Author 
Message 
Bilge science forum Guru
Joined: 30 Apr 2005
Posts: 2816

Posted: Mon Jul 10, 2006 4:34 am Post subject:
Re: Magnetic Idyll



Timo A. Nieminen:
Quote:  On Sun, 8 Jul 2006, Edward Green wrote:
The formal simularity of the Coriolis force and the Lorentz force law
2w x v vs. qB x v
suggests that the magnetic field may correspond to a local rotation of
space (inertial coordinate system) as seen by charge vs. that seen by
mass.
Very Maxwellian. Have you read Maxwell's papers on this kind of thing?
(Although he would have said "local rotation of the (a)ether", not space.)
For some insight: one can obtain Maxwell's equations from Coulomb's law
and special relativity. What happens if you start from Newton's law of
universal gravitation and SR? Surely you must get a gravitomagnetic term.
Heaviside did this, and it's a nice exercise. It isn't necessarily easier
to follow Heaviside than to do it from scratch.

Actually, jackson devotes several pages to explaining precisely why
one _cannot_ derive maxwell's equations from special relativity and
coulomb's law, giving gravitation as a counterexample as well a second
counterexample for a particle interacting with a scalar force.
(``Classical Electrodynamics,'' Jackson, J.D., 2nd ed. section 12.2). 

Back to top 


FrediFizzx science forum Guru
Joined: 01 May 2005
Posts: 774

Posted: Mon Jul 10, 2006 6:37 am Post subject:
Re: Magnetic Idyll



"Bilge" <dubious@radioactivex.lebesqueal.net> wrote in message
news:slrneb3q7q.5g8.dubious@radioactivex.lebesqueal.net...
Quote:  Timo A. Nieminen:
On Sun, 8 Jul 2006, Edward Green wrote:
The formal simularity of the Coriolis force and the Lorentz force
law
2w x v vs. qB x v
suggests that the magnetic field may correspond to a local
rotation of
space (inertial coordinate system) as seen by charge vs. that seen
by
mass.
Very Maxwellian. Have you read Maxwell's papers on this kind of
thing?
(Although he would have said "local rotation of the (a)ether", not
space.)
For some insight: one can obtain Maxwell's equations from Coulomb's
law
and special relativity. What happens if you start from Newton's law
of
universal gravitation and SR? Surely you must get a gravitomagnetic
term.
Heaviside did this, and it's a nice exercise. It isn't necessarily
easier
to follow Heaviside than to do it from scratch.
Actually, jackson devotes several pages to explaining precisely why
one _cannot_ derive maxwell's equations from special relativity and
coulomb's law, giving gravitation as a counterexample as well a second
counterexample for a particle interacting with a scalar force.
(``Classical Electrodynamics,'' Jackson, J.D., 2nd ed. section 12.2).

Hmm... Doesn't seem to be in the 3rd ed. Perhaps the 2nd ed. is a bit
outdated as I remember reading a paper that derives Maxwell's Equations
from Coulomb's law and SR and maybe that is why Jackson dropped it in
the 3rd ed.
Anywise, it is too bad that Maxwell gave up on his aether model as it is
the forbearer of the quantum "vacuum". As Timo points out, Maxwell
would not equate aether with space. Space has no properties. It is the
interaction of the virtual particles (fields) in the quantum "vacuum"
that seem to give space properties. Like c and hbar.
FrediFizzx
Quantum Vacuum Charge papers;
http://www.vacuumphysics.com/QVC/quantum_vacuum_charge.pdf
or postscript
http://www.vacuumphysics.com/QVC/quantum_vacuum_charge.ps
http://www.arxiv.org/abs/physics/0601110
http://www.vacuumphysics.com 

