Re: Maximum speed of light

From: Bill Hobba (bhobba_at_rubbish.net.au)
Date: 01/20/05 

Date: Thu, 20 Jan 2005 22:32:46 GMT

"PD" <pdraper@yahoo.com> wrote in message
news:1106251216.810509.178060@c13g2000cwb.googlegroups.com...
> w...@operamail.com wrote:
> > Chris O'Riordan wrote:
> > > wespe@operamail.com wrote:
> > > > Hi,
> > > >
> > > > OK, we know that speed of light is 300.000km/sec in space. But
> > also,
> > > > space is not totally empty and crawling with virtual particles.
> So,
> > > > what if these particles are slowing light down? Suppose speed of
> > > light
> > > > could go up to, say, 400.000km/sec, if space was less dense in
> > these
> > > > particles. Maybe in the future it will be possible to create a
> > > > super-conductor-vacuum and utilize this maximum speed. Why not,
> hm?
> > > Perhaps it could go up a bit more, say 500,000 km/s :-D
> >
> > Seriously, I guess it can. The replies so far sound promising,
> although
> > most of it is beyond me. If a modified fiberoptic cable can carry
> > information faster than 300.000km/sec, at least in theory, shouldn't
> > this be a breakthtrough?
>
> 1. Read the reference that David Smith linked to above and do a very
> rough back-of-envelope calculation to figure out how much the speed of
> light can change due to altering the vacuum. At least figure out the
> order of magnitude, so you know whether a doubling of c is possible, or
> whether an increase of 0.000001% is possible.
>
> 2. You mentioned changing the quantum *vacuum*, not the properties of
> any material that is carrying the light. Any gain to be had in the
> vacuum is irrelevant for a fiber.
>
> 3. The transmission of a light pulse in a fiber-optic cable is
> *substantially* lower than 3E5km/sec already. You'd have to work hard
> just to get it closer to c.
>
> I think it's highly unlikely anyone is going to make a gazillion
> dollars on this "breakthrough".

I have read this thread with some interest. However I remain unconvinced
due to fundamental considerations. First SR is not a theory about light -
it is a theory about space-time. The C (its existence - not its actual
value) that appears in the Lorentz transformations is deducible from the POR
alone. The reason light travels at that speed is a prediction of QED; the
theory combining SR and QM that makes the prediction of virtual particles -
the QED lagrangian demands it. Its speed is not affected by the existence
of virtual particles - they seem to be an unavoidable consequence of the
existence of off mass shell terms (chapter 1.4 Zee - Quantum Field Theory in
a Nutshell). AFAICS there is one reason and only one reason that light
would not travel at the speed C in the Lorentz transformations - the photon
lagrangian was described by the Proca lagrangian and had a slight mass. If
the mass of the photon is zero it must travel at the speed of light.

Thanks
Bill

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