If one looks at the interaction of two electrons using the classical
(no QM) Lorentz FORCE model one finds that the inter-particle forces
do not follow N3 and momentum/energy is only conserved by including
the momentum/energy of the E/M fields. The QED model recognizes this
at the outset and involves the (quantized) fields in the
momentum/energy exchanges a priori (a lesson carried over from its
ancestor, classical E&M). N3 is not an issue here (forces are not
relevant) but conservation of energy/momentum (classically the
generalization of N3) is a paramount concern. Hence, A PRIORI, the
quantized fields exchange energy /momentum with the electrons.
Bob Sciamanda
Physics, Edinboro Univ of PA (Emeritus)
www.winbeam.com/~trebor
trebor@winbeam.com
----- Original Message -----
From: "Jack Uretsky" <jlu@hep.anl.gov>
To: "Forum for Physics Educators" <phys-l@carnot.physics.buffalo.edu>
Sent: Sunday, August 05, 2007 11:07 PM
Subject: Re: [Phys-l] interaction
| Hi all-
| Jeff's series of pronouncements trnscend our usual understanding
| of QED, which proceeds in stages. In the first approximatioj, "wehn
tow
| charged particles are in the vicinity of each other, they simpley
scatter,
| according to Rutherford's law. It is legitiamate to ask aboot
| conservations of momentum in that approximation. There is, of
course, a
| certain probability of emitting a photon, in that case the overall
| conservation of momentum, e+ + e- + gamma, is observed. Each case
is
| usually considered separately (see, e.g., Jauch and Rohrlich's
book).
| Regards,
| Jack
|
|
|
|
|
| On Sun, 5 Aug 2007, Jeffrey Schnick wrote:
|
| > When two charged particles are in the vicinity of each other, each
charged particle is exerting force on the other. A charged particle
that is experiencing a net non-zero force is experiencing
acceleration. A charged particle that is experiencing acceleration is
emitting light. Light has momentum. If you tally up the momentum
vectors of the two charged particles at an instant prior to when the
charged particles are closest together, you get the total momentum of
the two charged particles at that instant, what Bob called the
momentum of the bare particles. If you tally up the momentum of the
two charged particles at an instant after the two charged particles
are closest together, you will get a new value for the total momentum
of the two charged particles (again what Bob called the momentum of
the bare particles) that differs from the original value by the
momentum of the emitted light. The total momentum of the system
consisting only of the two bare particles does no!
| t remain constant but momentum conservation still rules. The rate
of decrease of the momentum of the pair of bare particles is equal to
the rate at which momentum is being transferred to the surroundings.