Back to top 


Sue... science forum Guru
Joined: 08 May 2005
Posts: 2684

Posted: Mon Jul 10, 2006 8:11 am Post subject:
Re: Magnetic Idyll



FrediFizzx wrote:
Quote:  "Bilge" <dubious@radioactivex.lebesqueal.net> wrote in message
news:slrneb3q7q.5g8.dubious@radioactivex.lebesqueal.net...
Timo A. Nieminen:
On Sun, 8 Jul 2006, Edward Green wrote:
The formal simularity of the Coriolis force and the Lorentz force
law
2w x v vs. qB x v
suggests that the magnetic field may correspond to a local
rotation of
space (inertial coordinate system) as seen by charge vs. that seen
by
mass.
Very Maxwellian. Have you read Maxwell's papers on this kind of
thing?
(Although he would have said "local rotation of the (a)ether", not
space.)
For some insight: one can obtain Maxwell's equations from Coulomb's
law
and special relativity. What happens if you start from Newton's law
of
universal gravitation and SR? Surely you must get a gravitomagnetic
term.
Heaviside did this, and it's a nice exercise. It isn't necessarily
easier
to follow Heaviside than to do it from scratch.
Actually, jackson devotes several pages to explaining precisely why
one _cannot_ derive maxwell's equations from special relativity and
coulomb's law, giving gravitation as a counterexample as well a second
counterexample for a particle interacting with a scalar force.
(``Classical Electrodynamics,'' Jackson, J.D., 2nd ed. section 12.2).
Hmm... Doesn't seem to be in the 3rd ed. Perhaps the 2nd ed. is a bit
outdated as I remember reading a paper that derives Maxwell's Equations
from Coulomb's law and SR and maybe that is why Jackson dropped it in
the 3rd ed.
Anywise, it is too bad that Maxwell gave up on his aether model as it is
the forbearer of the quantum "vacuum". As Timo points out, Maxwell
would not equate aether with space.

<< Space has no properties. It is the
interaction of the virtual particles (fields) in the quantum "vacuum"
that seem to give space properties. Like c and hbar. >>
Have you conjured up a particlepair in your kitchen yet?
I am still trying but so far have only something that looks
like egg shells stuck to the walls of my microwave oven
with gooey yellow stuff.
I need to learn something about renormalization and dimensional
analysis to see if the bits might scale down to e+ and e . ;)
Sue...


Back to top 


Igor science forum Guru
Joined: 15 May 2005
Posts: 315

Posted: Mon Jul 10, 2006 7:59 pm Post subject:
Re: Magnetic Idyll



Tom Roberts wrote:
Quote:  Igor wrote:
Here's a good link:
http://abacus.bates.edu/~msemon/Noteon.pdf
The authors forgot to mention that the putative E field:
E = (m/q) w x (w x r) (eq. 5)
does not satisfy Maxwell's equations, because div E != 0 yet there are
no charges present.
Tom Roberts

Yeah, I can see your point. Well, nobody called it a perfect analogy.
I think the paper that was referenced and the original paper by Coisson
from 1973 were just to point out the similarities. They were both
published in the American Journal of Physics, which tends to deal with
new ways of looking at old physics more often than not. Unfortunately,
the Coisson paper does not appear to be available online, although I
know I have a copy of it somewhere. 

Back to top 


dda1 science forum Guru
Joined: 06 Feb 2006
Posts: 762

Posted: Mon Jul 10, 2006 8:08 pm Post subject:
Re: Magnetic Idyll



Igor wrote:
Quote:  Tom Roberts wrote:
Igor wrote:
Here's a good link:
http://abacus.bates.edu/~msemon/Noteon.pdf
The authors forgot to mention that the putative E field:
E = (m/q) w x (w x r) (eq. 5)
does not satisfy Maxwell's equations, because div E != 0 yet there are
no charges present.
Tom Roberts
Yeah, I can see your point. Well, nobody called it a perfect analogy.
I think the paper that was referenced and the original paper by Coisson
from 1973 were just to point out the similarities. They were both
published in the American Journal of Physics, which tends to deal with
new ways of looking at old physics more often than not. Unfortunately,
the Coisson paper does not appear to be available online, although I
know I have a copy of it somewhere.

American Journal of Physics is run by an imbecile (Jan Tobochnick) and
has as charter the publication of "no new reserach" (see the web page).
AmJPhys publishes regurgitations (as you well pointed out) of old
stuff, basically reinterpretations of older papers. Another junk
journal. 

