• Public

  • Public
  • Network
  • Groups
  • Popular
  • People

A test of general relativity using radio links with the Cassini spacecraft B. Bertotti', L. less' & P. Tortora' 'Dipartimento di Fisica Nucleare e Teorica, Università di Pavia, Via U. Bassi 6, 1-27100, Pavia, Italy "Dipartimento di Ingeneria Aerospaziale ed Astronautica, Università di Roma "La Sapienza", Via Eudossiana 16, 1-00184, Roma, Italy 'II Facoltà di Ingegneria, Università di Bologna, Via Fontanelle 40, 1-47100, Forli, Italy According to general relativity, photons are deflected and delayed by the curvature of space-time produced by any mass'-. The bending and delay are proportional to \gamma + 1, where the parameter y is unity in general relativity but zero in the newtonian model of gravity. The quantity \gamma - 1 measures the degree to which gravity is not a purely geometric effect and is affected by other fields; such fields may have strongly influenced the early Universe, but would have now weakened so as to produce tiny-but still detectable effects. Several experiments have confirmed to an accuracy of ~0.1% the predictions for the deflection*S and delay of photons produced by the Sun. Here we report a measurement of the frequency shift of radio photons to and from the Cassini spacecraft as they passed near the Sun. Our result, \gamma = 1 + (2.1 \pm 2.3) × 10^{-5}, agrees with the predictions of standard general relativity with a sensitivity that approaches the level at which, theoretically, deviations are expected in some cosmological models.