If the universe is quantum-random or deterministic, what remains of free will? What neuroscience, quantum physics and philosophy say.
🎲 Laplace's demon and the deterministic nightmare
In 1814, Pierre-Simon Laplace proposed a thought experiment: if a superintelligence knew the position and momentum of every particle in the universe, it could predict the future with absolute precision. In such a universe, every thought, every decision, every feeling is merely the consequence of prior events. Free will would be nothing but an illusion.
This "hard determinism" dominated physics for centuries. Until quantum mechanics arrived. Heisenberg's uncertainty principle (1927) showed that it is impossible to know both position and momentum simultaneously — Laplace's demon is impossible in practice. But does that mean we have free will? Probably not — because randomness does not mean freedom.
🧠 The Libet experiment: the brain decides before you do
In 1983, neuroscientist Benjamin Libet conducted an experiment that shook the world. He asked volunteers to flex their wrist whenever they wanted, while an electroencephalogram (EEG) recorded their brain activity. The volunteers noted the position of a moving clock when they felt the “urge” to move.
The result: the Bereitschaftspotential (readiness potential), an electrical signal in the motor cortex, appeared ~500 ms before the action. The conscious decision appeared only ~200 ms before. In other words: the brain had already started the process 300 ms before “you” decided.
In 2008, Soon, Brass, Heinze & Haynes went even further. They published in Nature Neuroscience that they could predict subjects' decisions (left or right hand) with 60% accuracy, up to 10 seconds before the subjects themselves became aware of them. Ten whole seconds your body “knew” what you would do before you did.
"Thoughts simply arise in the brain. What else could they do? The illusion of free will is itself an illusion."
— Sam Harris, Free Will (2012)Libet's “free won't”
Libet himself did not believe his results abolished free will. He proposed "free won't": consciousness may not initiate the action, but it has 100–150 ms to “cancel” it — a conscious veto. Freedom is not about creating actions, but about stopping them.
⚗️ The quantum loophole
Does quantum indeterminacy leave room for free will? Many philosophers proposed so: if the world is not deterministic, then there is “free space” for decisions. This is the position of metaphysical libertarianism (not the political kind).
However, Niels Bohr himself, one of the founders of quantum mechanics, stated: "There is no connection between the indeterminacy of nature and the freedom of will." The problem: randomness ≠ freedom. If a decision is merely random, it is not “yours” — it is dice. Quantum indeterminacy does not save free will — it replaces it with a lottery.
🎰 The Conway-Kochen theorem (2006)
In 2006, mathematicians John Conway and Simon Kochen published the Free Will Theorem in Foundations of Physics: if experimenters have free will (their choices are not a function of the past), then elementary particles must have it too. That is: if you have freedom, so do the electrons.
📌 Free Will Theorem
If experimenters' choices are not determined by the past, then neither are the results of measurements determined by anything prior. In 2009 a stronger version was published in the Notices of the AMS, and in 2022 Kochen proposed an even more general proof.
The theorem is provocative: it links the experimenter's freedom to the indeterminacy of particles. However, it does not prove we have free will — it proves that if we have it, so do atomic nuclei. A symmetry that is either profound or empty.
⚖️ The third way: compatibilism
Compatibilists — the majority of contemporary philosophers — argue that free will is compatible with determinism. Freedom does not mean absence of causation, but absence of external coercion. You are free when you act according to your desires, even if those desires are causally determined.
"Scientists risk making a serious mistake. Kinds of free will that are not compatible with science are not worth wanting. Other kinds are vital — and compatible with modern science."
— Daniel Dennett, Freedom Evolves (2003)Daniel Dennett argued that due to chaos and epistemic limits, the future is “undefined” for every finite being. Where prediction fails, there is room for freedom.
🔬 2012 and the end of Libet?
In 2012, Aaron Schurger, Jacobo Sitt and Stanislas Dehaene published in PNAS that the readiness potential is not an unconscious decision, but random fluctuation of neural activity ("noise"). When the signal crosses a threshold, the movement occurs — but this does not mean the brain “decided” before you did.
In 2019, Maoz, Yaffe, Koch & Mudrik (in eLife) found that the readiness potential is absent in deliberate decisions and appears only in arbitrary movements — exactly the kind Libet studied. And a 2021 meta-analysis revealed that the evidence supporting Libet is “weaker than often claimed.”
🧩 What now?
The question remains open. Determinism removes freedom, randomness does not give it back. Some (like Derk Pereboom) argue for "hard incompatibilism": free will is impossible whether the world is deterministic or not. Others (like Dennett) say that “having free will” simply means that actions come from oneself without external coercion.
Whatever the answer, it has consequences. Research by Vohs & Schooler (2008, Psychological Science) showed that those who read a text “proving” free will doesn't exist cheated more in a subsequent experiment. Belief in free will may not be true — but it is useful.