How can neutrons have magnetism if they have no electricity?
Radium
If all magnetism is electrical in origin, then how can a neutron --
being a completely non-electric entity -- have any magnetism at all?
http://www.answers.com/topic/neutron-magnetic-moment
http://adsabs.harvard.edu/abs/1994PhDT........62G
Thanks,
Radium
Souvik
magnitude as protons (~ 6.023e-8 eV/T). Their magnetic dipole moment is
anti-parallel to their spin. So, yes, they do create magnetic fields,
do respond to external magnetic fields, and contribute to the magnetism
of nuclei they may be part of.
One way to imagine how magnetism may arise in a neutron would be to
consider that though they are neutral, they have constituent quarks
which are charged, have intrinsic (fermionic) spins, and which maybe
orbiting each other in strange ways. To actually calculate the magnetic
moment from this picture would be very involved and far from classical.
-Souvik
Uncle Al
Quarks are chargedm and of inconstant location,
http://en.wikipedia.org/wiki/Nucleon
The question you should ask is "if the neutron has a magnetic moment,
why doesn't it have a non-zero electric dipole or quadrupole moment?"
--
Uncle Al
http://www.mazepath.com/uncleal/
(Toxic URL! Unsafe for children and most mammals)
http://www.mazepath.com/uncleal/qz3.pdf
Jonathan Thornburg -- remove -animal to reply
> If all magnetism is electrical in origin, then how can a neutron --
> being a completely non-electric entity -- have any magnetism at all?
The short answer is that while a neutron's _total_ electric charge
is zero, it has charged particles (quarks) within it, which can and
do generate a magnetic moment, both intrinsically and via their
movement.
--
-- "Jonathan Thornburg -- remove -animal to reply" <jth...@aei.mpg-zebra.de>
Max-Planck-Institut fuer Gravitationsphysik (Albert-Einstein-Institut),
Golm, Germany, "Old Europe" http://www.aei.mpg.de/~jthorn/home.html
"Washing one's hands of the conflict between the powerful and the
powerless means to side with the powerful, not to be neutral."
-- quote by Freire / poster by Oxfam
Jeremy Henty
> If all magnetism is electrical in origin, then how can a neutron --
> being a completely non-electric entity -- have any magnetism at all?
The neutron is *not* a completely non-electric entity - it's total
charge may be zero but it's made of charged particles - a u quark
(charge 2/3) and two d quarks (charge -1/3 each).
Regards,
Jeremy Henty
J. J. Lodder
> If all magnetism is electrical in origin, then how can a neutron --
> being a completely non-electric entity -- have any magnetism at all?
Have you asked yourself the same about the earth?
Jan
Igor Khavkine
> Hi:
>
> If all magnetism is electrical in origin, then how can a neutron --
> being a completely non-electric entity -- have any magnetism at all?
The neutron, as a particle, has zero charge, but that doesn't make it a
completely "non-electric entity". The neutron does have zero electric
charge and a non-zero magnetic moment, that is a measurable fact.
In analogy with atoms, which are also electrically neutral and also
have non-trivial magnetic moments, this property suggests that the
neutron is a composite particle. In fact the Standard Model of particle
physics posits that the neutron is composed of three quarks (two down,
one up). Their charges add up to zero, however their intrinsic spins
(which are half integral) can never add up to zero. Whenever an odd
number of fermions (particles with half integral intrinsic spin) form a
bound system, there must always be a residual total spin, and hence a
non-zero magnetic moment. You may take this as a theoretical
explanation.
Hope this helps.
Igor
Puppet_Sock
> If all magnetism is electrical in origin, then how can a neutron --
> being a completely non-electric entity -- have any magnetism at all?
It is an interesting premise that "all magnetism is electrical
in origin." It's not necessarily the case.
However, neutrons do not seem to be non-electric. They are
net neutral in charge, but they do have structure, and the
structure is three charged particles that total zero.
Ask yourself how a lump of iron, which is neutral, can have
a magnetic field? Well, of course, it's becaues the iron has
structure at a level below the size of the object.
Socks
Oh No
quarks, charge -1/3 each, and an up quark, charge +2/3.
Regards
--
Charles Francis
substitute charles for NotI to email
Paul Danaher
..
> The question you should ask is "if the neutron has a magnetic moment,
> why doesn't it have a non-zero electric dipole or quadrupole moment?"
Okay, if the neutron has a magnetic moment, why doesn't it have a non-zero
Arnold Neumaier
> Okay, if the neutron has a magnetic moment, why doesn't it have a non-zero
> electric dipole or quadrupole moment?
In order for particles to have electric dipole moments,
the forces concerned in their structure must violate both
space parity and time reversal symmetries.
This is not the case for the neutron.
Phys. Rev. Lett. 82, 904--907 (1999)
But the neutron is polarizable, which were impossible if it were a
completely non-electric entity (look for 'electric polarizability' in
http://pdg.lbl.gov/2004/listings/s017.pdf).
The quadrupole tensor is rank-2, and therefore by the Wigner-Eckart
theorem its expectation value, called the spectroscopic quadrupole
moment Q, vanishes for the spin-1/2 nucleons.
