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Path: utzoo!watmath!clyde!burl!ulysses!gamma!epsilon!zeta!sabre!petrus!mwg
From: mwg@petrus.UUCP (Mark Garrett)
Newsgroups: net.sci
Subject: Re: Questions on PHOTONS
Message-ID: <693@petrus.UUCP>
Date: Wed, 20-Nov-85 09:44:28 EST
Article-I.D.: petrus.693
Posted: Wed Nov 20 09:44:28 1985
Date-Received: Sat, 23-Nov-85 02:44:04 EST
References: <1092@mtuxo.UUCP> <petrus.679> <169@ccnysci.UUCP> <631@hlwpc.UUCP>
Organization: Bell Communications Research, Inc
Lines: 30

++
> Several people have responded to this question saying
> that since there is no such thing as a perfect mirror,
> the light inside the mirrored chamber would increase
> only to a finite limit.
> This doesn't make sense to me;  if you are constantly adding
> light (photons) and only a small fraction can go away (presumable
> as heat) then it seems to me the number of photons (and 
> intensity of light) should continue to increase unbounded.
> 
> Am I missing something here?

You're thinking in terms of losing a fraction of the incoming flow whereas
the actual loss is a fraction of the total intensity of light.  Here's a
simple analogy with water:

A tank is fed with a flow of water at the rate of 10 gal/sec.  The tank leaks
at a rate of 1% of its contents per second (not 1% of the influx).  How much
water accumulates?  Well, when there's 1000 gallons, then the input equals
the output.

Of course, with light, the photons aren't sitting still, and the leakage
really is a fraction of the photons *hitting the walls* (or interior material
if you consider absorbtion).  But ALL the light is constantly hitting the
walls, not just the newly added light.  Someone treated this in another
posting as a series of strobe flashes.  This is useful since it's easy to
work with discrete events.  To get a real situation, just take the limit
as the summation approaches an integral. 

-Mark Garrett