Is quantum mechanics relevant to the philosophy of mind (and the other way around)?

by Quentin Ruyant

There have been speculations on a possible link between quantum mechanics and the mind almost since the early elaboration of quantum theory (including by well known physicists, such as Wigner, Bohr and Pauli). Yet despite a few proposals (e.g. from Stapp, Penrose, Eccles [1]) what we could dub “quantum mind hypothesis” are often readily dismissed as irrelevant and are seldom discussed in contemporary philosophy of mind. My aim in this article is to defend the relevance of this type of approach.

For the purpose of this discussion it is useful to distinguish two different theses regarding the putative links between quantum mechanics and the mind:

1. The mind is relevant in interpreting quantum mechanics
2. Quantum mechanics is relevant in the philosophy of mind

Of course the two theses are not necessarily construed as independent by the proponents of quantum-mind hypothesis. One could argue that the mind is relevant in interpreting quantum mechanics, precisely for the same reasons that quantum mechanics is relevant in the philosophy of mind. This is actually what I will argue here (or at least that it is a promising hypothesis that should be pursued). However, the two theses face different kinds of objections and need to be distinguished.

Is consciousness a biological problem?

Quite logically, I will first tackle the second one: the idea that quantum mechanics could help us explain consciousness. Such claim is sometimes dismissed on the ground that the problem of understanding consciousness is a biological problem, not a physical one. Let me clarify a bit: by “biological/physical problem” I understand: a problem which is better informed by biology/physics, not necessarily a purely scientific (as opposed to philosophical) problem. Quantum mechanics, it is said, is only relevant at very small scales of reality, while conscious organisms are biological organisms, typically found at a macroscopic level, where quantum effects manifest themselves as mere noise. Besides, it is said, randomness is not a proper substitute for free-will, so quantum mechanics wouldn’t help anyway. Therefore quantum mechanics is irrelevant to philosophy of mind.

First, let us observe that typical quantum effects are not necessarily foreign to biology, as illustrated by the burgeoning field of quantum biology. Nor are they in principle confined to the microscopic level — this is the heart of the measurement problem, as illustrated by the famous Schrödinger’s cat thought experiment. Quantum effects such as entanglement also help explain macroscopically observable properties, such as heat capacities or magnetic susceptibilities [2]. It is generally assumed that decoherence precludes the observability of quantum effects on macroscopic objects, but as Zurek et al. note, decoherence is more a heuristic tool to be applied on a case by case basis than a generic consequence of the theory [3]. Finally, quantum entanglement is hard to measure on complex systems. The idea that no quantum effect exists at all on our scale is thus neither empirically nor theoretically grounded. At most we can say that no quantum effect is detectable in common physical objects whose behavior can be accurately described using Newtonian mechanics alone, such as tables and chairs, but of course these are not the sort of conscious objects we are interested in (unless, of course, you think that biological phenomena can be explained with Newtonian mechanics alone).

However, my main contention concerns the idea that the problem of consciousness is a biological problem. Let us follow Chalmers in distinguishing the “easy problems” of consciousness from the “hard problem.” The easy problems concern everything that is scientifically tractable from a third person perspective — how do we discriminate and integrate information, etc. that is, all the cognitive aspects of consciousness. These (not so easy) problems are undeniably biological or psychological. The “hard problem” concerns the phenomenal aspect of consciousness, the subjective first-person “what it’s like” to be conscious. And this question, Chalmers argues, is not scientifically tractable: it is a metaphysical problem.

Metaphysics addresses the most fundamental aspects of reality and arguably the phenomenal aspect of consciousness is one of them. Now, if there is a branch of science which more closely resembles metaphysics in its specific interest for the fundamental aspects of reality, it is physics — not biology. Physics and metaphysics overlap in many respects (just consider the wild speculations about a mathematical universe advanced by physicists such as Tegmark [4]) and there is probably a continuum between the two. On the contrary, a contribution of biology to fundamental metaphysical issues seems to me rather implausible. I could be wrong (and Chalmers could be wrong in thinking that phenomenal aspects of consciousness are metaphysical), but I contend that the hard problem of consciousness, if it exists, is not a biological problem, but a physical one: it is just too fundamental a problem to be addressed from a biological perspective. Note that I don’t mean to deny that there are relations between phenomenal and psychological aspects, in the sense that certain cognitive states are correlated with specific phenomenal aspects, but explaining such correlations is distinct from explaining why there are phenomenal aspects to begin with.

Of course, no metaphysician denies that physics is of interest in the philosophy of mind. Kim’s causal exclusion argument involves the principle of “physical closure.” The argument precisely addresses the problem of the relations between the physical and the mental [5]. What some metaphysicians apparently deny is that quantum physics or any actual physics is of particular interest for such issues: for these authors metaphysics can still produce interesting insights about the physical “in general,” that is, whatever actual physics says. They seem to assume that the physical “in general” poses no important problem of interpretation apart from the well entrenched problems of classical metaphysics.

