In the Middle Ages, it was obvious that the Earth was the center of the universe and the Sun and planets revolved around it. After Copernicus, everyone was convinced that the Sun was the center of the universe. Then it turned out that other stars were suns just like ours and so on. Scientific progress is changing our ideas about how the world works.
Similarly, in physics in the past, there were many theories that today’s science recognizes as incorrect or redundant. The aether theory is one of those concepts.
What is ether?
In the 17th century, first Descartes and then Huygens suggested that light propagates in an invisible, all-permeating medium called ether. The name itself is borrowed from the ancient Greeks. The theory of the ether evolved over the next two centuries and was quite well developed.
It was assumed that light is waves in the ether. Just as sound waves need a medium to propagate, so, according to the physicists of that time, light waves also needed a medium in which they could propagate. That is why the concept of an omnipresent, invisible aether appeared.
