The Free Will Theorem states:

Given the axioms, if the two experimenters in question are free to make choices about what measurements to take, then the results of the measurements cannot be determined by anything previous to the experiments.

This has been a debate in Philosophy for years but I think this is the first clear resolution in favor of free will.

What the theorem is saying is,when an Experimenter makes a choice as to how to measure a particle, this choice can't be determined by anything physical or it would violate Quantum Mechanics. You would have some hidden variable that's a physical super observer.

You can't have this because this physical mechanism would have foreknowledge of what history the particle will be in before a measurement occurs.

This is the first concrete refutation of Determinism and support of Free Will that's irrefutable.

This isn't a duplicate and that's a tactic used by some who can't debate the issue. Please show me where in that other posts where they talked about the Experimenter's choice as it relates to a physical mechanism that determines MIN which is one of the axiom's of the Strong Free Will Theorem and has foreknowledge of the particles history prior to measurement. That thread is talking about Panspsychism I haven't mentioned that.

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    But please, be careful in the use of words: many philosophical discussions are only about words, i.e. due to ambiguity or words with multiple usages/meanings. When you says : "if the two experimenters in question are free to make choices..." you are already assuming that their Will is Free. Mar 6, 2019 at 14:21
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    Our rule for duplicates is that the answers to the old question already answer the new question, not that the questions are similar.
    – Conifold
    Mar 6, 2019 at 19:00
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    @Conifold usually people scream duplicate when they can't debate the issue. Show me where in that other posts where they talked about the Experimenter's choice as it relates to a physical mechanism that determines MIN which is one of the axiom's of the Strong Free Will Theorem and has foreknowledge of the particles history prior to measurement. Mar 6, 2019 at 19:19
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    There is.no thought without time. So separating free will from causality is impossible. The question is, are causality and determinism the same thing?
    – Richard
    Mar 6, 2019 at 20:10
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    @Conifold How can Determinism be true in light of the Free Will Theorem? It's at the top of the post. This is why I talked about the Experimenter and a physical mechanism. If the choice of the Experimenter can't be determined by any known or hypothetical physical mechanism, how can determinism be true? You say I didn't ask anything answerable but a lot of people understood what I was asking and they responded. Mar 6, 2019 at 21:33

5 Answers 5


According to the Information Philosopher what John Conway and Simon Kochen have done in the Free Will Theorem and Strong Free Will Theorem is described indeterminism:

Although Conway and Kochen do not claim to have proven free will in humans, they assert that should such a freedom exist, then the same freedom must apply to the elementary particles. (Recall that Arthur Stanley Eddington was mistakenly charged with the idea that human free will was the same idea as that electrons are "free.")

What Conway and Kochen are really describing is the indeterminism that quantum mechanics has introduced into the world. While indeterminism is a necessary precondition for human freedom, it is insufficient by itself to provide free will.

Rather than proving free will they have shown a conditional: if we have free will then so do elementary particles.

Or, to put this in other words, one can still use one's free will to claim one does not have free will and not be accused of being irrational or unscientific.

However, the theorem does link our free will with the indeterminism of quantum systems. It is unlikely that free will for us will be completely explained by our having brains since these quantum systems do not have brains.

The Free Will Theorem Retrieved March 6, 2019, from Information Philosopher Web site http://www.informationphilosopher.com/freedom/free_will_theorem.html

  • Free will and randomness are not necessarily incompatible. This is one point. The second is that there are theories of libertarian Free Will that are based on quantum mechanics. In my opinion these theories are not very precise yet but they make the point that the two can be related and are not necessarily unrelated.
    – Nikos M.
    Jan 15, 2023 at 11:41

You would have some hidden variable that's a physical super observer.

What makes that improbable? You may be familiar with "Bob in 2D-Land", in which an entity, called Bob, lives in a 2D-Space, set in a multi-dimensional space itself. However, Bob only perceives his world as a two-dimensional space, like a piece of paper.

Now, a three-dimensional sphere falls through his flat world, not colliding with the matter. What will bob see? For Bob, a little dot will suddenly appear out of nowhere, widening, forming a circle which grows and grows until it suddenly shrinks again, eventually forming a dot again shortly before disappearing.

Now, of course, Bob will be incredibly confused, as he can't understand what just happened. Remember that Bob really only sees in one Dimension, quite like us, living in a 3D-World, only really see in two dimensions. So, although - as a entity of a higher dimension - we can explain what happens to Bob and his flat world, his thinking isn't even wired to be able to understand an extra dimension.

Now back to us humans. We see seemingly random particles popping in and out of existence. More specifically concerning your question, the result of an experiment can give you different results depending on how you measure it. Sounds familiar?

I haven't heard of any really smart people taking this into consideration, but maybe I didn't look hard enough, however - let me propose the theory, that everything which seems to be evidence against determinism, due to the seemingly random nature of it, is just the phenomenon of a higher-dimensional entity/object, leaving its marks in our reality.

It may also just be bollocks. We're just speculating here with our tiny dumb brains which are wired to survive in Africa.

