Trouton–Noble experiment

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). Recent (1998) controversial claims of a positive result by Cornille et al. are described below.

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).

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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—small effects due to external electric and magnetic fields, for example, can make it impossible to distinguish a positive from a null result. It is for such reasons that results like Cornille's can be subject to dispute.

Controversy

There has been recent controversy because of a 1998 claim by Cornille to have observed a positive result in the Trouton-Noble experiment, contradicting both relativity and the other experiments of this nature. This remarkable claim has not been subsequently replicated. Moreover, this experiment has been criticized (Nieves et al., 2001) e.g. for a failure to shield the apparatus from external electric fields (unlike earlier experiments) induced via nearby objects, and so the validity of relativity is not questioned by almost all scientists.

Nieves et al. also predict that a very slight positive result might arise from the interaction with the Earth's magnetic field and its axial rotation; such a result would be quantitatively different from the type originally sought by Trouton and Noble, but could explain the result by Cornille, as Cornille's observation was qualitative and not quantitative. This explanation is based on standard electromagnetism and relativity.

See also

• Trouton-Rankine experiment

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).
• P. Cornille, "Correspondence: Making a Trouton-Noble experiment succeed," Galilean Electrodynamics 9 (2), 33 (1998).
• P. Cornille, "A linear Trouton-Noble experiment which shows the violation of Newton's third law," Hadronic J. Supplement 13 (2), 191–202 (1998).
• 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 Trouton-Noble 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).