On Determinism

By Sean Carroll | December 5, 2011 10:19 am

Back in 1814, Pierre-Simon Laplace was mulling over the implications of Newtonian mechanics, and realized something profound. If there were a vast intelligence — since dubbed Laplace’s Demon — that knew the exact state of the universe at any one moment, and knew all the laws of physics, and had arbitrarily large computational capacity, it could both predict the future and reconstruct the past with perfect accuracy. While this is a straightforward consequence of Newton’s theory, it seems to conflict with our intuitive notion of free will. Even if there is no such demon, presumably there is some particular state of the universe, which implies that the future is fixed by the present. What room, then, for free choice? What’s surprising is that we still don’t have a consensus answer to this question. Subsequent developments, most relevantly in the probabilistic nature of predictions in quantum mechanics, have muddied the waters more than clarifying them.

Massimo Pigliucci has written a primer for skeptics of determinism, in part spurred by reading (and taking issue with) Alex Rosenberg’s new book The Atheist’s Guide to Reality, which I mentioned here. And Jerry Coyne responds, mostly to say that none of this amounts to “free will” over and above the laws of physics. (Which is true, even if, as I’ll mention below, quantum indeterminacy can propagate upward to classical behavior.) I wanted to give my own two cents, partly as a physicist and partly as a guy who just can’t resist giving his two cents.

Echoing Massimo’s structure, here are some talking points:

* There are probably many notions of what determinism means, but let’s distinguish two. The crucial thing is that the universe can be divided up into different moments of time. (The division will generally be highly non-unique, but that’s okay.) Then we can call “global determinism” the claim that, if we know the exact state of the whole universe at one time, the future and past are completely determined. But we can also define “local determinism” to be the claim that, if we know the exact state of some part of the universe at one time, the future and past of a certain region of the universe (the “domain of dependence”) is completely determined. Both are reasonable and relevant.

* It makes sense to be interested, as Massimo seems to be, in whether or not the one true correct ultimate set of laws of physics are deterministic or not. He argues that we don’t know, and that’s obviously right, since we don’t know what the final theory is. But that’s a rather defeatist attitude all by itself; we can look at the theories we do understand and try to draw lessons from them.

* Classical mechanics, which you might have thought was deterministic if anything was, actually has some loopholes. We can think of certain situations where more than one future obeys the equations of motion starting from the same past. This is discussed a bit in the Stanford Encyclopedia of Philosophy article on causal determinism. But I personally don’t find the examples that impressive. For one thing, they are highly non-generic; you have to work really hard to find these kinds of solutions, and they certainly aren’t stable under small perturbations. More importantly, classical mechanics isn’t right; it’s just an approximation to quantum mechanics, and these finely-tuned classical solutions would be dramatically altered by quantum effects.

* General relativity is a classical theory, so it’s also not correct, but we don’t have the final theory of quantum gravity so it’s worth a look. As Massimo points out, there are good examples in GR where traditional global determinism breaks down; naked singularities would be an example. (Basically, determinism breaks down when information can in principle “flow in” from a singularity or boundary that isn’t included in “the whole universe at one moment of time.”) We might sidestep this problem by arguing that naked singularities aren’t physical, which is quite reasonable. But there are much more benign examples, such as anti-de Sitter space — a maximally symmetric spacetime with a negative cosmological constant. This universe has no singularities, but does have a boundary at infinity, so a single moment of time only determines part of the universe, not the whole thing. On the other hand, like the classical-mechanics examples alluded to above, this seems like a technicality that can be cleared up with a slight change of definition, e.g. by imposing some simple boundary condition at infinity.

Much more importantly, these kinds of GR phenomena are very far away from our everyday lives; there’s really no relevance to discussions of free will. GR violates global determinism in the strict sense, but certainly obeys local determinism; that’s all that should be required for this kind of discussion.

