Gravitational waves propagate at the speed of light in a vacuum, which is approximately 299,792,458 meters per second (or about 186,282 miles per second). This value is denoted by the symbol "c" in physics.
The speed of gravitational waves is predicted by Einstein's theory of general relativity, which describes the behavior of gravity as the curvature of spacetime caused by mass and energy. According to this theory, gravitational waves are ripples in spacetime that propagate outward from sources of mass and energy, similar to how waves propagate in water.
The speed of light, being the maximum speed at which information or causal influence can travel in the universe, is also the speed at which gravitational waves are expected to propagate. This prediction has been supported by experimental observations.
One significant confirmation of the speed of gravitational waves came from the event GW170817. This event was the detection of both gravitational waves and electromagnetic waves (specifically, light) originating from the merger of two neutron stars. By analyzing the signals from both gravitational wave detectors and various telescopes, scientists were able to determine that the arrival times of the gravitational waves and the electromagnetic waves were consistent with each other, confirming that gravitational waves travel at the speed of light.
Additionally, the direct measurements of gravitational waves from binary black hole mergers and other astrophysical events have been consistent with the speed of light, providing further evidence for this property.
It's important to note that the precise measurement of the speed of gravitational waves is an ongoing area of research, and future observations and experiments will continue to refine our understanding of this fundamental property of the universe.