Autcsrgv.329
net.misc
utzoo!utcsrgv!donald
Sun May  2 17:05:57 1982
Of quantum, uncertainty, and bishops

(Can we drop the "psi" in the titles of these articles please?)

The Copenhagen interpretation of quantum mechanics is essentially
pragmatic:  it merely states that the theory predicts statistical
correlations of phenomena;  nothing is said about any underlying
"reality".  This view was championed by Niels Bohr of Copenhagen (who
was also the prime mover behind the view of the observer being an
inseparable part of an experiment).  Einstein disagreed strongly,
but was unable to argue, since quantum mechanics was and has remained
one of the most accurate and well-tested physical theories.

Schrodinger's Cat is a feline in a sealed box which has a device
which releases a poison gas if a certain random event happens, say
the decay of an atomic nucleus.  After a time, we open the box.
The classical view says that the cat is either dead or not dead;
that was predetermined before we ever opened the box.  The quantum
view is that before we opened the box, the cat was in limbo, and its
wave function described the *possibilities* of the cat being dead or
alive.  Our opening the box causes the collapse of the wave function
into one of the possibilites, so we observe a dead cat or a live cat.

The Uncertainty Principle has nothing to do with this.  The principle
merely describes the accuracy limits to which one can measure two quantities
*simultaneously*.  For example, quantum theory *does* allow one to measure the
location of a particle as accurately as one desires, but the catch is that
the more accurately you measure the location, the less accurately you
can measure its momentum at that location, the relation being
	(delta x)*(delta v) <= (h bar)
where x is the location along a coordinate, v is the velocity, and
h bar is Planck's constant over 2*pi.

People have misinterpreted it as meaning that a particle has some
"real" location before we try to observe it, but when we try to measure
it, we bollix it up so that it can appear anywhere.

Actually, the wave
function of the particle extends *everywhere* and its value squared at any
point is the probability of finding it there when we make an observation.
We can *never* observe its "real" location-- EVEN IN PRINCIPLE.  Therefore,
how can we say that it *has* a "real" location?  Science does not deal
in absolutely unobservable quantities; the question of the particle's
"real" location before the observation is such a quantity, hence
this question belongs to the realm of metaphysics, not physics.
The observer not only affects the reality, the observer IS the reality,
for he cannot (cannot!) be separated from the observee.
Disgusting, but true, it does hearken back to Bishop Berkeley and the
Eastern religions.  Apologies to  Charles Poirier, but it seems they
had an inkling of the right idea when it comes to quantum phenomena.

In the experiment I described previously with the electron jumping one
light year in one second, A's observation of the electron at his location
cannot reduce to zero the chance of B observing the electron later at
his location because that would imply that A's observation has a lasting
effect on the electron's wave function after the original collapse.

An interesting article in Scientific American appeared in November 1979
called "Quantum Theory and Reality" by Bernard d'Espagnat, describing
such weird things.  Another interesting article called "Quantum Logic"
by R. Hughes can be found in the October 1981 issue, and it describes how
in the quantum world, the statement P and (Q or R) is not equivalent (!!) to
(P or Q) and (P or R) at the quantum level.  This is, to put it mildly,
mind boggling.


					Don Chan, utcsrgv!donald

God not only plays dice with the universe,
He loads the dice too!