Do we have free will – a physicist’s perspective?

This blog was prompted by an online article I was alerted to by Roger Highfield on Twitter, which discussed how neuroscientists were conducting experiments suggesting that free will is indeed just an illusion. It was rather dismissive of the years (no, make that centuries) of philosophical debate that has seemingly not brought us any closer to an answer. Now, as a physicist I am usually at the front of the hard-nosed scientist queue when it comes to philosophy bashing. But on this issue, I am not so sure.

Are we really part of a clockwork universe?

Are we really part of a clockwork universe?

What follows is a bit of a cheat, because this is an edited version of part of a chapter from my book Paradox: The Nine Greatest Enigmas in Science, in which I discuss something called Laplace’s demon. Anyway, it is a theoretical physicist’s ramblings that may be seen by neuroscientists and psychologists as fluffy philosophy, and philosophers will just think it naïve. But there you go.

Let me begin by carefully distinguishing between three concepts: determinism, randomness and predictability. Firstly, by ‘determinism’ I mean what philosophers refer to as causal determinism: the idea that events in the past cause events in the future. And it follows, taking the idea to its logical conclusion, that therefore everything happens for a reason that can be traced all the way back to the birth of the Universe itself.

In the seventeenth century Isaac Newton came up with his laws of mechanics using the newly understood mathematics of calculus, which he was instrumental in developing. His equations allowed scientists to predict how objects move and interact with each other, from the firing of canon balls to the motion of the planets. Using mathematical formulas in which values for physical attributes of an object, such as its mass, shape and position, its speed and the forces acting on it, could be plugged into simple equations that could provide information on the state of the object at any future time.

This led to the widely held belief, which lasted for the next two centuries, that if all the laws of nature could be known it would in principle be possible to compute the future action of every object in the Universe. It was a universe in which everything – all movement, all change – was predetermined. There was no free choice, no uncertainty and no chance. It became known as the Newtonian clockwork universe. At first glance, it is not as bleak as Einstein’s block universe, in which everything that has ever happened and will ever happen in the future is laid out frozen in time before us. But in fact, the clockwork universe is no different in the sense that it also gives us a universe in which its state at all future times is indeed predetermined and fixed.

Then this view suddenly changed. In 1886, the King of Sweden offered a prize of two and a half thousand Kroner (a tidy sum and more than most would earn in a year) to whoever could prove the stability of the solar system; that is, whether the planets would continue to orbit around the sun forever or if there was a chance that one or more of them might one day spiral into the sun or escape the pull of its gravity and float away? The French mathematician Henri Poincaré took up the challenge and began by looking at a simpler problem involving just the sun, the earth and the moon – what is referred to as a three-body problem. He discovered that even with just three bodies, the problem was mathematically impossible to solve exactly. What’s more, certain arrangements of the three bodies would be so sensitive to initial conditions that the equations pointed to completely irregular and unpredictable behaviour. He won the King’s prize even though he didn’t come up with an answer to the original question about the stability of the whole solar system.

Poincaré had discovered that even the way a system of just three interacting bodies evolves in time could not be knowable exactly, let alone one involving all bodies in the solar system (at least all the planets and their moons, along with the sun). But the implications of this would have to wait another three-quarters of a century.

When it comes to what all this has to say about the nature of free will, there are still many different philosophical views and the issue is far from resolved. All I can do is give you my opinion as a theoretical physicist. You are free to disagree with me. Or are you?

There are four options available when it comes to the sort of universe we live in:

(i) Determinism is true so all our actions are predictable and we have no free will, just the illusion that we are making free choices;

(ii) Determinism is true but we can still have free will;

(iii) Determinism is false; there is built-in randomness to the Universe allowing us the room to have free will;

(iv) Determinism is false, but we still don’t have free will since events happen randomly that we have no more control over than we would if they were predetermined.

Scientists, philosophers and theologians have debated whether or not we have free will for thousands of years. I’m going to focus here on certain aspects of the nature of free will and its connection with physics. I certainly won’t be straying into the realm of what is called the mind-body problem, the nature of consciousness or the human soul.

Our physical brains, consisting of a network of a hundred billion neurons that are linked together via hundreds of trillions of synaptic connections are, according to everything we know about them so far, nothing more than sophisticated and hugely complicated machines that run the equivalent of computer software, albeit involving a complexity and interconnectedness far beyond anything a modern computer can achieve. All those neurons consist ultimately of atoms that obey the same laws of physics as the rest of the Universe. So if we could, in principle, know the position of each atom in our brains and what it was doing at any given moment and we understood fully the rules that govern how they all interact and fit together, then we should in principle be able to know the state of our brains at any time in the future. That is, with enough information I could predict what you will do or think next – provided of course you are not interacting with the outside world, otherwise I will need to know everything about that too.

