Experiments by Rayleigh and Brace

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The experiments by Rayleigh and Brace (1902, 1904) should show whether the Lorentz contraction leads to birefringence . It was one of the first optical experiments to measure the relative motion of the earth and aether , which was accurate enough to determine the second order magnitude of v / c. The results were negative, which was of great importance for the development of the Lorentz transformation and thus the theory of relativity (see tests of the special theory of relativity ).

The experiments

To explain the negative outcome of the Michelson-Morley experiment , George Francis FitzGerald (1889) and Hendrik Antoon Lorentz (1892) introduced the contraction hypothesis , according to which a body is shortened during its movement through the stationary ether .

John William Strutt, 3rd Baron Rayleigh (1902) interpreted the Lorentz contraction as mechanical compression. This should lead to materials becoming optically anisotropic , the different refractive indices occurring in the process lead to birefringence . To measure this effect, he attached a 76 cm long tube to a board that could be rotated in relation to the movement of the earth, the ends of which were closed by glass. The tube was filled with either carbon disulfide or water, with the liquid between two Nicol prisms . Light was then sent back and forth through the liquid, using an electric lamp as the source and, in the further course, mainly lime light . The experiment was accurate enough to observe delays of 16000 of a half wavelength, i.e. of the order . Depending on the orientation relative to the movement of the earth, the expected delay due to birefringence would be of the order , i.e. within the scope of the measurement accuracy. Thus it was, besides the Michelson-Morley experiment and the Trouton-Noble experiment , one of the few experiments which were able to detect quantities of second order . However, the result was completely negative. Rayleigh repeated the experiment with layers of glass plates (but with an accuracy of 100 times less) and also got a negative result.

However, these experiments were criticized by DeWitt Bristol Brace (1904). Rayleigh did not take into account both the effects of contraction ( instead of ) and the refractive index accurately enough that the results were by no means conclusive. Brace therefore carried out much more precise experiments. He used a housing 4.13 m long, 15 cm wide and 27 cm deep, which was filled with water and which, depending on the experiment, could be rotated around a vertical or a horizontal axis. Sunlight was directed into the water through a system of lenses, mirrors and reflecting prisms and reflected 7 times. The beam covered 28.5 m, whereby a delay of would have been observable. The result was also negative here. Another experimental arrangement with glass instead of the liquid (accuracy:) also produced no trace of birefringence.

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The lack of birefringence was originally interpreted by Brace as a refutation of the Lorentz contraction. However, Lorentz (1904) and Joseph Larmor (1904) showed that if one keeps the contraction hypothesis and additionally carries out the transformation of the time coordinates accordingly, i. That is, the complete Lorentz transformation is used, the negative outcome can be explained. If, as Albert Einstein (1905), in the context of the special theory of relativity , one now accepts the relativity principle as valid from the start, the negative result is self-evident, because an observer who moves uniformly can consider himself to be stationary and consequently will not have any effect on his own Experience movement. The Lorentz contraction is consequently not measurable for a moving observer and has to be taken into account together with the time dilation for a not moving observer , which was later also confirmed with the Trouton-Rankine experiment (1908) and the Kennedy-Thorndike experiment (1933).

See also

Individual evidence

General literature:

  1. Laub, Jakob: About the experimental foundations of the principle of relativity . In: Yearbook of radioactivity and electronics . 7, 1910, pp. 405-463.
  2. ^ Edmund Taylor Whittaker : A History of the theories of aether and electricity , 1st edition. Edition, Longman, Green and Co., Dublin 1910.

Primary literature:

  1. Lord Rayleigh: Does Motion through the Aether cause Double Refraction? . In: Philosophical Magazine . 4, 1902, pp. 678-683.
  2. ^ Brace, DeWitt Bristol: On Double Refraction in Matter moving through the Aether . In: Philosophical Magazine . 7, No. 40, 1904, pp. 317-329.
  3. Lorentz, Hendrik Antoon: Electromagnetic phenomena in a system that moves with any speed that cannot be reached by light . In: Blumenthal, Otto & Sommerfeld, Arnold (Ed.): The principle of relativity. A collection of treatises 1904/13, pp. 6–26.
  4. ^ Larmor, Joseph: On the ascertained Absence of Effects of Motion through the Aether, in relation to the Constitution of Matter, and on the FitzGerald-Lorentz Hypothesis . In: Philosophical Magazine . 7, No. 42, 1904, pp. 621-625.