[Phys-L] Re: Travel distance in a waveguide.

[David Bowman <David_Bowman@GEORGETOWNCOLLEGE.EDU>]

Regarding bc's observation:

> A Sci. Am discussion used speed of information.  They used, inter
> alia?, an example of something much faster than "C":  Moving  a
> flash lite beam;  by the time it reaches the moon it's traveling
> > "C".  But no info. is transferred from one side of the moon
> tother.
>
> bc

"Speed (limit) of information" is ok as long as that is understood as
*meaning* that it is the limiting speed that a causally informative
influence can locally travel.  I think that a one-word synonym for
the notion of a "causally informative influence" is a physical
"signal".  The physical significance of information transfer is in
how its presence or absence can trigger different cascades of events.
Thus it is the signaling feature of the information transfer that is
relevant for physics.  Otherwise the bare concept of just mere
information is a sterile abstraction without physical consequence.

David Bowman