Pitts’s Interactionist Dualism: Energy Conservation and Mental Causation

Philosopher-physicist J. Brian Pitts argues that the longstanding Leibniz-to-Dennett objection to interactionist dualism based on the conservation of energy and momentum suffers from circular reasoning, once neglected aspects of the physics of conservation laws are considered. Two typically neglected aspects of conservation laws, he says, are locality and the (bi)conditional relation to symmetries. With these features properly understood, non-conservation of energy and momentum could be a consequence of interactionism, but no reason has been provided thereby to find a reductio ad absurdum rather than an inference. On the other hand, a related and novel, though not broadly compelling, difficulty can arise from Einstein’s General Relativity, the standard theory of gravity, depending on one’s background beliefs.

The Conservation Objection

Pitts presents his case. Off and on since Leibniz’s day (Watkins, 1995, 1998; Pitts, 2019), but especially since the late 19th century, he says, conservation laws have been invoked as objections to interactionist substance dualism. For Leibniz, the argument was invoked in favor of pre-established harmony, whereas 19th-century authors invoked the objection to favor epiphenomenalism. 20th-century philosophers took the energy conservation objection to refute dualism.

Many views, especially physicalism, have problems with mental causation. Property dualism with distinctively mental causal powers also has energy conservation issues. Some types of panpsychism, given the ubiquity of mind, could have the same problem. With mental causation problems now common, Pitts suggests examining aspects of physics that emerged in the late 19th and early 20th centuries but have had little influence in the philosophy of mind.

Neglected Aspects of Conservation Laws

As noted, the traditional conservation objection to interactionist dualism, Pitts argues, “is vitiated by two typically neglected aspects of physics and their consequences, namely, locality and the (bi)conditional relation to symmetries (Cucu & Pitts, 2019; Pitts, 2020, 2021, 2022a, 2022b). While conservation laws often appear as a black box in the philosophy of mind and metaphysics, they have a well-understood theoretical basis in physics.

Pitts presents four arguments:

1. Conservation laws are primarily local, holding not for the universe as a whole but for every place separately as partial differential equations, describing how the density varies with time plus how the flux varies with place. (Global conservation follows by integration if one can discard a term at spatial infinity—which appears to be false according to standard cosmology, arguably making the total amount of, say, mass-energy in the world undefined and hence incapable of staying the same or changing.)
2. Consequently, local conservation laws form an infinite conjunction of conservations in different places. By De Morgan’s law (that the denial of a conjunction not (A and B) is the disjunction of negations (not A or not B)), non-conservation in some place(s) (e.g., brains) would not be catastrophic or perhaps even very bad, especially if one is not studying brains.
3. Conservation laws have a theoretical basis in symmetries due to Noether's theorem: energy (momentum) conservation is a consequence of the uniformity of natural laws over time (space, respectively). Hence, there is no theoretical reason to expect conservation of energy or momentum in the presence of mental causation, because one’s willing to raise one’s arm presumably would involve one’s mind/soul’s acting in one’s brain during one’s lifetime, not acting equally everywhere and always.
4. Noether's theorem has a converse: conservation laws imply symmetries, so by contraposition, violation of symmetries implies violation of conservation laws. Thus, one should positively expect conservation laws to fail, given dualism. To demand that conservation laws hold in the brain without an empirical neuroscientific basis is simply to beg the question against such interactionist dualism (substance or otherwise).

Pitts rejects interactionist proposals to uphold conservation, which, he says, tend to be either unsuccessful or unnecessary for addressing the objection. For example, non-local compensation purports to uphold conservation of energy by what is in fact an additional “violation” somewhere else, aggravating rather than ameliorating the (supposed) problem.

Some have proposed that quantum mechanics implies either non-conservation or interaction with conservation; such ideas commendably pay attention to quantum physics. However, invoking quantum mechanics is hardly necessary to defuse the objection, which already fails in the most conservation-friendly type of physics, namely, classical field theory, which is the launching pad for quantum field theory and hence is our second-best physics, which includes Maxwell’s electromagnetism and (as an unusual case) Einstein’s General Relativity (on which more below, however). Until recently, the work that came closest to reckoning with the 20th-century physics of conservation laws evidently was that by Averill and Keating (1981). If neuroscience casts doubt on interactionism empirically, then neuroscience provides a very different and much more recent argument than Leibniz’s.

General Relativity and Mental Causation

On the other hand, Pitts says, General Relativity makes interactionist mental causation more difficult (Pitts, 2022a, 2022b), not easier as is sometimes proposed. The calculations are coordinate-invariant (as one usually expects in General Relativity) and involve the generalized Bianchi identities, which in other contexts indicate that some of Einstein’s gravitational field equations logically imply others. It is possible, though not necessary, to interpret this result in terms of abundant pseudotensor conservation laws in General Relativity: General Relativity formally offers a superabundance (not an absence) of conservation laws, but the failure of equivalence between different conservation laws (coordinate-dependent “pseudotensors” rather than coordinate-independent tensors) that most people have desired has made it rare to take the formal conservation laws seriously.

Whatever one’s stance on gravitational energy (controversial since 1918) and hence on energy and momentum conservation laws (which are merely formal rather than physically meaningful if gravitational energy and momentum are not localized), General Relativity tends to trivialize efforts to introduce mental causation into (classical field) physics: the soul/mind is left doing either nothing or the same thing everywhere and always (which presumably implies that it does nothing), at least in simple cases. This tendency only goes so far, however, and might be overwhelmed. Hence the strength of this objection depends on background worldview assumptions; it is not very impressive given other beliefs, such as theism or broadly mind-first metaphysics, which proponents of such mental causation tend to hold. Most people for whom the new objection from General Relativity works already reject interactionist dualism on other grounds, but the occasional non-theist dualist (such as Popper or Beloff) would face a difficulty.