Category:Emission Theory

This category collects emission theories of light — the classical proposition, most closely associated with Walther Ritz (1878–1909), that light is emitted at speed c relative to its source, so that an observer measures c ± v.

Emission theory was a serious competitor to special relativity in the years after 1905, and its rejection turned on a small number of arguments: Willem de Sitter's 1913 claim that source-dependent light speeds would grossly distort the observed orbits of spectroscopic binary stars, the Sagnac effect, and later the observation of light from moving sources in accelerators. Ritz's early death removed its most capable advocate.

The tradition has continued on the margins, and the entries here take up de Sitter's argument directly — variously by disputing what binary star observations actually show, by combining emission theory with an entrained medium so that the light is regulated after emission, or by reinterpreting the accumulated wavelength changes over long light paths. See also Category:Light, Category:Aether and Category:Relativity.