Back to top 


Timo Nieminen science forum Guru Wannabe
Joined: 12 May 2005
Posts: 244

Posted: Mon Jul 10, 2006 8:32 pm Post subject:
Re: Magnetic Idyll



On Tue, 10 Jul 2006, dda1 wrote:
Quote:  American Journal of Physics is run by an imbecile (Jan Tobochnick) and
has as charter the publication of "no new reserach" (see the web page).
AmJPhys publishes regurgitations (as you well pointed out) of old
stuff, basically reinterpretations of older papers. Another junk
journal.

AJP is a physics _education_ journal, not a _physics_ journal. Why should
they publish new physics research? They do publish new physics _education_
research.
AJP is far from being a junk journal; I find that I'm more likely to get
long term value out of an AJP paper that a paper in the physics research
journals (because so many research papers are out of my field, are badly
written, present research that's been salamisliced into as many papers as
possible, are wrong, age rapidly, etc). It's not what you read to keep up
with cuttingedge research, but it isn't junk. All of the top 3 physics
education journals have lots of good stuff in them, and even if you're not
interested in teaching or teaching well, some of it is good physics,
explained well.
Your anonymous accusation of imbecility reflects badly on your character.

Timo Nieminen  Home page: http://www.physics.uq.edu.au/people/nieminen/
Eprints: http://eprint.uq.edu.au/view/person/Nieminen,_Timo_A..html
Shrine to Spirits: http://www.users.bigpond.com/timo_nieminen/spirits.html 

Back to top 


Timo Nieminen science forum Guru Wannabe
Joined: 12 May 2005
Posts: 244

Posted: Mon Jul 10, 2006 10:22 pm Post subject:
Re: Magnetic Idyll



On Mon, 10 Jul 2006, Bilge wrote:
Quote:  Timo A. Nieminen:
On Sun, 8 Jul 2006, Edward Green wrote:
The formal simularity of the Coriolis force and the Lorentz force law
2w x v vs. qB x v
suggests that the magnetic field may correspond to a local rotation of
space (inertial coordinate system) as seen by charge vs. that seen by
mass.
Very Maxwellian. Have you read Maxwell's papers on this kind of thing?
(Although he would have said "local rotation of the (a)ether", not space.)
For some insight: one can obtain Maxwell's equations from Coulomb's law
and special relativity. What happens if you start from Newton's law of
universal gravitation and SR? Surely you must get a gravitomagnetic term.
Heaviside did this, and it's a nice exercise. It isn't necessarily easier
to follow Heaviside than to do it from scratch.
Actually, jackson devotes several pages to explaining precisely why
one _cannot_ derive maxwell's equations from special relativity and
coulomb's law, giving gravitation as a counterexample as well a second
counterexample for a particle interacting with a scalar force.
(``Classical Electrodynamics,'' Jackson, J.D., 2nd ed. section 12.2).

Jackson states that one cannot derive Maxwell's equations from Coulomb and
SR without additional assumptions, the chief additional assumption being
that the source of the EM field is the chargecurrent 4vector. There are
quite a few other usuallyunstated assumptions as well. So what? It can be
done, Maxwell from Coulomb + SR, and has been done. Jackson even cites a
source where it is done in the very section you say he writes it
"_cannot_" be done.
The gravitational "counterexample" is useful to note, since the source is
a rank2 tensor, whereas the Heaviside approach is to assume the source is
a massflow 4vector. So what? The point is an exercise to help understand
the relationship between magnetism and SR and the constitutive relations,
not to come up with a useful Lorentzinvariant gravitational theory.

Timo Nieminen  Home page: http://www.physics.uq.edu.au/people/nieminen/
Eprints: http://eprint.uq.edu.au/view/person/Nieminen,_Timo_A..html
Shrine to Spirits: http://www.users.bigpond.com/timo_nieminen/spirits.html 

