35.4 Absolute Frame of Reference
The equivalence of all inertial frames of references as far as Newtonian Mechanics is concerned implies that no privileged frame of reference at absolute rest is required, relative to which all other inertial frames of references are in uniform translational motion. This is so because of the Invariance of Newton's laws of motion under transformations from one to another such frame. If the transformations of Maxwell's equations of the Electromagnetic field from one to another inertial frame of reference are carried out under equations (1) then it is found that Maxwell's field equations are not invariant.
The non invariance of Maxwell's equations under Galilean Transformations
implies that the mathematical form of the field equations will be
different in different inertial frames; but the equations as in
the form given by Maxwell represent the essence of experimental
laws and hence their form must be correct at least in one inertial
frame. This preferred inertial frame must be at absolute rest, then
and only then Maxwell's original equations will truly represent
the field equations. This hypothetical frame identified as the frame
of reference with the origin at the center of mass of system of
fixed stars is called the "Absolute Frame". In this frame
Ether the hypothetical medium of propagation of Electro magnetic
light waves must also be at rest. Thus, the non invariance of Maxwell's
equations under Galilean transformations implies the possibility
of detecting the relative uniform translational motion between two
inertial frames since each one is in absolute uniform translational
relative to the "Absolute Frame". In particular the velocity
of light in any inertial frame of reference in motion relative to
the "Absolute Frame" should be different by the value
C = 3 ´ 10^{8} m/s, which
is the speed of light in vacuum in the ether at rest i.e., "Absolute
Frame". The measurement of the speed of light on earth due
to its orbital motion around the Sun should turn out to be C + V
or C  V depending on whether light is traveling in the opposite
or same direction as that of the motion of the Earth with velocity
V = 3 ´ 10^{4} m/s.
In a famous experiment performed in 1885, Michelson and Morley found that speed of light on Earth is C = 3 ´ 10^{8} m/s and not C + V or C  V.
Two important conclusions are obvious as the consequences of the results of Michelson Morley experiments:
(i) The speed of light in vacuum is same in all inertial frames of references. Therefore the "Absolute Frame" does not exist.
(ii) Measurements of the speed of light in two inertial frames S and S' do not confirm the validity of the Galilean Law of Velocity Addition.
The following inferences can be drawn from the above conclusion :
(i) The relative uniform translational motion between two inertial frames cannot be detected by any experiment ( not only mechanical experiment, but including electromagnetic experiment) performed completely within any one given frame. The Principle of Relativity holds for Mechanics as well as Electrodynamics, i.e. it holds good for the whole of Physics.
(ii)Speed of light in vacuum universal constant.
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