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I've been thinking about the problem of free will. In a deterministic universe, it seems like everything is just dominoes falling, one after the other. No room for choice.

But what about quantum mechanics and superposition. A particle can be in two states at once, until you measure it. And then it collapses into one state or the other.

Could something similar be happening in our brains? Could some internal processes in our bodies be in a state of superposition? Could the act of choosing be the thing that collapses these superpositions?

Imagine your brain is in a superposition of two states: A1 and B1. And let's say that action C1 is only possible if your brain is in state A1, while action D1 is only possible if your brain is in state B1.

Now, if you choose to do C1, does that mean you collapse your brain's superposition into state A1? And if you choose D1, do you collapse it into B1?

If so, could this be a way to have free will? A way for your choices to actually affect the physical state of your brain?

  1. Is it possible that there are quantum superpositions in the brain, specifically in the processes involved in decision making?

  2. If so, could the act of making a choice collapse these superpositions in the way I described?

  3. Would this count as free will? Or is it just randomness masquerading as choice?

So, what do you think? Is there a quantum path to free will?

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    "randomness masquerading as choice" <- that.
    – NotThatGuy
    Mar 13 at 14:39
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    Determinism isn't the only problem with free will. As per the comments above, in your case now the choice is simply coming from randomness/fuzziness, and is therefore still "externally influenced choice", not "totally free choice"
    – Rabbi Kaii
    Mar 13 at 19:17
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    Who's making the choice here? That is to say, what's the difference between "you" and "your brain"? And why aren't "you" also subject to physical laws?
    – Joel Keene
    Mar 14 at 4:33
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    Roger Penrose is famous for invoking quantum processes as an explanation for free will and consciousness.
    – Barmar
    Mar 14 at 14:35
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    I think part of what muddies the waters here is that the concept of “you” is ill defined. What would it even mean for “you” to decide things? It could be like thinking your next thought before thinking it. It seems either contradictory or meaningless Mar 14 at 21:26

9 Answers 9

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I'm going to answer your question, but I'd also like to say some things regarding the nature of the question and how people's fascination with free will is more or less unfounded.

In short, yes, it's entirely possible. It actually coincides quite well with the many-worlds interpretation of quantum mechanics, which states that whenever a choice is made (or when a wavefunction collapses), a universe where a different choice was made branches off from our own, for every possible choice.

In terms of it being actual quantum mechanics, there have actually been some species of birds which have been found to use quantum entanglement to determine when and where to migrate. Nothing similar has been found yet in humans, but it's not implausible, and, at the electronic scale our brain signals work on, some would say it's more than likely.

And, as a third possible solution, it's possible that the quantum mechanical nature of reality is actually just how free will is physically encoded in our universe. The fundamental problem with free will is that it's typically taken to be some non-physical concept. However, maybe when the wavefunction of a particle collapses, it's the representation of a choice we've made (or have yet to make; time can be weird in quantum theory), and actually the "randomness" is just us making choices and the universe responding accordingly.

Ultimately, there are several ways in which what you're describing could be the case. However, I would argue that it actually doesn't matter. Let me explain:

Free will is an inherently non-scientific idea. It posits that there is some metaphysical force which influences how our choices are made. How could this ever be justified with science? Free will can't be physically observed, so proposing it in any theory of physics (or scientific theory in general) is kind of absurd. The cases I mentioned above are not physical observations of free will, but rather us interpreting physical observations as being manifestations of free will somehow. i.e., free will can never be observed, but instead only offered as an interpretation or "theory", more or less. So, just as with most metaphysical ideas (such as god), the existence of free will could never be proven nor disproven by science.

So what? whether or not free will exists, we, at the very least, have the illusion of choice, and this is enough to eliminate any practical difference between its existence or nonexistence. Truly, the only aspect of free will that actually effects our choices and lives is whether or not we believe in it. Believing in free will or determinism will change your outlook on the world which will in turn change how you make choices.

Because of this, I believe that we should simply not make a choice in whether or not free will exists. The belief either way is arbitrary, and ultimately unnecessary and unfounded. We should instead develop an outlook on life which is independent of any idea of free will, and not make a choice. If you're familiar with any formal or mathematical logic, it's akin to how the continuum hypothesis is independent of ZFC and whether or not its true is an arbitrary choice.

So, what you say may very well be the case, but it could never be shown to be true and could only be offered as an interpretation or explanation of what we do observe. Additionally, it doesn't and shouldn't matter whether free will exists or not. Instead, you should simply make the choice to not believe one way or the other.