  • Would you have a link to Bob in 2-D land? This does remind me of an older book, Flatland en.wikipedia.org/wiki/Flatland Perhaps they are the same source. Welcome to Philosophy! Mar 6, 2019 at 14:52
  • unfortunately, I don't have a source right now, but I remember that Michael Stevens aka "Vsauce" talked about this in one of his videos. I'll try finding it, the book you linked sounds interesting as well though :) Mar 6, 2019 at 16:29
  • Nicely put! Concise and to the point. Mar 11, 2019 at 20:24
  • An extra dimension where it is by definition unobserved is nothing more than explaining away the unknown with another unknown. The principles which this dimension would satisfy is for all we know nothing but completely random and ad hoc since we have nothing to base our reasoning on. Occam would happily disagree that this is a good explanation
    – Nikos M.
    Jan 15, 2023 at 11:35

You misunderstand the theorem. What it's saying, in plainer English, is:

If our determination of what to measure in an experiment was not caused by factors prior to the measurement, then neither was the result of our measurement.

Your mistake is twofold:

1) This is a conditional on us having free will, not an assertion that we have free will. (i.e. "If we have free will then X....")

2) The use of "free will" here is not loaded with the typical definitions of "free will" that philosophers generally use. Namely, all they mean by "free to choose what measurement to make" is that what measurement the experimenters make is not a function of the past. I doubt either Compatibilists or Libertarians would accept this as a sufficient condition for what they call "free will".

  • You're wrong, it's not conditional because at the heart of the Free Will Theorem, it refutes hidden variables. This shows why Human free will must exists. This is because if the Experimenter is not free to choose, this means particles aren't and there's some physical hidden variable that has some type of magic foreknowledge prior to measurement. Mar 6, 2019 at 15:56
  • @PoloHolographic The contrapositive of "free will -> ~hidden variables" is not "~free will -> hidden variables", it's "hidden variables -> ~free will". So it's perfectly compatible with the Free Will theorem for there to be no free will, and no hidden variables. Mar 6, 2019 at 16:06
  • Of course it does. Name me the physical mechanism that can determine the Experimenter's choice thereby knowing the history of the particle prior to measurement. Please add a link to this magical physical mechanism. Mar 6, 2019 at 16:09
  • @PoloHolographic I don't know what else to say. Just read the abstract of the original publication, and the closing remarks. arxiv.org/pdf/quant-ph/0604079.pdf "we prove that if the choice of a particular type of spin 1 experiment is not a function of the information accessible to the experimenters, then its outcome is equally not a function of the information accessible to the particles". This is clearly a proof that is conditional on there being free will. They even call it an "assumption" at the end. Nowhere do they "prove", or even attempt to demonstrate that free will exists. Mar 6, 2019 at 16:22
  • Even if you want to cite their motivation for doing this, all they say here is that they're not satisfied with the usual Bell Inequality way of disproving hidden variables. Assuming free will exists (in the way they define it) is simply an alternative. Mar 6, 2019 at 16:24

If someone were to reject the first premise, then they do not have to accept the conclusion. Anyone could reject the first premise because it has not been demonstrated and it needs to be demonstrated before it has to be accepted. Therefore, determinism can still be true because the first premise could be false.

Interestingly, there are arguments that living in an indeterministic universe eliminates the possibility of free will, but of course, that is because of the definition of free will that is used. If someone were to accept any of these definitions along with accepting the conclusion of the argument (that argument being the free will theorem) then they would say that free will does not exist. However, this does not address the main point of your question.

The biggest reason people have not rejected determinism is that it can be demonstrated. (I believe that we live in an indeterministic universe because I trust quantum mechanics, however, when operating at a scale as big as we usually do the indeterministic nature of things seemingly disappears. [Not the best way to put it but...]) That is, as long as the deterministic model of the universe continues to work for our everyday lives and a large portion of scientific fields, it will continue to be accepted. This also does not address the main point of the question.

  • "I believe that we live in an indeterministic universe because I trust quantum mechanics" ...but QM does not imply indeterminism
    – H Walters
    Mar 6, 2019 at 17:13
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    @HWalters Quantum mechanics does not necessarily imply indeterminism but a person has to give up their belief in locality or determinism. I have chosen the latter. Mar 6, 2019 at 17:46
  • "a person has to give up their belief in locality or determinism" ...that's incorrect; MWI is both deterministic and local (see "Deterministic" and "Local Dynamics" in that chart; I can explain why in chat but don't have time ATM, but it has to do with the "Real Wavefunction" and "Collapsing Wavefunction" entries).
    – H Walters
    Mar 6, 2019 at 18:21
  • @HWalters Many Worlds Interpretation has Many Problems
    – Nikos M.
    Jan 15, 2023 at 11:49

It's strange that some consider the Free Will Theorem to have resolved the determinism/free will debate in favor of free will when I would say it's quite the opposite: it has resolved it in favor of determinism. What's interesting about the result is that it is uncharacteristic - AFAIK - of any previous attack on resolving the debate amongst many over the millennia. It's a reductionist argument in the style of, say, the Cook-Levin theorem on reducing NP complete problems to 3SAT. It doesn't claim humans possess free will absolutely, only conditionally: if we do, then lowly atoms do as well.

Free will, were it to exist, should be a fundamentally human characteristic. Once it's tainted by being a property enjoyed by non-sentient elementary particles it loses all specialness.

A so-called free will that is shared by an inanimate elementary particle is tantamount to determinism. What self-respecting human would want to share something as wonderful as free will (were such a thing to exist) with a lowly particle?

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