Albert Einstein is arguably the most influential scientist of the 20th century. His general theory of relativity changed our understanding of space and time, becoming one of the two pillars of modern physics – the other being quantum mechanics. It led to a new way of looking at the universe: suggesting that space and time can’t be separated from one another, but rather are interwoven in a continuum. For example, although the sun’s gravity appears to pull the earth towards it, no such force really exists; instead, the geometry of space-time around the sun dictates how the earth moves. According to the theory, time moves more slowly when gravity is stronger: clocks tick slower at sea level than at the top of a mountain, where the tug of Earth’s gravity is weaker. Einstein’s general theory of relativity explained the motion of planets and the bending of light from distant stars and galaxies, and predicted the existence of black holes and gravitational waves. These waves – ripples in space-time – were detected directly for the first time in 2016, a century after he first theorised them.
