Why is Speed of Light Constant?

I fully accept that the speed of light is constant in a vacuum and that it fully conforms with all theories but is there a scientific model as to why it is constant and no other phenomena are?Thank you for this site, I just found it.
- Jim Meadows (age 65)
San Juan Cosala, Jalisco, Mexico

First, it's not true that only light travels at that fixed speed. Gravity waves travel at the same speed, in theory and also so far as can be determined from the observed slowing of binary pulsars.  So do gluons, but they interact so strongly that their long-range travel isn't observable. If other long-range fields show up (e.g. one that has been proposed recently as part of a possible explanation of dark matter) then they too will travel at the same speed.

The theory of the special speed limit is just the theory of relativity. The explanations of why certain fields lack rest mass (and thus must travel at c, according to relativity) and others have rest mass (and thus can't travel at c, according to relativity) is much more complicated. The current version goes by the name The Standard Model. It has something in common with relativity. Both consider how the universe must really be the same even when viewed in diferent representations. Both thus deal with "invariants", the set of phenomena which are independent of representation. The speed of light is perhaps the simplest of such invariants to describe, but there are many others.

We have some old discussions that may help: 

Mike W.

(published on 08/03/2015)