> This stuff might be outside of my area of expertise, or it might be sort of
> like flat earth agruments. I'm in a discussion with someone who discounts
> the astromical evidence of light speed and distance because the geometry of
> the universe is not euclidean. He's going to bring up the incredible
> plumetting speed of light theory I just know it.
The non-Euclidean character of space has a minor effect over
distances (a few million light years) sufficient to refute YE claims.
The possibility of variation in fundamental constants (c,h,G,e,
&c) has been discussed extensively since proposals of this sort were
made by Milne & Dirac in the 1930s. Fairly tight constraints are
imposed by astrophysical & geological data. E.g., some proposed
variations would mean that the solar luminosity would have been so high
as to be incompatible with life at epochs when life existed on earth.
A glance at the abstracts from peer-reviewed journals at the URL
you gave suggests that, while they're about varying "constants", they
are _not_ talking about significant variations of c on a time scale of a
few centuries. I suspect that they're being forced into service as
window dressing.
It's not easy to see what varying c could mean in relativity.
It's kind of like saying that the number of feet in a yard varies.
Someone else may comment on the observational data on c.
George Murphy