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Science > Physics |
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"" |
| Date: |
12 Sep 2005 03:14:42 PM |
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Re: attractive force via particle exchange - how? |
From: "shev...@yahoo.com" <shev...@yahoo.com>
Every now and then somebody expalains electromagnetic forces as
"exchanges of virtual photons". My question is simple: how can >this be, for the case of attractive forces?
Some have answered that the exchanged particles have a "negative
momentum" - supposedly a momentum directed oppositely to the >velocity vector!
The imagery of particle exchange is little more than a mnemonic device
for doing perturbation theory calculations with; and has no physical
meaning in itself. There are, in fact, instances of exactly solved
quantum field theories (e.g. in 1+1 or 2+1 dimensions) where the exact
form of the interaction bears very little resemblance to the
corresponding perturbation-theoretic picture -- underscoring by way of
case-in-point the point.
There is no substantial difference between the description of the
electromagnetic force classical or quantum theoretically. In both
instances, Maxwell's equations are satisfied. The only proviso is that
the corresponding quantum fields are (a) non-commutative instead of
numeric, and (b) singular (i.e. the same type of animal as delta
functions). The latter feature is also present in the classical theory
with point sources.
The reason you have to resort to perturbation theory (i.e., the
interaction picture) is because it isn't even known to be possible to
even so much as DEFINE the field equations for the fully interacting
system (by fully interacting, I mean the system which includes all the
field equations for the fields, particles and their non-linear
interaction terms). That's because of feature (b); and because there
is no well-defined mathematics (except Colombeau theory) for non-linear
operations on singular functions (and Colombeau theory has not fully
made its case in this application).
This problem is also present in the classical theory -- i.e., it too is
ill-defined! In fact, rectifying the classical theory has emerged
again as a major topic in the last decade or so.
Classically, the problem comes straight from the field concept. Since
electromagnetics is described by a field instead of
action-at-a-distance particle mechanics, then the self-interaction
slips in. For particles, the total field is always calculated as a sum
of all the contributions of everyone else, except the particle itself.
But for the field, there need not even be particles (instead, the
distribution of charge could be singular), in which case you can't even
say what's self-interacting with what, let alone determine what
self-interaction to exclude from the total. And if there are particles
(i.e. singular point-sources, or even line-sources), then the 2nd
problem is that there isn't even an unambiguous definition of what the
field "associated with" the particle is! A field is determined for a
given source only up to a +/- free field term, and there's no criterion
that determines what the latter +/- term should be. So, forces can't
even be defined unambiguously in the classical theory.
An attempt to define what self-interaction is to correspond to a
particle and then to exclude it amounts to a prescription for
renormalization. So, to get a well-defined classical theory amounts to
rectifying the problem engendered by going to the field concept --
getting rid of some self-interaction term. A renormalization, given
the above, is only determined up to a free field term.
The same problem is inherited in quantum field theory, and the same
infinity has to be removed in some fashion.
Maxwell, when he wrote the Treatise, also encountered the issue and
tried to deal with it. His take on the issue was that point sources
and even line sources were physically meaningless. The
quasi-experiment used to show this is that if you take a conductor in
the form of a sharp needle-like shape (so that charge gets concentrated
on the tip, thus simulating a point source), the surrounding medium
will become more and more polarized, the sharper the conductor is made
.... until it breaks down. Maxwell inferred by extrapolation that since
the breakdown occurs at higher and higher charges the more air is
removed from the surrounding space, that the breakdown for a complete
vacuum would be very large. But he specifically pointed out that it
must still be finite! That is, even in a perfect vacuum, there must
STILL occur a breakdown of the surrounding space for sources as the
source becomes more and more pointlike or linelike.
Thus, he concluded that no actual point or line sources existed in
reality, for they would be surrounded by a cloud of charges (even in a
vacuum) which would have the effect of screening the charge and keeping
singular electric or magnetic fields from actually arising the closer
you got to the charge. The charge, itself, would be effective smeared
out in space. Consequently, Maxwell also talked about the distinction
between the actual charge and effective (screened) charge.
All of these concepts were inherited by quantum field theory, almost
intact, though there is no clear continuity of thought dating from
Maxwell to Tomonaga/Feynmann/etc. It appears they came up with the
same ideas independently.
