What is now often called
Lorentz ether theory (LET) has its roots in
Hendrik Lorentz's "theory of electrons", which was the final point in the development of the classical
aether theories at the end of the 19th and at the beginning of the 20th century. Lorentz's initial theory was created between 1892 and 1895 and was based on a completely motionless aether. It explained the failure of the negative aether drift experiments to first order in
v/
c by introducing an auxiliary variable called "local time" for connecting systems at rest and in motion in the aether. In addition, the negative result of the
Michelson–Morley experiment led to the introduction of the hypothesis of
length contraction in 1892. However, other experiments also produced negative results and (guided by
Henri Poincaré's
principle of relativity) Lorentz tried in 1899 and 1904 to expand his theory to all orders in
v/
c by introducing the
Lorentz transformation. In addition, he assumed that also non-electromagnetic forces (if they exist) transform like electric forces. However, Lorentz's expression for charge density and current were incorrect, so his theory did not fully exclude the possibility of detecting the aether. Eventually, it was
Henri Poincaré who in 1905 corrected the errors in Lorentz's paper and actually incorporated non-electromagnetic forces (including
gravitation) within the theory, which he called "The New Mechanics". Many aspects of Lorentz's theory were incorporated into
special relativity (SR) with the works of
Albert Einstein and
Hermann Minkowski.