basis for the development of the Michelson interferometer and, in turn, Michelson and Morley’s attempt to measure the ‘ether wind’ as light travels through space. The null result of their attempt is one of the foundational experiments that lead ultimately to the theory of Special Relativity. Suppose you want to swim across a river with a width, D, that has a constant current, v. You can swim with a constant relative speed, u, and the goal is to return to your starting point. Determine the time it would take to swim a distance D directly upstream and return in terms of D, u and v. Then determine the time it would take to swim directly across the river and back again. (Notice in the second case that you must swim at an angle: u will be the hypotenuse of the righ
the basis for the development of the Michelson
interferometer and, in turn, Michelson and Morley’s attempt to measure the ‘ether wind’ as
light travels through space. The null result of their attempt is one of the foundational
experiments that lead ultimately to the theory of
Suppose you want to swim across a river with a width, D, that has a constant current, v. You can
swim with a constant relative speed, u, and the goal is to return to your starting point.
Determine the time it would take to swim a distance D directly upstream and return in terms of
D, u and v. Then determine the time it would take to swim directly across the river and back
again.
(Notice in the second case that you must swim at an angle: u will be the hypotenuse of the right
triangle.)
Follow up
Your equations should show that if v=0, then the times would be the same
ttot = 2D/u
But if the river’s velocity is not zero, then there is a time lag between the two trips.
This time lag would result in a phase shift between two light waves as they travelled
perpendicular to each other through the ‘ether’ (the proposed medium for light) and back
again, which would be identifiable as an interference pattern.
The fact that no interference was detected suggested that there was no ether wind, and
logically, no ether. So, then what is ‘waving’ for a light wave? Einstein’s answer: the
mathematics.
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