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This article is about the emission theory of relativity. For the emission theory of vision, see Emission theory (vision). Emission theory or extramission theory is the proposal that Visual perception is accomplished by rays of Light emitted by the Eyes This

Emission theory (also called "emitter theory") was a competing theory for the special theory of relativity, explaining the results of the Michelson-Morley experiment. Special relativity (SR (also known as the special theory of relativity or STR) is the Physical theory of Measurement in Inertial The Michelson–Morley experiment, one of the most important and famous experiments in the History of physics, was performed in 1887 by Albert Michelson and Emission theories obey the principle of relativity by having no preferred frame for light transmission, but say that light is emitted at speed "c" relative to its source instead of applying the invariance postulate. A principle of relativity is a criterion for judging physical theories, stating that they are inadequate if they do not prescribe the exact same laws of physics in Light, or visible light, is Electromagnetic radiation of a Wavelength that is visible to the Human eye (about 400–700 Thus, emitter theory combines electrodynamics and mechanics with a simple Newtonian theory. Classical electromagnetism (or classical electrodynamics) is a theory of Electromagnetism that was developed over the course of the 19th century most prominently Mechanics ( Greek) is the branch of Physics concerned with the behaviour of physical bodies when subjected to Forces or displacements

Contents

History

The name most often associated with emission theory is Isaac Newton. Sir Isaac Newton, FRS (ˈnjuːtən 4 January 1643 31 March 1727) Biography Early years See also Isaac Newton's early life and achievements In his Corpuscular theory Newton visualised light "corpuscles" being thrown off from hot bodies at a nominal speed of c with respect to the emitting object, and obeying the usual laws of Newtonian mechanics (although he did also assign wave properties to light). In Optics, the corpuscular theory of light, set forward by Sir Isaac Newton, says that light is made up of small discrete particles called "corpuscles" (little

Albert Einstein is supposed to have worked on his own emission theory before abandoning it in favour of his special theory of relativity. Albert Einstein ( German: ˈalbɐt ˈaɪ̯nʃtaɪ̯n; English: ˈælbɝt ˈaɪnstaɪn (14 March 1879 – 18 April 1955 was a German -born theoretical Special relativity (SR (also known as the special theory of relativity or STR) is the Physical theory of Measurement in Inertial

Special relativity's geometrical simplicity was persuasive, but a convincing general disproof of emission theory proposed was still difficult to find, and some considered the main competitor to Einstein's special theory to be the emission theory proposed by Walter Ritz. Walther Ritz (b February 22, 1878 in Sion, Switzerland - d 7 July, 1909 in Göttingen) was a Swiss theoretical

Many years later R. S. Shankland reports Einstein as saying that Ritz' theory had been "very bad" in places and that he himself had eventually discarded emission theory because he could think of no form of differential equations that described it, since it leads to the waves of light becoming "all mixed up".

In 1913 Willem de Sitter wrote that the expected consequences of emission theory on the appearance of double stars, an extreme scrambling of their lightsignals, did not happen. Willem de Sitter ( May 6 1872 &ndash November 20 1934) was a Dutch mathematician physicist and astronomer This was widely accepted as definitive proof that emission theory was not viable.

Problems with emission theory

The simplest form of emission theory says that radiating objects throw off light with a speed of "c" relative to their own state of motion, and (unless we have reason to believe that the light changes speed in flight), we then expect light to be moving towards us with a speed that is offset by the speed of the distant emitter (c ± v) ). This description generates three "odd" results:

  1. If a radiant star moves across our field of vision, light given off by differently-moving atoms in its atmosphere should take different amounts of time to reach us. Since the retreating atoms would have a "red" Doppler shift, and the approaching ones a "blue" Doppler shift, the passing star might be expected to appear as a "rainbow streak".
  2. Similarly, if a radiant star is eclipsed, one might expect the eclipsing shadow to appear to intercept different colours of Doppler-shifted light in sequence - the eclipse might appear to have coloured fringes.
  3. For the case of a double-star system seen edge-on, light from the approaching star might be expected to travel faster than light from its receding companion, and overtake it. If the distance was great enough for an approaching star's "fast" signal to catch up with and overtake the "slow" light that it had emitted earlier when it was receding, then the image of the star system should appear completely scrambled.
  4. The results of high speed reenactments of the Ives-Stilwell experiment disagree with the emission theory

De Sitter argued that none of the star systems he had studied showed the extreme optical effect behaviour in [3], and this was considered the death knell for Ritzian theory and emission theory in general. The Ives–Stilwell experiment exploits the Transverse Doppler effect (TDE described by Albert Einstein in his 1905 paper According to simple Emission theory, Light thrown off by an object should move at a speed of c with respect to the emitting object.

Newton appears to have enquired whether or not moons of Jupiter showed coloured fringes at eclipse, suggesting that he may have already been aware of these arguments and problems.

Variations on a theme

Furthermore, quantum electrodynamics places the propagation of light in an entirely different, but still relativistic, context, which is completely incompatible with any theory that postulates a speed of light that is affected by the speed of the source.

References


see also: de Sitter double star experiment

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