Evicting Albert Einstein

The curvature of space due to the sun's mass caused signals from the Cassini probe to curve on their way to Earth.

"I think [LATOR] would be quite an important advance for fundamental physics," says Clifford Will, a professor of physics at Washington University who has made major contributions to post-Newtonian physics and is not directly involved with LATOR. "We should continue to try to press for more accuracy in testing general relativity, simply because any kind of deviation would mean that there's new physics that we were not aware of before."

The experiment would work like this: Two small satellites, each about one meter wide, would be launched into an orbit circling the sun at roughly the same distance as Earth. This pair of mini-satellites would orbit more slowly than Earth does, so about 17 months after launch, the mini-satellites and Earth would be on opposite sides of the sun. Even though the two satellites would be about 5 million km apart, the angle between them as viewed from Earth would be tiny, only about 1 degree. Together, the two satellites and Earth would form a skinny triangle, with laser beams along its sides, and one of those beams passing close to the sun.

Turyshev plans to measure the angle between the two satellites using an interferometer mounted on the ISS. An interferometer is a device that catches and combines beams of light. By measuring how waves of light from the two mini-satellites "interfere" with each other, the interferometer can measure the angle between the satellites with extraordinary precision: about 10 billionths of an arcsecond, or 0.01 µas (micro-arcseconds). When the precision of the other parts of the LATOR design are considered, this gives an overall accuracy for measuring how much gravity bends the laser beam of about 0.02 µas for a single measurement.

"Using the ISS gives us a few advantages," Turyshev explains. "For one, it's above the distortions of Earth's atmosphere, and it's also large enough to let us place the two lenses of the interferometer far apart (one lens on each end of the solar panel truss), which improves the resolution and accuracy of the results."

Image courtesy Slava Turyshev The interferometer will be mounted to the solar-panel truss of the ISS, which automatically rotates to continuously face the sun.

The 0.02 µas accuracy of LATOR is good enough to reveal deviations from Einstein's relativity predicted by the aspiring Theories of Everything, which range from roughly 0.5 to 35 µas. Agreement with LATOR's measurements would be a major boost for any of these theories. But if no deviation from Einstein is found even by LATOR, most of the current contenders - along with their 11 dimensions, pixellated space, and inconstant constants - will suffer a fatal blow and "pass on" to that great dusty library stack in the sky.

Because the mission requires only existing technologies, Turyshev says LATOR could be ready to fly as soon as 2009 or 2010. So it may not be too long before the stalemate in physics is broken and a new theory of gravity, space, and time takes the throne.