Kennedy–Thorndike experiment

The Kennedy–Thorndike experiment first conducted in 1932, is a modified form of the Michelson–Morley experimental procedure, and tests special relativity.[1] [2] The modification is to make one arm of the classical Michelson–Morley (MM) apparatus shorter than the other one. While the Michelson-Morley experiment showed, that the speed of light is independent of the orientation of the apparatus, the Kennedy–Thorndike experiment showed that it is also independent of the velocity of the apparatus in different inertial frames. It also served as a test to indirectly verify time dilation: while the negative result of the Michelson-Morley experiment can be explained by length contraction alone, the negative result of the Kennedy–Thorndike experiment also requires time dilation besides length contraction to explain why no phase shifts will be detected while the earth moves around the sun. The first direct confirmation of time dilation was achieved by the Ives–Stilwell experiment. See also Tests of special relativity.

Contents

The experiment

The original Michelson–Morley experiment was useful for testing the Lorentz–FitzGerald contraction hypothesis only. Kennedy had already made several increasingly sophisticated versions of the MM experiment through the 1920s when he struck upon a way to test time dilation as well. In their own words:

The principle on which this experiment is based is the simple proposition that if a beam of homogeneous light is split [...] into two beams which after traversing paths of different lengths are brought together again, then the relative phases […] will depend [] on the velocity of the apparatus unless the frequency of the light depends […] on the velocity in the way required by relativity.

By making one arm of the experiment much shorter than the other, a change in speed of the earth would cause changes in the travel times of the light rays, from which a fringe shift would result except if the frequency of the light source would change to the same degree. In order to determine if such a fringe shift took place, the interferometer was made extremely stable and the interference patterns were photographed for later comparison. The tests were done over a period of many months. As no significant fringe shift was found, the experimenters concluded that time dilation occurs as predicted by Special relativity.

Recent experiments

Further information: Modern searches for Lorentz violation

Such experiments have been repeated with increased precision until today, using laser, maser, cryogenic optical resonators, etc.. Examples that considerably reduce the possibility of anisotropy, are Hils and Hall (1990),[3] Braxmeier et al. (2002),[4] Wolf et al. (2004).[5] Tobar et al. (2009)[6] which gave an upper limit of the velocity dependence of the speed of light of \leq10^{-13}.

Besides those terrestrial measurements, a Kennedy–Thorndike experiment was carried out by Müller & Soffel (1995) using Lunar Laser Ranging, i.e., signals between Earth and Moon have been evaluated. This experiment gave a negative result as well.[7]

See also

Isotropy of c
Lorentz invariance
Time dilation
Length contraction
Relativistic energy
Fizeau/Sagnac
Alternatives
General

References

  1. ^ Kennedy, R. J.; Thorndike, E. M. (1932). "Experimental Establishment of the Relativity of Time". Physical Review 42 (3): 400–418. Bibcode 1932PhRv...42..400K. doi:10.1103/PhysRev.42.400. 
  2. ^ Robertson, H. P. (1949). "Postulate versus Observation in the Special Theory of Relativity". Reviews of Modern Physics 21 (3): 378–382. Bibcode 1949RvMP...21..378R. doi:10.1103/RevModPhys.21.378. 
  3. ^ Hils, Dieter; Hall, J. L. (1990). "Improved Kennedy-Thorndike experiment to test special relativity". Phys. Rev. Lett. 64 (15): 1697–1700. Bibcode 1990PhRvL..64.1697H. doi:10.1103/PhysRevLett.64.1697. PMID 10041466. 
  4. ^ Braxmaier, C.; Müller, H.; Pradl, O.; Mlynek, J.; Peters, A.; Schiller, S. (2002). "Tests of Relativity Using a Cryogenic Optical Resonator". Phys. Rev. Lett. 88 (1): 010401. Bibcode 2002PhRvL..88a0401B. doi:10.1103/PhysRevLett.88.010401. PMID 11800924. 
  5. ^ Wolf, P.; Tobar, M. E.; Bize, S.; Clairon, A.; Luiten, A. N.; Santarelli, G. (2004). "Whispering Gallery Resonators and Tests of Lorentz Invariance". General Relativity and Gravitation 36 (10): 2351–2372. arXiv:gr-qc/0401017. Bibcode 2004GReGr..36.2351W. doi:10.1023/B:GERG.0000046188.87741.51. 
  6. ^ Tobar, M. E.; Wolf, P.; Bize, S.; Santarelli, G.; Flambaum, V. (2010). "Testing local Lorentz and position invariance and variation of fundamental constants by searching the derivative of the comparison frequency between a cryogenic sapphire oscillator and hydrogen maser". Physical Review D 81 (2): 022003. arXiv:0912.2803. Bibcode 2010PhRvD..81b2003T. doi:10.1103/PhysRevD.81.022003. 
  7. ^ Müller, J.; Soffel, M. H. (1995). "A Kennedy-Thorndike experiment using LLR data". Physics Letters A 198 (2): 71–73. Bibcode 1995PhLA..198...71M. doi:10.1016/0375-9601(94)01001-B.