Einstein's theory of relativity, particularly the special theory of relativity, does not explicitly reject the possibility of an aether as a medium through which electromagnetic waves propagate. However, it provides an alternative framework that does not rely on the existence of an aether.
One of the fundamental principles of special relativity is the constancy of the speed of light in all inertial frames of reference. This means that the speed of light in a vacuum is the same for all observers, regardless of their relative motion. This principle was supported by experimental evidence, including the famous Michelson-Morley experiment conducted in 1887.
The existence of an aether was postulated to explain how electromagnetic waves could propagate through space. According to the classical understanding of waves, they require a medium to propagate. It was believed that electromagnetic waves, such as light, required a substance called the aether to transmit their vibrations.
However, Einstein's approach to special relativity challenged the need for an aether. Instead of postulating the existence of a medium, Einstein formulated the theory based on the idea that the laws of physics should be the same in all inertial frames of reference, and the speed of light should be constant for all observers. This led to the development of the Lorentz transformations, which describe how space and time coordinates transform between different inertial frames.
Einstein's approach treated space and time as unified entities, known as spacetime, where the concepts of length and duration become relative and depend on the observer's relative motion. The constancy of the speed of light in all frames is a fundamental consequence of this unified spacetime framework.
In this way, special relativity provides an alternative explanation for the behavior of light and other electromagnetic phenomena without relying on the existence of an aether. While the theory does not explicitly reject the possibility of an aether, it offers a more elegant and comprehensive framework for understanding the behavior of light and the nature of spacetime.