vonroach wrote:
On Wed, 07 Jul 2004 17:45:13 +0200, Bjoern Feuerbacher
wrote:



The time *seems* to have moved slower when the light we observe now on
Earth left that galaxy.



And for the galactic observer, is not time on Earth slowed
down by the same factor wrt its own time?

The time *seems* to have moved slower when the light they observe now on
in that galaxy left the Earth.


Actually the expect spikes in the spectrum have shifted to longer wave
lengths (`lower' than expected)

Not "actually". *Additionally*.


interpreted as meaning we (the
observers) have moved further apart from the emitter since the light
was emitter if our prediction of what the expected spectrum should
show is correct,

No, interpreted as meaning that the space between us and the emitter
has expanded.


and the spectrum of Hydrogen, has been very reliable.

When studying supernovae, one does not rely on the hydrogen spectrum,
AFAIK.


A change in Hydrogen emission spectrum could be postulated but it has
never been observed.

One would also have to postulate that the emission spectra of all the
other elements which are studied change in the same way.



[snip]


As both clocks tick at the same rate,

Now they do. When the light left the source, the clocks seem
to have ticked at a different rate than they now do.


What have clocks (whatever that is supposed to mean) have to do with
it?

Read "clock" as a short hand for "every observable effect which measures
passages of time somehow" (in this case, e.g. the decay of the light
curves of the SN).


The speed of light has been measured many times and is thought to
be a constant.

Right.


It is the `clock mechanism' that produces an apparent
relative change.

What do you mean by "clock mechanism"?


An astronaut in a spacecraft sets his watch by
earthtime, then when he returns a slight error is noted, If not due to
a faulty watch mechanism, it merely means it has kept accurate time in
a different frame of reference than earth clocks. However you want to
stretch, bend or fiddle with space and time in your imagination, the
speed of light is a constant... or we go back to square one.

Agreed.


Bye,
Bjoern