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From: jhc@mtung.UUCP (Jonathan Clark)
Newsgroups: net.physics
Subject: (yet) More on repulsion and attraction (rather long)
Message-ID: <620@mtung.UUCP>
Date: Fri, 25-Oct-85 23:43:23 EDT
Article-I.D.: mtung.620
Posted: Fri Oct 25 23:43:23 1985
Date-Received: Sat, 26-Oct-85 08:26:33 EDT
Reply-To: jhc@mtung.UUCP (Jonathan Clark)
Organization: AT&T Information Systems Laboratories, Holmdel, NJ
Lines: 110

Messrs Rimey, Anderson, Maxwell (sic), myself and a few
others have been discussing the extreme difficulty of
translating concepts of QM into classical terms. A few points
have arisen in some recent postings which I shall attempt to
clarify but will probably just confuse everybody even more.
Anyway, here goes...

>Re: unstable gluons.
Mr Anderson summarizes quite neatly Yukawa's Nobel
Prize-winning work which predicted the pion, and reminds us
that the heavier the gauge particle, the more rapidly the
force it mediates weakens with distance (as an aside, are
gravitons supposed to be massless?). While this is true,
what I said was also true, viz that the more massive a
gauge particle, the smaller is its half-life. Massless
particles (photons, neutrinos [these are still massless
this week, aren't they?]) do not decay, while heavy ones
(pions &c) do, and the heavier they are the faster they
break up. His comment about the Uncertainty Principle
placing upper bounds on the lifetime of a virtual particle
is also quite true, but not relevent as free particles
(ones that decay) are not 'virtual'.

He also brings up the wave/particle duality of EM (and
other varieties of field), which is so distressing to
neophyte physicists, and points out that my description
should not be strictly interpreted in terms of classical
physics. Attempting this will provide some fairly severe
headaches and no satisfactory results! It was merely an
attempt to provide a classical-type picture of a mechanism,
and the analogy breaks down very quickly. In addition, he
correctly points out that the momentum of a virtual
particle bears very little relation to anything obvious.
The only rule of Nature here seems to be that the more
unlikely a phenomenon is then the shorter period of time it
lasts.

> What is unusual is that like-charged and oppositely-charged
> particles pick up one or the other, exclusively.
Well they don't really, actually. See below.

Mr Maxwell's question of:

> is there some sort of intuitive explanation for why like-
> or unlike-charged particles  "pick up" a photon with one or
> the other momentum exclusively?

does not have a satisfactory (aethsetically pleasing)
answer, I'm afraid. The answer is... 'because it is more
likely to happen that way'.

Imagine, if you like (help, here I go with the dubious
analogies again!), that an electron in an EM field (ie in
the Universe) is rather like a molecule in a gas (or a
liquid). It is continuously absorbing and emitting ('real'
and 'virtual') photons, and thus its energy, momentum and
direction of travel are constantly changing. Doesn't this
sound like Brownian motion?

Now remember Mr Anderson's point about the momentum of a
'virtual' particle being able to have any value, but for a
limited period of time. Well, in this limited period of
time the 'virtual' photon has a certain probability of
interacting with another particle. The closer the other
particle is, the higher the probablity if interaction.
These particles (they are 'virtual' if they are reabsorbed
by the source, 'real' if they interact with another
particle) have a certain distribution of energy and
momentum, according to some set of probabilities.

As to why particles with like signs repel each other, you
might hypothesize that the other particle disturbs the
probablities in such a way that it emits more particles
with a momentum vector which if absorbed by the other
particle would cause it to move away. A particle of unlike
sign has the opposite effect. The whole business balances
out over the Universe, leading to the results we observe
(think once again of the contrast between the motion of
individual molecules of a gas and the large-scale motion).

Then again, you might hypothesize something completely different.

If this sounds like a simple (sic) electron has an awful
lot of things going on at once, well it does. But an
electron is generally moving fairly fast, so its clock runs
really slowly :-) !

Bear in mind that QM treats the electric charge as
infinite, not some small number. The reason that we don't
measure it as infinite is that there is intense 'virtual'
pair production in the energy field surrounding the charge.
These particles are preferentially created with the unlike
charge near the particle, and the like charge away from it.
This has the effect of spreading the measurable charge out
in space. The degree of 'virtual' particle production is
just one of the fundamental constants of the Universe. For
an analogy to this, think of Steven Hawking's work on the
evaporation of black holes which follows a similar
mechanism.

--
Jonathan Clark
[NAC]!mtung!jhc

Personally, I doubt that a truly random walk would be interpreted as such.
-- 
Jonathan Clark
[NAC]!mtung!jhc

My walk has become rather more silly lately.