Re: "How Does Light 'Know' How Fast to Travel?"

Alex wrote:
On 4 Sep, 16:38, John Kennaugh <J...@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx>
wrote:
Tom Roberts wrote:
>John Kennaugh wrote:

The modern interpretation of SR is that the vacuum energy mediates
electromagnetism. There is an extraordinary Russian paper on SR and
modern quantum field theory that explains this:

http://uk.arxiv.org/PS_cache/arxiv/pdf/0708/0708.0929v1.pdf

The author, Silagadze, considers everything from relativistic mass to
the nature of the relativistic aether. Although the author hopes the
paper will help beginners(!) it would definitely repay hours of study
by intermediate students, it is especially good on the generalised
geometrical approach to physics.

Alex

I have started to go through the article. I have before come across the derivation of SR from 'only the first postulate' and I think such derivations are misleading - some more so than others. What they in fact show is that IF measurements are assumed to be transformed as a function of velocity THEN Lorentz transforms are the only option. Put simply Lorentz transforms use up all possible degrees of freedom.

Silagadze starts:

"Let inertial frame of reference S' moves along x-axis with velocity V relative to the 'stationary' frame S. A simple glance at the Fig.1 is sufficient to write down the Galilean transformation that relates x-coordinates of some event (for example, an explosion) in frames S and S'

x = V t + x'. (1)
But doing so we have implicitly assumed that meter sticks do not change their lengths when gently set in uniform motion."

Well he is supposed to be applying only the first postulate and the relativity principle says that there is no difference between a measuring stick in uniform motion and one which is stationary so yes I do implicitly assumed that meter sticks do not change their lengths when in uniform motion.

"Although intuitively appealing, this is not quite obvious. For example, according to Maxwell equations, charges at rest interact only through the Coulomb field while in motion they experience also the magnetic interaction. Besides, when the source moves very quickly its electric field is no longer spherically symmetrical. It is therefore not unreasonable to expect that a meter stick set in rapid motion will change shape in so far as electromagnetic forces are important in insuring the internal equilibrium of matter."

'when the source moves very quickly' - RELATIVE TO WHAT'. He is in fact invoking aether theory or assuming the maths of SR (same thing) from the onset.

They won't have it around here but it really is very simply. Einstein assumed the validity of Maxwell's aether theory, Interpreted the MMX as showing that every observer is stationary w.r.t the aether - which is what his second postulate is describing - and Maxwell's aether lives on mathematically in SR as "the observer's FoR" which has the same properties as an aether stationary w.r.t the observer.

What Silagadze is doing here can be explained as follows: The observer's FoR is equivalent to Maxwell's aether and the measuring stick is moving relative to that FoR/aether so its electric field is no longer symmetrical.

Silagadze is either deriving Lorentz transforms assuming Maxwell's aether - which Lorentz did, or he is assuming properties of Einstein's FoR which come from the second postulate - which Silagadze is supposed to be managing without. The second postulate of course retains those properties of the aether which Einstein needed. "...having taken from the idea of light waves in the aether the one aspect that he needed"

Another way of looking at it is that he is saying lets not assume the second postulate and show that that implies length contraction - lets assume length contraction and show that that implies the second postulate.

I will study more later.
--
John Kennaugh

.

Relevant Pages

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