Michelson-Morley Experiment

SITE CREATED BY NEIL MOORE

Introduction to Light

During the mid-1800's, James Clerk Maxwell showed that, in free space, light moved with a velocity of c = 3.00 x 10⁸ m/s.  At this time, little was fully understood concerning light except the fact that it was a wave.  Being a wave, however, brought up an interesting point; it needed a medium to propagate through just like the others. (i.e. mechanical, sound, etc.)

Physicists of the late 1800's believed that the medium for light was the "ether wind".  This hypothetical wind was believed to be at rest as the Earth traveled through it; or in other words, the Earth be at rest and the wind blow over it with a velocity v = 3.00 x 10⁴ m/s.

The question is:  Does light obey Galilean transformations?  Namely, when traveling with the wind, is its velocity c + v and when traveling against, c - v?  The direct approach would be to shoot a beam of light into the wind and have a mirror reflect it back.  The difference in velocity would be twice the ether speed, however, there was no feasible way to detect such a small change in velocity.  So Albert Abraham Michelson thought of the idea of using the wave properties of light rather than its translational properties in order to answer the question of the ether wind.