Can Science Explain Consciousness?

Taking physicalism seriously

Scientific progress has led to a physical explanation of an increasing number of phenomena. Phenomena that once seemed mysterious—like the propagation of light in vacuum or the spread of cholera in a population—have come to be understood in physical terms. It is therefore natural to ask: can physicalism explain everything?

The phenomenon most often claimed to resist a physical explanation is consciousness. We don’t fully understand it. It feels inherently private and subjective (Goff, 2019) and intuitively, it might seem impossible to explain in terms of physical processes like neural activity. However, we shouldn't let intuition settle the matter. Science provides a framework for comparing and evaluating theories, and we should apply that framework to the study of consciousness.

In this essay, I argue that doing so leads us to physicalism: the view that conscious experience is grounded in processes described by modern physics. This is not because physicalism already provides a complete account of consciousness, but rather because its alternatives rely on weak intuitions—and because physicalism offers the most promising starting point for understanding how consciousness fits into the natural world.

§ Physicalist views on consciousness

Physicalism about consciousness is the view that mental states supervene on physical states—that there can be no change in conscious experience without some underlying physical change. Physicalism encompasses a range of views, from identity theories that equate conscious states with particular brain states (Place, 1956; Smart, 1959), to functionalist accounts that treat consciousness as arising from certain patterns of causal interaction that could, in principle, be realised in different substrates (Putnam, 1960). All those theories share three characteristic commitments:

• Attitude toward science—Consciousness should be studied with the same empirical and theoretical tools we use to study other complex phenomena.

• Predictions about the future—As neuroscience and cognitive science progress, they will increasingly explain conscious experience in physical terms.

• Ontological claim—There are no non-physical substances or properties that are needed to explain consciousness.

Physicalism doesn’t claim that we already fully understand consciousness. Rather, it argues that we have good reasons to believe that closing the epistemic gap will close the explanatory gap—that as we learn more about consciousness, it should become increasingly clear that consciousness is part of the physical world.

§ What a theory of consciousness should explain

Defining the explanatory targets for a theory of consciousness provides a clear basis for comparison: we can consider how well each proposal answers these questions or how likely it is to answer them in the future. Any adequate theory of consciousness must address at least three questions:

• The origin question: What kinds of processes or conditions give rise to conscious experience?

• The metaphysical question: How does consciousness relate to the physical world?

• The content question: Given a particular physical stimulus, what kind of conscious experience does a system have?

So far, physicalism is the only framework that engages all three explanatory tasks. Physicalist theories—such as Global Neuronal Workspace (Baars, 1988; Dehaene et al., 1998) and Recurrent Processing Theory (Lamme, 2006)—propose candidate mechanisms that spell out how physical states give rise to conscious experience. Moreover, physicalism explains the relation between mental and physical states via supervenience: high-level, mental states depend on—or as philosophers say, weakly emerge from—lower-level, physical facts, while displaying coarse-grained regularities, and without multiplying the ontology or appealing to anything supernatural. It introduces no new substances or forces, so the “interaction problem” that dualism faces simply doesn’t arise. Finally, science has made remarkable progress on predicting the contents of experience by mapping physical configurations of brain states to reported experiences. All these predictions can be falsified when compared against further data.

§ The argument for physicalism

In the absence of a complete theory of consciousness, four considerations favour physicalism as the most promising route: (i) history shows that mysteries eventually yield to physical explanations, (ii) contemporary science leaves no room for non-physical causes, (iii) non-physicalist arguments rely on unreliable methodology, and (iv) physicalism is the simplest framework consistent with the data.

The argument from the history of science—Scientific progress has followed a clear, consistent pattern: phenomena once regarded as irreducibly “mysterious” have been repeatedly explained without invoking non-physical properties. Heat turned out to be molecular motion; lightning, an electrical discharge; genetics, a matter of nucleic acids and protein synthesis. Each time, alleged exceptions have been confronted by careful experiments. Physicalism has come to underly special sciences.

Vital-force theory offers a relevant prededent. Nineteenth-century biologists invoked a non-physical vis vitalis (Bergson, 1911) to account for the divide between living and non-living matter. The synthesis of urea from inorganic reagents (Wöhler, 1828), the discovery of metabolic pathways, and the molecular explanations for development, heredity, and homeostasis steadily replaced that intuition. Life now sits comfortably within biochemistry and physics; no extra “life stuff” is required.

Nothing in this record suggests the need for non-physical ingredients. On the contrary, the accumulation of successes makes it increasingly rational to expect that consciousness, too, will eventually yield to the same explanatory strategy.

