Speed of Light - History

History

History of measurements of c (in km/s)
1675 Rømer and Huygens, moons of Jupiter 220,000
1729 James Bradley, aberration of light 301,000
1849 Hippolyte Fizeau, toothed wheel 315,000
1862 Léon Foucault, rotating mirror 298,000±500
1907 Rosa and Dorsey, EM constants 299,710±30
1926 Albert Michelson, rotating mirror 299,796±4
1950 Essen and Gordon-Smith, cavity resonator 299,792.5±3.0
1958 K.D. Froome, radio interferometry 299,792.50±0.10
1972 Evenson et al., laser interferometry 299,792.4562±0.0011
1983 17th CGPM, definition of the metre 299,792.458 (exact)

Until the early modern period, it was not known whether light travelled instantaneously or at a very fast finite speed. The first extant recorded examination of this subject was in ancient Greece. The ancient Greeks, Muslim scholars and classical European scientists long debated this until Rømer provided the first calculation of the speed of light. Einstein's Theory of Special Relativity concluded that the speed of light is constant regardless of one's frame of reference. Since then, scientists have provided increasingly accurate measurements.

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