Re: Definition of LET and SR (was: Re: MMX, Contraction and Constancy)

"Gregory L. Hansen" <[EMAIL PROTECTED]> wrote in message
news:[EMAIL PROTECTED]
> In article <[EMAIL PROTECTED]>,
> Tom Roberts  <[EMAIL PROTECTED]> wrote:
> >On 11/25/2003 10:47 AM, Gregory L. Hansen wrote:
> >> Suppose [...] an
> >> aether wind blows past them.
> >
> >There is no "aether wind" in LET. Nor in SR (:-)).
> >
> >If you're going to change your theoretical context, you owe it to your
> >readers (and to yourself!) to make that explicit by saying so.
>
> Eh?  Lorentz had the idea that there was an aether that defined a
> preferred frame, and he may have expressed opinions on the nature of it
> but as far as I know his theory doesn't say anything at all about where
> the rest frame is, or that it's a universal rest frame.  It's easy to
> imagine an aether swirling in orbits around stars and planets, or aether
> currents moving through space.

It does say so; in his opinion all matter is some kinds of waves in the
ether, which is more or less the opposite of the currently popular
philosophy that everything is particles.
"Aether currents" would then risk to be detectable by seeming "space
deformation".

> If light is carried by a lumeniferous aether, and light can exert pressure
> on matter, it seems that the aether itself should be manipulable, too.
> How can we say that the aether can push on matter, but matter can't be
> made to push on the aether?  Build a fan, make an aether wind.

See above. Waves can't push and make a translational "wind" in the medium.

> >> Instead of blowing an aether wind across them, separate them on
launchers
> >> and launch them simultaneously in the same direction.  I suppose
notions
> >> of simultaneity would determine how a moving observer measures their
> >> separation.
> >
> >It's more than simultaneity. Say rather that the proper application of
> >the Lorentz transforms would determine this.
>
> I know the story from special relativity, but I'm trying to understand the

> aether version.
>
> >>>And it is virtually impossible to come up with an
> >>>aether theory that both agrees with the experimental record and is not
> >>>experimentally indistinguishable from SR.
> >>
> >> That doesn't make it uninteresting.
> >
> >IMHO a viable ether theory that is distinguishable from SR would be VERY
> >interesting! But the difficulties in doing that are immense, and nobody
> >has succeeded so far....
>
> I don't think you understood my earlier point, which was that I don't
> understand why so many people seem to think it's either/or.  The aether
> theory I had in mind would not be distinguishable from SR because SR would
> be assumed in its formulation.

That is exactly the point of Tom Roberts (and was the point of Lorentz and
Poincare...).
SRT is the mathematical formulation of the ether theory of Lorentz-Poincare,
just as the Maxwell equations are the mathematical formulation of the ether
theory of Maxwell.

> Write out a Lagrangian for some model
> fluid and demand it be invariant under Lorentz transforms, not because the
> aether changes the dimensions of objects but because you just assume the
> spacetime interval is invariant, just as with a field.  A relativistic
> aether theory.  Then the fluid would be quantized and its excitations
> called particles, except instead of calling them virtual particles we'd
> call them phonons or something.

That is more or less what Lorentz did. The consequence (with some
assumptions) was length contraction of objects.

Harald