Jim Higgins wrote:
If it isn't a Doppler effect, what is it, and why?

I'm not alone in asserting that the red shift is not
100% Doppler effect. There are many other possibilities
as can be seen from a web search.

Here's one simplified possibility. Assume that for
some undiagnosed reason, the objective length of one
second of earth time is gradually decreasing and we
are not aware of it. When the light from a galaxy was
emitted five billion years ago, it was a certain number
of cycles per second. Now, undetectable by us, we are
measuring the frequency of that light with a reduced
length of second. The measured frequency of the light
would be inversely proportional to the age of the light
and not necessarily attributable to its velocity away
from us.

We know that the length of a second of time varies with
position in the universe and with velocity. The earth's
velocity and position in the universe are probably
continuously changing. There's no reason to believe that
the length of earth's second of time is not also changing.

We once believed that the earth's position was the absolute
and unchanging center position of the entire universe. Now
we believe that earth's time is the absolute and unchanging
center of time for the entire universe. Those two concepts
are equally valid. Maybe an ever expanding universe is just
an illusion caused by our present localized subjective
standards of measurement.

My practical joker technician once repositioned the time
base knob on my oscilloscope off by one position. I adjusted
the length of a one-shot pulse based on the o'scope reading.
He bet me $5 that the pulse was not long enough.
--
73, Cecil http://www.w5dxp.com