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    "independent of any idea of free will" -- This can be difficult because concepts like responsibility and justice, and good vs. evil, are based on the assumption of free will. If the criminal didn't choose to commit the crime, it would be unfair to punish them for it.
    – Barmar
    Mar 14 at 14:39
  • @Barmar On the other hand, if one were to believe in determinism, then a person's actions are solely a product of their upbringing. Punishment wouldn't make sense in that case, and instead implies that criminals should only be subject to rehabilitation. In line with my answer, and choosing to ignore the implications of a belief in free will, I would instead rely on the humanitarian studies that show that rehabilitation is usually better for society, and I think that that's a much more solid justification than an approach from a belief in free will or determinism. Mar 15 at 7:18
  • While it's not a totally deterministic philosophy, progressive attitudes towards criminal justice have allowed for many more defenses based on influences outside the perpetrator's control. "twinkie defeneses", temporary insanity based on PTSD, etc.
    – Barmar
    Mar 15 at 16:05
  • I don't know how to turn it into an answer, but my general feeling is that free will is an emergent phenomenon. So even if the universe is deterministic, there's enough chaos that we can't predict complex actions of organisms.
    – Barmar
    Mar 15 at 16:10
  • @Barmar In your scenario, the persons imposing punishment would not be choosing to do so, either.
    – sdenham
    Mar 15 at 19:22
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The question assumes an incompatibilist view of free will, and then rests their notion of free will on the possibility of true quantum randomness. Two notes on that:

  1. Quantum mechanics may or may not be fundamentally, genuinely random. That's up to interpretation, and the jury is out among experts.

  2. Let's imagine you find the randomness you're looking for in QM -- then what? What have you gained?

You can now prove a part of your decision making process in your brain is random, and that makes you free? If a decision you're making is going to change depending on if an electron in your brain goes right instead of left, and that's decided by a random quantum process which crucially YOU don't control, then you haven't gained freedom - you're now a slave to randomness. Is being a slave to randomness any better than being a slave to determinism?

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    One should not conflate not predetermined with out of my control. Random in the sense of the first does not lead to the second.
    – Nikos M.
    Mar 13 at 17:40
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    @NikosM. Do you believe humans have control over quantum events?
    – TKoL
    Mar 13 at 17:42
  • Why do I have to believe that in order to say what I said? As my answer notes, usually libertarianism takes free will as a basic process by itself not necessarily reduced to other processes.
    – Nikos M.
    Mar 13 at 17:49
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    This is a thread about the idea of free will being rooted in quantum randomness. If that's not the idea of free will you're talking about, I'm concerned you may be having an out-of-place conversation. @NikosM.
    – TKoL
    Mar 13 at 17:51
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    @Gush so if quantum randomness is not part of the cause of the choice, then what use is it for explaining free will at all? If something other than quantum randomness is deciding stuff, then... it doesn't seem like quantum randomness is helping us understand choice at all. It isn't doing any work. Where do you suppose the choice comes from? Does it come from somewhere else in the brain? Does it come from an immaterial mind or soul?
    – TKoL
    Mar 14 at 14:16
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No, quantum superposition isn't really a plausible explanation, since processes in the brain seem to be macroscopic (ie they involve combinations of neurons which collectively contain oodles of quantum particles), and the brain itself is a warm, noisy environment from a quantum physics perspective, so it seems unlikely that the kind of weird effects that are popularly associated with quantum mechanics could account for free will.

As an aside, all quantum states can be expressed as superpositions of other states, so particles are never not in some form of superposition of other.

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  • Possibly the OP means "mixture of states" instead of "superposition"? - Ceterum censeo: To explain free will with quantum indeterminacy is ruled out - you recall the reason. And the subjective feeling of free choice is the contrary of randomness.
    – Jo Wehler
    Mar 13 at 15:43
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    There are actually species of birds that have been found to use quantum entanglement to help their brains determine when and where to migrate. It's opened up a whole new field of study called Quantum Biology. So, while we haven't found anything like that yet in humans, it's not entirely implausible. Mar 13 at 17:14
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    Chaos studies have shown many macro-scale systems are chaotic, such that QM indeterminacy can be leveraged up to macro scale consequences. All living things are such bounded chaotic systems, where a single QM event can have dramatic consequences for us. The "Schoedinger's cat" thought problem is an illustration of such macro-scale leveraging. Our brain states are chaotically under stable, so the possibility of QM effects having consequences on future brin states is highly plausible. Consider the effect of a single gamma ray causing cancer in a person, that will affect their thoughts!
    – Dcleve
    Mar 14 at 15:24
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    @Dcleve no, the Schrodinger's cat thought experiment is an illustration that extrapolating quantum concepts to everyday objects yields nonsense. That was Schrodinger's point is suggesting it. Mar 14 at 15:35
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    Hmm. That's not how the thought experiment was used in my physics classes. The principle works out fine -- a detector can sense a single decay, and leverage up macro-scale consequences. It is an illustration of a hair-trigger bounded chaotic system at macro scale. How to interpret this in QM theory -- is more problematic. The role of observer in collapsing QM events is suspect, as the cat is an observer, and "observer" versions of QM interpretation may need revision.
    – Dcleve
    Mar 14 at 17:29
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One cent.

