Register Log in  Scientific Method / Science & Exploration  How
a superluminal experiment should be conducted  Researchers
demonstrate superluminal pulse propagation in a rubidium vapor.
A couple of months ago we reported on an arXiv paper that
reported superluminal pulse propagation. The paper was such a
steaming pile of science that our report amounted to something
along the lines of "pfffft hahahahahaha." The reason was that
the researchers did not give a detailed explanation of their
experimental setup, did not present any data other than a rather
vague "about 2ps," and didn't try to make a distinction between
the group velocity and the phase velocity.  To examine these
sorts of experiments, let me give you a short introduction to
the propagation of light. Light has two speeds associated with
it: phase velocity, and group velocity. When Einstein formulated
special relativity, he did it using the empirically observed
evidence that the phase velocity of light was constant for all
observers. The conclusion