||The English used in this article may not be easy for everybody to understand. (September 2011)|
Luminiferous aether is something once believed to fill the Universe and explain how the transmission of waves of light can happen. People believed that light was a kind of wave. Waves travel over the surface of water in a pond, through the air in a room, etc. All waves that people had studied before had traveled through something. Sound waves traveled faster through steel than through air. So people imagined that light had to travel through something too. Since light travels faster than anything else, light should travel through something more rigid (like steel) than anything else. But at the same time this substance would have to be entirely yielding so that it would not slow down the movements of planets and cause them to eventually fall into their suns. The people coming before Albert Einstein believed this stuff to exist, and they called it the "Luminiferous aether."
If we were traveling on a boat moving through an ocean current, then we could see changes in the rate that waves appeared to travel depending on whether we were moving with the current, across the current, or against the current.
People who studied the physics of this problem made experiments to try to make this question become clear. The Michelson-Morley Experiment showed that there was no substance through which light traveled. This negative result was a great success for science. It took down one untrue belief that stood in our way of true understanding. It said that there is no luminiferous aether.
The easiest way to see the general idea is to imagine a very fast spaceship moving at one half the speed of light from one star to another. The spaceship has two light-speed meters, one pointing backward and one pointing forward. Since the spaceship is running away from the photons given off by the yellow star, and running toward the photons given off by the blue star, our ordinary experience leads us to expect that we would measure the speed of the yellow photons as 150,000 kilometers per second, and the speed of the blue photons as 450,000 kilometers per second. But the truth is that both photons are measured at 300,000 km/sec. That result indicates that speeds do not add up the way we ordinarily expect speeds to add together.
Albert Einstein made a basic change in how we understand things. He said that light always moves at 300,000 km/sec and we just have to accept that fact. If we do, then we will find that everything else makes sense. If we do not accept that fact, then we will have to make up explanations for all sorts of inconsistencies. We do not need the hypothesis of the luminiferous aether.
Outside readings [change]
http://physicsworld.com/cws/article/news/40355 A recent study is much more precise than the one by Michelson and Morley, but it still shows that the speed of light is constant no matter which direction one is moving in.