Part of the show Stars, Cosmology and the Beginning of the Universe
Tara, via email asked:
What's gravity made of?
That question would probably fox most scientists! There are various theories of gravity. The most straightforward one was put forward by Isaac Newton. He said that it was the force between two bodies that attracts bodies together, and the strength of the force is proportional to the masses of the two bodies over the distance between the two bodies times itself. So the bigger something is, the more it attracts something. There is also the Einstein theory, which is about gravity being the curvature of space time. This is often illustrated by a rubber sheet with a big ball bearing in the middle, which makes a dip. If you then take a smaller ball bearing and ping it off at 90 degrees, it will move round and round the big ball bearing, like an orbiting planet. There are also gravity waves, which are ripples in space time that propagate away from a massive body.