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From: mam@charm.UUCP (Matthew Marcus)
Newsgroups: net.physics
Subject: Re: Nature of Photons
Message-ID: <290@charm.UUCP>
Date: Wed, 28-Mar-84 20:47:08 EST
Article-I.D.: charm.290
Posted: Wed Mar 28 20:47:08 1984
Date-Received: Fri, 30-Mar-84 01:29:53 EST
References: <2367@allegra.UUCP>, <1258@pur-phy.UUCP>
Organization: Physics Research - AT&T Bell Labs MH
Lines: 26

The article this follows up on interprets laser action in terms of cavity
resonance and ends "which is it? Cavity or boson?". Answer: Both!
You need a cavity with a high Q to define a single mode. You need the radiation
to be made of bosons so that lots of them can be in this mode at one time.
Imagine the following electron gun (you'll have to *imagine* this one!):
	Between electron-reflecting walls (E-fields?) put a LOT of free
muons.  Muons are metastable, and decay into electrons (+ pair of
neutrinos, but let's not worry about those).  Usual arguments suggest that
a beam of electrons, with momentum such that an integer number of wavelengths
fit inside the cavity, will exit if one wall has a hole in it.  However,
this WON'T work! Why? The reason I have in mind is that electrons are
fermions, so you can't get more than two in one mode.  There can't be such
a thing as a coherent electron beam for this reason.
<Philosophy=On ,or post -philosophical , to taste>
	All physics is one subject.  The more physics you know, the more
connections you see between apparently disparate areas, methods, or limits.
Case in point: You can derive laser action semiclassically by assuming the
active medium to be one with a negative absorption coefficient.  Many of
the statistical properties of light can be derived without invoking the
notion of 'photons' at all.  The QED description of light is built around
Maxwell's equations, so both 'field' and 'boson' interpretations are
perfectly correct.

	Photons - You can make light of them (From a 'Mooney's Module'
					cartoon in Isaac's SF Mag.)
		{BTL}!charm!mam