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BREAK-DOWN OF OLD LAWS
The first blow to Newtonian theory came from the non-invariance of
Maxwell’s equations under Galilean transformation.
Modification of Maxwell’s equation could be done. But,
there were more troubles.
The trouble was related to the motion of electromagnetic
waves. It was still thought that waves needed medium
to propagate. So, a hypothetical medium called aether
(ether) was proposed which filled every space. Light
was supposed to be moving through this. Then, a
question arose. How do objects move relative to
others? Do they take the others away with them or partially
away or do the others remain stationary?
The two views (clearly opposite) tried to explain the nature in
various ways. The stationary ether hypothesis was
defended by Anton Hendrik Lorentz (Nobel Laureate
1902), who had contributed a lot to the development of
the fundamental basis of relativity. He was able to
explain various observations using this hypothesis.
Now, if ether was at rest and light moved in ether,
then it would be possible to observe the motion of
objects relative to ether as one can observe Doppler’s
effect for sound in various situations. A very famous
experiment known as Michelson-Morley experiment (by
Albert Abraham Michelson, Nobel Prize 1907) was
performed to give something which would keep nothing
altered.
The idea of experiment was very simple. Light moves with
speed ‘c’ in ether and the Earth moves with a fast
speed in Ether (around the Sun). So, it can be
possible to observe light in different ways and
compare the difference: |
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The instrument used is called Michelson-Morley
interferometer. Experiment was done this way [present
tense is used below]:
Light is sent through a half-silvered mirror as shown in the
figure below. It deviates into two parts. The first part
goes in a straight line. The second moves in a
perpendicular direction relative to the setup. So, it
takes a tilted path with respect to the other.
For a ray going up, time taken to go up = distance SMS˘/c |
Distance = Ö(l2 + v2t2)
Therefore, t = {Ö(l2 + v2t2)}/c
or, t
= l/Ö(c2 - v2)
So, total
return time = 2l/Ö(c2 - v2)
Time for
straight lines to come back
= time to
travel from SN + time to come back
= 1/(c-v)
+ 1/(c+v)
= 2cl/(c2 - v2) |
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These
times are different and hence, light reaching back will be
in different phases, thereby, producing a particular
interference pattern.
The experiment was performed and an unbelievable difference
of above 90% was obtained. So, stationary ether theory was
completely out of order. But, Lorentz was able to provide
an answer by changing almost everything. He replaced
Galilean transformation by ‘Lorentz’ transformation (so,
it is not called Einstein transformation). It was based on
the invariance of Maxwell’s equations. It successfully
explained the faulty result of the above experiment. A
phenomenon called Lorentz-Fitzgerald contraction was
supposed to take place, because of which, the length SN (=
l) would be contracted to lÖ(1-v2/c2).
This fixed the problem.
But, here
came the problem. This result was a very ad hoc
construction and was not a natural result of anything.
Thus,
some scientists started doubting the ether hypothesis as a
whole. And a young man, who himself had written a paper on aether at the age of fifteen, while going home in a taxi,
suddenly realized that he knew the answer, thanks to a
clock at the end of the road. About five years before the
clock struck 12 midnight, another breakthrough had already
taken place because of a German physicist named Max Karl
Ernst Ludwig Planck.
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