Libertarian free will requires negation of determinism. So indeterminism at the level of basic physics is a bonus point for libertarianism.

However, it is not required that free will functions in a quantum mechanical sense. It can as well be a basic process by itself, not reduced to other more basic processes.

Libertarianism usually takes free will as something of a basic process by itself.

That being said, there are indeed authors who use quantum mechanical models of free will in their arguments (see some online references..).

Furthermore the Free Will Theorem states that if one entity can have free will, then given the quantum nature of the universe, other entities can have it as well. So in a sense the quantum nature of reality can play a role.

PS: I cannot rule out quantum models of free will neither in principle nor via physical/neural arguments. Indeterminism (such that is suitable for choice) can manifest as a result of quantum mechanics, even if the brain/body is seen as purely macroscopic, because, for example, existing non-linearities can make the micro indeterminism relevant even at these macro scales (leaving aside purely quantum effects which are manifest even at macro scales and concepts like "quantum holism").

PS2: A state which is compatible with more than one future outcome (a "superposition" state) is a plausible model of free will and this state need not directly be related to quantum mechanics, as noted above, it can be formed with many other ways. Various areas can exhibit features similar and/or common to those peculiarly manifest in quantum mechanics. Finally, one should not conflate "not predetermined" with "out of my control", random in the sense of the first does not lead to the second.

Some references:

  1. Quantum Free Will Theorem
  2. Quantum Indeterminism, Free Will, and Self-Causation
  3. A Quantum Model of Non-illusory Free Will
  4. Quantum Approaches to Consciousness and Free Will, SEP
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This whole subject is fraught with pitfalls. There are two dual issues, both of which are very slippery: 1. To what extent is our understanding of the relevant physics good enough to make definite conclusions, 2. To what extent can we pin down what we mean by free will.

I'll throw in a third issue as well: 3. What we know from the history of mathematics, is that even where our definitions and assumptions are quite rigorous, even the hunches of the best mathematicians are sometimes dead wrong. I'm a bit of a chauvinist here; if you haven't worked in math, or thought pretty deeply about it, you probably don't really know how easy it is to be dead wrong about something that seems clear to you. I'd put a lot of theoretical physicists in this category, by the way. Many of them seem to thrive on public attention, writing popular books, and working with media producers, making exciting pronouncements about the world, with what is very likely unwarranted confidence.

As for 1., physics has taught us so far: a) our naive assumptions about the nature of the physical world, if there even is such a world, are quite unreliable, b) current theories in physics are incomplete, and known to be inconsistent, and therefore somewhat wrong at best, totally wrong at worst.

Despite this, many people argue with what I think is unwarranted confidence, as if they "know", at least roughly, how the future of physics going to work out. It's maybe a century or so that we've been able to explain why the sun is hot. Before that, we could easily argue, seemingly quite solidly, that no such thing as the sun could exist. A very detailed calculation of how much chemical energy the sun could possibly contain, could have been phrased in very technical, science-y terms, proving that the sun is a mere fiction. Yet, somehow, it always did seem to shine up there and give warmth. I have the same sense of these subjective experiences, like consciousness and free will. You can make an erudite argument why they can't exist based on crude arguments from physics know to be wrong ... yet ... there they are.

For this reason, I am unconvinced by arguments along the lines of "X can't be true, because physical theory Y contradicts it". In this category, I put arguments about what is supposedly impossible about the physical brain, an organ about which we have much to learn. In particular, there's a slowly growing list of biological phenomena believed to be "quantum" in nature, including photosynthesis, the sense of smell, and the navigational sense of migratory birds, among others. If you think you "know" what can and can't happen inside an organ we don't understand, built out of biology that only gets more surprising and more complex the closer we look, because of physical theories known to be wrong, I'd caution not to take yourself too very seriously.

