Free Will and Quantum Physics

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Quantum Physics

The predictions of Quantum Physics, which governs the behavior of atoms and subatomic particles, are probabilistic, for example:
- that a silver atom passing through a Stern Gerlach magnet will be deflected upwards, rather than downwards, with a probability of ½.
- that a free neutron will most likely decay (into a proton, electron, and an antineutrino) at approximately 14 minutes, 40 seconds after it comes into existence
According to the orthodox interpretation, the predictions of Quantum Physics are probabilistic, not because of unknown variables, but because quantum chance and probability are objective and fundamental.

Fundamental Difference between Quantum and Classical Physics

View Prediction in Quantum and Classical Physics
What’s going on in the physical systems between initial and final measurements?
The question is easily answered in Classical Physics: stop the variables from calculating at any time between measurements and the values of the variables describe the state of the system at that instant.
But Quantum Physics has nothing to say about the values of observables between measurements because Quantum Physics only makes a prediction when a measurement is made. Indeed there are simple physical systems where what’s going on between measurements is a mystery which, in Richard Feynman’s words, “we cannot make go away by ‘explaining’ how it works’.”

Does Quantum Physics Undermine Determinism?

General Determinism

Quantum Mechanics predicts that a silver atom passing through a Stern Gerlach magnet will be deflected upwards, rather than downwards, with a probability of ½.
- View Stern-Gerlach Magnet
The predictions of Quantum Physics are probabilistic. According to the orthodox interpretation of Quantum Physics, the predictions are probabilistic, not because there are unknown variables, but because the predictions are fundamentally probabilistic. Probability and chance are a basic feature of the physical world.
Thus, if the orthodox interpretation of Quantum Physics is correct, there are no “hidden variables” determining whether the silver atom is deflected up or down and therefore there are no laws of nature determining the observed result.
Therefore, if the orthodox interpretation of Quantum Physics is true, some events are undetermined and the thesis of General Determinism is false.

Neural Determinism

Argument that Quantum Physics does not undermine Neural Determinism:
- Though Quantum Physics undermines General Determinism, Neural Determinism is still true because quantum indeterminacies among subatomic particles are cancelled out at cellular and molecular levels. Thus, for all intents are purposes, the human nervous system behaves according to the laws of Classical Physics.

Levels of Entities of the Neuron
- Cellular and Molecular Particles
  - Cell
  - Organelles, e.g. nucleus, ribosomes
  - Molecules, e.g. proteins
  - Atoms, e.g. ions
- Subatomic Particles
  - Protons, Neutrons, Electrons
  - Quarks, Leptons, Higgs, Exchange Particles

Adolf Grunbaum, “Free Will and Laws of Human Behavior”, American Philosophical Quarterly, 1971
- Moreover, unless it is shown that a significant number of human responses are indeed subject to quantum indeterminacies, it would seem that the vast bulk if not all human responses and acts involve physical agencies of such magnitude that quantum indeterminacies become irrelevant to them and classical deterministic characterization holds to all intents and purposes for these physical agencies.
Jonathan Glover, Responsibility, 1970, p 47
- The statistical regularities at subatomic level may be quite adequate as a basis for causal laws at a higher level, where the units in terms of which the laws were stated would be unaffected in their behavior by ‘random’ motions of subatomic particles.
Richard Brandt, Ethical Theory, 1959, Chapter 20
- The behavior of the individual particles in a pan of water is unpredictable in theory; but it is not unpredictable that the water will boil. Similarly, the behavior of the particles in the brain is unpredictable in theory…but this does not preclude the possibility that decisions are in theory predictable. Unpredictability of the micro-events does not imply unpredictability of molar events.

Does Quantum Physics Make Room for Free Will?

Quantum chance is not free will

Suppose that a tiny organic quantum system in the brain determines whether certain upper motor neurons fire, which cause a person’s arm to rise. A neural measuring system effectively measures an observable of the system, causing it to take one of two values with a certain probability. One value results in the upper motor neurons firing. The other value does not.
If the upper motor neurons fire, the arm’s rising is the result of quantum chance, not something the person does. So the mere fact of quantum uncertainties in the brain would not mean people have free will.

Free will is incompatible with the probabilistic predictions of Quantum Physics

Libertarianism, the view that a person could have decided or done otherwise by being able to alter the course of events in their brain, is incompatible with determinism. But perhaps Libertarianism is nonetheless compatibile with the probabilistic predictions of Quantum Physics.

Suppose that a tiny organic quantum system in the brain determines whether certain upper motor neurons fire, which cause a person’s arm to rise. A neural measuring system effectively measures an observable of the system, causing it to take one of two values with a certain probability. One value (say it’s UP) results in the upper motor neurons firing. The other value (DOWN) results in no such firing.
A person might have control whether his arm goes or not by determining whether the measured value of the observable is UP or DOWN.
It might appear, then, free will is compatible with Quantum Physics.
But Schroedinger (below) long ago pointed out the problem. Quantum Physics predicts precise probabilities for the measured values of an observable. Suppose in this case the probabilities are UP 0.3 and DOWN 0.7. It appears that the person’s intervention resulted in probabilities 1.0 and 0, inconsistent with the postulates of Quantum Physics.

Erwin Schroedinger, Science and Humanism, 1951, page 61
- … quantum laws, though they leave the single event undetermined, predict a quite definite statistics of events when the same situation occurs again and again. If these statistics are interfered with by any agent, this agent violates the laws of quantum mechanics just as objectionably as if it interfered — in pre-quantum physics — with a strictly causal mechanical law. Now we know that there is no statistics in the reaction of the same person to precisely the same moral situation — the rule is that the same individual in the same situation acts again precisely in the same manner. … The inference is that … the direct stepping in of free will to fill the gap of indeterminacy … does amount to an interference with the laws of nature, even in their form accepted in quantum theory.

Quantum Theories

Quantum Mechanics
Quantified Field Theories
- Quantum Electrodynamics
- Chromodynamics
- Electroweak Theory
Standard Model of Particle Physics

Old Stuff

Difference between Classical and Quantum Physics (Standard Interpretation)
- Shooting a marble in space: location x of marble change over time per the laws of classical physics and you predict location x for a future time t
- Making a prediction in classical mechanics.
- Initial value of the location variables of a marble
- The values of the location variables change over time according to the laws of classical mechanics and forces on the object
- In QM, the initial values of the location variables determine the initial values of the state vector |Ψ＞ whose values change over time per the laws of QM,
- Shooting an electron: location variables x of an electron at initial time t is translated into state vector |Ψ＞, which changes over time per the laws of QM, and at future time t a mathematical calculation on |Ψ＞ gives the probabilities of possible locations of a subatomic particle.
- philosophersview.com/postulates-and-prediction/#prediction-in-classical-versus-quantum-physics
John Eccles: person can affect the quantum probability of events
- Inconsistent with predictions of QP
- Testable in theory
Bohm and different interpretations