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.
The German-born physicist’s most famous equation, E = mc2, states that anything with mass has an equivalent amount of energy, and vice versa.
It arose from his special theory of relativity, which proposed that in the vacuum of space, the speed of light is always the same, regardless of the movement of the person observing it. 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. It also suggested that measurements of distance and time both change as you get closer to the speed of light: clocks run slower and lengths appear to get shorter.
In the same year, aged just 26, he developed three other ground-breaking theories – on Brownian motion, mass-energy equivalence, and the law of the photoelectric effect, for which he went on to win the Nobel Prize in 1921.
Advertisement
Take our expert-led online general relativity course to discover more about Einstein’s seminal idea
Expanding his special theory, Einstein’s general theory of relativity states that what we perceive as the force of gravity between two masses actually arises from their warping of space and time. 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.
Going against the predominant view at the time, the theory also predicted that the universe is expanding, which the astronomer Edwin Hubble confirmed in 1929.
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.
