On Fri, 2 Dec 2005, Jeff Bechtel wrote:
Interesting. I wonder how evidence could even show that. What amount of redshifting (in %) would correspond to traveling away from us at the speed of light? Or is that just not taking the Einstein gamma into account properly?
My dime-store theory is that there would always be red shift, however tiny, in any object moving away from you.
Well, yes, of course.
Regardless of the fraction of the speed of light it may be travelling.
I asked about going at speed of light because it's a boundary case, because it's not possible to accelerate to faster than the speed of light-in-a-vacuum.
It might be a challenge to determine whether the red is due to movement, or is naturally there anyway.
The spectrum of hydrogen (due to absorption by quantum jumps) is presumably a thing common to all of the universe. Hydrogen is everywhere and we can't think of any reason it'd have a different spectrum anywhere else in the universe. The doppler effect stretches a spectrum around DC frequency (in a log-frequency diagram, it would instead just move the spectrum leftwards). There's no thinkable reason that shifting would occur because of other reasons than Doppler and/or the Einstein gamma, both of which are directly related to speed.
If anything weirder happened to light, chances are it'd lose the hydrogen signature (e.g. if captured by solarpanels and re-emitted to us using a big red neon because aliens think that confusing us is funny...)
But then: I am not a physicist... (nor an astronomer).
Mathieu Bouchard - tél:+1.514.383.3801 - http://artengine.ca/matju Freelance Digital Arts Engineer, Montréal QC Canada