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Time travel: Light speed results cast fresh doubts

http://www.bbc.co.uk/news/science-environment-14289114

by gps408 • 15 years ago

28 2 15 years ago

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2

hugh3• 15 years ago

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".

btilly• 15 years ago

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... 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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