[Thatcherite]

Who is to say that our current value of "c" is the same as at the beginning? Could it be that C(to) = 1e10 * C(t2005)

No, there is no evidence for your proposition, and substantial evidence against it.

[nasamn777]

Perhaps you could provide some evidence against this proposition.

Here is a possible equation for the speed of light:

c(t) = 2.9979e18*e^(-4.60517e-4 * t) [m/s]

where t is in years