* Quantum mechanics is where things get interesting. When a quantum state is happily evolving along according to the Schrödinger equation, everything is perfectly deterministic; indeed, more so than classical mechanics, because the space of states (Hilbert space) doesn’t allow for the kind of non-generic funny business that let non-deterministic classical solutions sneak in. But when we make an observation, we are unable to deterministically predict what its outcome will be. (And Bell’s theorem at least suggests that this inability is not just because we’re not smart enough; we never will be able to make such predictions.) At this point, opinions become split about whether the loss of determinism is real, or merely apparent. This is a crucial question for both physicists and philosophers, but not directly relevant for the question of free will.

The traditional (“Copenhagen”) view is that QM is truly non-deterministic, and that probability plays a central role in the measurement process when wave functions collapse. Unfortunately, this process is extremely unsatisfying, not just because it runs contrary to our philosophical prejudices but because what counts as a “measurement” and the quantum/classical split are extremely ill-defined. Almost everyone agrees we should do better, despite the fact that we still teach this approach in textbooks. Someone like Tom Banks would try to eliminate the magical process of wave function collapse, but keep probability (and thus a loss of determinism) as a central feature. There is a whole school of thought along these lines, which treats the quantum state as a device for tracking probabilities; see this excellent post by Matt Leifer for more details.

The other way to go is many-worlds, which says that the ordinary deterministic evolution of the Schrödinger equation is all that ever happens. The problem there is comporting such a claim with the reality of our experience — we see Schrödinger’s cat to be alive or dead, not ever in a live/dead superposition as QM would seem to imply. The resolution is that “we” are not described by the entire quantum state; rather, we live in one branch of the wave function, which also includes numerous other branches where different outcomes were observed. This approach (which I favor) restores determinism at the level of the fundamental equations, but sacrifices it for the observational predictions made by real observers. If I were keeping a tally, I would certainly put this one in the non-determinism camp, for anyone interested in questions of free will.

* Then there is the question of whether or not the lack of determinism in QM plays any role at all in our everyday lives. When we flip a coin or play the lottery, one might think that the relevant probabilities are “purely classical” — i.e. they stem from our lack of knowledge about the state of the muscles and nerves in my hand and the wind and the coin that is about to be flipped, but if I knew all of those things I could make a perfectly deterministic prediction about what would happen to the coin. (Indeed, a well-trained magician can flip a coin and get whatever result they want.)

This is actually a tricky problem, to which the answers aren’t clear. Yes, there may be a level of classical description in terms of a probability distribution; but where does that probability distribution come from? Physicists disagree about whether or not quantum mechanics plays a crucial role here. Since I have friends in high places, this weekend I emailed Andy Albrecht, who answered and brought David Deutsch into the conversation. They both argue — plausibly, although I’m not really qualified to pass judgment — that essentially all classical probabilities can ultimately traced down to the quantum wave function. And indeed, that this reasoning provides the only sensible basis for talking about probabilities at all! (David mentions that Lev Vaidman seems to disagree, so it’s not uncontroversial by any means.) They are both, in other words, firmly anti-Bayesian in their view on probability. A good Bayesian thinks that probabilities are always statements about our fundamental ignorance concerning what is “really” going on. Albrecht and Deutsch would argue that’s not true, probabilities are ultimately always statements about the wave function of the universe. If they’re right — and again, it looks plausible, but I need to think about it more — then QM effects are indeed of crucial importance in accounting for our inability to predict the future in the everyday world.

* I should say something about chaos, which always comes up in these discussions. In classical mechanics, even when the underlying model is perfectly deterministic, it can often be the case that a small uncertainty in our knowledge of the initial state can lead to large uncertainty in the future/past evolution. (E.g. for the tumbling of Hyperion.) This is sometimes brought up as if it causes problems for determinism: “since tiny mistakes propagate, you couldn’t realistically predict the future anyway.” This is about as irrelevant as it is possible to be irrelevant. The Laplacian viewpoint was always that if you had perfect information, you could predict the past and future. But that was always a statement of principle, not of practice. Of course, in practice, you have nowhere near enough information to make the kinds of calculation that Laplace’s vast intellect likes to do. That was perfectly obvious long before the advent of chaos theory. The correct statement is “in a classical deterministic system, with perfect information and arbitrary computing power you can predict the future in principle, but not in practice,” and that statement is completely unaltered by an understanding of chaos.

