Evicting Albert Einstein

According to Einstein's theory of general relativity, the sun's gravity causes starlight to bend, shifting the apparent position of stars in the sky.

The stalemate between these two theories has gone on for decades. Most scientists assume that somehow, eventually, a unifying theory will be developed that subsumes the two, showing how the truths they each contain can fit neatly within a single, all-encompassing framework of reality. Such a "Theory of Everything" would profoundly affect our knowledge of the birth, evolution, and eventual fate of the universe.

Slava Turyshev, a scientist at JPL, and his colleagues have thought of a way to use the International Space Station (ISS) and two mini-satellites orbiting on the far side of the sun to test the theory of relativity with unprecedented accuracy. Their concept, developed in part through funding from NASA's Office of Biological and Physical Research, would be so sensitive that it could reveal flaws in Einstein's theory, thus providing the first hard data needed to distinguish which of the competing Theories of Everything agree with reality and which are merely fancy chalk-work.

The experiment, called Laser Astrometric Test Of Relativity (LATOR), would look at how the sun's gravity deflects beams of laser light emitted by the two mini-satellites. Gravity bends the path of light because it warps the space through which the light is passing. The standard analogy for this warping of space-time by gravity is to imagine space as a flat sheet of rubber that stretches under the weight of objects like the sun. The depression in the sheet would cause an object (even a no-mass particle of light) passing nearby the sun to turn slightly as it went by.

In fact, it was by measuring the bending of starlight by the sun during a solar eclipse in 1919 that Sir Arthur Eddington first tested Einstein's theory of general relativity. In cosmic terms, the sun's gravity is fairly weak; the path of a beam of light skimming the edge of the sun would only be bent by about 1.75 arcseconds (an arcsecond is 1/3600 of a degree). Within the limits of accuracy of his measuring equipment, Eddington showed that starlight did indeed bend by this amount - and in doing so effectively impeached Newton.

LATOR would measure this deflection with a billion (10⁹) times the precision of Eddington's experiment and 30,000 times the precision of the current record-holder: a serendipitous measurement using signals from the Cassini spacecraft on its way to explore Saturn.