(Thomas Smid) wrote in message
...
I came across Ned Wright's webpage
http://www.astro.ucla.edu/~wright/tiredlit.htm which states that
alternative explanations for the redshift of galaxies would not be
consistent with the z-dependence of supernova lightcurves. However,
this assertion is not further substantiated and as far as I can see
any wavelength independent redshift mechanism should indeed result in
the change of the supernova lightcurves:
[...]

http://www.plasmaphysics.org.uk/research/#A11).


[[Mod. note -- I think the key point in this derivation is that the
redshift factor (1+z) is applied to *all* frequencies. This is
equivalent to rescaling *all* times by (1+z), and thus reproduces
the standard result. (Which implies that, for example, a light curve
which in the rest frame of the emitter has a (say) full width at half
maximum of 1 week, is observed to have a full width at half maximum
of 3 weeks when redshifted at z=2.)

As Ned Wright's web page points out, simply attenuating the energies
of all photons by a (1+z) factor (as classical "tired light" models
predict) would shift wavelengths, but wouldn't give this additional
time dilation (and would thus be inconsistent with the observations
of this time dilation quoted in Ned Wright's web page).

-- jt]]

The problem with this idea is that the motivation for a tired light model
is to preserve a static Universe. In a static Universe the light travel
time between the supernova and the observer has to be constant, and thus
the observed duration of the lightcurve has to be the same as the emitted
duration of the lightcurve. To say otherwise is to throw out the baby
with the bathwater.

However, it is true that if you halve all frequencies you double all
durations including the lightcurve duration. This is exactly what the
standard Doppler or expansion model for the redshift does. But you
really need an expanding Universe then to accommodate the greater
light travel time seen at the end of the lightcurve.

--Edward L. (Ned) Wright, UCLA Professor of Physics and Astronomy
See http:www.astro.ucla.edu/~wright/cosmolog.htm