

Time travel: Light speed results cast fresh doubts - gps408
http://www.bbc.co.uk/news/science-environment-14289114

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btilly
It should be noted that this result was completely expected. It turns out that
light traveling through a medium can have 3 different velocities: phase, group
and signal. Typically the latter two are the same and we can think of the
group velocity as being the real "speed of the particle", but that is not
always true. See
[http://en.wikipedia.org/wiki/Group_velocity#Physical_interpr...](http://en.wikipedia.org/wiki/Group_velocity#Physical_interpretation)
for more.

This experiment manages to measure the signal velocity for the leading photon
and verifies what we already knew for larger signals.

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hugh3
Kudos to the journalist here, it's hard to write a story on the subject
"Thing, once thought to be completely fucking impossible, turns out to be
completely fucking impossible".

