• DOI:10.1038/nature01997
• Corpus ID: 4337125

A test of general relativity using radio links with the Cassini spacecraft

@article{Bertotti2003ATO,
  title={A test of general relativity using radio links with the Cassini spacecraft},
  author={Bruno Bertotti and Luciano Iess and Paolo Tortora},
  journal={Nature},
  year={2003},
  volume={425},
  pages={374-376}
}

• B. Bertotti, L. Iess, P. Tortora
• Published 25 September 2003
• Physics
• Nature

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 γ + 1, where the parameter γ is unity in general relativity but zero in the newtonian model of gravity. The quantity γ - 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 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, γ = 1 + (2.1 ± 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.