Accounting for gravity

A brief explanation of gravity

This gives a very brief description of how physicists try and explain gravity, rather than just saying it is there.

The modern explanation for the gravitational force is based on Albert Einstein's general theory of relativity. According to Einstein, Newton's notion that gravity is due to a force that acts instantly, and at a distance, between objects with mass is wrong. There is no gravitational force. Rather, in Einstein's view, the gravitational force is a consequence of the geometry of space and time.

The essential idea is that space is rather like an elastic medium that can be distorted or curved and that this curvature is caused by the energy and momentum of matter and radiation.

So, in the case of the solar system, the Sun (which has a great deal of energy) causes a significant geometric distortion. A planet moving in this region of distorted (curved) space-time reacts to the distortion by moving differently to the way it would move if the Sun had been absent and the space undistorted. This is why the planets orbit the Sun, even in the absence of the invisible hand of the gravitational force reaching out to grasp them.