From: yergeau@cornu.phy.ulaval.ca (Francois Yergeau)
Newsgroups: sci.physics
Subject: Volume occupation (was Re: Vector Bosons?)
Date: 16 Aug 92 01:34:15 GMT
Organization: Universite Laval, Quebec

In article <1992Aug13.172944.8730@asl.dl.nec.com> terry@aslws01.asl.dl.nec.com (Terry Bollinger) writes:
>
> [nice elaboration on bosons deleted]
>
>FERMIONS
>
>If you're an elementary particle and you're not a boson, then you have to
>be a fermion.  Fermions are contrary cusses that are "anticommutative" --
>meaning when all is said and done that that like to have a little elbow
>room.  In contrast to the bosons, they most definitely do NOT like to be
>in exactly the same spots doing exactly the same thing at the same time,
>and will take extraordiary measures to avoid doing so.
>
>Having fermions around is a major factor in why you, the reader, are not
>currently part of a little grape-sized black hole orbiting where the earth
>used to be.  Fermions in general and atomic electrons (spin 1/2 fermions)
>in particular will strongly resist any compression beyond a certain point,
>making the volume-occupying properties of ordinary matter possible.

Funny, we had a discussion on just this subject in the departmental
coffee room the other day; the original question was: "Why doesn't this
table leg go right through the floor"?  Involved were a nuclear
physicist, an astrophycist, a theoretical phycisist and two opticists:
lots of points of view.  One took the position spelled out above, that
the antisymmetrization properties of fermions prevented the collapse of
ordinary matter.  In other words, he invoked the Pauli exclusion
principle.

I countered that plain electrostatic interaction must come before that,
making the following argument: forget about spin, and solve the good
old Schrodinger equation for a hydrogen atom.  You get a nice
non-collapsing ground state that occupies some space.  Add more
electrons and protons, resolve and lo, the occupied volume grows.

Granted, multi-electron atoms would be quite different in a spin-less
world: all their electrons would pack in the ground state, with only
electron-electron repulsion to liven things up a bit.  Ordinary matter
would be quite a bit denser, but, IMHO, its volume-occupying properties
are still possible outside of the exclusion principle, albeit
different. However...

>Just as importantly, the WAY ferions resist compression is complex enough
>to lead to all sorts of interesting "features" in atoms -- features that
>lead directly to what we call chemistry.
>
> [students-in-the-phone-both stuff deleted]
>
>Anyway, back to the main topic:  Complexity in the way fermions work out
>there differences, like the resistance itself, is critical to the world
>as we know it.  If electrons resisted compression merely by "balooning out"
>in some rather dull, uncomplicated way, YOU, dear reader, would be nothing
>more than part of an immensely dull soup of multi-element gasses compressed
>to roughly liquid form by their collective gravity.  A bit more interesting
>than being part of a grape-sized black hole, perhaps... but not by much!

Anyone cares to comment?

-- 
Francois Yergeau (yergeau@phy.ulaval.ca) |  De gustibus et coloribus
Centre d'Optique, Photonique et Laser    |  non disputandum
Departement de Physique                  |          -proverbe scolastique
Universite Laval, Ste-Foy, QC, Canada    |