Gravity is something we all take for granted. It’s the force that holds us to the surface of the Earth and what makes things fall. But it’s much more than that, too. It’s what holds Earth together and gives the planet its roughly spherical form. It’s what keeps Earth moving in its orbit around the Sun, ensuring that we always have the heat and light we need to live. In fact, gravity is one of the most fundamental things in the universe – the force that holds everything from asteroids to galaxies together.

Gravity is one of four fundamental forces, alongside electromagnetism and the two types of nuclear force. On very small scales it’s by far the weakest of these forces, but it comes into its own at large distances. That’s because the nuclear forces have a very limited range, while electromagnetic forces tend to get cancelled out because electric charge can be either positive or negative. Gravity, on the other hand, always acts in the same direction – it’s a force of attraction, which means there’s no limit to its range. And it’s a very democratic force, operating with equal effect between any two objects having mass. For these reasons, it’s far and away the most important force governing the universe on large scales.

Gravity also played a key role in the formation of the universe by causing matter to clump together and form atoms, stars and galaxies. If gravity never existed, then the universe would have remained completely featureless and the same everywhere. You might worry