Hector has it right. Also, it is interesting to note that a phase
velocity of an EM wave in a waveguide can be faster than c (much
faster, in fact). However, the group velocity cannot be. Phase
velocity is the velocity you get from picking a phase point on a
sinusoid and following it through space. Group velocity is the
velocity of a wave packet or modulated waveform through space (so
information would move at the group velocity).

Sean

On 3/14/07, Hector Martin <hector@marcansoft.com> wrote:
> John Ferrell wrote:
> > The following link addresses an instance of radiation traveling faster than the speed of light.
> > "Cerenkov Radiation comes from particles traveling at a speed greater than the speed of light in the medium in which they are moving."
> >
> > http://smthop.com/articles1details.asp?NewsNum=805
> >
> > There are other instances that I have run across that do not accept the speed of light as a limit.
> The limit is the speed of light in a vacuum, which is a constant, c. The
> speed of light in any other medium can be exceeded (as it is variable),
> it is the speed of light in a vacuum that can't. Exceeding the speed of
> light in a medium will cause nifty effects like Cerenkov Radiation, but
> it's certainly possible and commonplace around certain radioactive
> materials.
>
> Also, moving faster than the speed of light in a vacuum is supposedly
> possible (the mathematics allow for it), it's just crossing the boundary
> of the speed of light (both ways) that isn't.
>
>
> --
> Hector Martin (hector@marcansoft.com)
> Public Key: http://www.marcansoft.com/marcan.asc
>
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