The second issue, is even more troublesome. Verbal definitions can express certain kinds of logical relationships. My hunch is that phenomena like free will, are outside its expressive capabilities. Give me the precise definition of free will. I haven't seen such a definition so far. The same problem vexes such basic questions as "What is energy?", "What is matter?", "What is a force?", "What is a measurement?", "What is an action?", "What is the relationship between a physical law and the physical world?" Etc. We don't even have a stab in the dark at these things, as far as I'm aware.

And ... if we don't have something like free will, we don't really have science as most people understand it, because we can't do an experiment in any real sense. The scientist in the lab is just a bunch of matter bouncing around, their though processes are a bunch of matter bouncing around, and it's trivial to construct theoretical universes where the scientific theories of such bouncing around matter, are totally inconsistent with the actual workings of the universe they are in.

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No, the one does not seem correlated to the other.

"Free will" means that if we would rewind the universe to a point in time before a choice I made, perfectly, then I would be able to take a different choice next time.

"Quantum" means that choices might be random.

If people say that there is no free will, they do not mean that all future decisions can be known beforehand; i.e. it is perfectly possible that there is no free will, but the "quantum conjecture" from your argument is true at the same time. This would mean that when rewinding the universe, my decision could be different the next time around; but it would not make "me" (whatever that is) more in control of the decision, it would just be attributed to the randomness of that one "q-bit" falling the other way.

For free-will proponents, this quantum argument would be even worse! It would mean that choices are inherently random; and free will is probably the farthest away from randomness as you could want something to be.

So, TLDR: there might or might not be quantum effects introducing randomness in our brain (and heck, there could very well be non-quantum macro effects which introduce randomness - for example a random high-energy particle from outer space hitting one of your neurons just so, influencing a decision). If quantum superposition has a major influence in our decisions, then it would not influence the question of free will at all, very likely, or make it even less probable.

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As others have noted, the question is unanswerable on its own terms – when we speak of "free will", we're discussing the freedom of what you might call a "soul" or "mind" or some other metaphysical object which by definition does not exist within (any) physics.

If your mind can be fully explained by a theory consistent with the observed world – i.e. by science – then by definition you are not free to make choices inconsistent with that theory. If the theory is deterministic, then your choices are decided at the beginning of time, and if it's non-deterministic, they're decided by the roll of a dice on the day, but either way it's physics that decides them.

(You might want to say that a dice roll could be influenced from some higher plane, but that's just saying it's not random after all).

However, just because science doesn't admit (let alone justify) a concept of "free will", this doesn't mean morality doesn't exist. Skeletor isn't excused by the fact that he's written evil, and our responsibility for our actions isn't diminished by the role of physical processes, even if it amounts to 100%.

To butcher Daniel Dennett's position:

Yes, your choices are the result of (practically) random events, but the decision to murder or not murder someone doesn't come down to a single dice roll in the moment. It is the sum of all the dice rolls that ever happened to make you you. That unique and irreproducible set of circumstances is who you are, and so whatever it leads to is what you decided.

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Deep conceptual issues need to be untangled before attempting a quantum explanation of free choice

The Measurement Problem: How does measurement collapse the quantum wavefunction into definite states, and what constitutes a "measurement"?

Quantum-to-Classical Transition: How do quantum phenomena at the microscopic level manifest in the macroscopic classical world relevant to human cognition and agency?

Nature of Quantum Randomness: Is the apparent randomness in QM truly fundamental or due to hidden variables? Is it ontic or epistemic?

Compatibility with Determinism: Is free will compatible with a deterministic universe (compatibilism) or does it require genuine indeterminism (incompatibilism)?

Mind-Matter Relation: For QM brain processes to influence free will, consciousness must be related to material brain states, not e.g. epiphenomenal.

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First: The Universe is not deterministic. Determinism is only a simplified model of the physical reality, a model used only in classical physics.

Second: Free will, as the ability to make decisions, has nothing to do with physics. Decision-making does not involve any exhanges of matter or energy or any causal chains of events. Decision-making is purely a mental process where knowledge, desires, needs, imagination, emotions, opinions, beliefs, etc. interact to generate new knowledge about future actions.

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    "Decision-making does not involve any exhanges of matter or energy.." very well put
    – Nikos M.
    Mar 13 at 18:14
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    The brain alone consumes 20% of a person's metabolic energy. To say that any mental process, decision-making or otherwise, doesn't involve exchanges of matter or energy is only true if you reject materialism a priori. If you're doing that, all right, but you should probably make that more explicit in your answer.
    – Idran
    Mar 14 at 17:54
  • The truth of a statement does not depend on what philosophy I accept or reject. Mental processes are not physical processes and that is a hard fact, not a philosophical standpoint. Mar 14 at 18:36

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