Why people link consciousness and quantum physics
The link has two sources. One is the measurement problem: in quantum mechanics, a system seems to have definite properties only when measured, and early physicists such as John von Neumann and Eugene Wigner wondered whether the observer's mind plays a role. The other is the hard problem of consciousness: if ordinary neuroscience cannot explain why experience exists, perhaps a deeper layer of physics can.
Most physicists today separate the two. Measurement does not require a conscious observer; any interaction with the environment will do. But the second motivation keeps quantum theories of mind alive.
The main proposal: Orch-OR
Roger Penrose argued in The Emperor's New Mind (1989) that human understanding is not an algorithm, and therefore needs physics beyond standard computation. With the anaesthesiologist Stuart Hameroff he developed Orchestrated Objective Reduction (Orch-OR): quantum superpositions form in microtubules, protein tubes inside neurons, and collapse when a gravity-related threshold is reached. Each orchestrated collapse would be a moment of experience.
The theory makes contact with data: general anaesthetics bind to many proteins, including tubulin, the building block of microtubules, which fits Hameroff's view that anaesthesia works by blocking quantum processes there.
The decoherence objection
Quantum superpositions survive only while isolated from their environment. In 2000 Max Tegmark estimated that in the warm, wet brain, superpositions in neurons or microtubules would last roughly 10⁻¹³ to 10⁻²⁰ seconds (Physical Review E 61, 4194). Neural processing runs on the scale of milliseconds, a gap of ten or more orders of magnitude. Hameroff and colleagues replied that Tegmark modelled the wrong states and ignored shielding; the dispute continues.
What experiments show
- Quantum biology is real in places. Enzymes use tunnelling, and bird magnetoreception most likely relies on quantum spin states in cryptochrome proteins. These show that biology can exploit quantum effects; whether the brain does so for consciousness is a separate question.
- Microtubules and anaesthesia. In a 2024 rat study (eNeuro), a drug that stabilises microtubules delayed loss of consciousness under the anaesthetic isoflurane. It is consistent with Orch-OR's prediction, and also with less exotic explanations.
- Gravity-related collapse. A 2020 experiment in the Gran Sasso underground laboratory searched for faint radiation predicted by the simplest Diósi–Penrose collapse model and found none (Nature Physics, 2021), ruling that version out. Orch-OR relies on a related but not identical mechanism.
- Entanglement in the brain. A 2022 MRI study claimed a signal of entanglement in the brain; it has not been independently confirmed and its interpretation is contested.
What would decide it
A convincing case would need a quantum effect that lasts long enough to influence neural firing, measured in living brain tissue, and shown to track conscious states rather than just anaesthesia chemistry. No experiment has done that yet.
The research programme on this site does not depend on quantum effects in the brain. It treats consciousness as a question about how information is addressed and read in a network, and its preprint defines a consciousness measure, Φ_PA, on a classical computational substrate. See the hard problem of consciousness for how the main theories compare.
Bottom line
Consciousness may or may not involve quantum effects; the evidence does not currently require them. Orch-OR is the most developed quantum proposal and has become more testable, but decoherence remains its main obstacle.