**Electrodynamics and
"relativity"**

*Main article: Lorentz ether theory*

In 1892, with the attempt to explain the Michelson-Morley experiment, Lorentz proposed that moving bodies contract in the
direction of motion (see length
contraction; George FitzGerald had already arrived at this conclusion, see FitzGerald-Lorentz
Contraction). Lorentz worked on describing electromagentic phenomena (the propagation of light) in
reference frames that moved relative to each other. He discovered that the
transition from one to another reference frame could be simplified by using a
new time variable which he called *local time*. The local time depended on
the universal time and the location under consideration. Lorentz publications (of 1895[1] and 1899) [2] made use of the term local time
without giving a detailed interpretation of its physical relevance. In
1900, Henri Poincaré
called Lorentz's local time a "wonderful
invention" and illustrated it by showing that clocks in moving frames are
synchronized by exchanging light signals that are assumed to travel at the same
speed against and with the motion of the frame.[3]

In 1899, and again in 1904,[4] Lorentz added time
dilation to his transformations and published what Poincaré
in 1905 named Lorentz
transformations. It was apparently unknown to Lorentz
that Joseph Larmor
had used identical transformations to describe orbiting electrons in 1897. Larmor's and Lorentz's equations
look somewhat unfamiliar, but they are algebraically equivalent to those
presented by Poincaré and Einstein in 1905.[5]
Lorentz' 1904 paper includes the covariant
formulation of electrodynamics, in which electrodynamic
phenomena in different reference frames are described by identical equations
with well defined transformation properties. The paper clearly recognizes the
significance of this formulation, namely that the outcomes of electrodynamic experiments do not depend on the relative
motion of the reference frame. The 1904 paper includes a detailed discussion of
the increase of the inertial mass of rapidly moving objects. In 1905, Einstein
would use many of the concepts, mathematical tools and results discussed to
write his paper entitled electrodynamik known today
as the theory of special relativity.
Because Lorentz laid the fundaments for the work by
Einstein, this theory was called the *Lorentz**-Einstein
theory* originally.

**http://en.wikipedia.org/wiki/Hendrik_Lorentz**

What is now called **Lorentz****
Ether theory** ("LET") has its roots in Lorentz’**s**

"Theory of electrons", which was the final point in the
development of the classical “aethr theories” at the
end of the 19^{th} and at the beginning of the 20^{th} century.
An extension of the theory was developed in particular by Henri Poincaré,
who coined the name "The New Mechanics". One of its features was to
explain why no experiments had been able to detect any motion relative to an *immobile*
aether, which was done by introducing the Lorentz
transformation. Many aspects of Lorentz's theory
were incorporated into special
relativity (SR) with the works of Albert
Einstein and Hermann Minkowski.

Today LET is often treated as some sort of "Lorentzian"
or "neo-Lorentzian" interpretation of
special relativity. Introducing the effects of length contraction and time dilation in a "preferred" frame of reference leads to the Lorentz transformation and therefore it is not possible to
distinguish between LET and SR by experiment. However, in LET the existence of an *undetectable* ether is assumed and the validity of
the relativity principle seems to
be only coincidental, which is one reason why SR is commonly preferred over
LET.

**http://en.wikipedia.org/wiki/Lorentz_ether_theory**