Phys. Rev. D 66, 056002 (2002)
Arnold Neumaier
Daryl McCullough
>The question you should ask is "if the neutron has a magnetic moment,
>why doesn't it have a non-zero electric dipole or quadrupole moment?"
Are the electric dipole and quadrupole moments known to be zero? If
so, is that an experimental result, or does QED or QCD predict it?
--
Daryl McCullough
Ithaca, NY
Radium
Puppet_Sock wrote:
> Radium wrote:
> > If all magnetism is electrical in origin, then how can a neutron --
> > being a completely non-electric entity -- have any magnetism at all?
>
> It is an interesting premise that "all magnetism is electrical
> in origin." It's not necessarily the case.
Can you show me an example of non-electric magnetism? As hard as I've
looked, I haven't been able to find any.
Uncle Al
And thus we have it all. The neutron is a composite body whose
charged components' "circulation" generates its external magnetic
field. Even so, it has no electric dipole or quadrupole moment.
Observation is satisfied, theory is consisent, physics works without
contradiction or excuse.
One might ponder the magnetic and electric Aharonov-Bohm effects with
(polarized) neutrons - perhaps interesting for there being a magnetic
current without any net electric current.
Paul Danaher
> Arnold Neumaier wrote:
>>
>> Paul Danaher wrote:
>>
>>> Okay, if the neutron has a magnetic moment, why doesn't it have a
>>> non-zero electric dipole or quadrupole moment?
>>
>> In order for particles to have electric dipole moments,
>> the forces concerned in their structure must violate both
>> space parity and time reversal symmetries.
>> This is not the case for the neutron.
>> Phys. Rev. Lett. 82, 904--907 (1999)
>>
>> But the neutron is polarizable, which were impossible if it were a
>> completely non-electric entity (look for 'electric polarizability' in
>> http://pdg.lbl.gov/2004/listings/s017.pdf).
>>
>> The quadrupole tensor is rank-2, and therefore by the Wigner-Eckart
>> theorem its expectation value, called the spectroscopic quadrupole
>> moment Q, vanishes for the spin-1/2 nucleons.
>> Phys. Rev. D 66, 056002 (2002)
>
> And thus we have it all. The neutron is a composite body whose
> charged components' "circulation" generates its external magnetic
> field. Even so, it has no electric dipole or quadrupole moment.
> Observation is satisfied, theory is consisent, physics works without
> contradiction or excuse.
Except that AFAIK (I can't access many of the google references, thanks to
Springer et al - no relative) the jury is still out on whether T reversal
symmetry is experimentally confirmed. I'm looking at narrowing error bars on
upper limits and papers on systematic errors, but "observation is satisfied"
still leaves a question mark. (Can you say "Etvös"?)
Arnold Neumaier
>
> Except that AFAIK (I can't access many of the google references, thanks to
> Springer et al - no relative) the jury is still out on whether T reversal
> symmetry is experimentally confirmed. I'm looking at narrowing error bars on
> upper limits
Any deviation from a law can only be 'confirmed' by narrowing error bars
for the parameters modeling the deviation. As long as the error bars
contain zero, the law counts as confirmed.
With time, confirmation of the law may be at a higher level of accuracy,
or (as in the case of neutron masses) confirmation of the deviation
(if the more accurate error bars no longer contain zero).
If you dispute T reversal symmetry because of not enough confirmation,
you can as well dispute Lorentz symmetry, translation invariance,
zero photon mass, general relativity, etc., which are all confirmed only
to a certain precision.
Arnold Neumaier
Puppet_Sock
> Puppet_Sock wrote:
> > Radium wrote:
> > > If all magnetism is electrical in origin, then how can a neutron --
> > > being a completely non-electric entity -- have any magnetism at all?
> >
> > It is an interesting premise that "all magnetism is electrical
> > in origin." It's not necessarily the case.
>
> Can you show me an example of non-electric magnetism? As hard as I've
> looked, I haven't been able to find any.
If there are magnetic monopoles, then they may not have
any electrical part. As yet, there have been no confirmed
observations of monopoles, apart from the one event, and
that one is pretty suspect. (It happened when nobody was
in the lab, it happened on a Feb. 14, it has not been repeated,
and other considerations place bounds on the number of
monopoles in the local area that would mean we should not
expect such an event more often than once every <large
number of centuries>. Most people suspect that a grad
student gave his professor a valentine gift.)
Anyway, many unification theories predict monopoles.
Lots of fun. You whomp up Dirac's quantization of magnetic
charge, and you play with fibre bundles and topological stuff
for a while. You go cross-eyed a few times, trying to diagram
the suckers. You learn about theorms with such quaint
names as the "harry ball" theorm. Then you get discouraged
by the lack of observations, and study something else.
Socks
Cl.Massé
1161723430.4...@m73g2000cwd.googlegroups.com
> Anyway, many unification theories predict monopoles.
That's a matter of fact. What is also a matter of fact is that monopoles
*aren't* observed. The logical consequence is that these theories are
*wrong* and speculative, that we can't reason from them, and finally that
magnetism is always of electrical origin. I know, it's just the contrary to
the intended effect, but that's life. Nature is reluctant to any a priori
metaphysical bending.
