Quantum mechanics and free will what the science says and what it does not

[Renegade51]

TL;DR

• Classical physics suggested a clockwork universe, famously captured by Pierre-Simon Laplace's 1814 image of an intellect that could predict everything from the present state of the world
• Quantum mechanics introduced fundamental randomness, at least on standard interpretations, and Bell test experiments recognised by the 2022 Nobel Prize in Physics ruled out a broad class of hidden variable explanations
• Randomness is not the same as freedom: a choice made by chance is no more yours than one fixed in advance, which is why many philosophers think quantum physics does not settle the free will debate
• Neuroscience adds its own puzzles, such as Benjamin Libet's 1983 readiness potential experiments, though later work by Aaron Schurger and others offered alternative interpretations
• Compatibilists, including philosopher Daniel Dennett, argue that meaningful free will is compatible with physics of any kind, while others hold that genuine freedom requires something more

An old question meets new physics

Do we really choose our actions, or are they determined by forces beyond our control? This question has occupied philosophers for thousands of years. Ancient Stoics, medieval theologians and modern scientists have all wrestled with it. Quantum mechanics, the strange physics of the very small, is often brought into the conversation, sometimes helpfully and sometimes not

Popular writing occasionally claims that quantum physics proves we have free will, or that it proves we do not. Neither claim holds up well. The relationship between quantum mechanics and free will is subtle, and many careful thinkers believe physics alone cannot settle the matter. Understanding why is a rewarding journey through science and philosophy

This thread is meant for curious readers rather than physicists. It explains the key ideas in plain language, summarises the main philosophical positions and highlights what science does and does not tell us. Members are warmly invited to share their own views. There are no experts on the final answer here

The clockwork universe

In 1814, French mathematician Pierre-Simon Laplace described an imaginary intellect that knew the position and momentum of every particle in the universe and all the forces acting on them. Such an intellect, he argued, could calculate the entire future and past with certainty. This idea, often called Laplace's demon, captured the spirit of classical physics. Newton's laws seemed to describe a universe running like clockwork

If the universe is fully deterministic, every event, including every human decision, is fixed by prior causes. That seems to leave little room for free will in the sense of being able to do otherwise. Philosophers call the view that free will requires the ability to do otherwise, and that determinism rules this out, incompatibilism. It has been one of the main positions in the debate for centuries

Determinism does not necessarily mean predictability. Even in a deterministic universe, chaotic systems such as weather or brains can be practically impossible to predict. But practical unpredictability is not the same as genuine openness. The question remains whether the future is really fixed

Quantum randomness

Quantum mechanics changed the picture in the early twentieth century. On standard interpretations, it describes the world in terms of probabilities. A radioactive atom has a certain chance of decaying in a given time, but nothing in the theory determines exactly when. Measurements of quantum systems produce outcomes that, as far as we can tell, are fundamentally random

Albert Einstein was uncomfortable with this, famously remarking that God does not play dice. He and others suspected that hidden variables might lie beneath the randomness, restoring a deterministic picture. In 1964, physicist John Bell proved a theorem showing that any theory with local hidden variables would make predictions different from quantum mechanics in certain experiments. Experiments could therefore test the question

Over the following decades, experiments by John Clauser, Alain Aspect, Anton Zeilinger and many others confirmed the predictions of quantum mechanics. In 2015, several groups performed experiments closing the major loopholes. In 2022, Aspect, Clauser and Zeilinger shared the Nobel Prize in Physics for this work. Local hidden variable theories of the kind Einstein hoped for were ruled out

That does not end the story. Some interpretations of quantum mechanics remain deterministic, including the many worlds interpretation, in which all outcomes occur in branching worlds, and pilot wave theory, which uses non local hidden variables. Another minority view, superdeterminism, questions an assumption of Bell's theorem about the independence of experimental settings. Physicists continue to debate which interpretation is correct, and experiments cannot yet distinguish many of them

Does randomness give us freedom

Suppose quantum events are random in a deep sense. Does that help free will? Many philosophers say no. A decision caused by a random event in your brain is no more under your control than one fixed by prior causes. If you raised your hand because an atom decayed, that seems like luck, not freedom

This is sometimes called the luck objection. It suggests that neither determinism nor randomness provides what we want from free will, namely control by the self according to reasons. On this view, quantum mechanics replaces one problem with another. The real question is about agency, not physics

Some thinkers have tried to find a middle way. Philosopher Robert Kane, for example, has argued that indeterminism in the brain could play a role in self forming actions during moments of difficult choice, where both options reflect a person's values. Critics remain unconvinced that such indeterminism adds genuine control. The debate continues

The free will theorem

In 2006, mathematicians John Conway and Simon Kochen published a result they called the free will theorem. Roughly, it states that if experimenters have the freedom to choose which measurements to make, in the sense that their choices are not determined by the past, then particles must also have a kind of freedom, in the sense that their responses are not determined by the past either. The result builds on quantum mechanics and relativity. It made headlines with its striking name

Philosophers and physicists have pointed out that the theorem does not prove humans have free will. It shows that if human choices are not predetermined, then quantum outcomes are not predetermined either, under certain assumptions. Its use of the word freedom is technical rather than moral. Still, it illustrates how deeply questions of determinism are woven into quantum theory

What neuroscience adds

Neuroscience has its own contribution to the debate. In 1983, Benjamin Libet and colleagues reported experiments in which brain activity called the readiness potential appeared before participants reported consciously deciding to move. Some interpreted this as evidence that the brain decides before we are aware, undermining conscious free will. The experiments became famous and controversial

