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From: gjphw@ihuxm.UUCP
Newsgroups: net.physics
Subject: Re: Light as the boundary between matter and energy
Message-ID: <948@ihuxm.UUCP>
Date: Wed, 4-Apr-84 20:20:05 EST
Article-I.D.: ihuxm.948
Posted: Wed Apr  4 20:20:05 1984
Date-Received: Sat, 7-Apr-84 00:38:10 EST
Organization: AT&T Bell Labs, Naperville, IL
Lines: 65



   In an attempt to better define the issue of matter and energy, I went to my
 (dusty) copy of an encyclopedia of physics and looked up energy.  It did not
 say much but did mention the forms that energy can take.  Also, to my original
 question as to the classification of light, I have noticed three replys (I am
 not so certain about the relevance of the ongoing photons discussion).

   The encyclopedia essentially divided energy into the classical forms of
 potential and kinetic.  Potential energy is stored energy due to the
 configuration of matter (a charged particle in an electric field, a particle
 with mass in a gravitational field, chemical energy, or internal energy of
 thermodynamics fame).  Kinetic energy is associated with the motion of matter.
 Momentum is just another way to express energy (as mentioned by G. Harris).
 However, it appeared from this single reference that energy is nothing (is not
 observable) without matter.

   One difficulty with the original question as I phrased it is vocabulary.
 The question was couched in terms of Newtonian physics.  Einstein's theory of
 special relativity demonstrates the link between energy and matter even for
 classical physics.  In a reply from charm!mam, the issue was clarified in
 favor of matter and radiation categories, with radiation composed of bosons
 and matter composed of fermions.

   Unquestionably, the original question was naive.  Our modern perspective is
 to do away with the boundaries of matter and energy, and refer solely to
 energy.  This brings me to the long-winded article by G. Stern (bnl!stern)
 which introduces the rather confusing vocabulary of quantum field theory
 (fields are represented by mediating particles such as photons, gravitons,
 vector bosons, etc.).  All matter is merely localized energy and all energy is
 represented by particles??!

   In classical physics, the concept of a field was introduced to explain any
 action at a distance.  Quantum field theory employs all particles to describe
 action anywhere, distant or not.  While it is nice to say that all matter is
 constituted energy, it is not so clear that particle exchanges are sufficient
 to describe all actions.  In particular, QFT has difficulty with
 representations of nonlinear classical fields.  The most famous of these
 fields appears in Einstein's general theory of relativity.

   Using the full equations, Einstein theory is nonlinear.  Among other
 details, it does not permit radiation to travel very far from the source.
 Gravitational radiation is not a consequence of the original Einstein theory.
 A linearized version does allow for radiation, and this has become the basis
 for attempts to realize a quantum theory of gravity (supersymmetry appears
 to me to be a different track toward a unified field theory).

   Since Einstein theory has not been well verified, even though it is
 intellectually appealing to many, perhaps the linear version implied by a
 successful quantum theory of gravitation is correct (and Einstein made a
 mistake??? :-).  Anyway, it does not seem prudent to hold quantum field theory
 up as the final explanation for energy in the universe (to confirm your
 suspicions, I do not performed renormalizations well).

   After reading the comments, I am convinced that my original question was
 both too naive and vague for a good treatment of the issue.  The question was
 supposed to be manageable within the realm of physics, not metaphysics.
 However, I am unable to phrase it better, so I won't.  Thank you for the ideas
 and clarifications.
-- 

                                    Patrick Wyant
                                    AT&T Bell Laboratories (Naperville, IL)
                                    *!ihuxm!gjphw