Michelson and Morley used an interferometer to show that the speed of light is
constant, regardless of Earth's motion through any perceived luminiferous
aether. An analogy can be understood from the different times it takes for a
rowboat to travel two different round-trip paths in a river that flows at a
constant velocity \((u)\) downstream. Let one path be for a distance \(D\)
directly across the river, then back again; and let the other path be the same
distance \(D\) directly upstream, then back again. Assume that the rowboat
travels at constant speed, \(v\) (with respect to the water), for both trips.
Neglect the time it takes for the rowboat to turn around. Find the ratio of
the cross-stream time divided by the upstream-downstream time, as a function
of the given constants.