Bertotti B, Iess L, Tortora P
Dipartimento di Fisica Nucleare e Teorica, Università di Pavia, Via U. Bassi 6, I-27100, Pavia, Italy.
Nature. 2003 Sep 25;425(6956):374-6. doi: 10.1038/nature01997.
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 gamma 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 approximately 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, gamma = 1 + (2.1 +/- 2.3) x 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.
根据广义相对论，光子会因任何质量所产生的时空曲率而发生偏折和延迟。这种弯曲和延迟与γ + 1成正比，其中参数γ在广义相对论中为1，而在牛顿引力模型中为0。γ - 1这个量衡量了引力并非纯粹几何效应且受其他场影响的程度；此类场可能在早期宇宙中产生了强烈影响，但如今已经减弱，从而产生微小但仍可探测的效应。几项实验已将太阳所产生的光子偏折和延迟的预测结果验证到了约0.1%的精度。在此，我们报告了对往返卡西尼号航天器的射电光子在经过太阳附近时的频移测量结果。我们的结果γ = 1 + (2.1 ± 2.3)×10⁻⁵，与标准广义相对论的预测相符，其灵敏度接近理论上在某些宇宙学模型中预期会出现偏差的水平。
