Trouton–Noble experiment

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The Trouton–Noble experiment attempted to detect motion of the Earth through the luminiferous aether, and was conducted in 1901–1903 by Frederick Thomas Trouton (who also developed the Trouton's ratio) and H. R. Noble. It was based on a suggestion by George FitzGerald that a charged parallel-plate capacitor moving through the aether should orient itself perpendicular to the motion. Like the earlier Michelson–Morley experiment, Trouton and Noble obtained a null result: no motion relative to the aether could be detected.

This null result was reproduced, with increasing sensitivity, by Chase in 1927 and Hayden in 1994. Such experimental results are now seen, consistent with special relativity, to reflect the constancy of the speed of light and the absence of any absolute rest frame (or aether).

Contents 1 Experiment 2 Analysis 3 See also 4 References

[edit] Experiment

In the experiment, a suspended parallel-plate capacitor is held by a fine torsion fiber and is charged. If the aether theory were correct, the change in Maxwell's equations due to the Earth's motion through the aether would lead to a torque causing the plates to align perpendicular to the motion. On the other hand, the assertion of special relativity that Maxwell's equations are invariant for all frames of reference moving at constant velocities would predict no torque (a null result). Thus, unless the aether were somehow fixed relative to the Earth, the experiment is a test of which of these two descriptions is more accurate.

Like any experiment measuring very small forces, the Trouton–Noble experiment is very difficult to control so as to eliminate outside influences. For example, based on standard electromagnetism and relativity, Nieves et al. predict that a very slight deflection could result from the interaction with the Earth's magnetic field and its axial rotation. However, this effect would be far smaller than that originally sought by Trouton and Noble.

[edit] Analysis

The detailed relativistic analysis of the null result requires care to correctly reconcile, for example, the effects seen by observers in different frames of reference (see e.g. Teukolsky, 1996 and Jefimenko, 1999), but ultimately all such theoretical descriptions are shown to give the same result. The early history of descriptions of this experiment is reviewed by Janssen (1995).

The Trouton–Noble experiment is essentially equivalent to the so-called "right angle lever paradox" thought experiment, first discussed by Lewis and Tolman in 1909. In both cases an apparent net torque on an object (when viewed from a certain frame of reference) does not result in any rotation of the object, and in both cases this is explained by correctly accounting, in the relativistic way, for the transformation of all the relevant forces and momenta.

[edit] See also

• Trouton–Rankine experiment

[edit] References

• F. T. Trouton and H. R. Noble, "The mechanical forces acting on a charged electric condenser moving through space," Phil. Trans. Royal Soc. A 202, 165–181 (1903).
• Carl T. Chase, "The Trouton–Noble ether drift experiment," Phys. Rev. 30, 516–519 (1927).
• H. C. Hayden, "High sensitivity Trouton–Noble experiment," Rev. Scientific Instruments 65 (4), 788–792 (1994).
• Saul A. Teukolsky, "The explanation of the Trouton–Noble experiment revisited," Am. J. Physics 64 (9), 1104–1109 (1996).
• Oleg D. Jefimenko, "The Trouton–Noble paradox," J. Phys. A. 32, 3755–3762 (1999).
• J. Franklin, "The absence of 'torque' in the Trouton–Noble experiment", arXiv:physics/0603110.
• L. Nieves, M. Rodriguez, G. Spavieri, and E. Tonni, "An experiment of the TroutonNoble type as a test of the differential form of Faraday's law," Il Nuovo Cimento 116 B (5), 585–592 (2001).
• Michel Janssen, "A comparison between Lorentz's ether theory and special relativity in the light of the experiments of Trouton and Noble, Ph.D. thesis (1995). Online: TOC, pref., intro-I, 1, 2, intro-II, 3, 4, refs.
• Michel Janssen, "The Trouton Experiment and E = mc²," Einstein for Everyone course at UMN (2002).
• Kevin Brown, "Trouton-Noble and The Right-Angle Lever at MathPages.