Editing Cassini–Huygens (section)

=== Tests of general relativity ===

On October 10, 2003, the mission's science team announced the results of tests of [[Albert Einstein]]'s [[general theory of relativity]], performed by using [[radio wave]]s transmitted from the ''Cassini'' space probe.<ref name=Bertotti_2003/> The radio scientists measured a [[frequency]] shift in the radio waves to and from the spacecraft, as they passed close to the Sun. According to the general theory of relativity, a massive object like the [[Sun]] causes [[space-time]] to curve, causing a beam of radiowaves travelling out of its [[gravitational well]] to decrease in [[frequency]] and radiowaves travelling into the gravitational well to increase in frequency, referred to as [[gravitational redshift]] / blueshift.

Although some measurable deviations from the values calculated using the [[general theory of relativity]] are predicted by some unusual cosmological models, no such deviations were found by this experiment. Previous tests using radiowaves transmitted by the ''Viking'' and ''Voyager'' space probes were in agreement with the calculated values from general relativity to within an accuracy of one part in one thousand. The more refined measurements from the ''Cassini'' space probe experiment improved this accuracy to about one part in 51,000.{{efn|This is currently the best measurement of [[Parameterized post-Newtonian formalism|post-Newtonian parameter]] ''γ''; the result ''γ'' {{=}} 1 + (2.1 ± 2.3) × 10<sup>−5</sup> agrees with the prediction of standard General Relativity, ''γ'' {{=}} 1|name=post-newton}} The data firmly support Einstein's general theory of relativity.<ref name=Dume_2003/>