Why is the symbol for the speed of light the letter "c"? The International Standards Organization (ISO) recommended letter symbol for the velocity of sound, and for the velocity of wave propagation, is also c. Please also note that the IEC recommended symbol for the velocity (speed) of electromagnetic waves in vacuum is c_0 (c subzero) and this will eventually be adopted by ISO. Anders Thor, Chairman of ISO technical Committee comments on why the letter c is used as the symbol for the quantity speed of light and of all electromagnetic waves in vacuum: "The symbol for this quantity is given in the International Standard ISO 31, Quantities and Units, as c (italic) or c (italic) sub 0. ISO did not invent these symbols. They were used in physics and technology long before ISO was founded in 1947. ISO only implemented what was already well established practice in this field. I am not sure how the symbol c was first introduced in physics. The only thing I could think of is that it is derived from the French term "celerite," which means phase velocity. You could find this term in the French edition of ISO 31, Part 2." We may have to ask Einstein after all.

I dont know where or why I "know" this, but... I always understood that Maxwell a buddy of Al's used this. It came about, cause at that time Maths dudes and Maxwell was a good one used C as a constant, specially in calculas. And when he worked out the speed of light expecting an equation he ended up with just the constant C. Somehow this stuck and maths dudes started using the german k instead for arbitrary konstants. Probably urban myth, but a good yarn anyway...

I've always assumed that it's because it's the universal constant in relativity. c for constant. I would never have bet money on it of course because it was just an assumption. This is the way I look at it. The comprehensive definition of "c" is not "the speed of light" because that would be inadequate. In other words, it is accurate to say that the speed of light in a vacuum is equal to "c", but less accurate to say that "c" is the speed of light. That's because "c" is not just the speed of light, it is the maximum combined speed at which anything can travel through the 4 dimensions of space-time. "c" in all respects IS a constant. That is, in more ways than most people realize. It's not simply the maximum speed at which something can travel through space. It's the speed at which everything is travelling through the combined 4 dimensions of space-time all the time. As I said, this is just an assumption I made after learning about the concepts involved, but it does make perfect sense.

I always understood that the "c" was an abreviation for "wiCked fast," since light is, technically, wicked fast. Its the only logical explaination. I honestly always thought it was arbitrary. just a letter he pulled out of his arse. perhaps "a" and "b" were commonly used as constant coefficients in some math he was doing at the time, so he used "c" as the next available letter to represent a constant which happens to be the speed of light. -IggDawg

welp, ...the reason we know he didn't just "make it up" (but, theoretically, he did..but, eh....that's another issue) is that we have devised experiments that can actually test his theories. Please Register or Log in to view the hidden image!