The Michelson-Morley Experiment
The Michelson-Morley experiment was an attempt to detect the theorized
"ether." This ether was proposed because there did not
seem to be any medium for the waves of light to propagate through-light
behaved as though it was composed of waves, but waves of what? Thus,
scientists postulated an ether which would carry light waves, just
as air carries sound waves.
If there was an ether, then the speed of light should be dependent
on the ether. If the speed of light were constant with respect to
the ether, then the measured speed of light in perpendicular directions
should be different due to the movement of the earth through the
ether. In 1887, A.A. Michelson and E.W. Morley refined an experiment
that Michelson had performed a few years earlier. They split a beam
of light in two, sending the two halves in different directions.
Each ray of light was reflected back and the two beams combined
again. By observing the interference
patterns, they were able to determine the difference in the speed
of light in the two perpendicular directions. It was zero. This
negative result served to discredit the idea of ether and eventually
led to Einstein's 1905 special
relativity, stating that the speed of light is a universal constant.
The Scottish Scientist