book review: the quantum enigma

The Quantum Enigma: Finding the Hidden Key
by Wolfgang Smith (1995)

Smith makes one of the more promising attempts to connect classical metaphysics to modern physics.  Interestingly, he thinks this reconciliation is easier in quantum than Newtonian physics, the latter being too inhospitably Cartesian.  Quantum mechanics is famously weird.  First, there is the issue of noncommuting operators.  Thus, for instance, if my spin 1/2 particle is in a definite z-axis spin state, it cannot be in a definite x-axis spin state.  A particle being in a definite superposition of eigenstates with respect to at least some observables is inescapable.  Second, there is the “measurement problem”, that if I do measure the x-axis spin, the state vector will “jump” to one eigenstate or the other, and state vector collapse is nondeterministic, nonlocal, and not obviously consistent with the Schroedinger equation.  Regardless of your philosophical commitments, at least one of the above features is probably horrifying to you.  Smith thinks it’s just our false modernist beliefs that make this seem troubling.  He claims that in quantum superposition, we have rediscovered the Aristotelian principle of potency (a suggestion, he notes, also made by Heisenberg), and in state vector collapse we are witnessing “vertical” (i.e. formal) causation.

The early chapters hinge on a distinction Smith draws between the “corporeal” world that we directly perceive and the “physical” world that we measure.  This is reminiscent of the Cartesian/Lockean distinction between subjective, qualitative features and objective, geometrical features of the world, except Smith emphatically locates them both outside our minds yet maintains that they point to real, ontologically distinct aspects of objects.  I admit that I found this discussion difficult to follow, but “primary”/”secondary” quality distinctions have always confused me, and Smith would probably say that I shouldn’t understand what early modern philosophers wrote about them.

Things became much clearer for me in the last chapter.  As I understand it, Smith’s case is as follows.  Quantum particles being indeterminate (in some observables) allows them to act as a material principle (in the Aristotelian as well as modernist sense) that receives determination from its formal principle when incorporated–literally–into a corporeal being.  The distinguishing feature of being a corporeal object is not being macroscopic, but having a substantial form.  Substances (in the Aristotelian sense) have forms and are not subject to quantum superposition–they are the Copenhagen interpretation’s classical measuring devices.  A particle being incorporated into a corporeal object (e.g. by affecting the state of a corporeal measuring device) collapses its wavefunction, at least with respect to those observables that affect the substance’s corporeal state.

This is certainly an elegant move–Aristotelians are looking for a way to find formal causes in modern physics, while physicists are looking for a way to understand a type of causality that at least appears very different from the usual deterministic Schroedinger evolution, and lo, the two needs can be made to answer each other nicely.  Whether it works in detail would be a wonderful topic for further thought; this would no doubt have to deal with the usual Scholastic difficulty of identifying what qualify as substances (“corporeal” objects), but that would be an excellent project for Scholastics looking to re-engage with the corporeal world.