Henry Stapp (1928- ) is a quantum physicist who worked with both Wolfgang Pauli and Werner Heisenberg. In his 2004 book Mind, Matter, and Quantum Theory, he develops a psychophysical theory of mind that depends on our modern understanding of reality in the light of quantum mechanics. Stapp moves beyond the ideas of a world of classical material particles obeying the laws of Newtonian physics, in which mental events cannot exist. He challenges the mechanical view of man put in place by René Descartes and strengthened by Isaac Newton's laws of classical mechanics. Free Choice of the Experimenter: Niels Bohr introduced the free choice of the experimenter - who can decide for example to measure the x-component of spin sx, in which case the results will be a + or - value for sx and the other components sy and sz remain undetermined. Paul Dirac commented that it is Nature that decides between + and -. Quantum Zeno Effect: The Quantum Zeno is a direct consequence of the fact, pointed out by Henry Margenau, that a measurement is also a state preparation. When you measure a system and find sx = +, you have also prepared the system in state +. Dirac pointed out that if you measure a system in a known state +, it will be certain to be found in state +. This is called a non-demolition measurement. Quantum Zeno is a rapid series of measurements that keeps preparing the system in the same state. Exactly how consciousness in the relatively large brain can make such quantum measurements is, however, completely unclear. Stapp's unique quantum mechanical contribution to the free will problem is the claim that the observer's free choice of which experiment to perform, combined with the Quantum Zeno Effect, allows the observer, by his own free choices, to hold stably in place a chosen brain activity that would normally fade away. Stapp's ideas are similar in some respects to those of Roger Penrose, David Hodgson, and Michael Lockwood, exploring the implications of quantum-mechanical nonlocality first highlighted in the 1935 Einstein-Podolsky-Rosen (EPR) thought experiment. Stapp notes that in the EPR situation, the combined system of two far-apart particles acts as a single global entity, indicating that what a scientist decides to do in one place can influence how the system reacts to a simultaneous measurement far away, breaking classical local-reductionistic conceptions. Stapp's central idea is that the physical world described by the laws of physics is a 'structure of tendencies in the world of mind.' He builds on Werner Heisenberg's idea of Potentia and John von Neumann's two processes (random and determined), identifying Mind with a creative process inspired by Alfred North Whitehead's Process and Reality. Each wave function collapse represents an event that introduces a novel emergent quality and adds information to human knowledge. Stapp expresses discomfort with the idea that irreducible chance is an ultimate constituent of nature, asserting that 'Man's free will is no illusion. It constitutes his essence. And it rests upon the law of necessity. Any play of chance would falsify the idea that I, from the ground of my essential nature, make a true choice.' Information philosophy notes that chance provides alternative possibilities, while an adequate determinism accounts for selection. Stapp views the brain as a self-programming computer where mutually exclusive, self-sustaining neural patterns carry top-level codes. Conscious acts correspond physically to the selection of one superposed code among many generated by quantum-theoretic laws. Stapp emphasizes that quantum theory replaces classical bits of matter with nonlocalized bits of information, creating an evolving physical reality of informational propensities dynamically linked to conscious experience. Stapp organizes quantum dynamics into three processes: 1. Schrödinger Process (von Neumann Process 2): Deterministic, continuous unitary time evolution of the wave function according to the Schrödinger equation. 2. Dirac Process (von Neumann Process 1): Discontinuous, indeterministic collapse of the wave function into an eigenstate ('Nature's choice'). 3. Heisenberg Process: The 'free choice' of the experimenter regarding which question or measurement to put to nature. In Stapp's model of quantum brain dynamics, environmental interactions cause the brain to split into an ensemble of classically describable branches representing alternative possible courses of action. A mental event pairs with a physical event to select and actualize a compatible subensemble, discarding the incompatible branches. The Quantum Zeno Effect allows rapid repetitions of process 1 actions to freeze or sustain a 'template for action' in the brain. Ulrich Mohrhoff criticized Stapp's 2001 article 'Quantum Theory and the Role of Mind in Nature', claiming it contained 18 errors regarding quantum mechanics and mental causation. Stapp responded by framing the criticisms humorously as an '18-fold way' comprising 18 yes/no questions. - Mind, Matter, and Quantum Mechanics (2nd ed.) - Quantum Physics of Consciousness (with Roger Penrose) - Mindful Universe: Quantum Mechanics and the Participating Observer (2nd ed.) - Quantum Theory and the Role of Mind in Nature - 'The Copenhagen Interpretation', American Journal of Physics, 40, p.1098, 1972 Stapp argues that the 17th-century Newtonian clockwork universe reduced humans to mechanical automata and undermined moral philosophy. Quantum theory and the von Neumann-Wigner formulation restore human agency by integrating experiential mind and objective informational reality. By allowing conscious choices to causally influence brain processes without violation of physical laws, twentieth- and twenty-first-century physics bridges science, responsibility, and moral philosophy.