Back to top 


Bill Hobba science forum Guru
Joined: 02 May 2005
Posts: 2138

Posted: Tue Jul 11, 2006 12:58 am Post subject:
Re: Magnetic Idyll



"Edward Green" <spamspamspam3@netzero.com> wrote in message
news:1152494847.690736.32300@m73g2000cwd.googlegroups.com...
Quote:  Timo A. Nieminen wrote:
On Sun, 8 Jul 2006, Edward Green wrote:
The formal simularity of the Coriolis force and the Lorentz force law
2w x v vs. qB x v
suggests that the magnetic field may correspond to a local rotation of
space (inertial coordinate system) as seen by charge vs. that seen by
mass.
Very Maxwellian. Have you read Maxwell's papers on this kind of thing?
(Although he would have said "local rotation of the (a)ether", not
space.)
No I haven't. As regards rotation of the "aether" vs. "space", that is
of course merely (rather emotionally loaded, for some) semantics;
though we could say that if one of the watermarks of the aether is
"preferred rest frame", then the rotational aether, so to speak, has
never gone away.
For some insight: one can obtain Maxwell's equations from Coulomb's law
and special relativity.
The whole package? I knew that we could get a magnetic effect from SR
+ electric field (well, so I've heard), but I didn't know we could get
the whole deal.

Yes you can  check out
http://www.cse.secs.oakland.edu/haskell/SpecialRelativity.htm
However some other assumptions are also used eg charge is not dependant on
velocity and forces add linearly (it is a very interesting exercise to go
through the derivation and see exactly what the assumptions are). Bilge
correctly points out that Jackson notes it is not quite possible to do it
from SR and Coulombs law alone. However with the extra non stated
assumptions added it is derivable. It is interesting to see, for example,
exactly what breaks down in gravity. Here, while rest mass certainly is
invariant, E=MC2 strongly suggests that for moving mass not only should we
include mass as the source of gravitation but energy as well so the source
of gravity being the invariant rest mass may not be true. The linear adding
of forces looks doubtful with gravity as well.
Thanks
Bill
Quote:  Actually, I've heard mixed comments about this: the
derivations I've seen centered on length contraction, and charge
consequently appearing bunched up, and I've seen those dismissed as at
best heuristic (which I guess means plausibility results we don't
happen to like) and at worst nonsensical  i.e., as an example of a
failed oolie, like the infamous "flow above and below the wing must
meet up".
I suppose a proper relativistic derivation doesn't care how the distant
sources look to us, but focuses on the local properties of the field
and the requirements of Lorentz invariance. Something like?
What happens if you start from Newton's law of
universal gravitation and SR? Surely you must get a gravitomagnetic
term.
Heaviside did this, and it's a nice exercise. It isn't necessarily easier
to follow Heaviside than to do it from scratch.
Consider that E and B are defined in terms of the Lorentz force,
F=q(E+vxB), while D and H are defined in terms of source densities
(charge
and current densities) and are thus in different units. So, even in free
space, you need constitutive relations for unit conversion (unless you
choose a perverted set of units). What are the gravitational constitutive
relations?
When I set this as a P/F openbook exam, one student was cunning enough
to
find it on www, so you can search for it rather than doing it, but I
recommend trying it for an hour or so first.
Thanks for the constructive comments. One knows one should not be
sucked into profitless "no, what I said wasn't totally stupid"
arguments, but in the absence of positive feedback, one sometimes
falters. (Was it Pauli who said "You know, what professor Einstein says
is not so stupid...")?
I was just about prepared to stubbornly stand my ground: if we adopt as
the operational _meaning_ of "in the presence of a magnetic field
charged particles seem to see themselves at the center of a different
rotational rest frame than neutral massive particles" as "they obey an
appropriate Coriolis law analogue", then my musuing is a tautology.
And if one thinks about the geometric meaning of the cross product 
rotating the force relative to the velocity around a fixed axis in a
fixed sense, and proprotional in magnitude to the projection of the
velocity in a plane perpendicular to that axis  the sense of having
something to do with rotation is inescapable. I also venture that
every static magnetic source (even an infinitely long straight wires)
involves effective circulation of charge.
Frame dragging?