Were it not therefore for the weird and probabilistic quantum rules according to which those atoms behave, and in the absence of any non-physical, spiritual or supernatural dimension to our consciousness of which we have no evidence, we would have to admit that we too are part of Newton’s clockwork, deterministic universe and that all our actions are preordained and fixed in advance. In essence, we would have no free will.

So do we have free will or don’t we? The answer, despite what I have said about determinism, is yes I believe we still do. And it is rescued not by quantum mechanics, as some physicists argue, but by chaos theory. For it doesn’t matter that we live in a deterministic universe in which the future is, in principle, fixed. That future is only knowable if we were able to view the whole of space and time from the outside. But for us, and our consciousnesses, imbedded within space-time, that future is never knowable to us. It is that very unpredictability that gives us an open future. The choices we make are, to us, real choices, and because of the butterfly effect, tiny changes brought about by our different decisions can lead to very different outcomes, and hence different futures.

So, thanks to chaos theory our future is never knowable to us. You might prefer to say that the future is preordained and that our free will is just an illusion, but the point is our actions still determine which of the infinite number of possible futures is the one that gets played out.

Consider the situation, not from our own point of view looking out at the deterministic yet unpredictable world around us, but by examining the complexity of our brains and how they work. It is precisely this unavoidable unpredictability about how a complex system such as our brain works, with all the thought processes, memories, interconnected networks with their loops and feedbacks, that gives us our free will.

Whether we call it true freedom or just an illusion in a way does not matter. I can never predict what you might do or say next if you really want to trick me because I cannot in practice ever model every neuronal activity in your brain, anticipate every changing synaptic connection and replicate every one of those trillions of butterflies that constitute your conscious mind in order for me to compute your thoughts. That is what gives you free will. This despite the actions of the brain most probably remaining fully deterministic – unless quantum mechanics has a bigger say in the matter than we currently understand.

About Jim Al-Khalili

Professor of theoretical physics at the University of Surrey, author and broadcaster.
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27 Responses to Do we have free will – a physicist’s perspective?

  1. Margaret Yeats says:

    Thanks for early morning brain workout.

  2. @Nissemus says:

    But if the multiverse interpretation of quantum mechanics is correct, are we not doomed to make every possible choice in one reality or another? That doesn’t sound like free will to me.

  3. Very interesting perspective on free will. Thank you, Jim.

  4. SweynTUV says:

    I recently listened to your scipod on freewill and found myself agreeing that predictability is the key issue here. That was disappointing as I thought I was doing some original thinking. Not very likely on reflection.

    One point that is often skipped in discussing whether we have freewill is the definition of what “we” are. If I accept materialism and that my pre-conscious mental activity is within the boundary of what “I” am, then it’s not surprising that my actions are predictable or modifiable without my conscious awareness of it. If that makes freewill an illusion then it also makes me an illusion and I rather think that is chucking out the baby with the bathwater.

    • Adam says:

      I suppose one might see it that way; if one is committed to the reality of a discrete self. However, I think folks as varied as Siddhartha Gautama and David Hume would disagree with that notion..

  5. Jake says:

    Here are my thoughts after reading that:

    Some things are pre-determined, and follow certain laws and these things can be shown to perfectly follow these laid out paths until their conclusion. However, these things are also ultimately changeable and susceptible to influence. This influence may be easy or extremely hard to place, it doesn’t matter. Determinism and free will can co-exist.

    Others are chaotic and follow no clear path, and are therefore unknowable but still react to influence in much the same way.

    Basically, free will exists. But deciding to stand in front of a train because you want to stop it doesn’t mean you will be successful.

    In terms of the quantum universe, well, it could be argued that everything is both determined and chaotic at once, couldn’t it?

  6. Vyacheslav says:

    So basically the whole notion of “free will” is hard to define and we might as well say that we have it. Because it might cause depression if we don’t :)

  7. Alek says:

    Chaos theory in no way defends the free will.
    Even though chaotic systems are not predictable, their behavior is known as *deterministic* chaos. That means, even though their movement is far to complex to be calculable, is is still *determined*!

    • SweynTUV says:

      I don’t think anyone is suggesting that chaos theory implies that the universe is non-deterministic in any sense. It does however make things practically unpredictable which is the key point.