Later research challenged that interpretation. In 2012, Aaron Schurger and colleagues proposed that the readiness potential may reflect random fluctuations in neural activity that build up to a threshold, rather than an unconscious decision already made. Other researchers questioned how reliably people can report the moment of decision. Today, many neuroscientists think the Libet experiments tell us less about free will than once claimed

Some scientists have proposed that quantum effects in the brain might matter for consciousness or choice. Physicist Roger Penrose and anaesthesiologist Stuart Hameroff developed a theory called orchestrated objective reduction in the 1990s, suggesting quantum processes in neural structures called microtubules. Most neuroscientists and physicists are sceptical, partly because the warm, wet brain seems likely to destroy delicate quantum states very quickly, a point argued by physicist Max Tegmark in 2000. The idea remains a minority view

Compatibilism: freedom without metaphysics

Many philosophers today are compatibilists. They argue that free will, properly understood, is compatible with determinism and with randomness. Free will, on this view, means acting according to your own desires, values and reasoning, without coercion or compulsion. Whether the underlying physics is deterministic does not change whether you acted freely in this sense

Philosopher Daniel Dennett defended compatibilism in books such as Elbow Room in 1984 and Freedom Evolves in 2003. He argued that the kinds of freedom worth wanting, such as the capacity to reflect, plan, respond to reasons and change our minds, are real features of human beings. These capacities evolved and can be studied scientifically. Quantum mechanics, on this view, is beside the point

Critics argue that compatibilism changes the subject. If every action is fixed by prior causes or chance, they say, we cannot really do otherwise, and that is what free will means. This disagreement about definitions lies at the heart of the debate. Surveys of professional philosophers have found compatibilism to be the most common view, though far from unanimous

Why it matters

Questions about free will are not only academic. They influence how we think about moral responsibility, punishment, praise and blame. If nobody really chooses their actions, should anyone be held responsible? Most philosophers, including many who doubt libertarian free will, argue that responsibility practices still make sense for practical and social reasons

They also shape how people feel about their own lives. Some find the idea of determinism unsettling, while others find it liberating, encouraging compassion for those whose circumstances shaped their choices. Psychological research has explored whether belief in free will affects behaviour, with mixed and debated results. Our beliefs about freedom may matter as much as the metaphysics

Questions to discuss

• Do you feel that you freely choose your actions, and does physics change that feeling
• Does quantum randomness make free will more or less plausible to you
• Is compatibilism a satisfying answer or a clever redefinition
• Should our views on free will affect how we treat crime and punishment
• Can science ever settle the free will question, or is it ultimately philosophical

Closing thoughts

Quantum mechanics overturned the clockwork universe of classical physics, introducing randomness and entanglement that still puzzle us. Yet randomness alone does not seem to deliver the free will many people care about. Neuroscience has complicated the picture without settling it, and philosophers remain divided between compatibilists and their critics. The question of free will remains one of the deepest and most enjoyable puzzles we can discuss

Please share your thoughts in the replies, whether you lean towards determinism, freedom or something in between. Personal reflections are as welcome as philosophical arguments. This is a conversation where curiosity matters more than expertise


Further reading

• Pierre-Simon Laplace, A Philosophical Essay on Probabilities, 1814
• John Bell, On the Einstein Podolsky Rosen Paradox, Physics, 1964
• Nobel Prize in Physics 2022 (Aspect, Clauser, Zeilinger), nobelprize.org
• John Conway and Simon Kochen, The Free Will Theorem, Foundations of Physics, 2006
• Aaron Schurger and colleagues, An accumulator model for spontaneous neural activity prior to self-initiated movement, PNAS, 2012
• Daniel Dennett, Freedom Evolves, 2003
• Stanford Encyclopedia of Philosophy, Free Will and Compatibilism

[VB]

The luck objection is exactly what I always felt but could not express. Random is not the same as free

If my choices came from atoms decaying, they would not feel like mine at all. Freedom must be about reasons, not dice. That makes the quantum debate seem less important than people claim. The real question is about who we are. Character matters more than particles

Thank you for an accessible and fair overview. It cleared up years of confusion

[Weary Inlet]

Compatibilism seems like the only sensible view to me. I choose based on my values and reasons, and nobody forces me. That is freedom enough

Whether atoms are determined or random does not change my experience of choosing. Experience is what I have to go on

Maybe the deeper metaphysical question is unanswerable. I am happy to live with that. Life feels free, and that is what matters day to day. It also makes moral responsibility workable. Practical philosophy suits me

[Cobalt Pilgrim]

Compatibilism never convinced me. If everything I do was fixed before I was born, then I could not have done otherwise

Calling that freedom feels like changing the definition to win the argument. Philosophers may call it sophisticated, but it seems like a trick to me. Real freedom means real alternatives

I accept that I might be wrong. But the intuition is very strong

Intuitions matter in philosophy too. Many arguments begin with them. Some survive scrutiny and some do not. Mine has survived so far. I will keep testing it

[Nancy72]

Libet's section was really helpful. I had read years ago that neuroscience proved free will was an illusion, and it bothered me. It sat at the back of my mind for ages

Learning that later research challenged that interpretation is a relief. Science is more nuanced than headlines suggest. That seems true for almost every topic

I will be more careful about trusting dramatic claims in future. Thanks for the correction