--
The Surprise Guest
Jay R. Yablon
>
> That's a matter of fact. What is also a matter of fact is that
> monopoles
> *aren't* observed. The logical consequence is that these theories are
> *wrong* and speculative, that we can't reason from them, and finally
> that
> magnetism is always of electrical origin.
Or, that we have not yet raised enough energy in our accelerators to
view their interactions, because the vector bosons which mediate their
interactions are very heavy and the symmetry between electric and
magnetic charges is "hidden" at low energy. See
http://arxiv.org/abs/hep-ph/0508257.
Jay.
Cl.Massé
O972h.538$zB4...@twister.nyroc.rr.com
> Or, that we have not yet raised enough energy in our accelerators to
> view their interactions, because the vector bosons which mediate their
> interactions are very heavy and the symmetry between electric and
> magnetic charges is "hidden" at low energy. See
> http://arxiv.org/abs/hep-ph/0508257.
That's still speculation. The literature is full of "super-mega-heavy-
particles" that haven't, can't, and probably won't be
seen. That's the precise purpose of the "super-mega-mass", to make fit an
unverified theory with experiment. Remember the Higgs boson? Its predicted
mass has been kept just a little higher than the currently available energy.
Electricity and magnetism are perfectly symmetric, I see no purpose of
introducing still a spurious symmetry. When I see a duck with a beak ahead,
I don't feel compelled to look for a duck with a beak behind, its mirror
symmetry satisfies me fully. And that's it, symmetry appear to those who
know from which angle to see.
Of course many particles have been discovered by symmetry principles, so it
makes some sense. Though, the mass of those particles have the same order
of magnitude as the one of their partners.
--
The Surprise Guest
Radium
http://groups.google.com/group/sci.physics.research/msg/029a72c00e1c69c9?dmode=source&hl=en&output=gplain
:
>It is an interesting premise that "all magnetism is electrical
>in origin." It's not necessarily the case.
Can you show me an example of non-electric magnetism -- excluding
magnetic monopoles? As hard as I've researched, I haven't been able to
find any.
Any understanding, cooperation, and assistance is greatly appreciated.
Thanks a bunch,
Radium
Hendrik van Hees
> Can you show me an example of non-electric magnetism -- excluding
> magnetic monopoles? As hard as I've researched, I haven't been able to
> find any.
Take an electron. As far as we know, it's an elementary pointlike
particle and has both an electric charge and a magnetic dipole moment.
I would say, such dipoles are sources of magnetic fields as electric
charges are. Of course they are no monopoles, but you also cannot
easily re-interpret these mag. dipole moments as originating from
currents going in loops a la Ampere's model for a ferromagnet, because
this gives the wrong gyro factor which is (up to higher-order quantum
corrections) 2 and not 1 as for a classical current. In this sense I
would say this is the closest you can get to what you
called "non-electric magnetism".
On the other hand, "non-electric magnetism" is a contradiction in
itself, because relativity tells you that there is only one field,
namely the electromagnetic field, a massless spin-1 field, and you
cannot have magnetic without electric fields and vice versa, because
this distinction is an observer (i.e., frame) dependent splitting of
the field into space- and timelike components. So, I am not sure,
whether my idea with the "elementary magnetic dipole moments" of the
electron really is what you were looking for, and if not, you should
give a more detailed idea, what you mean when you say "non-electric
magnetism".
--
Hendrik van Hees Texas A&M University
Phone: +1 979/845-1411 Cyclotron Institute, MS-3366
Fax: +1 979/845-1899 College Station, TX 77843-3366
http://theory.gsi.de/~vanhees/faq mailto:he...@comp.tamu.edu
Radium
> Take an electron. As far as we know, it's an elementary pointlike
> particle and has both an electric charge and a magnetic dipole moment.
> I would say, such dipoles are sources of magnetic fields as electric
> charges are. Of course they are no monopoles, but you also cannot
> easily re-interpret these mag. dipole moments as originating from
> currents going in loops a la Ampere's model for a ferromagnet, because
> this gives the wrong gyro factor which is (up to higher-order quantum
> corrections) 2 and not 1 as for a classical current. In this sense I
> would say this is the closest you can get to what you
> called "non-electric magnetism".
>
> On the other hand, "non-electric magnetism" is a contradiction in
> itself, because relativity tells you that there is only one field,
> namely the electromagnetic field, a massless spin-1 field, and you
> cannot have magnetic without electric fields and vice versa, because
> this distinction is an observer (i.e., frame) dependent splitting of
> the field into space- and timelike components. So, I am not sure,
> whether my idea with the "elementary magnetic dipole moments" of the
> electron really is what you were looking for, and if not, you should
> give a more detailed idea, what you mean when you say "non-electric
> magnetism".
Thanks for the above info.
By "non-electric magnetism", I am referring to magnetic energy that
results from something other than the following [excluding magnetic
monopoles]:
1. Electric current
2. Electric charge[s] -- such as electron[s]
3. Electric field[s]