Dear Colleagues,Science & Ultimate Reality
In his excellent summary of John Wheeler's career, Kenneth Ford identified
three phases in Wheeler's thinking: the particle period, the field period
and the information period. The concept of information is inextricably bound
up with quantum mechanics, and Wheeler's incisive question "How come the
quantum?" stands as a challenge for any attempt to provide a unified
theoretical description of nature. It is not enough that the rules of
quantum mechanics are found to work. To fully understand nature at the
deepest level we need to know why the world obeys quantum rules. Part of the
answer involves knowing how the quasi-classical world of observation emerges
from the weird domain of quantum physics.
Wheeler's "It from bit" program proceeds from a well-known yet still
mysterious fact. The wave function describing a quantum particle expresses
what is known about that particle, i.e. it represents information, or
software, whereas the particle itself is an object, or hardware. How do
these fundamentally different concepts, associated with different levels of
description, fit together, and how does this fit recover the usual notion of
"reality"? This dualism (particle-wave, hardware-software, it-bit) lies at
the heart of quantum physics, yet it's true character continues to
tantalize. As the wavefunction evolves and obseravtions are made, harware
and software, its and bits, become entagled. Whenever we encounter
entanglements of different conceptual level, the possibilities for confusion
and dissent are legion. (Consider that other bone of contention, the
mind-body problem, with mind as software, body as hardware, somehow
intermingling descriptively if not physically when thoughts beget actions
and sense data beget thoughts; indeed, some people believe this problem is
intimately related to the it/bit quantum problem.)
Dieter Zeh from the University of Heidelberg is an expert on the conceptual
foundations of quantum mechanics, time asymmetry, and the emergence of
classicality through decoherence. His paper is available now in its
entirety, and I am attaching to this message as a pdf file. A summary of the
paper is set out below.
Paul Davies
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Title: The Wave Function: It or Bit?
Author: Dieter Zeh
Summary
Schroedinger's wave function shows many aspects of a state of incomplete
knowledge, or INFORMATION ("bit"): (1) it is defined on a space of classical
configurations, (2) its entanglement is, therefore, analogous to statistical
correlations, and (3) it determines probabilites of measurement outcomes.
Nonetheless, quantum superpositions (such as represented by a wave function)
define individual PHYSICAL states ("it"), as we know from many examples.
This dilemma may have its origin in the conventional OPERATIONAL foundation
of physical concepts, successful in classical physics, but inappropriate in
quantum theory because of the existence of mutually exclusive operations. In
contrast, a hypothetical realism, based on concepts that are justified only
by their universal and consistent applicability, favors the wave function as
a description of (nonlocal) physical reality. The (conceptually local)
classical world then appears as an illusion, facilitated by the phenomenon
of decoherence, which is consistently EXPLAINED by the very entanglement
that must dynamically arise in a universal wave function. Decoherence is
meaningful for observers that are ASSUMED to be local (for dynamical
reasons).
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