The causal closure of the physical—There is certainly much of physics remaining to be discovered—for example, we are yet to understand how information is preserved when black holes evaporate and how the Big Bang led to the rich structure necessary for life. Such problems are characterised by regimes of high energy scales with both quantum mechanical and gravitational effects. These conditions are very different to the conditions encountered by everyday life. In the specific regime covering the particles and forces that make up human beings and their environments, we have good reason to think that all of the ingredients and their dynamics are understood to extremely high precision. (Carroll 2022)

Science, therefore, strongly implies that physical events have purely physical causes (Papineau, 1995), at least in the regime relevant to human life. This leaves no room for mental events to cause physical effects. We are therefore presented with three options:

• We can deny the causal closure of the physical and modify the known laws of physics.

• We can accept the causal closure of the physical and posit that mental events have no physical effects.

• We can just accept that mental events have physical effects and are physical.

The first option is in line with property dualism (Chalmers, 2003b) and may appeal to those who wish to stay within a broadly naturalistic worldview while holding that phenomenal qualities are irreducible features of reality. This approach cannot be ruled out a priori; however, by denying the causal closure of the physical and maintaining that mental events have physical effects, we are forced to modify the existing laws of physics.

Carroll (2021) outlines in detail what such a modification should look like. The relevant theory that must be modified—the Core Theory—in principle allows for modifications. However, any proposed modification must be held to the same standards of rigour and experimental scrutiny that physics is held to. It must specify how it modifies both the ontology and the dynamics of our current theory, and it must be formulated quantitatively and precisely, while remaining compatible with experimental data. As Carroll (2021) points out, that should include modifications of the dynamics that obey unitarity, locality, particular symmetries, and conservation laws—unless, of course, we are prepared to throw our entire scientific picture out the window.

Such significant revisions are a serious and ambitious undertaking, and should not be adopted without compelling evidence.

The argument from methodology—The non-physicalist case rests on a conviction that physics, though adequate for every other domain, cannot capture the intrinsic phenomenal character of experience. This claim is grounded almost entirely in introspection—direct awareness of one’s own mental states—which seems to reveal irreducible “feels” or “qualia”. (Peirce, 1866; Lewis, 1929)

However, there is no good reason to believe that evidence from introspection is epistemically equal to, let alone superior to, the results of empirical investigation as a guide ti the metaphysical nature of consciousness. As Dennett (2021) argues, the intuition of non-physical qualia is unreliable: it is a cognitive illusion that misleads us about mental properties, analogous to an optical illusion which misleads us about visual properties. It might present a compelling appearance, but that appearance doesn’t track any metaphysically special properties.

The argument from parsimony—Some readers may remain unconvinced by the earlier considerations, yet recoil at the prospect of rewriting all of physics. Those readers may favour a second option: accept the causal closure of the physical while denying that mental events have physical effects.

One could posit an additional “mental field”, associated with an extra force, that never interacts with the known physical fields. Such epiphenomenalism—where mental states are causally inert—is self-undermining. It commits us to the existence of purely mental entities that leave physical dynamics unchanged, even though our conventional understanding suggests that consciousness shapes behaviour: we notice, react, and talk about our subjective experiences. Any construal of consciousness in which conscious experience has no causal impact on human behaviour is not capturing what we really care about. (Carroll, 2021)

This move introduces additional ontological commitments without yielding credible empirical insights. The only evidence for causally inert qualia is introspection, yet introspective reports are themselves physical events—verbal utterances, neural firings, or behavioural dispositions. If a mental field cannot influence those events, it fails to explain them. Epiphenomenalism therefore unnecessarily augments ontology with entities of no predictive or explanatory role. Physicalism, which avoids additional ontological entities beyond necessity, therefore remains the more economical and compelling option.

§ Final thoughts

To start with the least-well-understood aspects of reality and draw sweeping conclusions about the best-understood aspects is arguably the tail wagging the dog. — Carroll (2021)

Taken together, these arguments suggest that physicalism is most likely to advance our understanding of consciousness. The most promising route to understanding consciousness is likely to involve further neuroscientific insights and a more refined philosophical understanding of weak emergence, rather than revising our fundamental picture of reality. Epistemic humility urges us to start with the simplest hypothesis that fits the data and hold every extra postulate to strict evidential scrutiny. For consciousness, that hypothesis is physicalism. Absent reliable data to the contrary, we should presume that conscious experience arises from—and can, in principle, be explained by—the same physical processes that already account for every other observed phenomenon, remaining ready to revise this stance only if robust empirical findings demand it.

Acknowledgments

This essay draws largely from Carroll (2021).

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