From: sarfatti@well.sf.ca.us (Jack Sarfatti)
Subject: Star Ship Engineering & Time Travel 1
Organization: Whole Earth 'Lectronic Link
Date: Thu, 31 Dec 1992 06:32:48 GMT


Comments by Sarfatti:

From: mcirvin@husc8.harvard.edu (Matt McIrvin)
Subject: Re: Vacuum-Driven Power Exchange in the Free Electron Gas
Date: 30 Dec 92 22:23:34 GMT

lwall@netlabs.com (Larry Wall) writes:

>In article <1992Dec27.174901.7159@netcom.com> raicu@netcom.com (Eugen
Raicu) wr
ites:
>: I am not very knowledgeable, but I thought the energy of virtual
particles
>: is an effect of the uncertainty principle and is available only on very
>: limited time scales after which it must be given up.

>That's backwards, I think.  The uncertainty principle is a description
>of the way virtual particles make things look.  The virtual particles
>aren't a consequence of the uncertainty principle, except maybe in the
>sense that evolution is a consequence of how we classify various living
>things.  One generally prefers to state it the other way: that how we
>describe things is a consequence of how things came about.

These days it's usually described in a manner closer to Eugen Raicu's; the
virtual particles are artifacts of perturbation theory applied to quantum
field theory, whereas uncertainty relations are a fairly fundamental
consequence of how the quantum theory is set up.

*"artifacts of perturbation theory" ? The Lamb shift and Casimir force are
real effects so I'm not sure what "artifacts" means*

You can see energy as temporarily non-conserved via the time-energy
uncertainty principle if you use the non-covariant formalism of QFT, or
you can use a covariant formalism and treat energy as conserved, but
allow the virtual particles to violate laws of motion.

*Yes, this is why a virtual photon can be spacelike outside the light cone.
It explains the instantaneous action of the Coulomb potential in the rest
frame of the charge. Even when the charge is in motion the Coulomb force
acts faster-than-light - the spacelike action is frame invariant only the
simultaneity and the time order of cause and effect features are not frame
invariant.  That is, an interval between source event 1 and field event 2
outside the light cone in one frame is outside the light cone in every
frame in SR.*

These are different calculational techniques; they describe the same
theory, which is really
quantum field theory as it appears when treated perturbatively.

>In a very real sense, it would appear that there are *no* real particles,
>but *only* virtual particles that, by some clever accounting tricks, add
>up to make it look like there's a real particle here, or maybe there.
>Even the speed of light is not a real barrier to virtual particles--some
>can go faster than that, and some slower, but they all average out
>to make it look like the speed of light is what it is.

>That's basically a layman's interpretation of how Diagram Dick explained
>QED, so the professionals might want to disagree or amplify or obfuscate.

That's a fairly correct description of Feynman's view of the situation,
at least at the time he thought it up.  It's still a correct description
of how diagram calculations work.  It's been somewhat superseded
today in the sense that quantum field theory is now assumed to hold in
areas where perturbation theory doesn't work, such as QCD, so a
diagrammatic
treatment where the virtual particles are the primary objects doesn't
really make sense any more.  The problem, basically, is that if the
coupling constant is too large, the series you get by summing diagrams
becomes hopelessly divergent (you lose even the iffy, fudged-up sort of
convergence that holds otherwise), and you need other ways of handling
the calculations.  The objects on which everything else is based end
up being the quantized fields.

*Yes, but that's only because the starting point for the vacuum structure
is not right. The virtual particles are defined relative to the vacuum
structure. Diagrams relative the correct vacuum should converge.  Phase
transitions between different vacuum structures can release or absorb
energy - ultimately this is how we will amplify traversable wormholes out
of the foam for time travel and power our star ships. (Sarfatti)*

--
Matt McIrvin
Newsgroups: sci.physics