- The Washington Times - Thursday, February 27, 2003

CAMBRIDGE, Mass., Feb. 27 (UPI) — New research appearing Thursday suggests flexible objects can "swim" through the curvaceous landscape of space-time without need of thrust or external forces such as magnetic fields simply by contorting themselves.

"I don't at the moment see any way of making it practical. It's more of a fun result," researcher Jack Wisdom, a physicist at the Massachusetts Institute of Technology in Cambridge, Mass., told United Press International.

One consequence of Einstein's theory of relativity is that the presence of matter curves space and time, resulting in gravity.

To explain, imagine a crystal ball on a bed. The heavier the crystal, the larger the dimple it makes in the bed's surface and the more likely objects such as glass marbles rolling near the crystal ball would be captured by the geometry of the dimple.

In much the same way, the more massive an object is, the more it curves space and time and the stronger its gravitational pull becomes. Black holes concentrate so much mass together and curve space and time so much that they create gravitational fields strong enough to prevent everything from escaping, even light.

In findings appearing online Feb. 28 in the journal Science, Wisdom found by simply wriggling the right way, one could exploit the curves of space and time for propulsion.

Imagine a spikey ball perched atop a giant sphere. If one of the spikes retracted, the spiky ball would roll, even though it had not pushed against something. Cyclical motions such as extending and retracting spikes could help an object tumble across a curved surface.

"It really is just as simple as waving your arms in a swimming motion," Wisdom said. "Just reach the arms out, retract them, and reach them out again. We're just using the curvature."

Exploiting such effects might prove mathematically complicated, but Wisdom said it wouldn't prove hard to compute if desired.

"You would quickly learn it," he said.

The problem, Wisdom said, is the effects of "geometric propulsion" are negligible at best. For instance, each stroke of a 3-foot-long "swimmer" on the surface of the Earth would only push that swimmer a length about a billionth the diameter of an atomic nucleus.

"People laugh at that point," he explained. "It's far, far too small to be of practical."

The Wisdom effect "can be big only in enormous, destructive gravitational fields," said physicist David Finkelstein at the Georgia Institute of Technology in Atlanta. There, any novel spacecraft attempting geometric propulsion "probably would not survive," he added.

Still, when asked about the finding, Finkelstein said, "It's beauty. Physics has standards of beauty just as mathematics does." Moreover, this infinitesimal effect might one day provide another test for Einstein's theory of relativity, he said.

(Reported by Charles Choi, UPI Science News, in New York)

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