Father Inire's Mirrors and Wolfe Physics

Michael Buice · 19 Aug 2003, 18:50 · from urth-v0308.mbox · original

This is the message as the crawl holds it, before anything here touched it. What the conversation shows has been through ingest: transfer encodings decoded, attachments dropped, quote markers repaired, and the archiver’s ? resolved into quotation marks and dashes. Those repairs are judgements and some of them are wrong, which is what this page is for. Email addresses are obscured here as they are everywhere else on the site, so it is before our repairs rather than byte for byte.

From: Michael Buice <mabuice at uchicago.edu>
Subject: Re: (urth) Father Inire's Mirrors and Wolfe Physics
Date: Tue, 19 Aug 2003 13:50:55 -0500
Message-ID: <urth-v0308-3961 at digest.urth.net>
X-Urthmirror-Source: http://www.urth.net/urth/archives/v0308/3961.txt.shtml
MIME-Version: 1.0
Content-Type: text/plain; charset="utf-8"
Content-Transfer-Encoding: quoted-printable

On Tuesday, August 19, 2003, at 12:21  PM, Tony Martinez wrote:
> I don't have a copy of the book on hand, so forgive any
> misrememberings.  I seem to remember the argument goes something like
> this: light is, mathematically, made up of lots of different
> frequencies, from 0 upto infinity.  This means that some of the
> components of light travel *faster than light*.  I remember this scene
> as a speculation that if you could remove all the frequencies which,
> added together, slow down the sum total, you'd have the ones which
> travel faster than light. (*)

The fact I believe you are trying to get at is the concept that group=20
velocity and phase velocity are distinct.  This is not directly Quantum=20
Mechanics, per se, just wave mechanics (classical physics; however, it=20
does apply to QM).

Drop a stone into a pond.  You will see circular waves propagating from=20
the impact point.  These wave fronts are moving at a certain speed, the=20
speed of "sound" in water.  The velocity of those wave fronts is called=20
the "group velocity" and is the analogous speed referred to by the=20
"speed of light" for wave packets of light, when it is viewed as an=20
electromagnetic wave.

These same waves you see on the pond can also be seen as a combination=20
of waves which each have precise frequencies of oscillation.  These=20
constituent waves travel at all sorts of different speeds, and the same=20
situation is true of light as an electromagnetic wave.  Propagating=20
through a given material, there are components which travel faster and=20
slower than the speed of light in that material.  This velocity is=20
called the "phase velocity".  There have been many experiments which=20
have measured these two velocities and received far more press than=20
they should have for reporting such things as "speed of light broken"=20
and so forth.  You can't "separate" these components in the sense that=20
you can't use them to transmit any useful information faster than light=20
speed, which is one colloquial manner of stating the limits placed on=20
velocity by Lorentz invariance (i.e. special relativity).

The rub is that, under QM, all of these behaviors apply to matter and I=20
seem to recall more than a few descriptions of wave mechanical nature=20
(or at least what Severian can piece together from what he's been told)=20
in New Sun.

Michael

--=20

An unofficial mirror of a public mailing list · about & removal requests · download the archive · before the list · original archive at urth.net