🚀 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.

Hi; I'll try to explain spontaneous symmetry breaking and then I'll
venture a guess as to its applications to visual hallucinations.

Say you have a pencil standing perfectly vertically on its sharpened
point.  The slightest disturbance will make it fall over, and due to the
uncertainty principle quantum mechanics says it will fall over even if
there is NO disturbance.  It doesn't have any preference for falling
over in one direction or the other, but it will fall over in SOME
direction.  That's the "spontaneous symmetry breaking."  There is a
rotational symmetry to the original situation that will be broken when
the pencil "picks" a direction to fall in.  

Other examples: if you heat up a block of iron above a certain
temperature called the Curie point it will demagnetize.  When you cool
it back down it will spontaneously magnetize, randomly "choosing" one
axis as the north pole.  Ditto for water crystallizing into ice,
although here it is the crystal lattice which breaks the rotational
and translation symmetry of the liquid water.  

To get more biological, it is likely that the preference of biomolecules
to have one rather than the other handedness is a case of spontaneous
breaking of right/left symmetry.  This is debated, however.

For hallucinations, I can imagine this.  A subject looks at a
featureless wall and his visual field is roughly rotation and
translation symmetric (of course it has a finite size so translation
symmetry is only locally true).  If he is given a drug that encourages
visual hallucinations we can imagine his neurons being "ready" to fire
in all sorts of patterns, like the pencil is ready to fall, and the
slightest disturbance will make them fire and make him see patterns that
break the symmetry of the visual field.