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 consistent-histories 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, “hoped-for 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 extra-scientific 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 many-worlds and many-minds 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 “pattern-forming 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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