Why is there “something it is like” to be? Neuroscience explains how — but not why — consciousness arises. Can quantum physics offer new solutions to the impossible problem?
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A question in Tucson that changed philosophy
In the summer of 1994, at the University of Arizona in Tucson, a young Australian philosopher stood before an audience of neuroscientists and physicists. His name was David Chalmers and his question was simple: "Why is the processing of information in the brain accompanied by subjective experience?" The room fell silent. The question was not about how the brain distinguishes colours or processes sounds — those were the “easy problems.” It was about something deeper: why is there “something you feel” when you see the colour red?
A year later, in 1995, Chalmers published the landmark paper "Facing Up to the Problem of Consciousness" in the Journal of Consciousness Studies. There he explicitly distinguished for the first time the “easy” from the “hard” problem of consciousness — a distinction that shook both the philosophy of mind and neuroscience.
The easy problems — and the impossible one
The easy problems concern mechanistic explanations: how neural signals travel from finger to brain, how visual information is filtered in the cortex, how a word is retrieved from memory. They are technically difficult, but in principle analysable through structures and functions.
The hard problem is different. Even if we explain every neuronal connection, every chemical reaction, and every electrical signal in the brain, a gap remains: why are these processes accompanied by lived experience? Why does pain “hurt” instead of being merely an electrical signal? Chalmers argued that solving the easy problems does not automatically lead to solving the hard one — consciousness contains something that escapes physical description.
From Nagel to qualia — the precursors
Chalmers was not the first to recognise the difficulty. In 1974, philosopher Thomas Nagel published the famous essay "What Is It Like to Be a Bat?", arguing that experiences are essentially subjective — accessible only to the one who lives them. Even if we learned everything about a bat's sonar, we would not know what it “feels like” to be a bat.
In 1983, Joseph Levine introduced the concept of the "explanatory gap": even if consciousness is physical, we cannot explain how neuronal events produce subjective qualities — the so-called qualia. Qualia are what make red “look red,” pain “hurt,” and music “sound” in a unique way to each person.
A classic thought experiment, known as "Mary's Room," reveals the deeper difficulty: Mary knows everything about the physics of colour but has always lived in a black-and-white room. When she sees something red for the first time, she learns something new — knowledge that no physical fact had given her.
The quantum proposal — Penrose and Hameroff
In the early 1990s, mathematician and physicist Roger Penrose proposed a radical idea: consciousness cannot be explained by algorithmic computational processes. In his book The Emperor's New Mind (1989), he invoked Gödel's incompleteness theorems to argue that human mathematical understanding exceeds any computable algorithm.
Penrose identified in wave function collapse a possible basis for non-computable processes. He proposed “objective reduction” (OR), according to which quantum superpositions collapse on their own when the difference in spacetime curvature exceeds a certain threshold, at the Planck scale. This time is given by the relation τ ≈ ℏ / EG, where EG is the gravitational self-energy of the superposition.
Anaesthesiologist Stuart Hameroff proposed that microtubules — structural protein elements inside neurons — could host quantum processing. Microtubules are composed of tubulin dimers that contain hydrophobic pockets with π electrons — possibly close enough to become quantum entangled. The Penrose-Hameroff collaboration gave birth to the Orch-OR (Orchestrated Objective Reduction) theory: consciousness arises from orchestrated quantum collapse within microtubules.
Criticism and experimental evidence
The Orch-OR theory faced fierce criticism. In 2000, physicist Max Tegmark calculated that quantum coherence in microtubules would be lost in femtosecond timescales — trillions of times faster than the milliseconds needed for neural processing. Patricia Churchland commented sarcastically: "Pixie dust in the synapses is about as explanatorily powerful as quantum coherence in the microtubules."
However, more recent experiments reinvigorated the debate. In April 2022, two teams — one led by Jack Tuszyński (University of Alberta) and the other by Gregory Scholes and Aarat Kalra (Princeton) — announced experimental evidence of quantum vibrations in microtubules. The Tuszyński team showed that anaesthetics accelerate the quenching of delayed luminescence in microtubules, while the Scholes team found that laser excitation diffuses through microtubules far more than expected — a phenomenon that disappears under anaesthesia.
Conversely, a group of Italian physicists in 2022 failed to detect spontaneous radiation emissions predicted by the Diósi-Penrose collapse model — although Penrose's original model did not predict such radiation, and therefore was not considered ruled out.
Alternative theories — IIT and Global Workspace
Beyond Orch-OR, Integrated Information Theory (IIT) by neuroscientist Giulio Tononi (2004) proposes that consciousness is identical to the integrated information (Φ) of a system — a mathematically defined quantity. If IIT is correct, it could solve what Scott Aaronson called the “Pretty Hard Problem” — which physical systems are conscious — without however solving the authentic hard problem.
Global Workspace Theory by Bernard Baars proposes that consciousness arises when information becomes globally accessible across many brain subsystems. Chalmers himself observed that this theory explains how information becomes accessible, but leaves unanswered why this accessibility creates lived experience.
The great silence — why we still do not know
Thirty years after Chalmers' formulation, the community remains deeply divided. Daniel Dennett argued that the hard problem would “evaporate” once the easy ones are solved — consciousness resembles a magic trick that creates impressive illusions from ordinary materials. Thomas Metzinger likened the debate to vitalism — a theory that was not “solved” but simply abandoned.
On the other hand, Colin McGinn proposed "new mysterianism": perhaps the human brain, a product of evolution, lacks the cognitive capacities to understand itself — just as a bat cannot grasp relativity.
Quantum physics does not yet offer a definitive answer to the hard problem. Chalmers himself remains sceptical that any new physics can close the gap: "There is no particular reason to believe that a quantum feature generates consciousness, just as there is no reason to believe that a macroscopic feature generates it." The hard problem remains open — the only question in science that asks why nature is experienced rather than simply existing.