Editing Special relativity (section)

=== Lack of an absolute reference frame ===
The [[principle of relativity]], which states that physical laws have the same form in each [[inertial reference frame]], dates back to [[Galileo Galilei|Galileo]], and was incorporated into Newtonian physics. But in the late 19th century the existence of [[electromagnetic radiation|electromagnetic waves]] led some physicists to suggest that the universe was filled with a substance they called "[[Luminiferous aether|aether]]", which, they postulated, would act as the medium through which these waves, or vibrations, propagated (in many respects similar to the way sound propagates through air). The aether was thought to be an [[preferred frame|absolute reference frame]] against which all speeds could be measured, and could be considered fixed and motionless relative to Earth or some other fixed reference point. The aether was supposed to be sufficiently elastic to support electromagnetic waves, while those waves could interact with matter, yet offering no resistance to bodies passing through it (its one property was that it allowed electromagnetic waves to propagate). The results of various experiments, including the Michelson–Morley experiment in 1887 (subsequently verified with more accurate and innovative experiments), led to the theory of special relativity, by showing that the aether did not exist.<ref>Staley, Richard (2009), "Albert Michelson, the Velocity of Light, and the Ether Drift", ''Einstein's generation. The origins of the relativity revolution'', Chicago: University of Chicago Press, {{isbn|0-226-77057-5}}</ref> Einstein's solution was to discard the notion of an aether and the absolute state of rest. In relativity, any reference frame moving with uniform motion will observe the same laws of physics. In particular, the speed of light in vacuum is always measured to be ''c'', even when measured by multiple systems that are moving at different (but constant) velocities.