Re: Field Quanta

Thus spake Igor Khavkine <igor.kh@xxxxxxxxx>
On 2007-02-08, Oh No <NotI@xxxxxxxxxxxxxxxxxxxxxxxxxxxx> wrote:
Thus spake Arnold Neumaier <Arnold.Neumaier@xxxxxxxxxxxx>

[...] Exchange particles are ''virtual particles''
- as the name says, purely fictitious objects -, introduced solely
to let the complicated multidimensional integrals arising in quantum
field theory (and abbreviated by Feynamn diagrams) look somewhat
tangible. See the entry ''How real are 'virtual particles'?''
in my theoretical physics FAQ at
http://www.mat.univie.ac.at/~neum/physics-faq.txt

Thus any 'explanations' of what virtual particles do is meaningless.
You could as well ask how the person (virtual image) in the mirror
you are looking manages to move its hand when you lift your hand.

This is often asserted as though a definite fact, but it is actually
just a point of view, one to which Feynman himself did not subscribe. He
considered that we should not distinguish between real and virtual
particles.

There are many points of view and yours maybe one of them, Feynman's may
be another, and mine a third. All of these points of view may be equally
valid and allowed to disagree when discussing physics informally.

Indeed. Ultimately a particular view may be shown to be correct, but
that is not the situation at the moment. I merely caution against
adopting a particular view as though it is established fact.

However, the same can no longer be said when we leave the informal realm
in favor of the quantitative and scientific one. Then, a physicist, that
considers the question "What is a virtual particle?" in earnest, will
not be able to find a definition that satisfies what is usually mean by
both "virtual" and "particle".

Finding answers to such questions is what I would regard as the object
of scientific research. One should not be too restrictive in this kind
of research. It may well be that what is usually meant by the word
"particle" does not correspond to anything in nature. For example, I
think that many people envisage a particle as a classical object which
has a position in space. But we do also discuss particles as quantum
objects. The usual definition of particle must be revised, but it does
not follow from that that no definition is possible.

The only definition that I know of that most can agree on is: a "virtual
particle" is an internal line on in a Feynman diagram. Since Feynman
diagrams only lives on paper, then so do virtual particles. A
quantitative treatment of these wiggly lines on papar as "particles" is
truly impossible.

There I must disagree with you. One should not prejudge the results of
research. If correct definitions are found for terms like "particle" and
the ultraviolet divergence is avoided through the proper use of Wick's
theorem (see Scharf Finite QED), if in addition the Landau Pole is
avoided by a suitable small scale modification to QED (there is more
than one possible, but I use a particularly simple one), and if
critically and most importantly one pays proper heed to Von Neumann,
that quantum superposition is a property of a many valued logic, i.e. it
is a part of a language which one should learn to understand, just as
one needs to learn any language in order to understand what is said in
that language, then it is indeed possible to interpret the wiggly line
as an ontological entity, which one may call a particle, and there is no
need to distinguish this by use of the word virtual. Moreover, Feynman
rules, do give a quantitative treatment. The paper in a Feynman diagram
is another matter. That really does have no physical meaning.

Regards

--
Charles Francis
substitute charles for NotI to email

.

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