Gravitational waves propagate at what speed?

• A. Speed of light
• B. Speed of sound
• C. Infinite speed
• D. Speed of gravity

Answer: (A)

Gravitational waves propagate at the speed of light in vacuum. In general relativity, disturbances in spacetime that carry information about changing gravitational fields travel at the maximum speed allowed by the theory, which is c. This means these waves move through empty space without lag, just like light does, and their arrival times over cosmic distances match what you’d expect if they travel at light speed. Observations from detectors such as LIGO have confirmed this behavior, showing the timing of gravitational waves aligns with propagation at c within experimental precision. The other options don’t fit because sound travels through a medium and much more slowly, nothing travels instantaneously, and “speed of gravity” isn’t a separate speed here—gravity propagates at the same fundamental limit as light in general relativity.