Physics Banter - View Single Post - Empirically Confirmed Superluminal Velocities?

**Robert Clark**

(Bilge) wrote in message ...
Robert Clark:
wrote in message news: ...
I'll add here as a comment that the issue of group velocity is
generally misunderstood, perhaps due to the fact that lower level
textbooks don't explain it well. Group velocity *is not* signal
velocity. Under some circumstances, when the dependence of phase
velocity on frequency over the bandwidth of the signal is weak, group
velocity is a good approximation to signal velocity over distances
short enough so that the pulse shape does not change appreciably in
propagation. That's all. The conditions listed above are reasonably
well satisfied in most practical situations, but they totally fail
under anomalous dispersion situation.

Mati Meron | "When you argue with a fool,
| chances are he is doing just the same"

You're aware of the discussions on sci.physics.relativity that to
determine if a signal travelled superluminally what would be required
is a round-trip measurement.

That is not the case.

This is because of the uncertainty of synchronizing clocks in
two different locations.

It's completely unnecessary to synchronize anything.

It is well known among researchers in the foundations of relativity
the need to synchronize clocks at two locations for comparing times at
those locations.
See this post by Stephen Speicher:

From: Stephen Speicher )
Subject: Speed of light
Newsgroups: sci.physics.research, sci.physics.relativity
Date: 2003-06-24 20:06:03 PST
http://groups.google.com/groups?selm...st.localdomain

Bob Clark