Gravitational Waves

To understand the need for gravitational waves in the General Theory of Relativity, we should go back to the previous question:

What would happen if the sun suddenly disappeared?

Image courtesy of NASA/JPL-Caltech.

Artist's drawing of gravitational waves Image courtesy of NASA/JPL-Caltech.

According to the General Theory of Relativity, the planets orbit the sun because they are taking the shortest path through the curved spacetime (recall the tennis ball).

If the sun suddenly disappeared, the spacetime surrounding it would be changed. According to Einstein’s theory, the spacetime surrounding Mercury would be distorted before the spacetime surrounding Pluto, and Mercury would fly out of orbit first. These spacetime distortions travel as gravitational waves.

It may help to think of gravitational waves as the ripples that form when you throw a rock into a pond. When the rock hits the water, the water immediately surrounding the rock is disturbed and the disturbance spreads out from there. Similarly, a change in the mass or speed of a heavy object disturbs the surrounding spacetime and this effect spreads out as gravitational waves.

Before Einstein explained his theory of relativity, people thought the universe had a time dimension and a space dimension that were completely separate and did not influence one another. Einstein, however, changed all of that. He saw the world as a dynamic system where matter, space, and time interacted. Gravitational waves are intriguing because make the abstract idea of matter influencing spacetime detectable.