On 4/14/12 4/14/12 5:28 AM, Richard D. Saam wrote:
> But National Institute of Standards and Technology work as reference:
> arXiv:1204.0810v1 [quant-ph] 3 Apr 2012
> suggests that superluminal transfer of information is possible
This looks like anomalous dispersion in a new guise. As long as any individual
wave is restricted to speeds <= c, even though a superluminal group velocity is
possible, no information propagates faster than c -- the front velocity remains
<= c. The superluminal propagation of pulses is merely an artifact of the way
the different waves interfere with each other, but there is no pulse if there
are no waves, and if the individual waves travel <= c so does the front edge of
the waves, the forward limit of the pulse, and any information transfer.
See a direct demonstration of this (Java required):
http://gregegan.customer.netspace.net.au/APPLETS/20/20.html
Note how closing and then opening the shutter affects the waves. Note that a
NEGATIVE group velocity is possible, showing how artificial are these group
velocities, and that they do NOT represent any transfer of information; the
paper referenced above mentions a negative pulse velocity, implying they are
discussing a similar interference phenomenon.
Tom Roberts