Back to top 


Bill Hobba science forum Guru
Joined: 02 May 2005
Posts: 2138

Posted: Tue Jul 11, 2006 1:12 am Post subject:
Re: Magnetic Idyll



"dda1" <rangeravenger@yahoo.com> wrote in message
news:1152562084.536415.122010@75g2000cwc.googlegroups.com...
Quote: 
Igor wrote:
Tom Roberts wrote:
Igor wrote:
Here's a good link:
http://abacus.bates.edu/~msemon/Noteon.pdf
The authors forgot to mention that the putative E field:
E = (m/q) w x (w x r) (eq. 5)
does not satisfy Maxwell's equations, because div E != 0 yet there are
no charges present.
Tom Roberts
Yeah, I can see your point. Well, nobody called it a perfect analogy.
I think the paper that was referenced and the original paper by Coisson
from 1973 were just to point out the similarities. They were both
published in the American Journal of Physics, which tends to deal with
new ways of looking at old physics more often than not. Unfortunately,
the Coisson paper does not appear to be available online, although I
know I have a copy of it somewhere.
American Journal of Physics is run by an imbecile (Jan Tobochnick) and
has as charter the publication of "no new reserach" (see the web page).

That characterization is silly. He is a well respected legitimate scientist
and teacher.
Quote: 
AmJPhys publishes regurgitations (as you well pointed out) of old
stuff, basically reinterpretations of older papers. Another junk
journal.

Isn't it the Journal of the American Association of Physics Teachers? That
its focus is not on research but understanding known physics looks quite
reasonable to me. In fact whenever I get to a library the AMJP is one
publication I always browse and learn a lot.
Bill 

Back to top 


Edward Green science forum addict
Joined: 21 May 2005
Posts: 95

Posted: Tue Jul 11, 2006 1:25 am Post subject:
Re: Magnetic Idyll



Bilge wrote:
Quote:  Edward Green:
The formal simularity of the Coriolis force and the Lorentz force law
2w x v vs. qB x v
Actually, you mean 2m w x v.

Yes.
Quote:  suggests that the magnetic field may correspond to a local rotation of
space (inertial coordinate system) as seen by charge vs. that seen by
mass.
I'm not sure what you mean by the ``formal similarity...''

I think you meant "I'm not sure what you mean by 'formal simularity'.
That's similarity happening at the very same time. ;)
I meant something like "term by term identity, after changing the
labels".
Quote:  However, note that for a neutral particle, changing coordinates
to a rotating frame does not give it a charge and two different
particles with the same charge but different masses have different
radii of curvature in the same magnetic field.

True. As I mentioned, this seems to suggest that the rotational rest
frame seen by charge and that seen by mass are different. No don't ask
me to quantify this  but it doesn't seem like such a very weird idea.
After all, cannot EM and gravity be put on the same footing by a
geometric theory called KaluzaKlein? Possibly the extra dimensions
are exactly what is required to give this statement meaning.
Quote:  What we call spacetime coordinates are numbers we can use to describe
all of the objects we observe in experiments in the same way. The
only reason that gravity can be described as spacetime curvature
(and hence transformed away locally by a suitable change of coordinates)
is that the equivalence principle, in which gravitational and inertial
masses are postulated to e equivalent, holds to the precision experiments
can so far test.

I'm not sure what you are getting at, but I rather think I just
answered you. Yes, this idea would imply that not all particles
behaved similarly under "geometry", but then, I think we are by
implication talking about a more complicated theory than one involving
gravity and mass alone. Different aspects of the particle may sample
different aspects of the environment  like an ice skater feeling the
wind. 

Back to top 


Sorcerer1 science forum Guru
Joined: 09 Jun 2006
Posts: 410

Posted: Tue Jul 11, 2006 7:03 am Post subject:
Re: Magnetic Idyll



"Edward Green" <spamspamspam3@netzero.com> wrote in message
news:1152581101.395090.142470@h48g2000cwc.googlegroups.com...
 Bilge wrote:

 > Edward Green:
 > >The formal simularity of the Coriolis force and the Lorentz force law
 > >
 > > 2w x v vs. qB x v
 >
 > Actually, you mean 2m w x v.

 Yes.

 > >suggests that the magnetic field may correspond to a local rotation of
 > >space (inertial coordinate system) as seen by charge vs. that seen by
 > >mass.
 >
 > I'm not sure what you mean by the ``formal similarity...''

 I think you meant "I'm not sure what you mean by 'formal simularity'.
 That's similarity happening at the very same time.

 I meant something like "term by term identity, after changing the
 labels".

