Why physicists got involved

Quantum mechanics has a famous puzzle at its heart, the measurement problem: the theory describes systems as superpositions of possibilities, yet we always observe definite outcomes. Some early founders of the theory, including John von Neumann and later Eugene Wigner, discussed whether the observer’s consciousness might play a role in that transition. Most physicists today reject that reading, but it created a lasting link in the public imagination.

Orch OR (Penrose and Hameroff)

Speculative The most developed proposal. It reverses the old idea: instead of consciousness causing collapse, a physical collapse process (objective reduction) inside neuronal microtubules gives rise to moments of consciousness. Read the full guide: Orch OR explained, and the biology behind it: microtubules and consciousness.

Henry Stapp and the participating observer

Speculative The physicist Henry Stapp developed an interpretation in which conscious intention influences brain processes through repeated quantum observations (an application of the “quantum Zeno effect”). It is a philosophical interpretation more than an experimental programme, and critics argue that it faces the same decoherence problems as other brain-scale quantum models.

Quantum cognition: not what it sounds like

Debated Since the 2000s, researchers such as Jerome Busemeyer and Peter Bruza have used the mathematics of quantum probability to model human judgements that violate classical probability, such as order effects in surveys. These models make no claim that neurons perform quantum computation. They are useful as descriptive tools and are debated as theories of reasoning.

The main objections

• Decoherence. Warm, wet tissue should destroy quantum superpositions extremely quickly.
• Explanatory gap. Even if quantum processes occurred in the brain, it is not obvious why they would explain experience any better than classical ones.
• Parsimony. Classical neuroscience already accounts for many features of consciousness without quantum effects.

How to spot quantum hype

Be wary when “quantum” is used to promise healing, manifestation or instant transformation, when no equations, experiments or peer-reviewed papers are cited, or when the claim cannot say what result would prove it wrong. Real quantum proposals about the mind are cautious, specific and openly debated.

Guides in this section