Re: Symmetric Doppler Effect Between Two Observers in Special Relativity

From: David Park (djmp_at_earthlink.net)
Date: 12/13/04 

Date: Mon, 13 Dec 2004 14:36:39 GMT

>
> We had to blue shift the signals fed to Pioneer, in order for it to "hear"
> us. Does that count?
> TeV gamma photons are created by Compton scattering photons off of high
> energy chargged particles. Would that count?
> A radar gun clocks a stationary column at 100 kph as the police car drives
> along. As the police car is stationary, an oncoming motorist is clocked
at
> 100 kph. Is that symmmetric?
>
> David A. Smith
>

The first one helps if Pioneer also had to blue shift by the same amount so
we could 'hear' it. I assume that is the case. I'm not certain how the gamma
photons help.

The radar gun case certainly helps as a good example. Of course, it is not
exactly a rigorous test that sets limits. A little better example would be
two police cars approaching or receding and each measuring the velocity with
their radar guns.

As I said, I don't doubt that the symmetry is substantially true. I just
want to cite convincing empirical evidence. For example, for the invariance
of the speed of light we can cite the Kennedy-Thorndike experiment and its
modern version.

  http://qom.physik.hu-berlin.de/research_kt.htm

For symmetry of translation we can cite that the most delicate physics
experiments can be repeated at different times and places. If translation
symmetry weren't true then engineering would never work.

I think (but am not certain) that the symmetric Doppler shift is the same as
saying space is isotropic. Maybe the CMB would be evidence that could be
cited for this?

David Park
djmp@earthlink.net
http://home.earthlink.net/~djmp/

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