It might seem an obvious statement that there are limits to what we know, but the principle first expounded by the German physicist Werner Heisenberg in 1927 takes things to a new and weird level.
Think of a football. If you kick a football, knowing where it is doesn’t stop you knowing where it’s going, within the limits of your senses. But that’s not true in the quantum world of particles and forces that underlies our classical world. The more precisely you know a particle’s position, the less precisely you know its momentum, and vice versa.
This is the quantum uncertainty principle. It connects not just position and momentum, but energy and time and a whole host of other pairs of quantities. In the quantum world, uncertainty doesn’t come from the accuracy of our measuring devices (our eyes, in the case if the football): it is apparently a fundamental limit on how much we can know about the world.
Uncertainty shapes our world in unsuspected ways. It allows particles to “tunnel” through otherwise insurmountable energy barriers to initiate nuclear fusion in the sun, for example. It also enables them to pop up out of a seemingly empty vacuum for short periods – an ability that’s crucial for explaining how the quantum forces that shape reality operate.
Just 25 when he came up with his eponymous principle, Heisenberg made other seminal contributions to the emerging quantum theory – indeed, he was awarded the 1932 Nobel prize in physics “for the creation of quantum mechanics”.
The following year, Adolf Hitler’s Nazi regime came to power in Germany. He was investigated by the SS, who condemned him for supporting the “Jewish” theory of relativity. But the regime decided he was too useful to be silenced, and he later became a central figure in German efforts to compete with the United States’ Manhattan Project in building an atomic bomb.
Heisenberg’s own attitude towards these efforts remained equivocal, as shown in transcripts of conversations secretly recorded in 1945 when he and other German scientists were captured and interned at Farm Hall in England. Much speculation exists, for example, surrounding the purpose of a visit he made to his old supervisor Niels Bohr in Denmark in 1941, an event dramatised in British playwright Michael Frayn’s Copenhagen in 1998. Bohr later escaped occupied Denmark to Sweden and eventually the US, where he worked on the Allied nuclear bomb project.
After the second world war Heisenberg returned to Germany and continued to work as a respected physicist, dying in 1976 at the age of 75.
Full name: Werner Karl Heisenberg
Born: 5 December 1901, Würzburg, Germany
Died: 1 February 1976, Munich, Germany
Werner Heisenberg was a German theoretical physicist famous for his uncertainty principle and his work on nuclear fission.