This post is a continuation from The Boundaries of Science
To demonstrate how established scientific theories can be refuted, let’s look at the theory of Ether, which was the dominant theory for an entire generation of scientists.
Since Maxwell (1831–1879) formulated the electromagnetic theory in 1865, 19th century scientists had puzzled how electromagnetic waves, such as radio or light, traveled through vacuum and the emptiness of space. Just like waves in water or sound in air, the argument went, electromagnetic waves needed a physical medium to travel through. For this reason alone, a new substance, ether, was proposed. (Although the term ‘ether’ was borrowed from Aristotle, the 19th century’s ether was a different concept altogether.)
According to the theory, ether filled in the entire universe, including vacuum and the inside of material bodies. As such, it had to be a weightless, transparent, frictionless matter that did not take part in any physical or chemical interaction, and was, therefore, impossible to test or verify.
Yet, the theory of ether could predict that light emanating from a moving object in the direction of its movement would travel faster than light emanating from the same object in any other direction. (To illustrate, imagine an item thrown from a moving car. Clearly, if we threw it in the direction of our travel it would travel faster than if we threw it in the opposite direction.)
Michelson and Morley relied on this hypothesis in 1887, when they attempted to determine the speed of earth in space by measuring the difference between the speed of a beam of light traveling in the direction of earth, and that of a beam of light traveling perpendicular to earth’s movement.
Had Michelson and Morley detected the difference they expected, it would have put their names, in a side note, as the first scientists to measure the absolute speed of earth. As it turned out, the experiment failed and no difference was detected. Even though Michelson and Morley could not explain their result, it was sufficient to inflict a death sentence on the theory of ether, and to win Michelson the 1907 Nobel Prize for physics. This experiment subsequently led Einstein to develop the theory of relativity.