In the edition of Feb/Mar 2016 of the Philosophy Now Magazine says:

Under Feel Free to Differ it says:

[...] Determinism itself comes in different flavours. Hard determinism of the most absolute sort is the theory that the entire history of the universe was already fixed from its very beginning by the setting of the laws of nature and the original states of the matter in it. This is no longer tenable due to the intrinsic indeterminacy – the random behaviour – at the heart of matter that is explored in quantum physics. But physics does apparently allow a somewhat less absolute determinism – the idea that the behaviour of the world is determined by previous physical activities, but with some randomness as to what the particular outcomes will be. So a quantum determinist could defend an indeterministic determinism!

I might be reading this wrong, but I am understanding that quantum physics might have an effect in the causality chain.

Under Free Will is an Illusion, but Freedom Isn't it says

In quantum physics the so-called probability amplitude evolves according to deterministic laws but the transformation from many possible outcomes to one actual outcome takes place purely by chance. The statistical distribution for such chance events follows strict rules, but the outcome of an individual chance event is unpredictable and cannot be controlled by will. Thus any decision is either the predictable result of earlier causes (which may include quantum chance events) and is not free from determinism, or is itself a quantum chance event and is not willed. Either way, the free will we commonly take for granted is absent. What then is the freedom to choose that we so cherish and which politicians like to invoke at every opportunity?

I am neither a scientist or a profesional philosopher, but I would like to gain a better understanding of how quantum physics is supposed to affect the account of determinism and free will. Frequently I read philosophy articles like those above which imply there is some sort causal effect, but I have never read a clear explanation of what that is, at least not one that I can clearly understand.

Suppose I am at home, I open the fridge and I am about to choose between chocolate or strawberry ice cream. I can assume that there is a chain of events, cause and effects, that come all the way from the Big Bang until this moment. At this point the state of the universe, everything in it, is the result of that causal chain of events. The universe is about to move from the state in which I conceive my alternatives (choosing between chocolate or strawberry ice cream), to the state in which I realized I have made a choice (I chose and picked the strawberry envase from the fridge).

At making this choice I experienced that I could have chosen otherwise If had wanted to do so. I feel that I chose strawberry even when I like chocolate better because I know that chocolate is not good for my health and so it was an apparently reasoned and free choice.

Now suppose that we were able to rewind the universe back to the Big Bang and repeat all this chain of events to the very moment before I made my choice, being the universe in the same exact state as before, I would always end up choosing strawberry ice cream, regardless of my believe or experience that I could have done otherwise. This is my understanding of determinism.

But if the chain of events were slightly different, for example, in an alternative universe where I would have a preference for strawberry instead of chocolate, or if chocolate was not bad for my health, I may actually end up choosing differently, but I would also be predetermined by the state of the universe in that alternate reality.

The Question

Now if I rewinded the universe back to the Big Bang and replay it again, could quantum mechanics alter the final state of the universe up to the point where I apparently made my choice between chocolate or strawberry such that I could in this replay choose otherwise?

In other words, is possible that if I am at the exact same state of choosing between chocolate and icecream, if we rewind back to that moment over and over n times, in some occasions I may choose strawberry but in others I may choose chocolate?

Is that the way we could expect to interpret the quantum physics model in how things work in the universe?

Can somebody please enlighten me about how quantum physics discoveries affect the account of determinism and free will in this regard?

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    This was beautifully articulated... I have the exact same question, but I would not have worded it as clearly as you did.
    – AlexW.H.B.
    Apr 12, 2018 at 22:47
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    Great question. It may be avoided by assuming freewill is an illusion. (the perennial view) but becomes a difficult one when we try to defend freewill. Your choice of ice-cream may be determined by your circumstances, your state of mind and prior conditioning (this one is bad for my teeth, this is the one I liked last time etc) and so it is not easy to see how it can be called a free choice. We descend into confusion whenever we try to defend freewill and the confusion begins just as soon as we try to define it, and I don't consider that QM makes this problem any better or worse.
    – user20253
    Mar 3, 2019 at 13:41
  • The only place I've seen thoughts articulated in this way is by Isaac Arthur on YouTube. There's an uncanny similarity. I hope I can learn to articulate my thoughts so well.
    – john doe
    Jul 14, 2021 at 14:41

7 Answers 7


The OP quote draws a distinction between determinism ("hard determinism"), and causal completeness ("less absolute determinism"). The former means that the current physical state of the universe predetermines its future state in every detail, i.e. it is a "sufficient cause", this is the Laplacian view of classical mechanics. The latter means that although the current physical state is not a sufficient cause it is a complete one, nothing else has any causal effect on future states either, whatever is not physically determined is purely indeterministic.

