On the Electrodynamics of Moving Bodies
On the Electrodynamics of Moving Bodies is a paper published by Albert Einstein, originally in the German language journal Annalen der Physik (17, 891, 1905) as Zur Elektrodynamik bewegter Körper.
In this paper, Einstein was able to reconcile Maxwell's equations for electricity and magnetism with the laws of mechanics, by introducing major changes to mechanics close to the speed of light. This later became known as Einstein's Special theory of relativity.
At the time, it was known that Maxwell's equations, when applied to moving bodies, led to asymmetries, and that it had not been possible to discover any motion of the Earth relative to the 'light medium'. Einstein put forward two postulates to explain these observations. Firstly, he applied the classic principle of relativity, which stated that the laws of physics remained the same for any frame of reference, to the laws of electrodynamics and optics as well as mechanics. In the second postulate, Einstein proposed that the speed of light remained constant in all inertial frames of reference, independent of the state of motion of the emitting body.