

'Magnetic electricity' discovered  - theklub
http://news.bbc.co.uk/2/hi/technology/8307804.stm

======
kurtosis
This type of language can be confusing. It is not a "real" magnetic monopole
but an "emergent" one. The collective behavior of all of the spins in the
material shows the experimental signatures of a magnetic monopole. The idea is
pretty simple to visualize - if you take a normal solenoid, the magnetic flux
lines come out of one end and return into the other end. If you take the
solenoid and stretch it into an infinitely long infinitesimally thin string
the magnetic flux coming out of one end looks exactly like the magnetic field
of a monopole. This is an old idea called the "dirac string". In these spin
ice materials the magnetic moments of the rare earth atoms in the crystal are
"geometrically frustrated" and cannot become all aligned or anti-aligned as in
a normal magnetic material - so they apparently arrange themselves into
strings, and the ends of the strings look like monopoles. (note that a line of
tiny dipoles has approximately the same field as a solenoid)

Here are some other simple examples of particles with "emergent" properties:

(-) The conduction electrons in metals interact with the ions in the lattice
as well as with each other through electrostatic forces, nonetheless they can
be approximately described as a gas of non interacting electrons with a
different "effective mass". In some cases (e.g. graphene, bismuth) the
"effective mass" can be zero, in other cases (e.g. actinide compounds) they
can be nearly as heavy as a proton. Of course the electron mass is still
~10^-30 kg

(-) In semiconductors, when an electron is removed from the filled valence
band (e.g. by doping) it leaves behind a "hole" which behaves like a
positively charged particle. negative charged electrons and positively charged
holes can actually interact to form an "atom" called an exciton which shows a
spectrum just like a hydrogen atom. This is a collective "emergent" behavior
of the entire semiconductor - there aren't really positively charged particles
or hydrogen-like atoms in the semiconductor.

there are many other more exotic examples

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lbrandy
If you are anything like me you read this article and went "wait... they
discovered magnetic monopoles?"

Here's some wikipedia goodness:
[http://en.wikipedia.org/wiki/Magnetic_monopole#.22Monopoles....](http://en.wikipedia.org/wiki/Magnetic_monopole#.22Monopoles.22_in_condensed-
matter_systems)

which leads you to...

* [http://www.symmetrymagazine.org/breaking/2009/01/29/making-m...](http://www.symmetrymagazine.org/breaking/2009/01/29/making-magnetic-monopoles-and-other-exotica-in-the-lab/)

* [http://www.sciencedaily.com/releases/2009/09/090903163725.ht...](http://www.sciencedaily.com/releases/2009/09/090903163725.htm)

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ars
Maybe bbc did not understand the article, because what they wrote does not
make sense.

If someone really did discover a magnetic monopole, that would be HUGE! So I
doubt that's what it really is.

~~~
gamble
They're not true magnetic monopoles. If I understand correctly, they're
unusual crystal structures that approximate the behavior of a monopole in some
ways, but they aren't true monopoles. Div(B) still equals zero.

Here's an article I found from a month ago that explains spin ice better than
the OP:

[http://blogs.discovermagazine.com/80beats/2009/09/10/physici...](http://blogs.discovermagazine.com/80beats/2009/09/10/physicists-
after-the-elusive-magnetic-monopole-spot-a-look-alike/)

~~~
cgherb911
Thanks for the nice article. I read magnetic monopole and I became utterly
confused.

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jcdreads
Decent commentary (and a more sensibly written article) can be found in this
previous HN thread:

<http://news.ycombinator.com/item?id=804831>

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JabavuAdams
Is there some kind of duality relationship between "proper point/small smear
particles", and "emergent particle-like thingies dependent on the whole
material's state"?

I.e. if we look at things one way, we get a set F of fundamental particles,
and a set E of emergent particles.

But maybe there's some kind of transformation of the theory that takes E <->
F' and F <-> E'.

Can we "flip" the theory into another theory that reverses the notions
"fundamental", and "emergent"?

