[DannyTN]

"Actually we have defined an exact (fixed) value for the speed of light in a vacuum: 299,792,458 meters per second. By definition, the speed of light "c" is a constant. "

But does light still go the "defined" speed of light?

And I'd like your perspective on the redshift discussion on the "Is the speed of light slowing down?" thread.

[RadioAstronomer]

As I have statd the speed of light in a vaccum is a constant (non changing). What is even stranger is that no matter how fast you are travelling (even 90% the speed of light) The speed of light relative to you does not change. This is one of the fallouts of Special Relativity.

[jlogajan]

But does light still go the "defined" speed of light?

As humans living on a relatively cold planet, we have basically one yardstick to measure time -- the electric force. It controls the speed of the electron around the atom. It IS chemistry. It IS electronics. It moves at C.

So when we "measure" the speed of C, we are just comparing it to other manifestations of C. Basically we correlate a travel distance of C compared to the number of rotations of an electron around an atom.

If the value of "C" changes (whatever that means) -- so does the rotation rate of the electron, since it too is controlled by C.

C will always be constant because of the way it is measured.