Magazine article Science News

Stronger Support for Equivalence Principle

Magazine article Science News

Stronger Support for Equivalence Principle

Article excerpt

Stronger support for equivalence principle

The equivalence principle -- a cornerstone of the general theory of relativity -- dictates that all forms of matter and energy fall with the same acceleration in a uniform gravitational field. Researchers can test this principle by comparing the accelerations of the Earth and moon toward the sun, but there's a catch. Such experimental tests are accurate only if no long-range, nongravitational force interferes with the measurements in a way that happens to mask any anomalous gravitational effects.

Scientists have now closed that loophole. Drawing on precise laboratory experiments designed to ferret out a nongravitational, "fifth" force, Eric G. Adelberger and his colleagues at the University of Washington in Seattle conclude that such a force -- if it exists -- would be too feeble to affect significantly the results of experiment designed to detect differences in the accelerations of the Earth and moon toward the sun.

Tests of the equivalence principle hinge on the idea that the moon's orbit would be distorted in a particular way if the Earth's gravitational binding energy, which contributes about 5 part in [10.sup.10] to the Earth's total mass, doesn't behave in the same way as othe forms of mass and energy. The effect should be large enough to appear in precise measurements of variations in the distance between the moon and Earth -- it no other, unknown force gets in the way.

The new analysis, reported in the Sept. …

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