The best explanation of what's actually going on in an interaction --
particularly one that involves a change in particle identity and number
-- is more along the lines of what string theory provides. The
interaction is NOT concentrated at a point, but occurs distributed
throughout space. The picture provided by string theory visualizes two
or more loops that merge or split over time. If you plot the
time-development in 2+1-D, you might get something looking like
2-legged or 3-legged pants (the technical name is a cobordism). The
actual location of the split is not well-defined, because it's not
something that occurs at a point.
Whether string theory is valid or not is immaterial. The central
argument made by Maxwell still remains valid, so that whatever is going
on is happening in a distributed region of space, not at a single
point.
These are the physical interactions.
The pseudo-interactions involving virtual particles are an entirely
different animal and -- as related above -- have no physical meaning in
and of themselves.
For one, the whole photon concept pertains ONLY to free electromagnetic
fields. In fact, the only known well-defined quantum field theories is
3+1 dimensions or more are the ones for the free fields. What the
quanta for interacting fields look like (or whether the notion of
quanta is even meaningful) is an entirely different issue. So, out the
window goes the whole idea of virtual photons as describing anything of
fundamental physical significance.
The only reason you could even get away with talking about photons and
the like for the physical reactions, is that in those cases, the
reactions involve particles that fly off from each other into empty
space -- i.e. the fields underlying the particles become essentially
free fields). Even there, it's already known that this picture -- the
whole perturbation theory and interaction picture -- breaks down for
persistent long-range forces, which includes the electromagnetic force
(and gravity). Fields for long-range forces are never entirely free,
because the force never stops acting.
So, to some extent, even the actual observed occurrence of the physical
interactions (particles flying apart in a particle accelerator
experiment) remains somewhat of a mystery, for long-range forces.
And back to the original issue: the general picture of what an
interacting actually looks like (i.e. how to define the non-linear
terms of the fully interacting field theory) is open and unresolved.
It gets even more messy: even for the FREE electromagnetic field --
since this is now known to be an integral part of a much larger field
(the electroweak field), then the corresponding field equations aren't
even linear there anymore. Maxwell's equations for the free
electromagnetic field are linear, but not the corresponding equations
for the free electroweak field. In particular, the electroweak field
can form charges and magnetic monopoles, and the right hand sides of
all 4 Maxwell equations are non-zero (including those describing
magnetic sources). The field associated with the W+ and W- particles
can produce a non-zero magnetic charge, as well as a non-zero electric
charge.
So, the question of what the free electromagnetic field actually looks
like -- in the larger context of the electroweak field that it is a
part of -- isn't even resolved either, given the discussion above. The
photon concept even for the free field is thus, at best, only an
approximation of physical reality; never mind virtual particles.
.
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| User: "G=EMC^2 Glazier" |
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| Title: Re: attractive force via particle exchange - how? |
12 Sep 2005 11:44:23 PM |
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shev Repulsion can be explained easy with particles used like medicine
balls thrown back and forth. Attraction causes this theory to completely
break down. QM uses the graviton as the gravity messenger particle for
attraction,but what message it gives things to attract is in reality a
lot of fudging. Bert
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| User: "Double-A" |
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| Title: Re: attractive force via particle exchange - how? |
13 Sep 2005 12:36:38 PM |
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G=EMC^2 Glazier wrote:
shev Repulsion can be explained easy with particles used like medicine
balls thrown back and forth. Attraction causes this theory to completely
break down. QM uses the graviton as the gravity messenger particle for
attraction,but what message it gives things to attract is in reality a
lot of fudging. Bert
Let's say the medicine ball has a lot of top spin and bounces off the
top of your head. It's going to snap your head in the direction it
came from because of its spin. That's attraction mediated by a
particle. "Spin is In", Bert!
Double-A
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| User: "PD" |
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| Title: Re: attractive force via particle exchange - how? |
14 Sep 2005 08:26:03 AM |
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Double-A wrote:
G=EMC^2 Glazier wrote:
shev Repulsion can be explained easy with particles used like medicine
balls thrown back and forth. Attraction causes this theory to completely
break down. QM uses the graviton as the gravity messenger particle for
attraction,but what message it gives things to attract is in reality a
lot of fudging. Bert
Let's say the medicine ball has a lot of top spin and bounces off the
top of your head. It's going to snap your head in the direction it
came from because of its spin. That's attraction mediated by a
particle. "Spin is In", Bert!
Double-A
It's worth looking at the physics of this analogy to see what would be
required to extrapolate it to the case at hand.
