In E=MC2....Why is "C" used to designate the speed of light?
The variable "c" was chosen for light speed as it is representative of the universal physical "constant", or the defined constant for the measure of maximum speed at which all energy, matter, and information (e.g. gravity) in the universe can travel (in the vacuum of our Space-Time continuum). http://en.wikipedia.org/wiki/Speed_of_light