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Gravity Probe B

Testing Einstein's Universe

Special & General Relativity Questions and Answers

Does gravity travel faster than the speed of light?

No, it doesn't appear to. Einstein's relativistic equation for gravity based on general relativity demands that gravity travels at the speed of light, otherwise the predictions we get for the bending of light and the precession of the perihelion of Mercury would be quite different than what is experimentally determined. Also, we can send spacecraft on long journeys through the solar system, and the light travel delays can be up to several hours. If gravity traveled at any other speed than that of light, the trajectories that are calculated for spacecraft would always come out wrong because they include gravitational influences that change from moment to moment as the spacecraft, Sun and planets change their positions. We would never be able to get all the different time delays of these gravitational influences to add up to the measured trajectory of the spacecraft.

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All answers are provided by Dr. Sten Odenwald (Raytheon STX) for the NASA Astronomy Cafe, part of the NASA Education and Public Outreach program.