Luminiferous aether: Encyclopedia II - Luminiferous aether - End of aether?

Luminiferous aether - End of aether?

Aether theory was dealt another blow when the Galilean transformation and Newtonian dynamics were both modified by Albert Einstein's special theory of relativity, giving the mathematics of Lorentzian electrodynamics a new, "non-aether" context. Like most major shifts in scientific thought, the move away from aether theory did not happen immediately but, as experimental evidence built up, and as older scientists left the field and their places were taken by the young, the concept lost adherents.

Einstein based his special theory on Lorentz's earlier work, but instead of suggesting that the mechanical properties of objects changed with their constant-velocity motion through an aether, he took the somewhat more radical step of suggesting that the math was a general transformation, and that the Galilean transformation was a "special case" that worked only at the low speeds we had studied up to that time. By applying the transformation to all inertial frames of reference, he demonstrated that physics remained invariant as it had with the Galilean transformation, but that light was now invariant as well.

With the development of special relativity, the need to account for a single universal frame had disappeared -- and aether went along with it. For Einstein (but not for Lorentz) the transformation also implied something much more radical, that the concept of position in space or time was not absolute, but could differ depending on the observer's location and speed. This "oddness" of Einstein's interpretation led to special relativity being considered highly questionable for some time.

All of this left the problem of light propagation through a vacuum. However, in another paper published the same month, Einstein also made several observations on a then-thorny problem, the photoelectric effect. In this work he demonstrated that light can be considered as particles that have a "wave like nature". Particles obviously do not need a medium to travel, and thus, neither did light. This was the first step that would lead to the full development of quantum mechanics, in which the wave-like nature and the particle-like nature of light are both considered to be simplifications of what is "really happening".

Adapted from the Wikipedia article "End of aether?", under the G.N U Free Docmentation License. Please also see http://en.wikipedia.org/wiki