 > However, note that for a neutral particle, changing coordinates
 > to a rotating frame does not give it a charge and two different
 > particles with the same charge but different masses have different
 > radii of curvature in the same magnetic field.

 True. As I mentioned, this seems to suggest that the rotational rest
 frame seen by charge and that seen by mass are different. No don't ask
 me to quantify this  but it doesn't seem like such a very weird idea.
 After all, cannot EM and gravity be put on the same footing by a
 geometric theory called KaluzaKlein? Possibly the extra dimensions
 are exactly what is required to give this statement meaning.

 > What we call spacetime coordinates are numbers we can use to describe
 > all of the objects we observe in experiments in the same way. The
 > only reason that gravity can be described as spacetime curvature
 > (and hence transformed away locally by a suitable change of coordinates)
 > is that the equivalence principle, in which gravitational and inertial
 > masses are postulated to e equivalent, holds to the precision
experiments
 > can so far test.

 I'm not sure what you are getting at, but I rather think I just
 answered you. Yes, this idea would imply that not all particles
 behaved similarly under "geometry", but then, I think we are by
 implication talking about a more complicated theory than one involving
 gravity and mass alone. Different aspects of the particle may sample
 different aspects of the environment  like an ice skater feeling the
 wind.
Not all particles behave similarly when viewed from different frames of
reference. This ball is disobeying Newton's first law, which it cannot do
and it doesn't:
http://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/fw/gifs/coriolis.mov
Androcles. 

Back to top 


Bilge science forum Guru
Joined: 30 Apr 2005
Posts: 2816

Posted: Tue Jul 11, 2006 10:24 am Post subject:
Re: Magnetic Idyll



Edward Green:
Quote:  Bilge wrote:
However, note that for a neutral particle, changing coordinates
to a rotating frame does not give it a charge and two different
particles with the same charge but different masses have different
radii of curvature in the same magnetic field.
True. As I mentioned, this seems to suggest that the rotational rest
frame seen by charge and that seen by mass are different. No don't ask
me to quantify this  but it doesn't seem like such a very weird idea.

Depends upon one's notion of weird... But, I digress.
Quote:  After all, cannot EM and gravity be put on the same footing by a
geometric theory called KaluzaKlein?

``Seductively similar footing'' might be more accurate. KaluzaKlein
theory died due to some problems which were not well understood. However,
the idea was resurrected, improved, expanded and lives on in what is
now known as string theory.
Quote:  Possibly the extra dimensions are exactly what is required to give
this statement meaning.