So where does that leave us? My personal suspicion is that the ultimate laws of physics will embody something like the many-worlds philosophy: the underlying laws are perfectly deterministic, but what happens along any specific history is irreducibly probabilistic. (In a better understanding of quantum gravity, our notion of “time” might be altered, and therefore our notion of “determinism” might be affected; but I suspect that there will still be some underlying equations that are rigidly obeyed.) But that’s just a suspicion, not anything worth taking to the bank. For everyday-life purposes, we can’t get around the fact that quantum mechanics makes it impossible to predict the future robustly.

Of course, this is all utterly irrelevant for questions of free will. (I’m sure Massimo knows this, but he didn’t discuss it in his blog post.) We can imagine four different possibilities: determinism + free will, indeterminism + free will, determinism + no free will, and indeterminism + no free will. All of these are logically possible, and in fact beliefs that some people actually hold! Bringing determinism into discussions of free will is a red herring.

It matters, of course, how one defines “free will.” The usual strategy in these discussions is to pick your own definition, and then argue on that basis, no matter what definition is being used by the person you’re arguing with. It’s not a strategy that advances human knowledge, but it makes for an endless string of debates.

A better question is, if we choose to think of human beings as collections of atoms and particles evolving according to the laws of physics, is such a description accurate and complete? Or is there something about human consciousness — some strong sense of “free will” — that allows us to deviate from the predictions that such a purely mechanistic model would make?

If that’s your definition of free will, then it doesn’t matter whether the laws of physics are deterministic or not — all that matters is that there are laws. If the atoms and particles that make up human beings obey those laws, there is no free will in this strong sense; if there is such a notion of free will, the laws are violated. In particular, if you want to use the lack of determinism in quantum mechanics to make room for supra-physical human volition (or, for that matter, occasional interventions by God in the course of biological evolution, as Francis Collins believes), then let’s be clear: you are not making use of the rules of quantum mechanics, you are simply violating them. Quantum mechanics doesn’t say “we don’t know what’s going to happen, but maybe our ineffable spirit energies are secretly making the choices”; it says “the probability of an outcome is the modulus squared of the quantum amplitude,” full stop. Just because there are probabilities doesn’t mean there is room for free will in that sense.

On the other hand, if you use a weak sense of free will, along the lines of “a useful theory of macroscopic human behavior models people as rational agents capable of making choices,” then free will is completely compatible with the underlying laws of physics, whether they are deterministic or not. That is the (fairly standard) compatibilist position, as defended by me in Free Will is as Real as Baseball. I would argue that this is the most useful notion of free will, the one people have in mind as they contemplate whether to go right to law school or spend a year hiking through Europe. It is not so weak as to be tautological: we could imagine a universe in which there were simple robust future boundary conditions, such that a model of rational agents would not be sufficient to describe the world. E.g. a world in which there were accurate prophesies of the future: “You will grow up to marry a handsome prince.” (Like it or not.) For better or for worse, that’s not the world we live in. What happens to you in the future is a combination of choices you make and forces well beyond your control — make the best of it!

CATEGORIZED UNDER: Philosophy, Science, Top Posts
  • http://mmcirvin.livejournal.com/ Matt McIrvin

    Collins’ position, or a logically equivalent statement about free will, seems superficially plausible as long as you’re only looking at values of a single operator, like the position of a particle. The distribution has to have a certain shape over the long term–that leaves a lot of wiggle room for different patterns of results, right? You could do a lot with that! God could do a lot with that!

    Not so. QM makes predictions about the distribution of values of any observable operator, not just x. God, or free-will power, would have to work in ways so mysterious that they cannot be detected in the distribution of values of any observable quantity. That’s actually a pretty powerful constraint.

    • http://blogs.discovermagazine.com/cosmicvariance/sean/ Sean

      That’s a good way of putting it, yes.

  • Physicalist

    Yes, the real issue isn’t whether freedom is compatible with determinism, it’s whether freedom is compatible with the completeness of physics (or, if one rejects physicalism, with the completeness of natural laws).

    I would certainly put [many worlds] in the non-determinism camp, for anyone interested in questions of free will.