      When I make a choice, no-one can predict what that choice will be, not even me. The closest anyone can come to knowing what I will choose to do requires them to have my head in an fMRI scanner and even then they may get just a fraction of a second’s advance warning of what I might choose. All they are actually doing is watching what “I”‘ as a physical system that takes time to make choices, is doing. Determinism and freewill are only incompatible if one insists on seeing oneself as a non-physical being that makes instantaneous choices and that is something that can be shown experimentally to be incorrect.

      It’s the immaterial self that is the illusion, not the freewill. A material self having a meaningful kind of freewill is the reality. To ignore that is to focus only on the atoms and not the person they comprise, which misses the most interesting thing about them.

      • Alek says:

        When I make a choice, no-one can predict what that choice will be, not even me
        “Unpredictable” is not the same as “free”. In fact they exclude each other:
        if even you cannot predict your choice, how can that be called a free will?
        That means free will is impossible in both deterministic and non-deterministic universe.

        • SweynTUV says:

          If our focus is down at the fundamental level then yes, each state of the universe is fully determined by the previous state and the entire universe is on rails from start to finish. You might argue that because conscious beings exist in such a universe they cannot be “free” but I think that is a very narrow and rather dull definition of freedom. When something is complicated enough to be conscious it’s behaviour is “practically” free because it can internally model possible future states and act to bring about the state that best serves its interests. Moreover those actions cannot be predicted “in practice”. If you like you can insist that consciousness and the possible futures it imagines are all illusions. In one sense they are but they are also the most interesting things that the universe has brought about so I don’t think a focus that excludes them is helpful or interesting. And if our view of reality expands to encompass consciousness, then I think that some meaningful form of freewill (pseudo-freewill if you absolutely must) has to come with it.

  8. Shahzad Chaudhry says:

    I can not prove it scientifically but I still have to go with the second option “Determinism is true but we can still have free will” due to a simple yet very strong belief:
    - “Determinism” because everything must come to an end one day; judgement day.
    - “Still have free will” because of our actions we will earn either heaven or hell.

  9. Tony G says:

    I really enjoyed your blog post this morning. It helped me to see a different purely physical perspective on Freewill. I have always found Wayne Grudem’s definition of free will, in his book titled Systematic Theology, to be helpful for me also. He says that only a being that is eternal, self-sufficient, that does not depend on anything to exist, has free will. That our free will is not really free, because we will always be dependent on universe in order to exist. I enjoyed your purely physical perspective on Freewill because it helps me to understand the phenomenon without the need of theology. This making free will intelligible for me!!!thank you.

  10. Wrrn D F says:

    Ok boss. I see what you’ve done. By distilling the theory down to something akin to the 3 body problem. Perhaps that arc of view will give light to the greater problem. The fact that mathematically even keeping track of the 3 body problem becomes practically impossible should give an indication of the scale of the task ahead. Thanks for throwing in a ’4th body’; The mind body problem…(raising the question, what is the ‘greater, I am’)

    May I use analogy… If a scientist wants to study the Solar System. He sets up his telescope and trains it on the moon. He spends a lifetime observing the white, bleak body. Undoubtedly He would have a very good view of the moon. However will this give Him ALL the universes answers?

    Determinism and freewill. We’re even crossing the theology boundary on this one. As you point out there are simply too many variables. We can observe for 100000 yrs and (if the universe is like a huge 3d snooker table) still not be able to plot when a rogue planet may be on a collision course… Was it going to collide with Us at that day and time from day 1 week 1? Which would give weight to one side of the argument. And if we had suitable warning and was able to affect the planets course… It would seem to give weight to another side of the argument. Or does it! Ok we need to work these problems amoung others out. But the more We see the more questions will be raised, typically. Bright Men and Women will continue to be driven to madness, in pursuit. What if ‘The Gleik’ infinite within the finite does hold true. Then were destined to ask and to continue to ask infinitely. There being no real grand unified theory… Just more riddles to solve. Haha, almost by design! P.s pls excuse any undersights and of course, auto correct!

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  13. Abdullahi Bello says:

    Determinism and free will can also be explained by this analogy

    It is determined that if you jump from an aeroplane that is at a very high altitude, you will die, but you are free to decide whether to jump or not to jump

  14. If you consider the Many Worlds Interpretation and that anything that can happen does happen then its not a case of determinism. It’s a case that every possible outcome from the subatomic level is invoked. All these potential outcomes are possible and we subjectively experience a varied single trajectory through one of these routes. Therefore, free will is not an illusion it is a subjective experience through one of these myriad ‘worlds’. Rather than the Universe being deterministic it could be entirely stochastic due to the idea that everything that’s possible happens. This presents each conscious individual an infinite selection of outcomes in which to experience their life.

