Hi The Michelson-Morley experiment and similar linear interferometers are actually rotating when they are in use. They are thus similar to Sagnac-interferometers.
A rotating Michelson-Morley interferometer looks like in the attached picture. [image: image.png] The black interferometer in this picture rotates and thus has different positions at different times. The light-ray however is moving along a straight line and hits the end of the interferometer at time t0+dt and is reflected back at the origin at t0+2dt. As is seen in the picture the light is moving a somewhat shorter distance than the length of the interferometer. The path length of the light ray can be easily calculated. With angular velocity omega and length L of the interferometer and speed of light c the light ray path l becomes l = L*cos(omega*L/(2*c)) or relative to the interferometer length l/L = cos(omega*L/(2*c)) = sqrt(1-sin(omega*L/(2*c))^2) which for small angles approximates to sqrt(1-(omega*L/(2*c))^2) Compare this with the Lorentz-contraction L/L0 = sqrt(1-v^2/c^2) The expresions are definitely similar. They imply that v = omega*L/2. For an 11 meter long interferometer, the length that Michelson and Morley used in later experiments, v becomes 7.3 *10^-5 *11/2 = 4 * 10^-4 m/s which is a very low speed. Much lower than is detectable with such an interferometer. <http://en.wikipedia.org/wiki/Michelson%E2%80%93Morley_experiment#Early_experiments>The null result of the Michelson-Morley-interferometer is explained by Lorentz contraction: http://en.wikipedia.org/wiki/Michelson%E2%80%93Morley_experiment#Length_contraction So, would you say that the interferometer is shortened as special relativity says or that the light rays are shortened as shown above? David David Jonsson, Sweden, phone callto:+46703000370
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