    Really? It strikes me as even more deterministic than classical mechanics in a way — it seems like on this account it would be nearly impossible to avoid any action (since in some world that action will occur).

    At least given classical determinism I can choose to perform some actions and avoid others. With many worlds, it will (often? always?) be the case that the action both will be performed and won’t be performed.

    I suppose choices will make a difference to the extent that quantum uncertainties wash out and are irrelevant to large-scale bodily behavior, but given the multiplicity of real worlds, it’s not really clear how much of a difference this makes. It’s pretty hard to make sense of rationality and morality in a many-worlds scenario.

  • http://scienceblogs.com/startswithabang/ Ethan Siegel

    Oh please.

    You get one three-body collision in there — in the past or the future — and all your predictive power is gone.

    And surely if Newton knew this, LaPlace knew it too.

  • http://mmcirvin.livejournal.com/ Matt McIrvin

    Greg Egan wrote some science-fiction stories set in a world in which post-human beings made sure their brains were specially engineered such that their choices would never be indeterminate on the quantum level, because they felt that only then would their decisions really matter!

  • Physicalist

    Ethan Siegel says:

    You get one three-body collision in there . . . and all your predictive power is gone.

    That’s why Sean listed “arbitrary computing power” in there. We’re interested in the metaphysics, not in our practical abilities to predict. (Which is also why Sean rightly dismisses chaos as irrelevant.)

    The relevant point is that the behavior does follow the physical laws.

    And note that even though we can’t solve the three-body problem to predict future behavior, once we have the behavior in hand, we can confirm that it didn’t violate the laws. If I give you the solution, it’s generally pretty straightforward to confirm that it is indeed a solution to the equations of motion. That’s all we need to establish the completeness of physics.

  • http://scienceblogs.com/startswithabang/ Ethan Siegel

    No physicalist @6, not the “three body gravitational problem,” but a simultaneous collision between three particles.

    You know, where particles “1” “2” and “3” collide, each with some initial momentum, simultaneously.

    That, classically, is a totally unpredictable system. As you can imagine, if “1 hits 2 which then hits 3” you get a different answer than if “3 hits 2 which then hits 1.” But if “1, 2, and 3 collide simultaneously,” your system is under-constrained, and there are multiple possible solutions to what the final momenta of the three particles will be. Classically.

    It’s non-deterministic, and — like I said — LaPlace surely knew this.

    • http://blogs.discovermagazine.com/cosmicvariance/sean/ Sean

      Ethan, as I said in the post, there are non-deterministic problems in classical mechanics (albeit they appear to be a set of measure zero). Whether Laplace knew this is an empirical question, about which I don’t have any data. But he certainly did write the famous passage about a vast intelligence, as quoted in Wikipedia.

  • max

    The free will discussion has never really seemed that interesting for reasons that Sean outlines above. Everyone has a different definition, and everyone just seems to talk over each other. We would really need a robust theory of consciousness before we’d be able to tackle free will in a more meaningful way, and we’re nowhere near that.

    For what it’s worth, the compatibilist view seems like the sensible way to think about it. If you want to do something and you choose to do it and you do do it, then you’ve acted freely. It doesn’t matter whether your base desires are “freely” chosen or not (whatever that might mean).

  • Physicalist

    “a simultaneous collision between three particles.”

    Ah. Then I take it that this will be a case like the one that Norton discusses, and that Sean refers to in the S.E.P. entry.

    Then the relevant question (as Sean points out) is whether such a scenario is realistic enough to worry about. Two issues:

    (1) Does the real world ever admit of actually instantaneous interactions of this sort? As you say, you get different answers depending on which collision happens first — but if as a matter of fact one does occur first, then the outcome is determined (though we might be in a position to predict that outcome). So, are there real collisions in which three bodies really collide at precisely the same instant?