  15. Luka says:

    So we have free will in same way clouds do? We cant really determine their future because of chaos theory so they have a mind of their own? I don’t think that counts as free will, but good to know we don’t need quantum randomness to be unpredictable! :-)

  16. Ken says:

    Seems there is another option beyond the four offered here. Actually, one could argue that there is a codicil to options (ii) and (iii):

    Even if one determines that free will is possible, given the physical state of the universe, who’s to say that free will is also practically accessible to everyone?

    Because of the situations we have encountered in our lives up to this point, each person has some degree of psychological conditioning. The conditioning influences all choice and in some cases completely determines a choice. A decision made under such circumstances cannot properly be considered free, since there’s an ever-present influence.

  17. Paul Hudson says:

    In respect of how consciousness (and various interpretations of the “Free Will” concept) is described and understood in terms of a determinate/indeterminate universe, I think we must first accept that the human brain did not evolve to accurately interpret and understand the many layers of perception, processing and motor operations it carries out in the unconscious “subroutines” of its existence and functioning. This essentially reduces human consciousness to no more than a sort of ‘fuzzy’ interpreter between these unconscious processes and our fully intended interactions with the world (a kernel in computer speak) that has continuously evolved as a selective advantage throughout hominid ascendency to where we are now.
    When considered in this discrete (and imho correct) context, consciousness and free will become a little easier to quantify, at least in terms of your chaos theory interpretation, which incidentally is plausible enough as a philosophy, but is somewhat unsatisfying as a conclusion. I don’t see that saying at a fundamental level we probably live in a deterministic universe, and only have an illusion of free will based on inordinately complex systems is true free will (at least not in a fundamental sense).
    Until we explore particle physics enough to rule in/out genuinely random impulses being somehow invoked to inform the quantum function of the brain, then I think these (admittedly attractive and interesting) philosophical navel gazing exercises are always bound to lack real satisfaction.
    So anyway, it’s number (iv) in your list of options… at least that’s what Schrödinger’s Cat just whispered to me. :)

  18. Jon Jermey says:

    This is like saying that a coin has ‘free will’ because when I throw it there are so many diverse and unmeasured forces acting upon it that I have no way of knowing whether it will turn up heads or tails. But nobody thinks that coins have free will; so any argument that people have free will which is based on the same evidence must be missing the point.

    Nobody claims that we can predict what a person will be doing in a year, or a day, or even an hour; but we can be sure that whatever they do, it will be what physical causes acting within and upon them and their surroundings caused them to do.

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  21. 31428571J says:

    ”So do we have free will or don’t we? The answer, despite what I have said about determinism, is yes I believe we still do. And it is rescued not by quantum mechanics, as some physicists argue, but by chaos theory. For it doesn’t matter that we live in a deterministic universe in which the future is, in principle, fixed. That future is only knowable if we were able to view the whole of space and time from the outside. But for us, and our consciousnesses, imbedded within space-time, that future is never knowable to us.”

    Just because the future consequences of ‘chaos’ are unknowable, it doesn’t mean that they aren’t still deterministically ordered in some way.
    (even ”random” could be purposeful… but remain forever beyond the scope of human ability)

    ”So, thanks to chaos theory our future is never knowable to us. You might prefer to say that the future is preordained and that our free will is just an illusion, but the point is our actions still determine which of the infinite number of possible futures is the one that gets played out.”

    An infinite number of possible futures running parallel with (the same) infinite number of universes sounds rather ordered to me.

    ”That future is only knowable if we were able to view the whole of space and time from the outside.”

    Thanks for this professor, now I know why I am a panentheist:-)

  22. Ray says:

    Every person who responds to this blog is exercising his free will.
    No one or no thing is exerting influence or pressure to respond.

    However, the ability to agree or disagree with what has been said by others is not in the realm of free will.

    A response will be governed by the past experience and motivation of the respondent and they no more have the ability to deny the imperative need to respond as they do in taking their next breath.

    Schopenhauer’ : “a man can do as he will, but not will as he will.”

  23. 31428571J says:

    “So if we could, in principle, know the position of each atom in our brains and what it was doing at any given moment and we understood fully the rules that govern how they all interact and fit together, then we should in principle be able to know the state of our brains at any time in the future. That is, with enough information I could predict what you will do or think next – provided of course you are not interacting with the outside world, otherwise I will need to know everything about that too.”

    Ouch, that is a very big number:-)

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