Trouton–Rankine experiment

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The Trouton-Rankine experiment was an experiment designed to measure if the Lorentz-FitzGerald contraction of an object according to one frame (as defined by the luminiferous aether) produced a measurable effect in the rest frame of the object, so that the ether would act as a "preferred frame". The experiment was first performed by Frederick Thomas Trouton and Alexander Oliver Rankine in 1908.

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The famous Michelson-Morley experiment of 1887 showed that the then accepted aether theory needed to be modified. FitzGerald and Lorentz, independent of each other proposed a length contraction of the experimental apparatus in the direction of motion (with respect to the Luminiferous aether) that would explain the null result of the Michelson Morley experiment. Trouton made several experiments seeking for a measureable effect of this contraction in the lab frame (the inertial frame of reference of an observer co-moving with the experimental apparatus). He made several attempts with Henry R. Noble in the Trouton–Noble experiments and later in 1908 with Rankine in the Trouton-Rankine experiment.

By 1908 however, the current theories of electrodynamics at the time, both Lorentz ether theory and Special Relativity which did not include an aether, both predicted that the Lorentz-FitzGerald contraction is not measurable in a co-moving frame. Even before the modern version of Lorentz ether theory finalized by Poincare in 1906, Lorentz advocated an immovable pervading aether which he felt was the correct frame to work out Maxwell's equations in. Trouton instead did the calculations using his own interpretation of electrodynamics, calculating the length contraction according to the velocity of the experimental apparatus in the aether frame, but then calculating the electrodynamics by applying Maxwell's equations and Ohm's law in the lab frame. According to Trouton's view of electrodynamics, the calculations then predicted a measurable effect of the length contraction in the lab frame.

Trouton, together with A. O. Rankine, set out to verify this in 1908 by attempting to measure the change of the resistance of a coil as they changed its orientation to the "aether velocity" (the velocity of the lab through the luminiferous aether). This was done by putting four identical such coils in a Wheatstone bridge configuration which allowed them to precisely measure any change in resistance. The circuit was then rotated through 90 degrees about its axis as the resistance was measured. Because the Lorentz-FitzGerald contraction is only in the direction of motion, from the point of view of the "Aether frame" the length of the coils depended on their angle with respect to their Aether velocity. Trouton and Rankine therefore believed that the resistance as measured in the rest frame of the experiment should change as the device was rotated. However their careful measurements showed no detectable change in resistance.[1] This suggested that if the Lorentz-FitzGerald contraction existed, it was not measurable in the rest frame of the object.

A similar experiment was performed several times by Chase and Tomaschek at a higher precision, but with the same results.[2][3][4][5][6]

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[edit] References

  1. ^ Trouton F. T., Rankine A. (1908). "On the electrical resistance of moving matter". Proc. Roy. Soc. 80 (420). doi:10.1098/rspa.1908.0037. 
  2. ^ Carl T. Chase (1927). "The Trouton-Noble Ether Drift Experiment" (subscription required). Phys. Rev. 30 (516): 516–519. doi:10.1103/PhysRev.30.516. 
  3. ^ R. Tomaschek (1924). "The conduct of light of extraterrestrial light sources". Annalen der Physik 73: 105–126. 
  4. ^ R. Tomaschek (1925). "Attempt at the locating of the electrodynamic effect of earth movements at high altitudes I". Annalen der Physik 78: 743–756. 
  5. ^ R. Tomaschek (1926). "Concerning an experiment on the location of electrodynamic effects of the movement of the Earth at high altitudes II". Annalen der Physik 80: 509–514. 
  6. ^ R. Tomaschek (1927). "Comments on my tests on the detection of electrodynamic effects at high altitudes". Annalen der Physik 84: 161–162. 

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