If you allow another dimension, then it's not only relatively
straightforward to create a (somewhat naive, but suggestive) theory,
but also to see how it relates to traditional E&M. In the kaluzaklein
theory, the fifth dimension was postulated to be intrinsically circular,
so that the metric had the form,
ds^2 = dt^2  dx^2  dy^2  dz^2  (Rdw)^2
A typical wavefunction for a charged particle would then be of the form,
\Psi(t,x,y,z,w) = \Psi(0)\exp[i(Et  p.x  Rp_w w)]
where p.x means p_x x  p_y y  p_z z and p_w is the momentum in the
fifth dimension. So, we can write that as,
\Psi(t,x,y,z,w) = \Psi(t,x,y,z)\exp[iR p_w w]
with \Psi(t,x,y,z) defined by \Psi(0)\exp[i(Et  p.x)]
Now compare that with the standard theory in which we have some initial
wavefunction, \Psi(t,x,y,z) = \Psi(0)\exp[i(Et  p.x)]. The standard
theory requires that the physics remain invariant under a change of
_phase_, i.e., a gauge transformation,
\Psi > \Psi' = \Psi\exp(iS)
must not result in any change of physics. (This requirement alone leads
to the existence of a globally conserved charge).
If you then make the identification: S = Rp_w w, you have some
basis for your claim. You can make that stronger by allowing S to
be a function of the coordinates (i.e., a local rather than
global gauge transformation). The goals of the kaluzaklein theory
were even more ambitious. Note that the massenergymomementum relation
(from which the earlier wave equation was obtained) now becomes,
E^2  p.p  (p^4)^2 = 0
which suggests identifying p^4 with the usual mass, so that if you
redefine the mass as a five dimensional quantity, the electron is
massless. From there one can try to quantize the mass based on the
fact that the 5th dimension is intrinsically circular, so that one
might hope to explain the ratios of the charged particle masses
via a winding number, since \Psi(w) = \Psi(w + 2n\pi) must hold.
While that is suggestive, I don't think that sort of idea has lead
anywhere.
But, there are still more similarities. Note that in general
relativity, one defines a covariant derivative, such that when
operating on a fourvector, V^a, D_u V^a = d_u V^a + C^a_ub V^b,
where the C^a_ub are the connection coefficients (christoffel
symbols). The riemann (curvature) tensor is then obtained from
the commutator of the covariant derivatives:
[D_u, D_v] V^a = R^a_buv V^b
In qed, one obtains a gauge covariant derivative,
D_u == d_u + ieA_u
which suggests identifying iA_u as the ``electromagnetic connection
coeficients.'' (But note the factor of `i'.) By taking the commutator
of the covariant derivatives, we get:
[D_u, D_v] = (1/ie)F_vu
where F_vu is just the faraday tensor from classical E&M. Now, we
can take the partial to recover maxwell's (inhomogeneous)
equations, d_v F_vu = j^u. One then views the faraday tensor as
the electromagnetic ``curvature.''
As a final analogy, the homogeneous maxwell's equations
d^a F^bc + permutations = 0, are (in this language) a purely
geometric result, analogous to the bianchi identities.
(Look under ``fiber bundles,'' for more information on this
approach. This also analogizes to the weak and strong interactions,
and yangmills theories, in general.)
However, the bottom line is that if you want to treat E&M
as some sort of space(time) rotation, you can't do it in
4d. In 4d, E&M corresponds to invariance under a change of
phase.
Quote:  What we call spacetime coordinates are numbers we can use to describe
all of the objects we observe in experiments in the same way. The
only reason that gravity can be described as spacetime curvature
(and hence transformed away locally by a suitable change of coordinates)
is that the equivalence principle, in which gravitational and inertial
masses are postulated to e equivalent, holds to the precision experiments
can so far test.
I'm not sure what you are getting at, but I rather think I just
answered you.

Essentially, my point is that the traditional concept of space and
time applies to everything in the universe, so any adaptation of
the geometry to account for forces must apply in the _same_ way to
everything we can measure. That idea begat general relativity. By
simply eliminating one's preconceptions of how geometry has to be,
one find that gravity has a geometric origin and is not a real force,
in that it can be transformed away.
That is impossible for E&M (at least in 4dimensions). To do what
you propose is equivalent to finding a coordinate transformation that
transforms away the electric charge.
Quote:  Yes, this idea would imply that not all particles
behaved similarly under "geometry", but then, I think we are by
implication talking about a more complicated theory than one involving
gravity and mass alone. Different aspects of the particle may sample
different aspects of the environment  like an ice skater feeling the
wind.

Well, it certainly is more complicated theory  it's called string
theiry (or Mtheory), it requires 11 dimensions and it is so complicated
that nobody understands it. To the extent that some physicists understand
something about it, none have been able to suggest a realistic experiment
to test it. (This is not to say that it's wrong, but merely a fact). Once
you try to include E&M as a geometric artifact, you are stuck with having
to include the strong and weak interactions as well and start using
phrases like ``CalabiYau manifold'' when you speak of geometry.
Orthogonal rotations don't cut it. 

Back to top 


Daryl McCullough science forum Guru
Joined: 24 Mar 2005
Posts: 1167

Posted: Tue Jul 11, 2006 7:11 pm Post subject:
Re: Magnetic Idyll



In article <1152400330.145973.161020@s13g2000cwa.googlegroups.com>, Edward Green
says...
Quote: 
The formal simularity of the Coriolis force and the Lorentz force law
2w x v vs. qB x v
suggests that the magnetic field may correspond to a local rotation of
space (inertial coordinate system) as seen by charge vs. that seen by
mass.

