Since the subject has been broached...
One world versus many: the inadequacy of Everettian accounts of evolution,//
//probability, and scientific confirmation/
by Adrian Kent
(Dated: August 24, 2010)
"There is a compelling intellectual case for exploring whether purely
unitary quantum theory
defines a sensible and scientifically adequate theory, as Everett
originally proposed. Many different
and incompatible attempts to define a coherent Everettian quantum theory
have been made over the
past fifty years. However, no known version of the theory (unadorned by
extra ad hoc postulates)
can account for the appearance of probabilities and explain why the
theory it was meant to replace,
Copenhagen quantum theory, appears to be confirmed, or more generally
why our evolutionary
history appears to be Born-rule typical.
This article reviews some ingenious and interesting recent attempts in
this direction by Wallace,
Greaves-Myrvold and others, and explains why they don't work. An account
of one-world randomness,
which appears scientifically satisfactory, and has no many-worlds
analogue, is proposed.
A fundamental obstacle to confirming many-worlds theories is illustrated
by considering some toy
many-worlds models. These models show that branch weights can exist
without having any role
in either rational decision-making or theory confirmation, and also that
the latter two roles are
Wallace's proposed decision theoretic axioms for rational agents in a
multiverse and claimed
derivation of the Born rule are examined. It is argued that Wallace's
strategy of axiomatizing a
mathematically precise decision theory within a fuzzy Everettian
quasiclassical ontology is incoherent.
Moreover, Wallace's axioms are not constitutive of rationality either in
theory or in theories in which branchings and branch weights are
precisely defined. In both cases,
there exist coherent rational strategies that violate some of the axioms."
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