From: scerir (scerir@libero.it)
Date: Thu Sep 12 2002 - 01:47:41 MDT
Lee Corbin wrote:
> > Perhaps, but would you say more about why you suppose the Copenhagen
> > view to be subjective, especially in its historical context? I submit
> > that if you had talked to Heisenburg, Bohr, Dirac, or Schroedinger in
> > 1929, they would have claimed to be speaking quite objectively---except
> > maybe Bohr, who was always defending his father's philosophical points.
> > They thought that the wave function was quite objective. Only later did
> > certain people such as Von Neumann and Wigner conclude that the standard
> > interpretation was subjective?
' The question of whether the waves are something "real" or a function
to describe and predict phenomena in a convenient way is a matter of
taste. I personally like to regard a probability wave, even in 3N-dimensional
space, as a real thing, certainly as more than a tool for mathematical
calculations ... Quite generally, how could we rely on probability
predictions if by this notion we do not refer to something real and
objective? '
Max Born, 'Natural Philosophy of Cause and Chance',
p. 107, Dover publ., 1964.
I must say that the early interpretation by Born was less "realist".
But interference experiments with "single" photons (just one particle
in the apparatus) showed very soon that the "statistical" nature
of randomness has nothing to do with ensembles of particles.
So he was forced to a more "realist" position.
Btw the so called Born's rule is nothing more than the extrapolation
of old concepts: Einstein's 1909 phantom field and Bohr-Kramers-
Slater (BKS) ghost field.
H. Kragh (in 'Dirac: a Scientific Biography', Cambridge U.P., 1990)
describes a 1927 discussion between Dirac, Born and Heisenberg
about what actually gives rise to the "collapse". For Born and Dirac it
is the Nature who makes the choice of measurement result. Heisenberg
maintained that behind the collapse, the choice of which branch of the
wavefunction would be followed, was the observer itself. Like von
Neumann, London and Bauer, Wigner, etc.
Heisenberg changed opinion later, and developed his "later interpretation"
in terms of "potentia", which is close to Popper's interpretation in terms
of "propensities".
The original term, for "collapse", was "reduction of the probability packet",
sometimes also "reduction of wave packet", and the concept (according
to Born) is due to Heisenberg (circa 1926). Heisenberg and Born
at that time were puzzled because waves were spreading, in space, but
the same waves became particles, (i.e. drops in the Wilson
chamber).
Interesting to note that Pauli did not like the "reduction" and he was thinking,
at that time, about a sort of 'many dimensions' interpretation, a sort
of MWI ante litteram, nothing new under the sun!.
Heisenberg wrote about the "collapse":
" In relation to these considerations, one other idealized experiment
(due to Einstein) may be considered. We imagine a photon which is
represented by a wave packet built up out of Maxwell waves.
It will thus have a certain spatial extension and also a certain range of
frequency. By reflection at a semi-transparent mirror, it is possible
to decompose it into two parts, a reflected and a transmitted packet.
There is then a definite probability for finding the photon either in
one part or in the other part of the divided wave packet. After
a sufficient time the two parts will be separated by any distance
desired; now if an experiment yields the result that the photon is, say,
in the reflected part of the packet, then the probability of finding the
photon in the other part of the the packet immediately becomes zero.
The experiment at the position of the reflected packet thus exerts
a kind of action (reduction of the wave packet) at the distant point
occupied by the transmitted packet, and one sees that this action is
propagated with a velocity greater than that of light. However, it
is also obvious that this kind of action can never be utilized for the
transmission of signals so that it is not in conflict with the postulates
of the theory of relativity." [The Physical Principles of the Quantum
Theory, W. Heisenberg (University of Chicago Press, Chicago, 1930),
reprinted by Dover Publications, p. 39.]
According to Folse (Bohr's major expert) even Bohr was a "realist".
But, imo, his "reality" concept was a bit "blown up" (or Eintein's was
too "restricted" as Bohr once said).
Actually even Bohr's complementarity principle (which is not as
strong as he supposed to be - Zurek, Wootters, Noyer showed
that the complementarity is "smooth", definitely it is not a yes/no,
particle/wave, localization/superposition situation) has, perhaps,
a bit of "realism" in it.
< [Bohr] ... attached reality, i.e. reality as it was defined by
him, to those aspects that could be directly observed in certain
limiting circumstances by direct macroscopic observation.
And, of course, in the case of radiation it is clear that direct
observation in the limiting case of small values of
h nu / K T
gives the usual classical wave description of Hertz and
Maxwell. As to the photon or the light quantum concept,
introduced by Einstein, Bohr regarded it as a useful but
an "auxiliary" concept, one which he later called symbolical,
meaning thereby that it was not an aspect of the radiation
phenomena which could be directly observed as such ...
Bohr always made this distinction between the two aspects
of radiation.>
Thus the photon is the expression for the exchange
of energy and momentum between matter and radiation.
< For matter, the aspect which is in correspondence
with classical observation is the particle aspect, of course;
whereas the wave aspect is a symbolical one .... >
[Rosenfeld, 1973, p. 252, p.260, Reidel publ., "The Wave-Particle
Dilemma", in Mehra (editor) "The Physicist's Conception of Nature"]
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