How and why was the theory of aether rejected by science?


In the Middle Ages, it was obvious that the Earth is the center of the Universe and the Sun and planets revolve around it. After Copernicus, everyone was convinced that the center of the universe was the sun. Then it turned out that other stars are the same Suns as ours, and so on. Scientific progress is changing our understanding of how the world works.

Similarly, in physics in the past, there were many views that are recognized by the current science as incorrect or redundant. One of these theories is

In the 17th century, first Descartes and then Huygens suggested that light propagates in an invisible, all-pervading medium called ether. The name itself is borrowed from the ancient Greeks. The ether theory developed over the next two centuries and was pretty well developed.

It was assumed that light is waves in the ether. Just as sound waves need a medium in order to propagate, so according to the ideas of physicists of that time, light waves also needed a medium in which they can propagate. Therefore, the concept of the all-pervading, invisible ether appeared.

It was believed that light is a mechanical vibration of the ether caused by a light source and propagating at a tremendous speed. With the discovery of electromagnetism and the laws of classical electrodynamics, the opinion arose that the ether also serves as a medium for the propagation of electromagnetic waves.

Ether has also been tried to be used for a physical explanation of gravity. Since Newton’s law of universal gravitation had the form of a postulate, an axiom, i.e. statements without evidence.

The problem with the ether theory was that, according to it, the speed of light should be different for different frames of reference. If the observer moves in the ether towards the light source, then the speed of light should be greater, and if, on the contrary, the observer moves away from the light source, then for him the light should slow down.

But this was not confirmed by experiments. At first, it was believed that this is because the speeds at which we can move are negligible in order to notice the difference in the speed of light and this has long been considered a completely reasonable explanation.

Observing and measuring techniques improved and at the end of the 19th century Michelson and Morley set up a series of experiments to prove the existence of the ether.

The Earth revolves around the Sun and its direction of motion relative to the ether must constantly change. For half a year, the earth would have to move relative to the ether in one direction, and then half a year in the other. This means that one half of the year the speed of light should have been greater, and the second — less.

However, experiments have shown that this is not the case. Regardless of the direction of the Earth’s movement, the speed of light has always remained the same. Scientists have repeated experiments many times, looking for a problem in the accuracy of measurements, but in the end they were forced to admit that no «etheric wind» exists.

Many scientists tried to reconcile the theory of ether with the results of experiments. Lorenz did it best. He suggested that the ether is motionless and undetectable. Developing this theory, Lorentz came to formulas similar to the equations of the special theory of relativity, in particular, Lorentz came to the same conclusions about time dilation and length contraction when moving at near-light speeds.

Later, Einstein, who, although in his works did not mention the Michelson-Morley experiments, but was familiar with them, proposed the special theory of relativity (SRT), according to which there is no need for ether and which perfectly describes all the results of observations.

Unlike others, Lorentz’s theory of the ether is not wrong. The predictions made on its basis are identical to the predictions made on the basis of the STR. But there are two reasons why modern science prefers SRT to Lorentz’s theory of aether:

Thus, the early theories of the ether did not find experimental confirmation in the course of the Michelson-Morley experiments (as well as many subsequent ones), since the dependence of the speed of light on the frame of reference followed from the early theories of the ether, which was not found.

The updated theory of Lorentz’s ether is experimentally indistinguishable from Einstein’s SRT, however, the alleged presence of an undetectable ether is indistinguishable from its absence, in addition, the development of Lorentz’s theory does not give important scientific results, in contrast to the theory of relativity. That is why the ether theory was considered outdated.