> I had read of ceasium(sp?) gass heated to a certian high temprature
that
> has an IOR of less than 1. i.e. light traveles faster than the speed
of
> light in a vacuum. I havent seen this article disputed yet either. So
maybe
> it is true.

I've had a look, but there are not too many clear explanations on this
matter.  It seems that the Caesium was used to create a region of
"anomalous dispersion", which means that the wavelength dependence of
the IOR is reversed.  Shining a laser pulse through this caused a pulse
to be emitted from the other side of the chamber BEFORE the original
pulse had even reached it.  Sounds amazing, and sounds like
faster-than-light, but apparently it isn't.

What had happened was that the group velocity of the light had been
increased above the normal speed of light.  Normally, the group velocity
of light is the same as the signal velocity, ie information is
transmitted at the group velocity.  However, in the case of anomalous
dispersion, the group velocity is no longer the signal velocity, and no
information is carried at this speed.  The peak of the pulse travelled
at the group velocity, but energy did not.

More than this I can't tell you, I'm afraid.  However, many people note
that this kind of thing is very prone to media misinterpretation, mostly
because the "speed of light" NORMALLY refers to the speed of energy
transfer, but in fact a wave has many different speeds of propagation,
depending on exactly what property of the wave you are looking at.

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