Re: On the observation of a moving object.
From: kenneth couesbouc (kencouesbouc_at_yahoo.fr)
Date: 11/13/04
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Date: 13 Nov 2004 08:30:38 -0800
"Harry" <harald.vanlintel@epfl.ch> wrote in message news:<41934895$1@epflnews.epfl.ch>...
> "kenneth couesbouc" <kencouesbouc@yahoo.fr> wrote in message
> news:1c9636fc.0411090601.1d3bb16f@posting.google.com...
> > Sorry about my short tempered annoyance but if you had read my posting
> > you would know that I said :
> > "4.In the real universe (as opposed to the imaginary universe we have
> > described so far), nothing is at rest. Everything is in motion, either
> > together or separately."
> > I have yet to find an explanation which takes this fact into account.
> > I would welcome such a link. Also a "good SR course". So far I've only
> > found some lunatic stuff about trains, clocks and fixed observation
> > posts. Is there more to it than that?
>
> Instead of Einstein's explanations, you could try the explanations of
> Lorentz and Poincare who worked it out before him. In particular relative
> motion was discussed by Poincare, you may be interested in this (starting
> with the phrase "principle of relativity"):
> http://www.thesciencebookstore.com/etext/poincarephysics.html
How can anything be fixed (see below)?
How can an observer imagine he is motionless? Inside some sort of
Platonic cave!
> > May I add that if the rod is moving faster than the observer, it will
> > seem to get shorter. And if the rod is moving slower than, the
> > observer, it will seem to get longer.
>
> Here you seem to have mixed up some things: it will only seem to get longer
> as determined in an independent frame of reference in which the person you
> labeled "observer" is moving. Usually it is tacitly supposed that the
> "observer" is at rest in his/her/its frame of reference. Relative to such a
> frame in which the observer is in rest, the rod that is moving slower than
> the observer as determined from the independent frame, will actually appear
> to be shorter again.
In my original posting (see paragraph 4 above), I started with an
observer at rest and went on to say that no such thing could exist.
This being so, I examined the case of both observer and rod moving in
the same direction at the same speed (same frame?). The rod would seem
longer, as the observer is therby moving away from one perceived
end(A') and towards the other perceived end(B'). I would, I hope, be
less mixed up, if you could comment what I wrote.
Regards, Ken
> > The apparent length depends on
> > proportionate speeds. Is this still optical aberration?
> > Regards, Ken
>
> This is certainly not optical aberration. Optical aberration refers to the
> apparent position of an object, whereby the angles to the extremes are
> approximated to be the same, and thus the lengtt is neglected.
> To the contrary, length contraction should also occur even at zero distance
> at which optical effects don't play a role at all.
> Harald
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