Most people associate Albert Einstein, probably the most famous scientist of all time, with a single equation: E = mc2.
Most people associate Albert Einstein, probably the most famous scientist of all time, with a single equation: E = mc2.
But Einstein contributed much, much more, perhaps most notably his Special Theory of Relativity, which changed our understanding of the universe.
A German-American physicist, Einstein (1879–1955) wrote four enormously important papers in 1905, often dubbed his ‘annus mirabilis’ or ‘wonderful year’.
The first was a piece of mathematical brilliance that explained ‘Brownian motion’ – the constant, random movement of tiny pollen grains in water seen under a microscope.
It had puzzled scientists since the 1820s.
Einstein said it was caused by water molecules bumping into the pollen.
His other three papers were ground-breaking and revolutionary.
The first involved a phenomenon called the photoelectric effect, in which light causes electrons to be ejected from the surface of a metal.
Before 1905, most scientists believed light is simply a wave motion, a disturbance in electric and magnetic fields. But that could not fully explain the photoelectric effect.
Einstein said light is a stream of particles called photons.
We now know that both interpretations are correct: light and other forms of electromagnetic radiation behave as both waves and particles.
Einstein’s explanation won him the Nobel Prize for physics in 1921.
The next paper introduced a radical new idea we now call the Special Theory of Relativity, which transformed scientists’ understanding of space and time.
Special Relativity gave rise to the idea that there was more to the universe than the familiar three dimensions.
Einstein described the universe as a four-dimensional place where things happen in ‘space-time’ – rather than a three-dimensional one where time ticks away independently of space.
He also said time and space are not fixed, contrary to Isaac Newton’s view that they are both absolute.
Einstein’s famous mass-energy equation appeared in the last of his 1905 papers.
One of the consequences of Special Relativity is that mass and energy are two forms of the same thing, which physicists call mass-energy.
Mass (m) can be converted into energy (E), and vice versa.
And because the two are related by a huge number – the speed of light squared (c2), which is 34,596,000,000 – a tiny amount of matter yields a huge amount of energy.
A spent fuel rod in a nuclear reactor weighs a fraction of a gram less than a fresh one, even though it has produced enough energy to power thousands of homes for months.
Special Relativity included what scientists knew about electric and magnetic forces.
It did not, though, deal with gravity.
In 1916, Einstein published his General Theory of Relativity, showing that gravity can be explained as the ‘warping’ of space-time.
He said clocks would run more slowly in intense gravitational fields near very massive objects and that light, normally assumed to travel in perfectly straight lines, would follow the curve of warped space-time.
Photographs taken during a total solar eclipse in 1919 proved that light from distant stars bent as it passed close to the sun – by exactly the amount Einstein’s theory predicted.
When the news broke it made Einstein an instant worldwide celebrity – very unusual for a scientist.
And all the tests of relativity to date have proved Einstein’s ideas correct.