Whether this has an effect on free will is controversial, see Is there a causal influence of the mental on the physical? For you to sometimes choose strawberry and sometimes chocolate "in exact same circumstances", we have to additionally assume that microscopic indeterministic processes of quantum mechanics are sufficiently amplified to affect macroscopic behavior of the brain. In other words, there needs to be a trigger mechanism, such as the one in the Geiger counter, which amplifies an indeterministic atom decay into a macroscopic click. Whether such a mechanism exists in the brain is currently unknown, but many free will libertarians (Compton, Popper, Eccles, Kane), and even some compatibilists (Dennett, Mele), believe that it does, see Two-Stage Models for Free Will.

There is also a problem with the "exact same circumstances" in the question, because quantum indeterminacy excludes exact registration or reproduction of a state, so the question itself presupposes classical intuitions. Strictly speaking, under quantum mechanics it can not even be asked, the best we can do is ask if it can happen in "similar" circumstances.

Kane's suggestion is that the system of firing neurons can become chaotic in some circumstances, which would mean that the macrostate of the brain becomes sensitive to even microscopic quantum fluctuations. This by itself does not resolve the issue of free will however, because the question of conscious control over the outcomes also has to be addressed. How to address that, and when exactly quantum indeterminism is injected into the decision process, are also subject to controversy. Libertarians tend to place it closer to the time of physical action, while compatibilists place it earlier in the deliberation process.

Kane pays special attention to effects of quantum indeterminacy on free will, you can read a short version of his account in On Free Will, Responsibility and Indeterminism, see also online review. Mele's book Free Will and Luck is a comprehensive survey of most current positions on both indeterminism and control issues.


First a point of clarification, from what you are describing, you are talking about libertarian freewill, not compatibilist freewill. More on that later.

At the heart of your question is a confusion that you need to clarify, then you will understand the second paragraph you quoted better. You are confusing "Determinism" with "Lack of freewill" due to a logical fallacy. The two concepts are related, but they are not the same.

Specifically, the following relationship holds:

  • (A) If determinism is true, libertarian freewill is false.

The complement of this relationship is:

  • (B) If libertarian freewill is true, determinism is false.

The fallacy lies in the fact that people confuse (B), with the following relationship:

  • (C) If determinism is false, libertarian freewill is true.

But (B) and (C) are not the same: It is entirely possible that determinism is false, but that freewill is false as well. The fact that quantum mechanics disproves determinism doesn't mean that freewill is true in anyway.

To use your example: per the results of quantum mechanics, if we rewind the clock and replay your opening the fridge scenario, it is entirely possible that the second time around you chose chocolate instead of strawberry. But this has nothing to do with any metaphysical ability you have to determine your own future. It is simply due to randomness over which your mind has no more control than it did over Newtownian laws of physics.

So quantum randomness doesn't really effect the debate of whether we have libertarian freewill or not, even though it does disprove determinism, in the Laplace sense of the word (Laplace was the one who claimed that the entire evolution of the universe was predetermined by the laws of physics).

Two footnotes:

  • Roger Penrose proposes a model which ties quantum mechanics to freewill, called the Orch-Or model. But Penrose's model is disputed by most physicists and biologists, and as I mentioned above, the fact that the universe follows quantum mechanical rules doesn't imply in anyway that we do have freewill.
  • There is a second position on the freewill problem called compatibilism: compatibilist hold that both freewill and determinism are compatible, but they do so by changing the definition of freewill (which is what the title "Free Will is an Illusion, but Freedom Isn't" is hinting at.

The way quantum mechanics is commonly discussed makes this a very confusing issue. I will discuss this problem first and then move on to free will. People like to say there are multiple interpretations of quantum mechanics, which have different implications for what is happening in reality. These then claim that these different explanations all have the same implications for experimental results.

Some of those "interpretations" include randomly picking one possible measurement outcome out of a hat to be the real state in situations where the measured quantity has non-zero probabilities for several states. Some of these theories, such as the Copenhagen and statistical interpretations, do not explain what is happening in reality. Such theories can't be used to make any predictions because making a prediction depends on understanding how an experimental apparatus works so you can tell if it's working properly, and adjust it so that its state corresponds with the state you want to do a particular test. Other theories such as the Ghirard-Rhimini-Weber theory make less vague statements, but have problems with locality, Lorentz-invariance and so on. In such theories the universe may have a different history if you started it over again. But the probabilities of each possible history occurring would be the same each time.

