# Why is $c$ considered as the speed of the photons?

Maxwell equations brought $\ c_{o}=\frac{1}{\sqrt{\mu_{o}\varepsilon_{o}}}\$. Since this is a constant, it made all physicists at that time wonder where was the frame of reference? They ended up with an aether answer until the Michelson–Morley experiment denied it.

Now there was no frame of reference, but the genius of Einstein resolved it.

However, although Einstein's theory is mathematically good, it does not imply there can not be other ones mathematically good. I just read an article written by someone not knowledgeable about physics who had this interesting idea:

There is no need to consider c as the speed of the photons unless natural evidence tell us that, we could consider c as the difference between the speed of the photon that just appeared (c value) and the one at (0 value) that is going to speed up and the result is a constant speed as well, c, for all references.

That is what he says, if I understood it correctly. Here is the article:

http://jesusgonzalezllorente.com/

http://vixra.org/abs/1202.0013

The pictures are horrible though.

So, is it actually possible to consider light as he states or is there any logical, mathematical physical law that does not allow it?

• That article considers only the Michelson–Morley experiment. Nowadays, there's plenty of other evidence that relativity, not classical physics, is the correct model for our universe, so honestly I don't think it's worth the effort of trying to work out what the author is trying to say or where he's gone wrong. – Harry Johnston Feb 4 '12 at 21:55

## 2 Answers

The speed of light has been measured experimentally to be a certain constant, call that constant $c$. Light waves have been experimentally found to consist of photons...the photo-electric effect, for example. From this, one would naturally deduce that the photons are travelling at the speed of light. But more, the equations for photons have been worked out, in their connexion with light waves, and these equations only allow one speed for photons, the speed of a light wave. The equations have been tested experimentally and verified. Even if physical theory changes in the future, the future changes have to preserve these experimental facts, so that photons travel at the speed of light is true even if other things change.

(In General Relativity, the speed of light $c$ does change depending on the strength of the gravitational field, and this has been verified too, but it still leaves the photons travelling at the speed of light, which changes.)

• Thanks for your answer joseph, I appreciate your effort to explain it. – user23090 Feb 5 '12 at 1:04

This paper is similar to a discredited idea called the source theory which was popular at the turn of the 20th century. It isn't as clear as the source theory, though. The source theory says that when something is moving, it emits light at the speed with which it is moving. This is not correct, it is incompatible with EM for example, and it would lead binary star pictures to be completely off, because the star moving toward us would appear in the wrong place relative to the star moving away. It's nonsense. But this paper seems to be rediscovering this idea.