Re: c+v and c-v or not?
- From: gehan_ameresekere@xxxxxxxxxxx
- Date: 18 Aug 2006 01:45:08 -0700
4. The speed of light (c) may very well be constant but not because of
SR. Light travelling between source and target has a constant speed
c...
Tend to agree with you, however is there a formal proof?
Peri of Pera wrote:
c+v and c-v or not?
Henri Poincaré wrote in his 1897 paper The Relativity of Space:
Quote.........According to a hypothesis of Lorentz and Fitzgerald, all
bodies carried forward in the earth's motion undergo a deformation.
This deformation is, in truth, very slight, since all dimensions
parallel with the earth's motion are diminished by a hundred-millionth,
while dimensions perpendicular to this motion are not altered. But it
matters little that it is slight; it is enough that it should exist for
the conclusion I am soon going to draw from it. Besides, though I said
that it is slight, I really know nothing about it. I have myself fallen
a victim to the tenacious illusion that makes us believe that we think
of an absolute space. I was thinking of the earth's motion on its
elliptical orbit round the sun, and I allowed 18 miles a second for its
velocity. But its true velocity (I mean this time, not its absolute
velocity, which has no sense, but its velocity in relation to the
ether), this I do not know and have no means of knowing. It is,
perhaps, 10 or 100 times as high, and then the deformation will be 100
or 10,000 times as great.
It is evident that we cannot demonstrate this deformation. Take a cube
with sides a yard long. it is deformed on account of the earth's
velocity; one of its sides, that parallel with the motion, becomes
smaller, the others do not vary. If I wish to assure myself of this
with the help of a yard-measure, I shall measure first one of the sides
perpendicular to the motion, and satisfy myself that my measure fit s
this side exactly ; and indeed neither one nor other of these lengths
is altered, since they are both perpendicular to the motion. I then
wish to measure the other side, that parallel with the motion ; for
this purpose I change the position of my measure, and turn it so as to
apply it to this side. But the yard-measure, having changed its
direction and having become parallel with the motion, has in its turn
undergone the deformation so that, though the side is no longer a yard
long, it will still fit it exactly, and I shall be aware of nothing.
What, then, I shall be asked, is the use of the hypothesis of Lorentz
and Fitzgerald if no experiment can enable us to verify it? The fact is
that my statement has been incomplete. I have only spoken of
measurements that can be made with a yard-measure, but we can also
measure a distance by the time that light takes to traverse it, on
condition that we admit that the velocity of light is constant, and
independent of its direction. Lorentz could have accounted for the
facts by supposing that the velocity of light is greater in the
direction of the earth's motion than in the perpendicular direction. He
preferred to admit that the velocity is the same in the two directions,
but that bodies are smaller in the former than in the
latter...........End of Quote
Albert Einstein wrote in his 1905 paper 'The Special Theory of
Relativity':
QUOTE.........In one of the most notable of these attempts* Michelson
devised a method which appears as though it must be decisive. Imagine
two mirrors so arranged on a rigid body that the reflecting surfaces
face each other. A ray of light requires a perfectly definite time T to
pass from one mirror to the other and back again, if the whole system
be at rest with respect to the æther. It is found by calculation,
however, that a slightly different time T1 is required for this
process, if the body, together with the mirrors, be moving relatively
to the æther. And yet another point: it is shown by calculation that
for a given velocity v with reference to the æther, this time T1 is
different when the body is moving perpendicularly to the planes of the
mirrors from that resulting when the motion is parallel to these
planes. Although the estimated difference between these two times is
exceedingly small, Michelson and Morley performed an experiment
involving interference in which this difference should have been
clearly detectable. But the experiment gave a negative result - a
fact very perplexing to physicists. Lorentz and Fitzgerald rescued the
theory from this difficulty by assuming that the motion of the body
relative to the æther produces a contraction of the body in the
direction of motion, the amount of contraction being just sufficient to
compensate for the difference in time mentioned above. Comparison with
the discussion in Section 11 shows that also from the standpoint of the
theory of relativity this solution of the difficulty was the right
one.......End of Quote
*to detect the existence of an aether-drift
Commentaries:
1. Poincaré does not mention the Michelson-Morley experiment (MMX)
but it is clear that he refers to it and the Lorentz and Fitzgerald
explanation of the absence of the predicted phase shift in MMX due to
contraction of the parallel arm. According to Poincaré, the anisotropy
of light would have explained the null result of MMX not less plausibly
than contraction but Lorentz had admitted a preference for contraction.
2. Contraction explains the null result of MMX but only if a number of
arguments against it are ignored (refer to some of my other posts in
this news group). The contraction hypothesis in my view has no more
value than explaining gravity by saying that all physical bodies are
connected by invisible rubber bands exerting a pull. Both contraction
theory and rubber band theory are 'ad hoc' theories and bizarre
ones as well.
3. Another ad hoc theory is the theory that expansion of the
perpendicular arm of the interferometer apparatus in MMX has the same
effect as the contraction of the parallel arm. Both contraction and
expansion explain the null result with equal justification but without
any validity at all.
4. The speed of light (c) may very well be constant but not because of
SR. Light travelling between source and target has a constant speed c
(originally established by Maxwell and incorporated into his EM
equations). The speed of the source does not affect c but the speed of
the target (v) affects the time for light to transit from source to
target. It is correct to use formulas that include expressions such as
c+v (speed of light plus speed of approaching target) and c-v (speed of
light minus speed of target going away). In these cases, c remains the
same but to allow for the change in the distances between source and
target, v is added to c if the distance is shortened or subtracted from
c if lengthened.
5. M&M used c+v and c-v in the logic underlying their interferometer
experiment. They believed the experiment would create an observable
phase shift of two rays of light interfering. The phase shift did not
occur. The null result was explained by Lorentz to be caused by a
contraction of the parallel arm of the equipment. He published the
contraction theory in mathematical form, called the Lorentz transforms.
These are used by the special relativity theory. However, SR is not
comfortable with c+v and c-v because it seems to undermine the
postulate of the constancy of light. But without these two expressions,
no MMX, no contraction theory and no SR. It is a case of having a cake
but not wanting to eat it.
Peter Riedt
PS If you like fairytales, download one from
http://www.geocities.com/sintao06/index
.
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