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From: gjphw@ihuxm.UUCP
Newsgroups: net.physics
Subject: A smoking gun for QED...
Message-ID: <957@ihuxm.UUCP>
Date: Wed, 11-Apr-84 12:34:15 EST
Article-I.D.: ihuxm.957
Posted: Wed Apr 11 12:34:15 1984
Date-Received: Fri, 13-Apr-84 06:09:55 EST
Organization: AT&T Bell Labs, Naperville, IL
Lines: 73



   This is both a criticism of QED and a request for some precision.

   Quantum field theory (QFT) and quantum electrodynamics (QED) are not
 interchangeable.  The theory with the impressive computational successes for
 the hyperfine transition in hydrogen is QED (18 significant figures at my last
 count).  QED was started in 1933, shortly after the establishment of quantum
 mechanics itself.  The best aspect of QED is that it handles the particle-wave
 duality of the photon in a consistent fashion.  Unfortunately, the infinities
 that arose in QED, plus the absence of experimental results for comparison
 with theory, stopped most work in QED until after World War II.  Then came
 microwave measurement techniques (e.g., the hyperfine transition) and
 renormalization to handle the infinities.

   QFT is an extension of QED.  Where QED involves only electromagnetic
 interactions, QFT attempts to include the two nuclear interactions (strong
 nuclear and weak nuclear).  The Weinberg-Salam theory, showing that the weak
 nuclear and the electromagnetic interactions are merely manifestations of a
 single interaction (now being called the electroweak interaction), received
 the Nobel Prize because of the increasing experimental support for this union.
 Due to the apparent infinite order required for strong nuclear interactions,
 QFT has been virtually useless for many body interactions (e.g., nuclear
 physics) and has been relegated to few-significant-figure precision
 calculations with elementary particles.  According to an article that I
 recently read, written by Weinberg, QFT may be wholely inappropriate as the
 starting point for quantization of general relativity.

   While I took a year of QFT, I did not do well in the course.  It appears to
 require a few "leaps of faith" to proceed, and I wasn't up to the task.  This
 statement is being made so that you might know my biases and prejudices.

   After consulting my Encyclopedia of Physics (1980) for the article on QED
 (written by Bjorken of Bjorken and Drell fame), I have a criticism to offer.
 QED cannot be the final theory covering electromagnetic interactions, despite
 its substantial computational successes.  QFT is even further removed from
 nature.  According to Bjorken, the presence of "bare" masses and charges has
 never been considered a satisfactory treatment of what classically seemed
 easy.  This conflict between bare properties and experimentally observable
 quantities is resolved through renormalization, which is also an unsatisfying
 technique.  Some of the more subtle issues around QED are ungoing experimental
 investigation in an effort to resolve these unsatisfying features.

   It is difficult to accept the concept that nature performs a renormalization
 during all interactions.  Though, to be fair, it is equally unlikely that a
 particle explores alternate paths in the search for the path of least action
 before making a move (perform a variational calculation to discover the
 appropriate lagrangian as required in classical mechanics).  At some point, no
 matter how successful a theory has been up til then, some consideration must
 be given to the "metaphysical" or conceptional aspects of a theory.  Newton's
 theories and definitions for dynamics worked well (except for Mercury) but
 also required an absolute time (at least according to Newton).  The success of
 Einstein's special relativity (a theory that really treats the transformations
 of absolutes such as mass and charge) shows the value of its conceptual
 foundations, though it does have clear limitations (no accelerations).  We
 should recognize that the usual impetus for revising a theory has always been
 the degree of inadequacy for explaining experimental results and how
 uncomfortable the peer group feels about it.

   QED has been greatly successful for calculating electromagnetic
 interactions.  QFT has been less successful, but is generally considered
 adequate for most elementary particle interactions.  Both require
 renormalizations to work, and carry masses and charges that are different than
 the observable quantities.  I don't like the need for renormalizations, and
 this makes these theories unattractive.  Let us render unto the theories their
 due (calculational successes) and look askance at their conceptional
 implications (renormalization).
-- 

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