The history of special relativity consists of many theoretical results and empirical findings obtained by Albert A. Michelson, Hendrik Lorentz, Henri Poincaré and others. It culminated in the theory of special relativity proposed by Albert Einstein and subsequent work of Max Planck, Hermann Minkowski and others.
Introduction Although Isaac Newton based his physics on absolute time and space, he also adhered to the principle of relativity of Galileo Galilei restating it precisely for mechanical systems.Principia, Corollary 5 to the Laws of Motion This can be stated: as far as the laws of mechanics are concerned, all observers in inertial motion are equally privileged, and no preferred state of motion can be attributed to any particular inertial observer. However, electromagnetic theory and electrodynamics, developed during the 19th century, did not obey Galileo's relativity. The wave theory of electromagnetism or light viewed as a disturbance of a "light medium" or luminiferous aether was widely accepted. The theory reached its most developed form in the work of James Clerk Maxwell. Maxwell thought all optical and electrical phenomena propagate through an aether, making his equations valid only for systems at rest with respect to that aether. The concept of this aether was widely discussed and subjected to many unsuccessful efforts experimentally determine motion relative to the aether.Whittaker (1951), 128ff
The failure of any experiment to detect motion through the aether led Hendrik Lorentz, starting in 1892, to develop a theory of electrodynamics based on an immobile luminiferous aether (about whose material constitution Lorentz did not speculate), physical length contraction, and a "local time" in which Maxwell's equations retain their form in all inertial frames of reference. Working with Lorentz's aether theory, Henri Poincaré, having earlier proposed the "relativity principle" as a general law of nature (including electrodynamics and gravitation), used this principle in 1905 to correct Lorentz's preliminary transformation formulas, resulting in an exact set of equations that are now called the Lorentz transformations.
A little later in the same year Albert Einstein published his original paper on special relativity. He independently derived and radically reinterpreted the Lorentz transformations by changing the fundamental definitions of space and time intervals, while abandoning the absolute simultaneity of Galilean kinematics, avoiding the need for any reference to a luminiferous aether in classical electrodynamics.Chen (2011), Page 92 Before Einstein's paper Galilean relativity applied to particle mechanics and Lorentzian relativity to electrodynamics; afterwards both systems used Lorentz transformations. In subsequent work Hermann Minkowski, introduced a 4-dimensional geometric "spacetime" model, Arnold Sommerfeld developed the electromagnetic tensor, and Max Planck applied the concept of special relativity to relativistic Lagrangian mechanics.Darrigol (2005), 22
The special theory of relativity gave invariant laws of physics in inertial frames of reference, but the meaning of these frames was unclear until Einstein's later development of his equivalence principle and general theory of relativity. In comparing to the general theory, Einstein specifically called his earlier work "special theory of relativity" (German: Spezielle Relativitätstheorie) in two short papers published in November 1915; English translation on pp. 98-107 of "The collected papers of Albert Einstein", English translation volume 6; English translation on pp. 117-120 of "The collected papers of Albert Einstein", English translation volume 6; See also the alternative translation The Field Equations of Gravitation on Wikisource and in a long review article published in 1916,; English translation The Foundation of the Generalised Theory of Relativity by Satyendra Nath Bose on Wikisource saying he meant a restriction to frames in uniform motion, and was featured in the title of Einstein's popular book Relativity: The Special and the General Theory first published in 1916.
