I've seen a headline of a publication somewhere that read something along the lines of "Why photons traveling between Casimir plates don't violate causality". Back then I didn't really think much of it but now I realize that it would've been a rather interesting to read. There are phenomena where something goes FTL but not information, right? But in this case if the photons themselves are traveling at superluminal speeds (due to energy densities lower than that of "normal" vacuum), I guess it makes things a bit different? I searched for information about this but couldn't find any (thus this post).

 

Edit: Hmm. I wonder if this is better off in the Relativity-section.

Have you tried wikipedia?

Always telling people to "Wikipedia it" is rather counterproductive when discussing matters like this especially when the information simply isn't there, or goes by the name of some phenomenon I haven't even heard of (which makes searching for it quite hard considering the keyword system isn't the best). I wish life was so easy that you would always get a correct answer from a source such as Wikipedia whenever you had a question.

There are phenomena where something goes FTL but not information, right?

Right.

 

But in this case if the photons themselves are traveling at superluminal speeds (due to energy densities lower than that of "normal" vacuum)

Are you sure that's correct?

 

You're saying that between close plates (as used in the casimir effect) the vacuum is 'more complete' due to the reduced number of virtual particles (fact), so the permitivity is less and therefore light travels faster (does it)?

 

Using [math]c = \frac{1}{\sqrt{\varepsilon_0 \mu_0}}[/math] formula you would seem to be correct. That is; between two close plates, where there are noticeably (casimir effct) less virtual particles, [math]\mu_0[/math] would decrease (or so it seems, to me, at the moment) and therefore c increases.

 

Well now you've got me interested! *Investigating*

 

OK, so the Scharnhorst effect is what you're talking about. The Scharnhorst effect is the predicted effect that a photon moving between two close plates will travel faster than c.

 

Scharnhorst was able to some mathematical analysis of this using QED (quantum electrodynamics), I haven't found his work yet though.

 

In 2002 a 25 page paper, which can be found here:

http://arxiv.org/PS_cache/gr-qc/pdf/0107/0107091.pdf

shows that the Scharnhorst effect does not "automatically lead to causality violations" (quote from the abstract of the paper).

I haven't read that paper yet, although I hope to soon. Maybe I'll be able to answer your question when I have.

Hmm interesting, thanks for the link. I'll have to look into that too.

[math]\langle q_2, t_2|q_1, t_1\rangle =\int_{Q(t_1)=q_1}_{Q(t_2)=q_2}\mathcal{Q(t)}\int\mathcal{P(t)}\exp\left[i\int dt\left(\sum_iP_i\dot{Q}^i-H(Q, P)\right)\right][/math]