Quantum & Dimensions—Overview

Quantum theories of consciousness take seriously the idea that quantum mechanics plays a necessary, if not sufficient, role in the specific generation of phenomenal consciousness in certain physical entities like brains—beyond the general application of quantum mechanics in all physical entities. The kinds of quantum theories or models on offer differ radically.

Most well-known in contemporary theories of quantum consciousness is the Penrose-Hameroff Orchestrated Objective Reduction (Orch OR), formulated in the mid-1990s. The hypothesis fundamentally bridged non-computable spacetime geometry and cellular neurobiology by proposing that consciousness arises from gravitationally induced quantum-state reductions localized within the hydrophobic pockets of neuronal microtubules. The theory initially faced severe, seemingly fatal criticism from the mainstream physics and neuroscience communities—most notably through formidable decoherence arguments asserting that the brain’s "warm, wet, and noisy" environment would instantaneously collapse delicate quantum superpositions long before neurophysiological timescales could be reached. Despite this profound early skepticism, Orch OR has demonstrated remarkable conceptual resilience over the ensuing three decades, evolving to incorporate mechanisms like topological error correction to defend its viability. In recent years, this theoretical tenacity has been invigorated by tangible, albeit nascent, experimental support from the burgeoning field of quantum biology, with independent researchers demonstrating long-lived quantum coherence, exciton resonance, and delayed luminescence within microtubule lattices, suggesting that macroscopic quantum states might indeed survive and function within the biological brain.

The Quantum Wave Function Collapse Theory

The theory that consciousness causes the collapse of the quantum wave function—that the linear Schrödinger dynamics cannot by itself yield a determinate measurement outcome, and that the chain of physical interactions running from measured system through apparatus and nervous system terminates only when a conscious observer registers a result—is conventionally credited to John von Neumann and Eugene Wigner in that order, and is standardly labeled the von Neumann-Wigner interpretation. In Mathematische Grundlagen der Quantenmechanik (1932/1955), von Neumann distinguished two irreducibly different modes of state change: continuous, deterministic, reversible unitary evolution, and the discontinuous, probabilistic, irreversible transition associated with measurement. Nothing in the formalism specifies when one applies rather than the other. Because treating an apparatus quantum-mechanically merely entangles it with the measured system, and treating the observer's retina and cortex the same way extends the entanglement further, the boundary at which collapse is introduced can be placed anywhere along this causal chain without altering any empirical prediction—a theorem, not a convention. Von Neumann used it to secure the principle of psycho-physical parallelism—the requirement that subjective perception and physical reality stay in correct correspondence—rather than to assign consciousness a causal role. Twenty-nine years later, Wigner (1961) made the commitment von Neumann had withheld, holding that quantum mechanics cannot be consistently formulated without reference to consciousness. His "Wigner's friend" thought experiment dramatized the point: a friend measuring inside a sealed laboratory must, on the universal application of the formalism, be described from outside as superposed between having seen one outcome and the other, yet afterward reports a single determinate experience and reports having had it at the time. A minority of philosophical and historical treatments invert the order—to the “Wigner-von Neumann interpretation”— on the ground that Wigner alone explicitly linked consciousness to collapse.

The explicit thesis that consciousness terminates the quantum measurement chain was first published not by Eugene Wigner in 1961 but by Fritz London and Edmond Bauer in 1939, in the short French monograph La théorie de l'observation en mécanique quantique, and the twenty-two-year gap is not the only reason their priority claim is strong. Their analysis supplies the argumentative template Wigner later dramatized: treating object, apparatus, and observer as a composite, they show that unitary evolution leaves all three entangled with no determinate outcome anywhere in the compound state, then locate the resolution in something the observer alone possesses—a faculty of introspection by which he takes immediate cognizance of his own state and, on the strength of that immanent knowledge, separates himself from the composite. This is far more explicit than anything in von Neumann, who named the observer's "abstract ego" as one possible terminus of the chain but ascribed no power to it, and who Becker (2004) argues did not regard collapse as a physical process at all. Wigner acknowledged the priority, citing the London-Bauer treatment in a footnote to his 1961 essay. That their names dropped from the standard label owes more to circumstance than substance: the monograph was brief, written in French, and issued in a minor series; Bauer was a laboratory physicist with no program in foundations; London emigrated to Duke that year and turned to superfluidity, never returning to measurement; and no English translation appeared until Wheeler and Zurek's Quantum Theory and Measurement in 1983, by which time Wigner's version had circulated for two decades. One qualification is essential and cuts against the simple priority narrative. London held a doctorate in philosophy, taken before he turned to physics, and French (2002) argues the 1939 account is best read as importing a phenomenological conception of reflective self-awareness into physics rather than positing mind-matter causation. London and Bauer thus have clear priority for making consciousness the explicit terminus of the chain—but not for the interactionist doctrine Wigner defended.