Another problem with such theories is that they don't solve any problem that can't be solved by quantum mechanics without such vague additions - the Everett interpretation. In the Everett interpretation, measurable quantities typically have multiple possible values before measurement and all of those possibilities occur in reality. This is necessary to explain the outcome of experiments such as single particle interference experiments, see "The Fabric of Reality" by David Deutsch, Chapters 2 and 9 and "The Beginning of Infinity" by David Deutsch, Chapter 11. In this theory if you started the universe over again, it would evolve the same way each time, and that evolution would include the existence of multiple histories, some of which are slight variants of the history you are in now. There might be one history in which you had a different cereal for breakfast or another in which you are wearing a shirt of a different colour. But all of those histories would occur each time the universe was started again.

The discussion of free will in the article somewhat misses the point. Free will is primarily a moral idea, not a metaphysical idea. If a rock falls off a cliff and kills somebody, there is no point in talking to the rock to try to persuade it to refrain from killing people in the future. In addition, there is no particular reason to expect the rock to kill more people in the future. But if a person kills somebody, then the killer may kill other people in the future because that murder is a result of what he values. For example, if Jim finds Bob in bed with Jim's wife and murders Bob, then he may murder somebody else in the future out of sexual jealousy. As a result, it can be a good idea to lock up a murderer to stop him from enacting his values, e.g. - to stop Jim from killing his wife. In addition, it is possible for a person to change his mind about what to value. So discussing why murder was bad in that situation might change Jim's mind about what he should do in the future. Free will is about the fact that is possible for a person to have values, and to change those values as a result of critical discussion. To say that this is all just atoms moving about or something like that privileges a particular kind of explanation of how the world works. But there are other kinds of explanations that feature abstractions like computation, thought, institutions and so on. Those explanations are indispensable to even discuss issues like what sort of political system we have, how we do science and that sort of thing. To use those explanations in terms of abstractions and deny free will doesn't make much sense. For a discussion of abstractions, see "The Beginning of Infinity" by David Deutsch, Chapter 5.


Quantum mechanics is difficult to interpret. Many questions about its interpretation are still open to discussion. And many proposals look strange to our every-day experience.

1) Take your example:

In other words, is [it] possible that if I am at the exact same state of choosing between chocolate and icecream, if we rewind back to that moment over and over n times, in some occasions I may choose strawberry but in others I may choose chocolate?

According to the many worlds interpretation of Everett this already happens each time you open your fridge: The world splits into one world where you prefer strawberry and a second where you take chocolate. At least, when opening the fridge is a quantum mechanical event like the decay of a atomic nucleus - which I have to suppose for the sake of the argument :-)

The whole effect has been coined Schrödinger’s cat in combination with Everett many worlds interpretation.

See the “Chapter 8 The Many Worlds of Quantum Measurement” from Greene, Brian: The Hidden Reality. Parallel Universes and the Deep Laws of the Cosmos (2011).

2) On the level of microphysical events quantum mechanics brings into play indeterminism: It is completely undetermined when a particular atomic nucleus decays.

The article correctly states that the state function of a microphysical object (“the so-called probability amplitude”) evolves in a deterministic way. But in general, this knowledge does not help to predict the outcome of a single measurement, only the probabilities of the different possible outcomes. The outcome of the single mesurement is indetermined.

Processes on the level of microphysics played a fundamental role during fractions of the first second of our world. According to the inflation theory of cosmology they were enlarged to inhomogenities in spacetime. Hence rewinding the universe will not result in the same state after a given time period.

See “Chapter 11 Quanta in the Sky with Diamonds” from Greene, Brian: The Fabric of the Cosmos. Hidden Reality. Space. Time. And the Texture of Reality (2004).

3) For the problem of free will quantum mechanics is rather irrelevant: Because the decisive processes in our brain happen on the level of assemblies of neurons, much bigger than single atomic nuclei.

Here neuroscience is left with the big task to explain the subjective experience of free will (libertarianism) by the deterministic heuristics of science (determinism) in a compatibilist way.

A good introduction is Walter, Henrik: Neurophilosophy of free will: from libertarian illusions to a concept of natural autonomy (2001).

Aside: The term “indeterministic determinism” from one of the articles can be misleading.


I've been going over this discussion with some friends for ... well over a decade. This discussion does cover things pretty well, especially some good descriptions of determinism, but may I make two points that I have made to my friends:

  1. We don't know.

  2. Why are you mentioning "determinism" and "free will" together? One is a characteristic of physics and the other is a religious term. You seem very aware that mechanistic determinism, whether true or not, is an attribute of physics. No one has pointed out that "free will" is a religious concept. That is where it originated. That is where its meaning lies. Perhaps it could also exist in the legal realm. Sorry, but that's just the case. It is not about physics at all and has no meaning there. ... And that is before I put on my biologist hat.

