Now that is a really interesting topic! Kinda suprised that there hasn't been a topic on it.

Personally, I'm still skeptical of it. Relativity has passed so many tests by now that it seems unlikely to be wrong. But, of course, experiments always win -- if they reliable measured it, then we need to tweak the theory. Exciting!

But, again, the relative difference to the speed of light is very small, and the errors given in the paper can't explain them, it might just be that they've "forgotten" effects, or perhaps underestimated others.

What I'm saying is: To overturn a huge, established theory such as relativity, it takes more than a single experiment, I'm afraid.

Of course, neutrino-experiments are notoriously difficult anyhow...

What do you guys think about it?


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From what I've been told - and mind you, it hasn't been long since then, is that the modern interpreation is that an object, any object, does only have it's "intrinsic" mass, that is, it's mass is ALWAYS it's rest mass.
Of course, for a massive particle it is:

E=\gamma m c^2

causing people to "define" \gamma m as some kind of "relativistic mass". This, however, hasn't proved to be very helpful or enlightning, and thus, nowadays, most people do not use that terminology anymore. Contrary to the above, the formula

E = mc^2

is unfortunate, since E here is *NOT* the total energy, but the "rest energy". And that term is, for a massless particle, such as the photon, simply zero.

The history of physics, and relativity, is interesting, I give you that, but I feel that this is a different discussion. "Do photons have mass?" is a physical question, and there's no need to invoke history to answer it. The answer is, quite simply, no. (Real) Photons are completely massless.

This can be seen and shown in theory (such as in Quantum field theory, but we find the same in relativity -- in fact, the very fact THAT photons move with c means they cannot HAVE mass). It is the same in relativity (see my post above). It also does not apply to the Photon in the Higgs-mechanism, which, if true (News on Tuesday, everyone!), would be further proof of this.

Of course, you can say that any energy could technically be turned into mass (as you later in your post do). That is true, but unless we observe that happen, it does not seem likely. Photons, in particular, seem perfectly happy with just having a frequency

Let's nitpick a little.



Well, again, photons do not have mass. But they're not the only massless particles. Gluons don't have mass, either, at least not in the standard model. Of course, no one has ever seen a free gluon (since they have color, they instantly hadronize), but there's very strong evidence for their existance (3-jets).





Wait. What? I'm sorry, I don't think I understand what you're trying to say with this sentence