Jonathan S. wrote,

Good point, but is Bill (or anyone else)
suggesting that the speed of light has
varied since the universe became the
way we see it now?

Yes. As was posted previously in this thread and numerous threads
before, some credentialed 'mainstreamers' (not just loonytooners) are
indeed questioning universal c-invariance. Again, see-
http://ldolphin.org/setterfield/earlycosmos.html
Also see-
www.Lns.cornell.edu/spr/1999-11/msg0019253.html
http://www.ldolphin.org/troitskii and
www.sciencenews.org/20011006/bob16.asp
Though their models differ superficially, these guys
are proposing a gradual c-drop across the age of the observable
universe.

What happens if it only varies during the
first 300,000 years, when the universe is
unobservable and problems like the
stability of stars are irrelevant? That time changes, and conditions
in that time
change, but does anything else?

As was posted previously in this thread and numerous times before,
'mainstreamers' Drs. Joao Magueijo and Andy Albrecht (Albrecht was one
of the founders of inflation theory) have proposed the VSL (variable
speed of light) model as an alternative to inflation. Basically, their
model has a very precipititous c-drop across the 'inflation' spike,
completely eliminating the need for inflation. Again, see-
http://theory.ic.ac.uk/~magueijo/vsl.html
A quick web search under 'Magueijo-Albrecht VSL' will turn up many
more hits on this model. By eliminating inflation, their VSL solves the
horizon problem while 'magically' eliminating inflation's niggling
problems such as the flatness paradox and the 'first Doppler peak'.
Their model has c dropping almost instantaneously to its present value,
unlike the more-gradual drop proposed by the other guys. And they
likewise believe it's necessary to violate the Lorentz invariance in
order to have a c-drop. It is **NOT** necessary to violate the Lorentz
invariance, and here's why:

Here's the kicker- as stated previously in this thread and numerous
times before, ALL these guys, Magueijo-Albrecht, Barrow, Moffatt, and
Troitskii, are still operating in the void-space regime. They are not
connecting their proposed c-drop to a *density gradient* in the spatial
medium of the expanding universe.

To re-quote an earlier post in this thread, Dennis Taylor wrote,

One of the unstated assumptions..... is
that you can change one rule or law or
constant (such as C in this case) and
everything else will operate as before,
except light will travel at a different
speed.... The trouble with this is the
implications involved in in changng basic
constants. For instance, changing C
changes the results you get from
E=mc^2, which means among other
things that the energy a star gets from
fusing hydrogen to helium will change.
This means the whole "main sequence"
chart for types of stars will be different,
and the difference will be detectable.
To which the oc said:
Yes Dennis, all that you state is absolutely true under
the void-space regime, that is, the premise that space is a functional
void or 'nothingness' all the way to the limit of visibility and thence
back to the BB itself. Under void-space, you cannot change c without
violating the other constants, as you state.
But the point you're missing (the 'kicker') is- if
space, far from being "nothing", is an expansible, compressible fluid,
it will display a *densty gradient* aross the expansion of the
universe.. and the speed of light will drop with the thinning of the
spatial medium (as by analogy the speed of sound in air drops with
thinning air density ^altitude). The greatest density-drop (and geatest
c-drop) will occur immediately following the BB, leveling out on a log
curve to the present value. *Some* of this density-gradient c-drop will
appear in the most ancient light visible to us, rendering that light
"dimmer than it should be" at a given redshift, just as is observed in
the recent 1a supernova data.
C is always constant *locally*, in the absence of a
density-gradient in the spatial medium. And all the other constants are
likewise fixed, locally. "Local" in this case applies out to a few
billion LY, where the density-gradient remains negligible, c remains
(nearly) constant, space can be treated _as if_ it were a void, and
relativity 'works' acceptably well out to these distances. At greater
distances the spatial density and c begin climbing exponentially.
There in that denser space, lightspeed is constant
locally, just as lightspeed is constant here, locally. In that denser
space, all constants INCLUDING THE LORENTZ INVARIANCE are fixed, just as
they are fixed here, locally. The prime variable from location to
location in the universe is spatial density. The relative value of c
varies with space density. Light propagating from denser space into
'our' less-dense space loses amplitude (brightness) due to the
*relative* drop in c between the two locations.

In the real world however, stars 5 billion LY away look just like the
ones next
door.

Yes at 5 BLY they look the same. At 10+ BLY they still "look" the same,
with the exception of being 'dimmer than they should be', due to c-drop.

But then, if space is functionally void, none of the foregoing applies.
We are stuck with a 'one-shot' BB, ever-accelerating expansion of the
"nothing", universal c-invariance, and an open-ended entropic rundown
back to 'nothing'.
oc

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