Heisenberg’s Uncertainties: 1927–

Until Heisenberg proposed the uncertainty principle in 1927, it was an open question whether models for the structure of matter reflected actual reality or were useful fictions for operational purposes. There wasn’t any sense in either case that there might be parameters it was impossible to determine. The uncertainty principle says that it is impossible to determine simultaneously the location and momentum of an electron. While it applies to a specific situation, ‘uncertainty’ is a good description for the entire approach of quantum theory. Schrödinger’s equations show that electrons behave simultaneously as waves and particles. The double-slit experiment, when a beam of light or electrons passes through two parallel slits, shows that the act of observation influences the behavior of the wave–particle duality. The ability of a pair of ‘entangled’ electrons (or other particles) to influence each other instantaneously appears to exceed the speed limit of light. Paradoxes of quantum behavior may even extend to biological situations. Intuition or common sense are no guide to quantum behavior.