Luminiferous Ether:

In the year 1800s, physicists established that light has wavelike properties and in some manners looks like sound. Though light travels faster than sound. Though, light can travel via a vacuum, while sound cannot. The sound waves need a material medium like water, air, or metal to propagate. Most of the scientists considered light also should need some kind of medium, however what? What could subsist everywhere, even in a jar from which all the air was pump out? This unsolved medium was termed as luminiferous ether, or merely ether. It turned out to be nothing though a figment of the imagination.

When the ether exists, some of the scientists doubted, how it could pass right via everything, even the whole Earth, and obtain inside an evacuated chamber? How could the ether be noticed? One thought was to view when the ether "blows" against the Earth as our planet orbits about the Sun, and as the Solar System orbits about the center of the Milky Way galaxy, and as our galaxy drifts via the cosmos. When there is an "ether wind," then the speed of light must to be diverse in various directions. This, it was reasoned, must take place for the similar reason a passenger on a fast-moving truck measures the speed of sound waves coming from the frontage as faster than the speed of sound waves coming from at the back.

In the year 1887, an experiment was completed by two physicists named Albert Michelson and Edward Morley in an effort to find out how fast the "ether wind" is blowing and from which direction. The Michelson-Morley experiment, as it became recognized, showed that the speed of light is similar in all directions. This cast distrust on the ether theory. When the ether exists, then according to the outcomes obtained by Michelson and Morley, it should be moving right all along with the Earth. This seems to be so great a coincidence. Efforts were made to elucidate away this outcome by recommending that the Earth drags the ether all along with itself. Einstein could not believe that. He took the outcomes of the Michelson- Morley experiment at face value. The Einstein supposed that the Michelson-Morley experiment would have similar outcome for witnesses on the Moon, on any other planet, on a space ship, or anywhere in the world.