Quantum Features and Conscious Experience

Philosopher of science Paavo Pylkkänen explores whether the dynamical and holistic features of conscious experience might reflect “the dynamic and holistic quantum physical processes associated with the brain that may underlie (and make possible) the more mechanistic neurophysiological processes that contemporary cognitive neuroscience is measuring.” If so, he says, “these macroscopic processes would be a kind of shadow, or amplification of the results of quantum processes at a deeper (pre-spatial or ‘implicate’) level where our minds and conscious experience essentially live and unfold.”

At the very least, Pylkkänen says, “a quantum perspective will help a ‘classical’ consciousness theorist to become better aware of some of the hidden assumptions in his or her approach.” What quantum theory is all about, he stresses, is “learning, on the basis of scientific experiments, to question the ‘obvious’ truths about the nature of the physical world and to come up with more coherent alternatives” (Pylkkänen, 2018).

There is certainly growing interest in the putative quantum-consciousness nexus. For example, Quantum and Consciousness Revisited, with papers the product of two conferences, presents various philosophical approaches to quantum paradoxes, including further considerations of the Copenhagen Interpretation and alternatives with implications for consciousness studies, mathematics, and biology. Topics include observation and measurement, collapse of the wave function, and time and gravity. All the papers, the editors write, “reopen the questions of consciousness and meaning which occupied the minds of the early thinkers of quantum physics” (Kafatos et al., 2024).

Approaches and Applications

In his technical review article, “Quantum Approaches to Consciousness,” theoretical physicist Harald Atmanspacher describes three basic approaches to the question of whether quantum theory can help understand consciousness: (1) consciousness as manifestation of quantum processes in the brain, (2) quantum concepts elucidating consciousness without referring to brain activity, and (3) matter and consciousness as dual aspects of one underlying reality (Atmanspacher, 2020a).

For example, one approach considers how quantum field theory can describe why and how classical behavior emerges at the level of brain activity. The relevant brain states themselves are properly considered as classical states. The idea, Atmanspacher says, is “similar to a classical thermodynamical description arising from quantum statistical mechanics” and works “to identify different regimes of stable behavior (phases, attractors) and transitions between them. This way, quantum field theory provides formal elements from which a standard classical description of brain activity can be inferred” (Atmanspacher, 2020a).

Atmanspacher reports applications of quantum concepts to mental processes, focusing on complementarity, entanglement, dispersive states, and non-Boolean logic. These involve quantum-inspired concepts to address purely mental (psychological or cognitive) phenomena, without claiming that actual quantum mechanics is necessary to make it work. This includes research groups studying quantum ideas in cognition (Patra, 2019).

While the term “quantum cognition” has gained acceptance, Atmanspacher says that a more appropriate characterization would be “non-commutative structures in cognition,” and he questions whether it is “necessarily true that quantum features in psychology imply quantum physics in the brain?” (Atmanspacher, 2020a).

After reviewing major quantum theories of consciousness (several are discussed below), Atmanspacher suggests that progress is more likely made by investigating “mental quantum features without focusing on associated brain activity” (at least to begin with). Ultimately, he says, “mind-matter entanglement is conceived as the hypothetical origin of mind-matter correlations. This exhibits the highly speculative picture of a fundamentally holistic, psychophysically neutral level of reality from which correlated mental and material domains emerge” (Atmanspacher's Dual-Aspect Monism).

To position quantum theories of consciousness, consider each as representing one of two forms: (i) quantum processes, similar to those in diverse areas of biology (e.g., photosynthesis), that uniquely empower or enable the special activities of cells, primarily neurons, to generate consciousness; and (ii) the more radical claim that these two great mysteries, consciousness and quantum theory, are intimately connected such that the solution to both mysteries can be solved only together.