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    If you have relevant references they would support your answer. For example, does anyone else make the distinction between determinism and free will that you do? Providing them would also be a way to guide the reader in a direction you favor should that reader want to research this further. Welcome. Mar 2, 2019 at 15:41
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    So how do I communicate with this person? I look to Wikipedia as the commonest knowledge. There I find every conceivable position, including my own and opposing views. According to what is there, I am completely right and completely wrong, so siting authority seems silly. You can find authority for any position. Sew... as usual, I resort to reason and logic to create understanding, not to argue. There are exceptions but through all of history, the relevant debate is whether humans have free will to chose between good and evil, which then and now has always been considered in religious terms. Mar 2, 2019 at 16:31
  • You won't know whether the reader agrees with you or not or whether the reader is unsure. When you provide an answer with references you protect yourself against the reader who disagrees with you and you guide the reader who is unsure to sources that are similar to those you accept. As you will notice many people who answer questions don't provide references. I think they are missing a valuable opportunity when they don't. Your post appeared in a "new user queue" that I review.That is why I commented as a welcome to you and guide on how to improve an answer. Mar 2, 2019 at 16:50
  • Welcome to Philosophy SE! If you want to respond to a comment remember to use "@" and the name, eg. @FrankHubeny. If you have conflicting references cite them both, we love "further reading" here.
    – christo183
    Mar 2, 2019 at 16:53
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    @FrankHubeny Thank you for your welcome and for your reminder. I guess I take this for granted as my introduction to this was long ago. My position would come from Thomas Aquinas as the most thoughtful philosophers in Western religion were usually Catholic and he was the best of those. While free will has been discussed since before the Greeks in many contexts, I think its important meaning is about freedom to choose right and wrong. Interestingly TA said that free will of humans was compatible with everything being a creation of God - the way it was. I may report what the email group says. Mar 3, 2019 at 16:49

Already, over two millennia ago Aristotle notes that some philosophers argued that

Chance was a cause.

Due to the overwhelming success of Newtonian Mechanics determinism was enshrined within physics, even to the point that its often said that Einstein was for it. His famous:

God does not play dice with the universe

Most assuredly He does not. He was complaining, or more accurately, expressing his surprise, about the overthrowing of mechanical determinism (it not generally understood that he later came to terms with this). In fact, to other, just as philosophical physicists, mechanical determinism could not be true by simple observation of the world around us. For example: Wilhelm Ostwald said in his 1895 address at the Deustche Gesselschaft fur Naturforscher und Artze:

The proposition that all natural phenomena can ultimately be reduced to mechanical ones cannot even be taken as a useful working hypothesis: it is simply a mistake.

This mistake is clearly revealed by the following fact. All the equations of mechanics have the property that they admit sign inversion in the temporal quantities. That is to say, theoretically perfectly mechanical processes can develop equally well forward and backward [in time].

Thus in a purely mechanical world there would not be an after or a before as we have in our world: the tree will become a shoot and a seed again ... the actual irreversibility of natural phenomena thus proves the existence of processes that cannot be described by mechanical equations and with this, the verdict on scientific materialism is settled.

In other words, Newtonian Mechanics, and along with it, Newtonian, mechanical or ‘hard determinism.’

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    Wilhelm Ostwald‘a position doesn’t seem to hold water. He claims that a deterministic universe should be reversible but ignores entropy, which clearly demonstrates that time is not reversible and was known about at least since the 1850s thanks to Rudolf Clausius.
    – Frog
    Jul 8, 2021 at 11:15

Free will is completely independent of the processes that give rise to it. That process can be deterministic or probabilistic. It can be classical stuff, it can be quantum stuff, it can be hot stuff, or it can be all at once.

Free will is nothing but the possibility for this stuff to develop freely. For the stuff-based processes to unfold freely. Free will needs some basis.

Even if there are unconscious processes going on it can still be free.

It changes if the processes are said to be in charge of our thinking (or actions). This is exactly what is done in the academic version of free will. Is my thinking determined? Is my thinking determined by chance, which makes it less free? These are typical questions to a typical version.

Now of course the free will can be restricted. There are many examples of unconscious processes that are implanted in our brains. What should we do without them? There are unconscious processes there in decision-making (it is possible to predict what finger you raise before you raise it).

There are unconscious and unwanted processes. Maybe these are imparting free will. And of course, in our schools, the free will and thinking are heavily restricted by the state-induced obligation (high fines or even prison!) to go visit them every day ("for the children's own good"...my foot!).

Free will can be tramped on by many feet. Wearing all kinds of boots. The best education would be to make the young immune for any kind of systemized education, allowing them to develop freely and... But I am running off right now...

So, probability in QM doesn't have an influence on my free will. If all brain processes were deterministic only I wouldn't notice a difference I guess. Though I am not sure what I would feel like in that case. QM is a magical theory and the brain needs magic to experience anything, so.

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