Portal:History of science/Article/Week 11, 2006
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In the late 19th century luminiferous aether ("light-bearing aether") was the term used to describe a medium for the propagation of light. Later theories including special relativity were formulated without the ether concept, and today the aether is considered to be an obsolete scientific theory.
Isaac Newton had assumed that light was made up of numerous small particles, in order to explain features such as its ability to travel in straight lines and reflect off surfaces. This theory was known to have its problems; although it explained reflection well, its explanation of refraction and diffraction was less pleasing. In order to explain refraction, in fact, Newton's Opticks (1704) postulated an "Aethereal Medium" transmitting vibrations faster than light, by which light (when overtaken) is put into "Fits of easy Reflexion and easy Transmission" (causing refraction and diffraction).
As optical theories changed, new, increasingly technical ether theories were proposed to explain the known properties of light; by the late 19th century, ether theories were important across the sciences, from physical chemistry to electron theory to optics and astronomy. In the early 20th century, after the acceptance of special relativity, many of the aether's hypothetical functions quickly became unnecessary.
