The speed of light is generally considered to be the fastest known phenomenon in the universe. In a vacuum, light travels at a constant speed of approximately 299,792,458 meters per second (about 186,282 miles per second) in the theory of relativity.
Gravity, on the other hand, is a fundamental force of nature that acts between objects with mass or energy. It is responsible for the attraction between objects and the motion of celestial bodies. However, gravity does not have a specific speed associated with it as light does.
According to Albert Einstein’s theory of general relativity, gravity is the curvature of spacetime caused by mass and energy. Objects with mass or energy create a gravitational field that affects the curvature of spacetime around them. This curvature influences the motion of other objects in the vicinity.
Changes in the gravitational field propagate through spacetime as gravitational waves, which are ripples in the fabric of spacetime. Gravitational waves do indeed travel at the speed of light, but they are not the same as gravity itself. Gravity itself is considered to be an instantaneous force that acts across space, even though its effects may take time to propagate.
It is important to note that the current understanding of gravity and its behavior is based on Einstein’s theories, which have been highly successful in describing the nature of gravity. However, there are ongoing efforts in theoretical physics to unify general relativity with quantum mechanics, and these efforts may lead to a deeper understanding of gravity in the future.
The dead cores of two stars collided 130 million years ago in a galaxy somewhat far away.
The collision was so extreme that it caused a wrinkle in space-time — a gravitational wave. That gravitational wave and the light from the stellar explosion traveled together across the cosmos. They arrived at Earth simultaneously at 6:41 a.m. Eastern on August 17.
The event prompted worldwide headlines as the dawn of “multimessenger astronomy.” Astronomers had waited a generation for this moment. But it was also the first-ever direct confirmation that gravity travels at the speed of light.
We all know light obeys a speed limit — roughly 186,000 miles per second. Nothing travels faster. But why should gravity travel at the same speed?
That question requires a quick dive into Albert Einstein’s general relativity, or theory of gravity — the same theory that predicted gravitational waves a century ago.
Einstein overthrew Isaac Newton’s idea of “absolute time.” Newton thought time marched onward everywhere at an identical pace — regardless of how we mortals perceived it. It was unflinching. By that line of thinking, one second on Earth is one second near a black hole (which he didn’t know existed).
Changes in the distribution of mass and energy create ripples in the fabric of spacetime, which we perceive as gravitational waves. These waves propagate at the speed of light, as predicted by Einstein’s theory. However, gravity itself, the curvature of spacetime, is instantaneous in its effect.
This means that if a massive object were to suddenly appear or move, the gravitational influence of that object would be felt by other objects in its vicinity immediately, without any delay associated with the speed of light. This aspect of gravity is often described as “action at a distance.” However, the effects of changes in gravitational fields do propagate at the speed of light in the form of gravitational waves.
Therefore, based on our current understanding of physics, light and gravity both travel at the same speed, which is the speed of light.