Quantum
QBism’s Primitive, Participatory Experience: Quantum Agency and the First-Person World
Experience as the Primitive of Quantum Theory
QBism (Quantum Bayesianism) is an interpretation of quantum mechanics, not a theory of consciousness, but it puts an agent's personal experience at the foundation of physics. A quantum state is an agent's personal degrees of belief about the consequences of her actions, and a measurement outcome is the new experience that action produces. Experience therefore enters physics as a primitive, which leaves the hard problem unsolved but changes where physics starts.
Christopher A. Fuchs, Rüdiger Schack, Carlton Caves
What consciousness is
QBism does not say what consciousness is; it treats an agent's experience as a primitive term, with a measurement outcome being the experience an action elicits for that agent.
Mind and body
Agents act on a real external world that resists them and responds with something new; experience arises at that interface, and the quantum formalism organizes an agent's expectations about it.
Mechanism
The Born rule is a normative rule of rationality for agents in a quantum world, an empirically discovered extension of Bayesian coherence, rather than a law of nature.
Core claims
- A quantum state is an agent's personal probability assignment about the consequences of her actions, not a property of the system.
- A measurement is any action an agent takes on the world, and its outcome is the experience it elicits.
- In Wigner's-friend scenarios, the friend's outcome is her own experience, and an outside agent need not treat it as an observer-independent fact before interacting with her.
- Representing states through symmetric informationally complete measurements lets the Born rule be read as a modified form of classical probability coherence.
Criticisms
If ‘agent’ means a conscious subject, QBism takes the thing to be explained as a primitive, so quantum theory cannot then explain consciousness. If experience is generalized into elementary events across nature, QBism inherits the combination problem of panpsychism.
Implications
- AI consciousness: Uncertain
- QBism supplies no criterion for which physical systems are conscious agents, so it cannot settle whether an artificial system would be one.
Related theories
- Wigner–von Neumann’s Consciousness-Collapse: Experience at the Quantum Cut (Contrast)
- James’s Radical Empiricism of Monistic Pure Experience (Influence)
- Merleau-Ponty's Embodied Perception and the Lived Body (Overlap)
- Gefter’s Enactive-QBist Engagement (Extension)
Sources
- An introduction to QBism with an application to the locality of quantum mechanics, Christopher A. Fuchs, N. David Mermin, Rüdiger Schack (2014)
- Quantum-Bayesian coherence, Christopher A. Fuchs, Rüdiger Schack (2013)
- QBism and the Greeks: Why a quantum state does not represent an element of physical reality, Christopher A. Fuchs, Rüdiger Schack (2015)
- Quantum measurement and the Paulian idea, Christopher A. Fuchs, Rüdiger Schack (2014)
- On participatory realism, Christopher A. Fuchs (2016)
- QBism, where next?, Christopher A. Fuchs (2023)
- QBism, polishing some points, Christopher A. Fuchs, B. C. Stacey (2025)
- Born’s rule as a quantum extension of Bayesian coherence, J. B. DeBrota, Christopher A. Fuchs, J. L. Pienaar, B. C. Stacey (2021)
- Quantum dynamics happens only on paper: QBism’s account of decoherence, J. B. DeBrota, Christopher A. Fuchs, Rüdiger Schack (2024)
- When will two agents agree on a quantum measurement outcome? Intersubjective agreement in QBism, Rüdiger Schack (2023)