It seems to me that there is no such thing as “the physical in general, whatever actual physics says”: our conception of the physical changes with our physics. There is no point in reasoning on the physical without taking into account what our best current physics says about it. And our best current physics is quantum mechanics (quantum field theory to be precise). For this reason I think, following Ladyman, Ross and Spurrett [6], that metaphysicians should be informed by our best physics rather than work on a dated conception of the physical, or, as they say provocatively, on “A-level chemistry.” (Ladyman, Ross and Spurrett note that some of Kim’s central arguments rely on conceptions of the physical that are no longer accepted by physicists. The same goes, I would say, of thought experiments involving clones and mind duplication: the no-cloning theorem in quantum mechanics precludes the possibility of such perfect physical duplication [7]).

I am not saying that all metaphysicians should be trained in contemporary physics to produce valuable work (Kim’s Mind in a Physical World is very valuable and important, in my opinion), but contemporary physics is definitely a place we should look at to address fundamental issues in the philosophy of mind. My overall impression is that this is hardly the case today, although such inputs are considered in Chalmers’ The Conscious Mind [8].

Does embracing a quantum mechanical view of the physical really change the perspective for the metaphysics of mind? At the very least metaphysical interpretations of the physical inspired by contemporary physics could open new avenues to be explored, and, perhaps, help make progress on important conundrums in the field, such as the problem of mental causation. It seems to me that there are no good reasons not to follow this path.

Is the mind foreign to the measurement problem?

Which leads us directly to the second point, i.e., the first thesis sketched above: that the mind is relevant in interpreting quantum mechanics. The idea was initially proposed by some physicists as a solution to the measurement problem — the problem of reconciling the theoretical structure of quantum mechanics, which describes non-local “superpositions of states,” with actual phenomena, where no superposition is ever observed. The theoretical structure does all the predictive job, so to speak (apart from the Born rule, which maps the structure with outcome probabilities [9]) and ultimately, the fact that no superposition exists for measured quantities is only ascertained by our conscious observation. Hence the idea that it is the mind which makes the wave-function “collapse.” Of course there are other, less anthropocentric theories, such as Bohm’s, Ghirardi-Rimini-Weber [10] or the infamous many-worlds interpretation [11].

The main type of objection against interpretations involving an observer, I would say, is that they seem too reminiscent of either 19th century Idealism or early 20th century neo-Kantian and phenomenalist views (which did strongly influence said physicists). These doctrines have declined in favor of a renewal of scientific realism in the course of the 20th century.

From a realist perspective, such interpretations seem to attribute a privileged ontological status to the human brain, which is increasingly not acceptable. Was there really no definite reality before life appeared on earth? Does the moon vanishes when no one is looking? All this seems barely good enough for mystics and new age gurus (there might be more sensible anti-realist interpretations, but let’s not quibble…) However, having previously rejected the idea that phenomenal aspects of consciousness are to be addressed by biology, all of this is easily defused: a privileged ontological status of human observers only makes sense for those who pretend that biology can inform deep metaphysical questions.

Let me be more specific and draw on an example. I suggested that phenomenal aspects of consciousness could eventually be explained under a proper interpretation of physics. A possible such explanation could take the form of panpsychism: the idea that, somehow, all matter is conscious. In fact, by distinguishing phenomenal aspects from cognitive aspects of consciousness and relegating the former to physics and the latter to biology or psychology, we would have something like panphenomenalism: the idea that all matter is “phenomenal.” Anyway, in the context of either panpsychism or panphenomenalism, granting a particular role to phenomenality in physics, say, in the collapse of the wave function, does not amount to granting a privileged ontological status to the brain.

Perhaps panpsychism is implausible, but panphenomenalism fares a bit better in my opinion. Obviously, tables and chairs are not conscious. Following panphenomenalism, what they lack is not phenomenality (which would be a feature of their fundamental constitution) but cognitive abilities. Phenomenality without memory, persistence, information integration and a capacity for world and self representation is simply not awareness, or not full awareness — it is at best being transiently aware of nothing identifiable, without the very possibility of knowing that one is or was aware,nothing close to consciousness. I would readily grant this feature to electrons if it could convincingly explain some relevant metaphysical issue.

Another frequent objection against panpsychism is the so-called combination problem: if phenomenal aspects are present in the microscopic constituents of reality, how is it that we have a unified phenomenal experience? I don’t have an answer to this question, but it is not specific to panpsychism (it is a version of the binding problem also found in computational theories of mind, for example). My guess is that it has something to do with a link between quantum entanglement and cognition, perhaps in line with Tononi’s integrated information theory [12], but this is pure speculation. In any case, quantum holism, if accepted, seems to provide a good basis to answer this [13], whatever quantum-mind theory we endorse.

