For the ancient Greeks, ether was a fifth element that formed a celestial sphere outside the Earth.
This element, according to ancient Greek theory, was different from the elements found on Earth (air, water, fire and earth), because it would be something more magnificent and grandiose than the air we breathe.
It was believed that through the ether it would be possible to identify whether the analyzed bodies were in motion or inert.
Based on this theory, or against it, physicists began to analyze the behavior of light. After such observations, around the 17th century, two theories were put forward.
The first was Newton’s theory, which believed that light was corpuscular in nature. For him, the formation of light happened by beams of small particles.
The second theory was that of Huygens, who defended the fact that light results from a continuous transmission of pressure from a medium more relative to ether than air.
Newton performed several experiments in order to confirm his theory and was able to conclude that light is the result of several colors, not just a single color. He believed that light was composed of one or several corpuscular types.
According to Newton, the speed of light would increase when passing from a less dense to a denser medium. Example: Light passing from vacuum to water.
A fact that was overturned in 1850 by Foucault, when proving that Newton’s theory was wrong, and that light increases its speed when passing from a denser to a less dense medium.
Huygens, in turn, believed that the light came from an oscillating medium, which allows us to understand today that in a homogeneous medium with the same characteristics, the wave moves maintaining its shape throughout its journey: this happens with the condition of there are no obstacles.
The idea and theories about the existence of the ether fell apart when Albert Einstein published and showed the world his Theory of Relativity, in which he proved that we cannot rely on an absolute reference, due to the constant changes that occur in nature.