Polkinghorne, John. “Physical Process, Quantum Events, and Divine Agency."
Although it has been
“spectacularly successful” in its predictive power, John Polkinghorne begins by
stressing that we do not fully understand quantum theory. The central
difficulty is the “measurement problem”: how do determinate macroscopic states
(i.e., particular results) come about when a measurement is made on apparently
indeterministic quantum states? Viewing this as a “collapse of the wavepacket”
only renames the problem, since such a collapse contradicts the dynamical
(Schrödinger) equation under which the wavepacket evolves smoothly. Niels Bohr
spoke dualistically about classical and quantum worlds that had to intermesh,
but this does not really work in principle since there is only a single
physical reality in which even the classical apparatus is made of quantum
constituents. Polkinghorne also finds unsatisfactory a statistical
interpretation of quantum mechanics which refrains from speaking about
individual quantum processes, including consistenthistories approaches. He
then outlines various groups of proposals for interpreting quantum theory which
seem more promising.
The first group starts with
quantum theory as it is and attempts to resolve the measurement problem by
including “decoherence.” According to the superposition principle, exclusive
classical states (e.g., “here” or “there”) are admitted together as a viable
physical quantum state (e.g., “here” and “there”). Superposition gives rise to
“interference” effects suggesting the wavelike aspect of quantum states. Why,
then, don’t we see superposition and interference in our everyday experience?
Some have proposed that decoherence, which involves interactions between the
quantum process and its radiative environment, helps solve the problem by
rapidly minimizing all but one state and by canceling interference effects. The
problem is that decoherence does not tell us why any particular outcome, and
not one of the other possibilities, actually occurred.
The second group, “hopedfor
physics,” believes that the interaction with large systems brings about the
collapse of the wavefunction. In Polkinghorne’s opinion, the irreversibility of
the behavior of macroscopic systems may provide a clue to how this happens, but
it has not done so yet. A third group seeks what Polkinghorne calls “unknown
new physics,” where, for example, the amount of matter involved in the
interaction determines whether the collapse occurs, or where quantum gravity
plays a crucial role. David Bohm’s work represents a fourth approach: “hidden
new physics.” For Bohm, there is no collapse of the wavepacket, but Bohm’s
approach offers no predictive advantages over conventional quantum physics. According
to Polkinghorne, the choice between Bohm and Bohr has to be made on the basis
of extrascientific criteria, including metaphysical principles. Theologians
who believe that divine action requires indeterministic physical processes have
every right to prefer Bohr’s conventional approach, as long as they do not
claim that science alone supports their choice. The final group appeals to
“unknown but ‘nearby’ metaphysics” in reaching out to additional factors in
nature to solve the problem. These include the role of consciousness of the
observer and the manyworlds and manyminds strategies, which accept the
formalism of quantum mechanics but actualize all states in the quantum
superposition.
All of these proposals seem
to assign a special role (or “preferred basis”) to spatial position in their
formulation of and solution to the measurement problem. If so, this would imply
a change in the way we think about physics, which, since its inception, treats
all dynamical variables equally. They also limit their focus to laboratory
measurements, and they may not be extendable to the wider context of natural
physical processes. Polkinghorne then suggests that the standard classical
account of macroscopic processes may need to be reconsidered. Complex classical
systems point to the presence of a “patternforming causality of an holistic
kind (‘active information’).” Perhaps the equations of classical physics are
“downward emergent” approximations of a more complex account of macroscopic
physics as well as “upward emergent” from quantum physics. Still, the
unresolved complexities of quantum chaology pose a challenge to such an
approach. Even the meaning of the term “quantum event” cannot be reduced either
to occasional measurements or to the general unfolding of the wavefunction
governed by the Schrödinger equation.
Finally, Polkinghorne turns
to the theology of divine and human agency. Though autonomous in many ways, the
metaphysical backing for such discourse should still take account of science, particularly
where quantum mechanics and chaos theory suggest ontological openness. But many
unresolved problems beset such attempts. Quantum theory may not be helpful
because of the limited and episodic character of measurement events in which
indeterminacy seems to hold. Moreover, although some quantum processes, such as
gene mutation, may lead to macroscopic consequences, they do not seem to
generate a basis for the “flexible actions of agents.” Chaos theory provides a
more “flowing character” for agency. Of course, chaos theory is normally framed
within a deterministic, Newtonian, context, but it could be given a wider
framework. The real problem is how to combine chaos theory with quantum
mechanics, and in the process, solve issues in quantum chaology. Polkinghorne
believes that the best hope for future progress will lie in an increased
understanding of the nature and implications of quantum chaology.
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