Competing Theories and Critiques

Physicist Carlo Rovelli disagrees. Consciousness and quantum mechanics, he says, have no special, intimate relationship. With respect to quantum mechanics, Rovelli says, “Consciousness never played a role … except for some fringe speculations that I do not believe have any solid ground. The notion of ‘observer’ should not be misunderstood. In quantum physics parlance an ‘observer’ can be a detector, a screen, or even a stone. Anything that is affected by a process. It does not need to be conscious, or human, or living, or anything of the sort” (Rovelli, 2022).

Philosopher of physics David Wallace sees “potentially intriguing connections between consciousness and quantum mechanics, tied partly to the idea that traditional formulations of quantum mechanics seem to give a role to measurement or observation—and, well, what is that?” He says, “the natural hypothesis is that measurement or observation is conscious perception,” which somehow implies “a role of a conscious observer.” Although this would be “extremely suggestive for connecting the two”—consciousness and quantum mechanics—“but you can connect them in a lot of ways.” Some, Wallace says, might try to explain consciousness reductionistically in terms of quantum mechanical processes. But, “In my view, that works no better than explaining consciousness in terms of classical processes.”

However, “Another way is not try to reduce consciousness, but find roles for consciousness in quantum mechanics. That's one of the big questions about consciousness. What does it do? What is it here for? How can it affect the physical world? So, I'm at least taking seriously the idea that maybe consciousness plays a potential role in quantum mechanics. It's a version of the traditional idea that consciousness collapses the wave function. It's not an especially popular idea among physicists these days, partly because it takes consciousness as fundamental—but if, like me, you think there are independent reasons to do that, then I think it's an avenue worth looking at” (Wallace, 2016b).

Chalmers and McQueen readdress the question of whether consciousness collapses the quantum wave function. Noting that this idea was taken seriously by John von Neumann and Eugene Wigner but is now widely dismissed, they develop the idea by combining a mathematical theory of consciousness (Integrated Information Theory, 12) with an account of quantum collapse dynamics (continuous spontaneous localization). In principle, versions of the theory can be tested by experiments with quantum computers. The upshot is not that consciousness-collapse interpretations are clearly correct, but that there is a research program here worth exploring (Chalmers and McQueen, 2022).

More recently, McQueen supported claims by philosopher of physics Emily Adlam and her colleagues who “have examined the idea of purely quantum agency, which is a prerequisite for consciousness, and found it doesn’t work…. Adlam and team formulated a minimal definition of agency using clear physical requirements. Quantum theories of consciousness, even if they focus on specific mechanisms in the brain, like in Penrose and Hameroff’s proposal, ought to be compatible with this definition if they are to be plausible…. ‘There will be a step in terms of taking information out of the environment that you’re going to respond to, and then some kind of [information] copying steps,…,’ says Adlam. But if the agent is quantum—so must behave according to the laws of quantum mechanics—the copying step is impossible. This is because of the “no-cloning theorem”, which says that quantum states that describe all information about a system can’t be copied or duplicated….These conclusions challenge quantum theories of agency, free will and consciousness, as well as impose technological constraints on any agents that quantum computers may be able to simulate in the future, said team member Kelvin McQueen… ‘These results help us understand how agency and human-like perception can emerge in an otherwise quantum mechanical universe,’ he said (Padavic-Callaghan, 2026).

Physicist Tim Palmer argues that our ability for counterfactual thinking—the existence of alternative worlds where things happen differently—which is both an exercise in imagination and a key prediction of quantum mechanics—suggests that “our brains are able to ponder how things could have been because in essence they are quantum computers, accessing information from alternative worlds” (he recruits the Many Worlds Interpretation of quantum mechanics). Consciousness (along with understanding and free will), he states, “involves appealing to counterfactual worlds,” and thus “quantum computing is the key to consciousness” (Palmer, 2023).

At the very least, for quantum processing to play a content or informational role in the brain, it would require some mechanism that stores and transports quantum information in qubits for sufficiently long, macroscopic times. Moreover, the mechanism would need to entangle vast numbers of qubits, and then that entanglement would need to be translated into higher-level chemistry in order to influence how neurons trigger action potentials (Ouellette, 2016). Experiments with anesthetics and brain organoids hint that quantum effects in the brain may be in some way involved in consciousness (Musser, 2024).

Although most physicists and neuroscientists have not taken quantum theories of consciousness seriously, such theories are proliferating, becoming more sophisticated and mainstream, and are increasingly backed up by claims of experimental evidence. Personally, I [RLK] started out an incorrigible, utter skeptic about quantum consciousness; I'm still a skeptic, though no longer so incorrigible, no longer so utter.