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- 3.5 - New look on Michelson and Morley 1887 experiment

by Denys LÉPINARD

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During the XIXth century, it turned more and more evident that light is formed of waves (double-slit experiment of Thomas Young in 1801; works of Augustin Fresnel on undulatory optics from 1814 to 1827; description of light as an electromagnetic wave by Clerk Maxwell in 1860). Therefore it became obvious that matter and radiations was steeping in an ideal medium, called ether and which allowed this radiations to propagate. Michelson and Morley attempted in 1887 an experiment aiming at measuring the movement of the Earth in ether. They constructed an interferometer, a device with two perpendicular and equal arms went through by two light beams from the same source. Their hypothesis was if the apparatus travelled, jointly with Earth, in one direction of space, light rays, them solid with ether, would not be propagated at the same speed in both arms and would be out of a phase when reunited. One could then observe interference fringes.
The experiment, carried out several times did not give any result, neither then, nor later on. Although recently some authors think they can prove, under certain conditions, a difference in the march of light between the two arms; they propose to do the experiment again, once more. (Catching the cosmic Wind - New Scientist, 2 April 2005, Vol 186- N°2493)
Scientific community, struck by that lack of result, has soon argued about possible explanations and has formulated some hypothesis. Lorentz and Poincaré proposed equations of motion where light speed was treated as impassable limit. In 1905, Einstein, taking back these works, publishes a series of articles, founder of special Relativity. He states in his preamble, "the introduction of a "light-ether" will prove to be superfluous"; Scientifics hasten to interpret :"ether does not exist". And that became an intangible dogma in the XXth century, in spite of Einstein own denials; in 1920 for instance :"the hypothesis of ether in itself is not in conflict with the special theory of relativity" (Ether and the theory of Relativity, an address delivered on May 5th, 1920, in the University of Leyden)

At the beginning of the XXth century, experiments confirm the wave nature, not only of light, but also of matter. Louis de Broglie, in his 1924 thesis, set up the general equation :

hν = mc2

Following that, Quantum Mechanics develops and owes its success to equations that deal with matter as waves; but it does not seem to put to itself this question : in what can those waves vibrate ? And the dogma of non-existence of ether holds always well.

At the end of this short historical reminder, let's come back to origin, to say the Michelson and Morley experiment.
- The arms of the interferometer are made of matter; therefore, as we have just seen, of waves. If ether exists, matter and light, when moving in this ether, are both bound by the same constraints from it. The arms of the interferometer deform exactly in the same way as light rays that travel in them. Then, there is no difference of march between light beams. And experiment is inevitably negative.
As soon as 1893, FitzGerald then Lorentz have put forward such an explanation, but that has not been held. We can take it back now with more strength, supported by the consideration that matter is made of waves. This is a fondamental point of our theory : that that grows shorter is wave-made matter; it does so because these waves, in the direction of their absolute motion, shrink like every train of waves emitted by a moving source; or like a moving wave-receiving can feel. This is a physical phenomenon quite understandable, explained and measured. That is no longer mysterious modifications of space and time according to speed as assumes Special Relativity
Contrarily to conclusions that were made, the Michelson and Morley experiment does not prove the non-existence of ether, but quite the identical wave nature between light and matter. As for ether, we can't always say anything, except that a medium is much needed for these waves to vibrate and to propagate. An ideal medium on which we will have occasion to come again; we will be enlighten by which we have already treated : the wave nature of matter and how it behaves in motion.

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april 2005