Re: QED and the speed of light

From: Igor (thoovler_at_excite.com)
Date: 09/16/04 

Date: Thu, 16 Sep 2004 12:09:19 +0000 (UTC)

Hans de Vries <hansdevries@chip-architect.com> wrote in message news:<Hans.de.Vries.1cds07@physicsforums.com>...
> Mike Helland Wrote:
> >
> > <quote>
> > It may surprise you that there is an amplitude for a photon to go at
> >
> > speeds faster or slower than the conventional speed, c. The
> > amplitudes
> > for these possibilities are very small compared to the contribution
> > from speed c; in fact, they cancel out when light travels over long
> > distances. However, when the distances are short...these other
> > posibilities become vitally important and must be considered.
> > </quote>
> >
> > The question is, does this apply to all photons or just virtual
> > photons? In the context of this quote, there is nothing to suggest
> > virtual photons, but when I say that photons can travel at speeds
> > other than c no one believes me.
> >
> > If this is specific to virtual photons, can someone provide a cite or
> >
> > reference that makes this clear? Preferably can someone cite Feynman?
> >
> >
>
>
> You can read more about Feynman arguments in:
>
> Elementary Particles and the Laws of Physics.
> Richard Feynman, Steven Weinberg
> (Dirac Memorial Lectures 1986)
>
> See page 7..10
>
> His argument is based on the Fourier decomposition of
> the wave function with positive energies only:
>
> On page 8:
> "If you start a series of waves from a particular point they can
> not be confined to be inside the light cone if all the energies
> are positive."
>
> and on page 9:
> "In other words, there is an amplitude for particles to travel
> faster than the speed of light and no arrangement of super-
> position (with only positive energies) can get around that."
>
>
> Regards, Hans
>
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That's a very interesting reference. He essentially correlates the
non-vanishing amplitudes outside the light cone with the sense of
reverse causality in that region and uses it as a justification for
antiparticles. I'm just curious what other implications can be
carefully derived from this result.

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