Aether and electrodynamics of moving bodies
Aether models and Maxwell's equations Following the work of Thomas Young (1804) and Augustin-Jean Fresnel (1816), it was believed that light propagates as a transverse wave within an elastic medium called luminiferous aether. However, a distinction was made between optical and electrodynamical phenomena so it was necessary to create specific aether models for all phenomena. Attempts to unify those models or to create a complete mechanical description of them did not succeed,Whittaker (1951), 128ff but after considerable work by many scientists, including Michael Faraday and Lord Kelvin, James Clerk Maxwell (1864) developed an accurate theory of electromagnetism by deriving a set of equations in electricity, magnetism and inductance, named Maxwell's equations. He first proposed that light was in fact undulations (electromagnetic radiation) in the same aetherial medium that is the cause of electric and magnetic phenomena. However, Maxwell's theory was unsatisfactory regarding the optics of moving bodies, and while he was able to present a complete mathematical model, he was not able to provide a coherent mechanical description of the aether.Whittaker (1951), 240ff
After Heinrich Hertz in 1887 demonstrated the existence of electromagnetic waves, Maxwell's theory was widely accepted. In addition, Oliver Heaviside and Hertz further developed the theory and introduced modernized versions of Maxwell's equations. The "Maxwell–Hertz" or "Heaviside–Hertz" equations subsequently formed an important basis for the further development of electrodynamics, and Heaviside's notation is still used today. Other important contributions to Maxwell's theory were made by George FitzGerald, Joseph John Thomson, John Henry Poynting, Hendrik Lorentz, and Joseph Larmor.Whittaker (1951), 319ffJanssen/Stachel (2004), 20
Search for the aether Regarding the relative motion and the mutual influence of matter and aether, there were two theories, neither entirely satisfactory. One was developed by Fresnel (and subsequently Lorentz). This model (stationary aether theory) supposed that light propagates as a transverse wave and aether is partially dragged with a certain coefficient by matter. Based on this assumption, Fresnel was able to explain the aberration of light and many optical phenomena.Whittaker (1951), 107ff
The other hypothesis was proposed by George Gabriel Stokes, who stated in 1845 that the aether was fully dragged by matter (later this view was also shared by Hertz). In this model the aether might be (by analogy with pine pitch) rigid for fast objects and fluid for slower objects. Thus the Earth could move through it fairly freely, but it would be rigid enough to transport light.Whittaker (1951), 386f Fresnel's theory was preferred because his dragging coefficient was confirmed by the Fizeau experiment in 1851, which measured the speed of light in moving liquids.Janssen/Stachel (2004), 4–15
Albert A. Michelson (1881) tried to measure the relative motion of the Earth and aether (the "aether-wind"), as it was expected in Fresnel's theory, by using an interferometer. He could not determine any relative motion, so he interpreted the result as a confirmation of the thesis of Stokes.Whittaker (1951), 390f However, Lorentz (1886) showed Michelson's calculations were wrong and that he had overestimated the accuracy of the measurement. This, together with the large margin of error, made the result of Michelson's experiment inconclusive. In addition, Lorentz showed that Stokes' completely dragged aether led to contradictory consequences, and therefore he supported an aether theory similar to Fresnel's.Whittaker (1951), 386ff To check Fresnel's theory again, Michelson and Edward W. Morley (1886) performed a repetition of the Fizeau experiment. Fresnel's dragging coefficient was confirmed very exactly on that occasion, and Michelson was now of the opinion that Fresnel's stationary aether theory was correct.Janssen/Stachel (2004), 18–19 To clarify the situation, Michelson and Morley (1887) repeated Michelson's 1881 experiment, and they substantially increased the accuracy of the measurement. However, this now famous Michelson–Morley experiment again yielded a negative result: no motion of the apparatus through the aether was detected (although the Earth's velocity differs by 60 km/s in the northern winter compared to the summer). So the physicists were confronted with two seemingly contradictory experiments: the 1886 experiment as an apparent confirmation of Fresnel's stationary aether, and the 1887 experiment as an apparent confirmation of Stokes' completely dragged aether.Janssen/Stachel (2004), 19–20
A possible solution to the problem was shown by Woldemar Voigt (1887), who investigated the Doppler effect for waves propagating in an incompressible elastic medium and deduced transformation relations that left the wave equation in free space unchanged, and explained the negative result of the Michelson–Morley experiment. The Voigt transformations include the Lorentz factor for the - and -coordinates, and a new time variable which later was called "local time". However, Voigt's work was completely ignored by his contemporaries.Miller (1981), 114–115Pais (1982), Chap. 6b
FitzGerald (1889) offered another explanation of the negative result of the Michelson–Morley experiment. Contrary to Voigt, he speculated that the intermolecular forces are possibly of electrical origin so that material bodies would contract in the line of motion (length contraction). This was in connection with the work of Heaviside (1887), who determined that the electrostatic fields in motion were deformed (Heaviside Ellipsoid), which leads to physically undetermined conditions at the speed of light.Miller (1981), 99–100 However, FitzGerald's idea remained widely unknown and was not discussed before Oliver Lodge published a summary of the idea in 1892.Brown (2001) Also Lorentz (1892b) proposed length contraction independently from FitzGerald in order to explain the Michelson–Morley experiment. For plausibility reasons, Lorentz referred to the analogy of the contraction of electrostatic fields. However, even Lorentz admitted that that was not a necessary reason and length contraction consequently remained an ad hoc hypothesis.Miller (1981), 27–29Janssen (1995), Ch. 3.3
Lorentz's theory of electrons