Matrix mechanics
The first form of quantum mechanics, born in 1925: it describes electrons in atoms using only observable quantities, calculated as tables of numbers called matrices.
In July 1925 Werner Heisenberg dropped the electron's path, which nobody had ever seen, from the theory and tried to rebuild mechanics from observable quantities alone: the frequency and intensity of the light an atom gives off. When he multiplied these quantities together, something strange happened: the answer depended on the order of multiplication.
Max Born, who received the paper, recognised this as the multiplication of what mathematicians call matrices. In September that year, with his student Pascual Jordan[1], and in November with Heisenberg as well[2], he set it out as a new mechanics. At its heart is the relation that swapping the order in which position and momentum are multiplied changes the result by a fixed amount set by Planck's constant.
In 1926 it was shown to be the same theory, underneath, as Schrödinger's wave mechanics, which looked nothing like it. Quantum mechanics today is used in a form that unites the two.
Related terms
- Schrödinger equationThe basic equation of quantum mechanics, which governs how the wave of an electron or other particle varies in space and time. Written down by Erwin Schrödinger in 1926.
- Correspondence principleThe principle that quantum results must agree with classical physics in the limit of large quantum numbers — large objects and high energies.
- Uncertainty relationThe quantum relation that a particle's position and momentum cannot both be pinned down as precisely as you like at the same time. Set out by Werner Heisenberg in 1927.