Re: There are materials with negative refractive indexes.
Neat, I'll have to look at that some more.
Just to close this issue - C is *not* a barrier or a limit or even the speed of anything in particular. It's a parameter that characterizes the actual world.
Note that Euclidean geometry has exactly such a parameter - but it is imaginary! That is, in relativistic geometry we can think of the equation
x^2 - (ct)^2 = 0
and factor this to
(x-ct)(x+ct) = 0
so either x/t = c or x/t = -c. The parameter then represents the relative scale of the space to the time axis.
Now, it turns out that metric geometry (with a Pythagorean-like theorem) is a special case of projective geometry, and that the special type of metric geometry (Euclidean or pseudo-Euclidean = relativistic) is determined by the equation for a "degenerate conic", which is one that looks like
x^2 + y^2 + ... = 0
Euclidean plane geometry is then characterized by the equation
x^2 + y^2 = 0
which can be factored into
(x+iy)(x-iy) = 0
The characteristic parameter of Euclidean geometry is i, the imaginary unit! The points x and y satisfying this equation are called the "circular points at infinity". So, in a sense, Euclidean geometry has a thing called "infinity" that is such that you can never get closer to it. This is exactly analogous to the parameter c in relativity, which has a speed that can never be attained. Thus
relativity = the light cone
Euclidean geometry = the points at infinity
-drl
