Lorentz ether theory

Lorentz ether theory is a pre-relativistic account of electromagnetic phenomena in which space contains an undetectable ether and matter contracts through motion relative to it. It reproduces special relativity’s observable predictions while assigning a preferred rest frame.

Lorentz transformation: A set of equations relating space and time coordinates between inertial reference frames in relative motion. The transformations encode how ether theory links moving measurements to its preferred frame.
Hendrik Lorentz: A Dutch physicist whose work on electromagnetism and electron theory helped establish the Lorentz transformations. He developed the theory's mathematical account of moving bodies and electromagnetic fields.
Special relativity: A theory of space and time in which physical laws are the same in all inertial frames and the speed of light is invariant. It uses the same Lorentz transformations but dispenses with an undetectable preferred ether frame.
Einstein's 1905 paper on special relativity: Albert Einstein's 1905 paper that derived the kinematics of special relativity from the relativity principle and light-speed constancy. Einstein reached Lorentz transformations without treating ether-induced distortions as hidden mechanisms.
Lorentz contraction: The shortening of an object's length along its direction of motion relative to a reference frame. Lorentz treated contraction through the ether as a physical cause of null ether-drift measurements.
James Clerk Maxwell: A Scottish physicist whose equations unified electricity, magnetism, and light as electromagnetic phenomena. Maxwell's wave theory of light made an ether seem necessary to many nineteenth-century physicists.
Galilean transformation: The classical equations relating space and time coordinates between inertial frames at speeds far below light speed. Its absolute time and velocity addition conflict with the transformations required by Lorentz ether theory.
Kennedy–Thorndike experiment: An interferometer experiment testing whether light's measured speed varies with the apparatus's orientation or velocity through space. Its null result constrained ether theories that predicted observable effects from a preferred frame.
Local time: A time coordinate introduced in Lorentz's electrodynamics that transforms with position and velocity between frames. Its role in Lorentz's equations anticipated the time transformation without making time equally fundamental.
George FitzGerald: An Irish physicist who proposed that bodies contract along their motion through the ether. His contraction hypothesis supplied a physical explanation Lorentz incorporated into his theory.

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