Re: Photons was COLLISION 2

[Bob Sciamanda <trebor@VELOCITY.NET>]

Fizzlers,
I have been rather quiet, of late - partly because I would have to (ad
nauseam) try to express again what is said so well by JD below - thanks,
John!

Hear! Hear! Hear!

Bob

Bob Sciamanda (W3NLV)
Physics, Edinboro Univ of PA (em)
trebor@velocity.net
http://www.velocity.net/~trebor

----- Original Message -----
From: John Denker <jsd@MONMOUTH.COM>
To: <PHYS-L@lists.nau.edu>
Sent: Thursday, December 02, 1999 2:23 PM
Subject: Re: Photons was COLLISION 2


> At 12:33 PM 11/30/99 -0700, Jim Green wrote:
> >  Now if you understand what a "photon" is please
> > tutor me -- and perhaps a few others on the list.
>
> I'll pass on that.  Let me explain why:
>
> 1) The topic of "photons" is well covered in standard textbooks, and
even
> in the semi-popular literature such as Feynman's _QED_.  It would not be
a
> good use of Phys-L bandwidth to parrot the standard discussion.
>
> 2) QED is irrelevant to this thread, which started out as a discussion
of
> the dynamics and energetics of rail-car collisions.
>
> 3) A more general and important point is this:  There are many people
who
> find it useful to use the notion of "photon" and the notion of "local
> conservation of energy" to solve physics problems.  OTOH, certain
Fizzlers
> have repeatedly objected to these notions.  To them I say:
>
>    a) If you aren't interested in solving physics problems, that's fine,
> but don't bother the list about it.
>
>    b) Unlike pure mathematics, practically every physical theory is
inexact
> if you look closely enough.  But let's not panic; "inexact" is not the
same
> as "wrong".  Normally these physical theories have a large domain of
> applicability.  It is good to know where the domain of applicability
ends,
> but it is bad manners to criticize good applications just because
> misapplications are possible.
>
> For example:  there are good applications of classical thermodynamics,
and
> there are good applications of classical electrodynamics.  We use them
even
> though we know that the two theories together produce the black-body
> paradox.  To say it another way:  Potholes don't keep us from driving on
> the road.  We just steer around them.
>
> The notions of "photon" and "local conservation of energy" are on much
> better footing than classical electrodynamics or classical thermo.
>
> If you think you have caught somebody using such a notion in a situation
> that is clearly outside its domain of applicability, the burden is on
*you*
> to show that it has led to an incorrect prediction of some measurable
> quantity.  (Philosophical objections with no measurable consequences
don't
> count.)
>
>    c) Perhaps you wish to argue that local conservation of energy, while
> not wrong, is just less convenient than some other techniques you
> know.  Well, then you should explain those other techniques in a
positive
> way so that the community may benefit.