I'm not sure about that, but there is a sense in which Lorentzlike
forces should be expected, in the lowvelocity limit.
Let L be an arbitrary lagrangian for a pointmass written in terms
of spatial coordinates and spatial velocities. Assume that the velocities
are not too large, so that L can be expanded as a power series in velocity.
Taking the first few terms, we have
L = A + B_i V^i + C_ij V^i V^j + ...
where A, B_i and C_ij are functions of the coordinates (but are
independent of velocity).
Whatever the origin of the terms A, B_i, and C_ij, we can make
the following interpretations
A = scalar potential, which gives rise to gradient forces
proportional to d/dx^i A
B_i = vector potential, which gives rise to Lorentz forces
(as well as Coriolis forces), which are proportional to
curl(B) x V
C_ij = tensor potential, which gives rise to centrifugal force
(as well as the usual kinetic energy term 1/2 mv^2).
Two contributions to B_i are the following:
1. If the particle is charged and there is an electromagnetic
vector potential A_i, then there is a contribution to B_i of
the form q A_i. This is what gives rise to the Lorentz force.
2. If you are using noninertial coordinates, then there is
a contribution to B_i of the form m g_0i, where g_uv is the
metric tensor. This is what gives rise to the Coriolis force.

Daryl McCullough
Ithaca, NY 

Back to top 


Edward Green science forum addict
Joined: 21 May 2005
Posts: 95

Posted: Tue Jul 11, 2006 11:44 pm Post subject:
Re: Magnetic Idyll



Bill Hobba wrote:
Quote:  "Edward Green" <spamspamspam3@netzero.com> wrote in message...
Timo A. Nieminen wrote:
For some insight: one can obtain Maxwell's equations from Coulomb's law
and special relativity.
The whole package? I knew that we could get a magnetic effect from SR
+ electric field (well, so I've heard), but I didn't know we could get
the whole deal.
Yes you can  check out
http://www.cse.secs.oakland.edu/haskell/SpecialRelativity.htm

Thanks very much for the reference.
The problem with discussing interesting topics with knowledgable people
is that they invariably come up with challenging follow on reading. ;)
Quote:  However some other assumptions are also used eg charge is not dependant on
velocity and forces add linearly (it is a very interesting exercise to go
through the derivation and see exactly what the assumptions are). Bilge
correctly points out that Jackson notes it is not quite possible to do it
from SR and Coulombs law alone. However with the extra non stated
assumptions added it is derivable. It is interesting to see, for example,
exactly what breaks down in gravity. Here, while rest mass certainly is
invariant, E=MC2 strongly suggests that for moving mass not only should we
include mass as the source of gravitation but energy as well so the source
of gravity being the invariant rest mass may not be true. The linear adding
of forces looks doubtful with gravity as well.

I've started to think about how one would approach such a derivation.
I think I would have assumed the invariance and velocity independence
of charge without a qualm, also the linear addition of forces. Special
relativity has "linear" written all over it, anyway. I assume
classical EM is a linear limit of a more general classical theory of
the electromagnetic phenomenon. 

Back to top 


Edward Green science forum addict
Joined: 21 May 2005
Posts: 95

Posted: Wed Jul 12, 2006 12:37 am Post subject:
Re: Magnetic Idyll



Tom Roberts wrote:
Quote:  Edward Green wrote:
Tom Roberts wrote:
Snip profound argument that if we express the Coriolis force in such a
way that there is no Coriolis force, then there is no Coriolis force
Not at all! You ignored the fact that my equations used
_physical_quantities_.
I'm well aware that the Coriolis force is a socalled fictious force.
Then you should abide by the consequences.

You entirely missed the point.
Given that the Coriolis force is a fictious force  one in particular
arising in a rotating reference frame  and given that the Lorentz
force is formally identical to it  changing labels but keeping
velocity as itself  then the suggestion arises that in the presence
of a magnetic field charged particles, vis. a vis. their charge,
effectively see themselves in a frame rotating with respect to whatever
frame we would otherwise consider not to be rotating, when we use
massive neutral particles to establish the latter.
Whether these comments are deep or shallow, they do _not_ suffer from
ignorance of the meaning of the Coriolis force, nor its "fictitious"
origin. On the contrary, this awareness is at the heart of the thing.
<...> 

Back to top 


Google


Back to top 



The time now is Wed Mar 05, 2014 1:01 pm  All times are GMT

