Quantum tunnelling outside the light cone?

[BWV]

Zee's QFT in a Nutshell makes a short comment in the first chapter about the possibility of particles tunnelling outside their light cone - is there some probability that a particle could do this? I know the neutrino thing has been debunked as a faulty cable, but did not see this offered as an explanation - why not? i

 

[BWV]

No thoughts?

I did find this site
http://www.aei.mpg.de/~mpoessel/Physik/FTL/tunnelingftl.html

In recent years, some physicists have conducted experiments in which faster-than-light (FTL) speeds were measured. On the other hand, Einstein's theory of special relativity gives light speed as the absolute speed limit for matter and information! If information is transmitted faster, then a host of strange effects can be produced, e.g. for some observers it looks like the information was received even before it was sent (how this comes about should be described in elementary literature on special relativity). This violation of causality is very worrysome, and thus special relativity's demand that neither matter nor information should move faster than light is a pretty fundamental one, not at all comparable to the objections some physicists had about faster-than-sound travel in the first half of this century.

So, has special relativity been disproved, now that FTL speeds have been measured?

 

[Bill_K]

BWV, Zee's book has an easygoing style, but can be hard to nail down in places. The function he's talking about is the Feynman propagator, which falls off exponentially outside the light cone with a characteristic distance equal to the Compton wavelength, ħ/mc. This does not represent a violation of causality or influences going faster than light. In fact when combined with the existence of antiparticles it's exactly what is necessary to avoid such problems. Take a look at a more careful treatment, such as Weinberg Vol I, Sect 5.2.