From: scerir (scerir@libero.it)
Date: Thu Sep 12 2002 - 15:13:36 MDT
Amara writes:
> > Although Einstein and many physicists would disagree with him [Bohr]
> > and say that science is about learning what is reality, and what are
> > its 'laws', Bohr is pointing out that any theory about reality can
> > have no consequences testable by us, unless that theory can also
> > describe what humans can see and know.
There was also some other extreme position. W. Pauli, i.e., wrote
(Pauli Letter Collection, Cern, Geneve, 9992.063, October
13, 1951, to Markus Fierz) " That which is physically unique
cannot be separated from the observer anymore - and therefore
falls through the net of physics. The individual case is 'occasio'
and not 'causa'. I am inclined to see in this 'occasio' - which
includes the observer and his choice of the experimental setup
and procedure - a 'revenue' of the 'anima mundi' (of course
in 'changed shape') that was pushed aside in the 17th century.
'La donna è mobile' - also the 'anima mundi' and the 'occasio' ."
Pauli also wrote (letter to Max Born, in 'A. Einstein, H. and M.
Born, Briefwechsel 1916-1956, Nymphenburger Verlag,
Munchen, 1991) about the quantum measurement issue that
"the appearance of a definite position of an electron during
an observation is a creation outside the laws of nature."
Following the Spirit of Copenhagen (which is Bohr, plus
Heisenberg's principle - an implementation of complementarity -
plus Born's rule - the collapse, the consciousness, the delayed
choice, and all the rest is sometimes called the Spirit of Princeton)
the observer has no influence on the specific element of the
world which becomes reality. If, in the double slit experiment,
the observer chooses to determine the path, he does not influence
the particle going through the first or the second slit. If the
observer chooses to see the interference pattern he has no influence
on the specific point of the screen he will observe the spot.
So the observer's influence is merely qualitative, that is to
say: he can just choose the apparatus, not the outcome.
Bohr wrote (in 'The Unity of Science') " [Complementarity should]
be seen as a logical expression of our situation concerning objective
description in this area of experience. The realization that the
interaction between measuring devices and the physical systems
forms an integrating part of quantum phenomena, has not only
revealed an unexpected limitation of the mechanistic view of
nature which attributes well defined properties to the objects
themselves, but it has forced us to give special attention to
the problem of observation when ordering the experiences. "
Bohr also wrote (in Atomic Physics and Human Knowledge,
Wiley, 1959) " ... a subsequent measurement to a certain degree
deprives the information given by a previous measurement
of its significance for predicting the future course of phenomena.
Obviously, these facts not only set a limit to the extent of the
information obtainable by measurement, but they also set a
limit to the meaning which we may attribute to such information.
We meet here in a new light the old truth that in our description
of nature the purpose is not to disclose the real essence of the
phenomena but only to track down, so far as it possible, relations
between the manifold aspects of our experience."
Note he uses the terms 'information' and 'limit'. They are the very
essence of the Copenhagen Interpretation. Quantum information is
limited in many ways (discreteness, finiteness, no-cloning possibility
for states, etc.). Paradoxically enough the 'quantum bit' is represented
by a continuum (in a 2-dimensional Hilbert space, a unit sphere)!
And this leads us to what Lee Corbin writes:
> I don't understand. Say that I have a theory that traffic is
> backed up because a railway train is blocking the road ahead.
> Or that I have a theory that a peculiar structure in a tree
> was made by a bird. It doesn't seem to me that you or Bohr
> could be correct---such theories certainly don't address what
> humans can see and know, nor should they, right?
There is no superposition of states, there. In the quantum domain
there is a huge objectification problem (and theorem). Which
says that the hypothetical assignment of potential or actual
values or states (eigenvalues, eigenstates) to some observable
on a system, (which is in a superposition of eigenstates in relation
of that observable or which is in a eigenstate of another non
commuting observable), is not compatible with QM.
And there are not a couple of theorems, there. One says that
a measurement reduction of a quantum system leads to
contradictions if in the formalism one does not consider
the apparatus (which is linked to and chosen by the observer).
The second says that the value of a macroscopic pointer of
an apparatus is not an eigenvalue of a quantum observable
but is a sort of average (over large numbers of Hilbert spaces
and over many observables).
(The case of a mechanical observer, or a quantum robot,
which (pre)measures itself is for sure interesting, because it
follows, from the analysis of Albert, that there is something
'indexical' or subjective in this kind of quantum knowledge).
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