[extropy-chat] Many worlds and Hugh Everett

scerir scerir at libero.it
Tue Dec 30 19:59:36 UTC 2003


> As it stands the [MWI] interpretation can only be verified
> subjectively, and only if true.
> Dirk

There are several different "interpretations", or "models",
or "theories", not just one QM. And they are not equivalent,
in physical terms, i.e., the energy conservation law in MWI
is a statistical law; i.e., the von Neumann density operator
depends on the specific subjects performing measurements
on the same system (the "whose knowledge?" issue); etc.

There are measures, probabilities, entropies, informations,
effects dependent on the specific "interpretation" you choose:
Physical collapse interpretation, Copenhagen interpretation,
decoherence and environment interpretation, conditional density
matrices, two-state time symmetrical quantum formalism, instantaneous
non-local influences, superluminal influences, Eberhard's superluminal
"realistic" influences, retro-causality models, modal interpretations,
consistent histories, consciousness, non-local hidden variables,
witnessing interpretations, superselection rules, modified or
non-linear dynamics, statistical interpretation of (proper and
improper) mixtures, Einstein's statistical interpretations, GWR theory,
Brownian quantum theory, Ne'eman's geometric interpretation,
Finkelstein's physics of logic interpretation, Bell's iper-deterministic
interpretation, Bohmian mechanics, Barut's mechanics, MWI, Hugh Everett,
many minds, Pitowsky's reformulation of a local hidden variable theory
based on the Banach-Tarski theorem, quantum diffusion theory,
Ithaca interpretation, informational interpretation(s), etc. etc.).

One of the reasons is that QM (complete or not, in the sense of EPR)
in general (excepting perhaps MWI) is assumed not to be a "closed"
theory, even if it pretends to be universally valid.
As Bohr stated, since the very beginning of QM, the "observer",
measuring a quantum system by means of an "apparatus", remains out,
it is not described by QM. This is the von Neumann "cut", this is
one of the mysteries, this is the source of (many of) the above
"interpretations", or "theories". Although QM would describe
anything, it cannot include everything, and it must introduce
a "cut", an "interface", somewhere, from which the probability
rules can be derived. As you have maybe already realized there are,
perhaps, also Goedelian issues in QM, because the theory is not
closed, it is not self-supporting. These issues are many, i.e.
the subject-object separability is unclear (Albert-Peres self-
measurements, Finkelstein's 'introspective' systems); i.e., it is 
well known the fact that linear combinations of "elements of reality", 
as defined by EPR, may not be themselves "elements of reality", 
thus also the mathematical framework of QM (but not the experimental) 
seems to be "fuzzy". About all that, and many more, see, in example, 
T.Breuer at http://www.staff.fh-vorarlberg.ac.at/tb/tbpublisteengl.html

But, on the experimental side, a lot of work has been done, and now
the situation is much different from that described by Bohr
(a realist, but "sui generis"), and von Neumann (the "cut"), and
London and Bauer and Wigner and the young Heisenberg (the
"consciousness"), and Pauli (the "occasio", or "creation").
Now quantum macro-objects are under direct "investigation",
and the Nobel laureate A. Leggett wrote this interesting paper
www.nobel.se/physics/symposia/ncs-2001-1/leggett.pdf
against the "macro-realism", as he calls it. We could say
that the observer and the apparatus are, thus, close to
become objects of performed physical experiments.

It is important to remember here the precise domain of validity
of Bell's theorem. Its proof requires the observed system to be
*deterministic*, while the observer is *not*. (As Bell himself
realized, if the observer too is deterministic, there is no problem
at all with QM, and local hidden variables, because everything
would be pre-determined, our free will be entangled with quantum
systems, by a totalitarian conspiratorially theory). Thus Bell's
theorem, requiring determinism and direct counterfactual reasoning
(if we would measure ... if instead we would measure ...) has a 
limited validity within a theory based on intrinsic randomness and
indeterminism.

As you maybe already realized, if you wish to disprove QM,
or one of its "interpretations", you have many different
narrow "avenues".

I do not agree with the usual song that if you want to disprove
MWI you must just disprove QM. That is a bit simplistic. Because,
in example, we can schrink the entire QM into a set of 5 or 6 axioms,
with are robust indeed.

Being MWI (or MWI + decoherence) a "realistic" theory, in the sense
of EPR (*), if you wish to disprove this theory you could start
from a precise criterion (still to be invented, to my knowledge) 
to distinguish, by performing experiments, a coherent superposition 
of states, from a (proper or improper) mixture of states. 

Algorithmic information theory could provide some insight here. 
And also some new development of the theory of entanglements. 
(For mixed states, it is harder to establish a good measure of 
entanglement, since such a measure has to distinguish between 
entropy arising from classical correlations in the state, and 
entropy due to purely quantum correlations. Two measures of entanglement 
that have explicit physical meaning in the processing of quantum 
information have emerged, the entanglement cost of a quantum state and 
the distillable entanglement of a quantum state).

s.

(*) ""if, without in any way disturbing a system, we can predict
with certainty (i.e. with probability equal to unity) the
value of a physical quantity, then there exists an element
of physical reality corresponding to this physical quantity."
>From the specific point of view of MWI, the statement above
is perfectly right, true, valid, consistent. (From the MWI
pov EPR were a bit incorrect, regarding the specific observables
whose values can be predicted).






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