Dirac equation
The equation describing the electron in a way that satisfies both quantum mechanics and special relativity. Written by Paul Dirac in 1928.
The Schrödinger equation could not correctly handle particles moving near the speed of light. Dirac sought the simplest equation meeting the demands of both relativity and quantum mechanics, and arrived at it by making the electron's wave a set of four[1]. Electron spin, which had until then been added on from outside, then came out of the equation by itself. The fine structure of hydrogen's spectral lines was reproduced without approximation.
The equation also came with strange solutions of negative energy. Dirac did not discard them; thinking them through, he reached the prediction that a particle must exist with the electron's mass and the opposite charge. The positron was found in 1932 and the prediction was borne out. It is the starting point of the modern understanding that particles have antiparticles.
Related terms
- SpinA property that electrons and other particles are born with, making them behave like tiny magnets. For an electron it takes only two values: "up" or "down".
- PositronA particle with the electron's mass and a positive charge. It is the electron's antiparticle; when the two meet, both vanish into light.
- Fine structureThe splitting of what looks like a single line in an atom's spectrum into several closely spaced lines when examined in detail.
- RelativityEinstein's theory that measurements of time and space depend on the observer's motion and on gravity — special relativity (1905) and general relativity (1915–16).