|
Variable speed of light (VSL) is a hypothesis that states that the speed of light, usually denoted by ''c'', may be a function of space and time. Variable speed of light occurs in some situations of classical physics as equivalent formulations of accepted theories, but also in various alternative theories of gravitation and cosmology, many of them non-mainstream. In classical physics, the refractive index describes how light slows down when traveling through a medium. The speed of light in vacuum instead is considered a constant, and defined by the SI as 299792458 m/s. Alternative theories therefore usually modify the definitions of meter and seconds. VSL should not be confused with faster than light theories. Notable VSL attempts have been done by Einstein in 1911, by Robert Dicke in 1957, and by several researchers starting from the late 1980s. Since some of them contradict established concepts, VSL theories are a matter of debate. ==Einstein's VSL attempt in 1911== While Einstein first mentioned a variable speed of light in 1907, he reconsidered the idea more thoroughly in 1911. In analogy to the situation in a medium, where a shorter wavelength , by means of , leads to a lower speed of light, Einstein assumed that clocks in a gravitational field run slower, whereby the corresponding frequencies are influenced by the gravitational potential (eq.2, p. 903): : Einstein commented (pages 906–907): In a subsequent paper in 1912, he concluded that: However, Einstein deduced a light deflection at the Sun of “almost one arcsecond” which is just one-half of the correct value later derived by his theory of general relativity. While the correct value was later measured by Eddington in 1919, Einstein never gave up his VSL theory but calculated it differently in his General Theory of 1915 and 5 editions of his book beginning with equation 107 and the several paragraphs that follow it. Notably, in 1911 he had considered variable time only, while in general relativity, albeit in another theoretical context, both space and time measurements are influenced by nearby masses. Many scientist including Peter Bergmann are in disagreement with Einstein while other scientist most notably Max Born are in agreement. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Variable speed of light」の詳細全文を読む スポンサード リンク
|