Speed of Light in Various Directions
Most recent answer: 10/08/2016
- Russ Harris (age 68)
People worried about this possibility for a long time. If light traveled in a medium, like sound waves in water, then the speed of the wave would depend on the direction of the light with respect to the speed of the medium. The name people gave to this fictitious medium was the stationary lumineferous aether. If the earth were moving in this medium then the velocity of light would depend on the direction the earth is moving with respect to it. In 1887 Michelson and Morley performed an experiment that proved that this was not true.
They constructed a light interference experiment mounted on a stone block floating in a bath of liquid mercury. As the apparatus was slowly rotated they expected the interference fringes to change as the light beams alternatively were parallel or anti-parallel to the earth's motion with respect to a presumed stationary ether. Their results were null. No evidence was seen. Since then this experiment has been improved by many orders of magnitude. The conclusion is that light travels with the exact same speed in all directions.
(published on 10/08/2016)