most perfectly round objects ever manufactured. The project's spiritual and actual leader is Francis Everitt, a physicist at Stanford University.
Mr. FRANCIS EVERITT (Physicist, Stanford University): My present age is 73. When I began on Gravity Probe B, I was 28 years old.
KESTENBAUM: Everitt now has gray hair down to his shoulders, some of which could be due to the job. In recent years, other scientists have found other ways to observe the subtle warpings of space predicted by Einstein. So for this experiment to be counted as a success, it has to do what it set out to: make very, very precise measurements. Over the course of a year, they hoped to be able to detect tiny shifts in the gyroscopes, less than one millionth of one degree.
Mr. EVERITT: That is the width of one of your hairs seen at a distance of about 10 miles.
KESTENBAUM: The team had planned to release its results around now, but there have been problems.
Mr. EVERITT: This is a prophecy that people make to you before you launch a spacecraft. Well, you're going to find that all things you knew were going to be impossibly difficult will work perfectly. And some things that couldn't possibly cause you any trouble will be the real issue.
KESTENBAUM: And there are issues. The results so far are 1,000 times less precise than what the team had designed for. Much of the unexpected trouble came from the gyroscopes. The spheres inside carried small patches of electric charge, which suddenly disturbed their motion. Everitt says he thinks the team will be able to subtract the disturbance and correct the data, improving the overall accuracy by a factor of a hundred.
Mr. EVERITT: I am completely confident. Of course, a critical person should ask, is my confidence justified?
KESTENBAUM: Everitt presented his results at the conference. One physicist, Eanna Flanagan from Cornell, sat with a notebook and a selection of fine-point pens for writing out equations. He is withholding judgment.
Mr. EANNA FLANAGAN (Associate Professor of Physics, Cornell University): I'm hopeful that they can push to the levels of activity, which they said they could, because that was a very expensive experiment. A lot of resource went into it, it would be a shame if (unintelligible) it's essentially a failure. But I don't think it's disappointing yet.
KESTENBAUM: The Gravity Probe B team hopes to have better results by the end of the year. Einstein had the genius to perceive something so profound it could barely be tested. He is safe for another nine months, probably more.
David Kestenbaum, NPR News. Transcript provided by NPR, Copyright National Public Radio.
