🚀 go-pugleaf

In article <1992Oct6.183626.24921@mnemosyne.cs.du.edu>, aankrom@nyx.cs.du.edu (Anthony Ankrom) writes...
> 
> I have never read this group so I have no idea if it has been sloshed
>around before, butI would like to know, in a nutshell, just what
>Spontaneous SymmetryBreaking is. I read an article in a quantum chemistry
>journal that discussed SSB in the visual cortex in relationship to viual
>hallucinations. (I can provide a reference if it would be handy. I have
>studied verylitlle quantum mechanics, but feel free to use technical
>terms...) This would put an interesting perspective on my study of
>neurology.

Spontaneous Symmetry Breaking (SSB) occurs whenever the underlying equations
have a certain symmetry, but the ground states of the physical system which
they govern do not.  The most familiar example is the ferromagnet.
You probably know that if you heat a common household magnet above its
"Curie" Temperature, that its magnetism disappears.  When the magnet
cools, it will regain its magnetism as it passes the Curie temperature. 
But how does the magnet which pole should be North and which should be South?
There is nothing in the equations which describe the magnetism to tell
it which way its North should point.  And yet it must point one way or
the other.  This "ground state" does not have the symmetry of the underlying
Lagrangian.

At some point during the cooling of this lump of metal, SSB occurs, and the
magnet "chooses" a direction, and the original directional symmetry is broken
by the newly formed magnetic field of the bar.  The same magnetic, heated
and cooled over and over again, will, in principle, end up with the North
pole at either end of the bar with equal probability.  

-Scott
--------------------
Scott I. Chase			"The question seems to be of such a character
SICHASE@CSA2.LBL.GOV		that if I should come to life after my death
				and some mathematician were to tell me that it
				had been definitely settled, I think I would
				immediately drop dead again."      - Vandiver