At any rate, although I find it attractive, my goal is not to convince you that panphenomenalism is the one true theory of mind, but to illustrate the fact that one can make sense of an involvement of the mind in the interpretation of quantum mechanics without falling back into Idealism. And, of course, there are other alternatives too, such as Eccles’ dualism for example, or Stapp’s kind-of dual aspect theory, or perhaps some versions of neutral monism.

Another common objection to considering a role of the observer in the measurement problem is that it involves non-locality, which is at odds with Lorentz invariance in special relativity. This is actually a potential problem for most collapse interpretations of quantum mechanics (but apparently, GRW theory does not face it). However, invoking phenomenal aspects in a solution to the measurement problem does not necessarily involve an objective wave-function collapse: it could involve, say, a relational or a modal interpretation of quantum mechanics [14]. Which interpretation of quantum mechanics best fits our needs to account for phenomenal aspects depending on which theory of mind we endorse is precisely the kind of question which should be addressed in the philosophy of mind.

In sum, my goal is not to defend one or the other interpretation of quantum mechanics, nor to defend one or the other theory of mind, but rather to stress the relevance and potential fruitfulness of discussions relating these two domains of inquiry. The hard problem of consciousness and the measurement problem in quantum mechanics share a strong conceptual affinity: both concern the relations between physical structure and phenomenal aspects of reality, broadly construed. Either the world viewed from the mind, or the mind viewed from the world, if you like. This conceptual affinity should not be neglected on the ground of unfounded suspicions of Idealism or anti-realism or any other similar concern. The example of panphenomenalism above shows that a common treatment to both problems might be explored without presenting insurmountable obstacles, something worth pondering.

Yet, in spite of the conceptual affinity between these two central problems of philosophy, talk of quantum mechanics in the philosophy of mind is often brushed aside. At the same time, talk of consciousness and rational agents in, say, discussions on the many-worlds (or many-minds) interpretation of quantum mechanics is ubiquitous, and difficult to avoid. Both camps act as if important issues in the other camp were already settled. This is a strange situation. Aren’t we perhaps missing something by being too compartimentalized? One of the main roles of philosophy — and metaphysics in particular — is after all to provide a unified picture of the world. Is it inconceivable that some considerations in the philosophy of mind (or other areas of philosophy) might inform our interpretations of physics as much as the converse?

Is quantum mechanics useful at all?

To conclude, let me address a final worry that I have so far left aside: that quantum mechanics is of no help in explaining the mind at all. I don’t know about the debate concerning the relationship between free-will and randomness — except that randomness in quantum mechanics is closely tied to the measurement problem, and that what we mean by “randomness” is also up to interpretation. (Shouldn’t we say “unpredictability” instead? Or shall I suggest “physical privacy”?)

Besides, I do not claim that quantum mechanics can explain consciousness. My argument is more modest: the question of phenomenal aspects of consciousness should be addressed in relation to quantum mechanics, because only our best physics can inform such metaphysical questions, and because quantum effects are not necessarily confined to the microscopic realm. Moreover, it should be addressed in relation to the measurement problem, because they share conceptual affinities, and because the “threat” of Idealism is unfounded. All I claim is that a suitable metaphysical interpretation of quantum mechanics could eventually explain the metaphysical problem of consciousness.

Having said that, some features of quantum mechanics such as non-locality/holism or the no-cloning and the free-will theorem [15], could eventually help address some questions in the philosophy of mind, such as the binding problem or the problem of causal exclusion.

In light of this, quantum mechanics certainly deserves more consideration in the philosophy of mind. In my view, claiming that quantum effects reduce to “microscopic noise” simply disregards the epistemic depth of the measurement problem, just as claiming that the problem of consciousness is essentially biological disregards its ontological depth. These two “dogmas” of philosophy of mind are mutually reinforcing and we should reject them altogether if we want to make sense of consciousness as well as of quantum mechanics.

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Quentin Ruyant is a PhD student in philosophy of science in Rennes, France and former engineer. He maintains a blog dedicated to the popularization of philosophy of science (in French)

[1] Quantum approaches to consciousness, Stanford Encyclopedia of Philosophy.

[2] Macroscopic entanglement witnesses.

[3] Deconstructing decoherence.

[4] Our mathematical universe;  and Why physicists are saying consciousness is a state of matter, like a solid, a liquid or a gas.

[5] See “The completeness of the physical,” in Mental causation, Stanford Encyclopedia of Philosophy.

[6] Every Thing Must Go: Metaphysics Naturalized.

[7] No-cloning theorem.

[8] The Conscious Mind: In Search of a Fundamental Theory.

[9] The Born rule.

[10] On collapse theories and the Ghirardini-Rimini-Weber model.

[11] See this recent essay by Sean Carroll about why the many-worlds interpretation of QM is not that crazy after all.

[12] Integrated information theory.

[13] See: Holism and nonseparability in physics, Stanford Encyclopedia of Philosophy.

[14] Modal interpretations of quantum mechanics and Relational quantum mechanics, Stanford Encyclopedia of Philosophy.

[15] Free will theorem.