25
September 2003
Gravity: learning curve
The deflection of light or other electromagnetic waves by the gravitational field of the Sun provides a fundamental test of any theory of gravitation. Einstein's theory has so far been confirmed, but during the past 20 years, the accuracy has been limited to about 0.1%. The Saturn-bound Cassini space mission, using a new method, has provided a new measurement of the deflection with a 50-fold better accuracy of 0.002%. The test involved tracking the frequency shift of the radio signals from Cassini as they passed near the Sun. No violation of general relativity was found. But it is thought that discrepancies may show up at a finer level, as a residual from early cosmological evolution, when gravitation was very different from Einstein's conception.
A test of general relativity using radio links
with the Cassini spacecraft
B. BERTOTTI, L. IESS & P. TORTORA
Nature 425, 374–376 (2003); doi:10.1038/nature01997
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