1. Your head only snaps forward in this case because it is attached to
the neck, which provides a pivot point for the medicine ball's contact
force to apply a torque about. If it were not for the neck, and your
head were disembodied, it would *not* snap forward in the direction the
medicine ball came from, any more than a glancing blow from the cue
ball onto the 8-ball will cause the 8-ball to recoil backwards in the
direction the cue ball came from, no matter how much spin is applied to
the cue ball.
2. For the medicine ball to apply a torque, it has to have a
measurable, physical extent, translating spin into tangential velocity
at its perimeter. For the same thing to be true of a boson, it would
have to also have physical extent, which you have not established.
3. For the contact between medicine ball and head to exert a torque on
the head, there must be friction present between the two surfaces that
resist the surfaces slipping against each other. In macroscopic
objects, this friction is due to *linear* forces between the atoms of
each surface. In the case of a boson interacting with a fermion, what
is the interaction that provides the *friction* between the surfaces of
those two objects?
As usual, looking in detail at analogies shows exactly how far the
analogy can be taken before it breaks dramatically.
PD
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| User: "Y.Porat" |
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| Title: Re: attractive force via particle exchange - how? |
14 Sep 2005 08:44:25 AM |
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moreover
if the messenger is spinning and hit
you right ahead
the result will be that both of you
will be swayed *sideways*
not an inch of approach
2 dont forget the direction of the linear
motion of the ball (messengers) it is
in direction that will repel you further apart.
common guys
do you have some emotional block to accept my
'Circlon' ??
it is inevitable!!
you have no chance to run away from it !!!
ATB
Y.Porat
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| User: "Y.Porat" |
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| Title: Re: attractive force via particle exchange - how? |
13 Sep 2005 05:05:34 AM |
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the only thing i agree with you is that the *physical* problem is
unresolved
but you could say it just in one line
no need for so much talking and walking around the bush!!
there is only a partial mathematical solution.
now the devil is in the details!!
it is not good enough to say that we have some 'agent' that makes that
miracle to fit the mathematics
and the prove that the devil is there is
that people believe that that agent is a photon
just claim it carelessly without giving it a second thought
while at the second thought they should realize that the photon as
an attraction messenger is 'dead by arrival'
since it moves in straight lines!!
it must be something that does not move in a straight line!!
to hit the other particle from behind!!!
so you see that getting into details could save us for false
assumptions
right at the beginning and save us decades of false self deluded
satisfaction
that *prevented us from looking for a better answer!!
and one of the big sins of scientists was
the sin or arrogance!! (the very ancient sin!! it is a sin because it
it caused damage)
not to speak about the W bosons that are utter nonsense
or at the good case a fake solution!!
ATB
Y.Porat
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| User: "Autymn D. C." |
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| Title: Re: attractive force via particle exchange - how? |
13 Sep 2005 08:37:04 AM |
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Prove it or shut up, schizoPorat.
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| User: "Y.Porat" |
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| Title: Re: attractive force via particle exchange - how? |
13 Sep 2005 09:30:28 AM |
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have you ever heard about pioneering science
beside the more established one Psycho??
can anyone tell us what was the first date in which 'AUty'
first arrived to this Ng??
may be even Auty can tell us ??
TIA
Y.Porat
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| User: "PD" |
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| Title: Re: attractive force via particle exchange - how? |
13 Sep 2005 11:49:29 AM |
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Y.Porat wrote:
the only thing i agree with you is that the *physical* problem is
unresolved
but you could say it just in one line
no need for so much talking and walking around the bush!!
there is only a partial mathematical solution.
now the devil is in the details!!
it is not good enough to say that we have some 'agent' that makes that
miracle to fit the mathematics
and the prove that the devil is there is
that people believe that that agent is a photon
just claim it carelessly without giving it a second thought
while at the second thought they should realize that the photon as
an attraction messenger is 'dead by arrival'
since it moves in straight lines!!
Photons do not move in straight lines. No one says they do.
Your obsession of finding a better answer is based on a falsely assumed
flaw.
it must be something that does not move in a straight line!!
to hit the other particle from behind!!!
so you see that getting into details could save us for false
assumptions
right at the beginning and save us decades of false self deluded
satisfaction
that *prevented us from looking for a better answer!!
and one of the big sins of scientists was
the sin or arrogance!! (the very ancient sin!! it is a sin because it
it caused damage)
not to speak about the W bosons that are utter nonsense
or at the good case a fake solution!!
ATB
Y.Porat
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