Heisenberg's Uncertainty Principle
Werner Heisenberg published the uncertainty principle in March 1927, in a paper written largely at night in his rooms in Copenhagen while Niels Bohr was away skiing. Its statement is that the position and momentum of a particle cannot both be known precisely: the more sharply one is determined, the less sharply the other can be. The product of the two uncertainties has a floor set by Planck's constant. Heisenberg arrived at it from his own matrix mechanics, and his first explanation was operational — a thought experiment in which locating an electron with a gamma-ray microscope requires a photon energetic enough to disturb the momentum being measured. Bohr returned and objected that this made it sound like a limitation of instruments. The two argued for weeks, at times bitterly, and the published version was revised to make the point that the indeterminacy is a property of nature rather than of measurement — that the particle does not possess both quantities sharply for an experiment to be clumsy about. It became one half of the Copenhagen interpretation, with Bohr's complementarity as the other. Einstein spent the rest of his life objecting. The Solvay conferences of 1927 and 1930 are a series of thought experiments he devised to defeat it and Bohr answered, including one Bohr refuted using Einstein's own general relativity overnight. The principle is not about disturbance and is now derived formally from the non-commutation of operators. Heisenberg received the Nobel Prize in 1932, at thirty-one. He led Germany's wartime nuclear programme, and what he was trying to achieve there is still argued about.
- Year: 1927 CE
- Category: Scientific
