Re: A little challenge for relativists.


John Kennaugh wrote:
> Tom Roberts wrote:
> >John Kennaugh wrote:
> >> PD wrote:
> >>> 1. Experimental evidence of source independence.
> >> There was none in 1905
> >
> >Strictly speaking, no. But there certainly was A LOT of evidence that
> >only relative velocities matter for E&M phenomena. Einstein knew of
> >several [quoting from the FAQ]:
> >
> >When A. Einstein wrote his famous paper: "The Electrodynamics of Moving
> >Bodies" in 1905, he already had experimental support for his new
> >theory:
> >
> > ".... Examples of this sort, together with the unsuccessful
> >attempts to discover any motion of the Earth relatively to the "light
> >medium" suggest that the phenomena of electrodynamics as well as of
> >mechanics possess no properties corresponding to the idea of absolute
> >rest. They suggest rather that, as has already been shown to the first
> >order of small quantities, the same laws of electrodynamics and optics
> >will be valid for all frames of reference for which the equations of
> >mechanics hold good..."
> >
> >What was the experimental support for this claim?
>
> I do not dispute this claim. Relativity is about symmetry. The argument
> is for symmetry and I do not dispute the strength of those arguments.
>
> The simplest way to achieve symmetry consistent with the facts was to
> assume that in every FoR "the speed of light is found to be constant
> w.r.t the source emitting it". It is perfectly consistent with symmetry
> it is the simplest explanation of MMX and if light is particulate it
> would be a natural assumption that the speed of such particles would be
> imparted to them by the source.
>
> Ether was the cause of asymmetry in the contemporary thinking. The MMX
> was looking for the asymmetry believed to exist because of the ether
> where every FoR could in theory be uniquely identified by its velocity
> relative to the ether. It discovered no such asymmetry and there were
> enough other experiments which indicated the same to conclude that that
> asymmetry does not exist in nature.
>
> If one assumes this absence of asymmetry is due to there being no ether
> c cannot be a property of the ether and must be the speed of light
> relative to the source because there is no possible causality to make it
> constant w.r.t the observer without the help of an intermediary (ether).
>

Right there is the point of departure that is unjustified. You
apparently reject the notion that fields have enough structure on their
own to account for the mechanism of their own propagation. It is not
enough to challenge it and say, "What precisely *is* the mechanism for
fields to propagate themselves?" For, flipping it around, you make the
contrary assumption that the speed of light *must* be with respect to
the source but do so *without* any detailed mechanism for how the
source accounts for the propagation of the field either.

If you have a model that describes *why* the source accounts for the
propagation of the field, and this model correctly accounts for
experimental observation, *then* you have the right to say that this
model is *potentially* superior to the model that light neither needs
an ether substrate nor the particulars of the source to account for its
propagation. Mind you, it still needs to meet experimental tests that a
source-dependent speed would imply (and for which there is a wealth of
data suggesting that such a model would fail).

In summary, your argument seems to be: "There are three models for the
propagation of light. Model A is ether-supported propagation, model B
is self-propagation, and model C is source-supported propagation. I
don't understand how model B could possibly be correct as my
understanding is the field has no independent causal ability on its
own. So if the MMX rules out model A, then it *must* be model C,
despite the fact that I don't have a good idea how model C would work."
That is not a good argument.

PD

.

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