    Of course, when you try to get down to such fine-grained detail, you notice that classical mechanics’ description of colliding rigid bodies isn’t exactly right — so the answer is that there are not collisions of this sort in the real world. Which leads us to the second issue:

    (2) Given that the real world is quantum mechanical, what should we say about determinism? Sean has given his answer above. The main thing that I would add is that we shouldn’t rule out non-local hidden variable interpretations like Bohm’s. It seems to me that such a theory is robustly deterministic. (And I’m inclined to say that many worlds and spontaneous collapse are just as non-local as Bohm’s theory, but that’s an argument for another day.)

  • http://scienceblogs.com/startswithabang/ Ethan Siegel


    I don’t think you give the simple example of a three-body collision its due; if you were willing to consider it, you’d arrive at the same non-determinism that arises in the final momenta in neutron decay. While the examples you link to in the Stanford Encyclopedia may be of measure zero, this one isn’t; it’s far more general than the very specific example given there. You can take a simultaneous collision between any three classical objects with a combination of any initial momenta, and your final state is not determined.

    LaPlace didn’t know about the densities and energies of the early stages of the Big Bang (where the three-body collision, at those high densities, are simultaneous if one considers timescales smaller than the Planck time to be simultaneous), nor of simple matter-antimatter processes (electron-positron annihilation, treating it as classically as possible), but if one is willing to accept these basic things that happen, you cannot keep determinism even if you don’t step into the quantum realm.

    Not saying LaPlace didn’t “forget” (or ignore) a 3-body collision when he wrote his passage, just that — given some very basic things that we know — that argument holds no water, even classically (that is, without any reference to or consideration of a quantum mechanical wavefunction).

    • http://blogs.discovermagazine.com/cosmicvariance/sean/ Sean

      Ethan, three particles in three dimensions describe an eighteen-dimensional phase space. The constraint that all three particles are at the same location at some time is a six-dimensional constraint (choose one position, the other two positions are determined). We’re left with a twelve-dimensional submanifold of an eighteen-dimensional space. That is bigger than a point, but is certainly a set of measure zero in the larger space. Said another way, more directly relevant to this discussion: a generic perturbation in phase space moves you off the constraint surface.

      Everyone agrees that classical mechanics allows for non-deterministic evolution, but it’s not the generic case, so I’m not sure what the argument is here.

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  • Dan L.

    That, classically, is a totally unpredictable system. As you can imagine, if “1 hits 2 which then hits 3″ you get a different answer than if “3 hits 2 which then hits 1.” But if “1, 2, and 3 collide simultaneously,” your system is under-constrained, and there are multiple possible solutions to what the final momenta of the three particles will be. Classically.

    Hmm, a really interesting point that gets to the core of the failures of classical mechanics that led to both relativity and QM. Einstein was pretty explicit that a lot of his reasoning about special relativity came from questions about what “simultaneity” meant. And, although I don’t have the acumen to fairly judge, it seems to me like demanding that A, B, and C collide simultaneously violates the uncertainty principle (you are demanding absolutely zero error in your time measurements of the collisions of A, B, and C pairwise).

    Would you mind providing some kind of citation or link where I can read more, though? Wikipedia doesn’t seem to treat this particular version of the “three body problem” on the relevant page.

    I’d be really curious to hear more about the conversation with Albrecht and Deutch, Sean. I’ve been trending Bayesian (I guess the pun is intended…sorry folks) but I’d be love to hear some of the arguments against.

  • http://rohanmedia.co.uk Rohan

    So in Many-worlds free-will. Consciousness would be some 5D snake like thing branching when a conscious action takes place?

  • Somite

    Whatever biologists make out of consciousness and free will my feeling is that it will have very little to do with physics and specially QM. Just like nature abhors a vacuum biology abhors indeterminacy. You can see this on biological process that could involve quantum phenomenona but don’t, like the electron transport chain and photoreceptors. Both of these processes have quite deterministic outputs.

    Consciousness will be a matter of competition and selection, with an aggregator that measures the output of different neuronal constellations that represent each competing thought. This aggregator will turn out with something as mundane as the level of neurotransmitter or number of active synapses. It will not involve physics or QM in an interesting way.

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  • Charlie

    @Somite Says #16,

    On the contrary, indeterminacy is sometimes useful in biological systems. Molecular signaling pathways can be “engineered” to be more or less deterministic versus stochastic, and there are probably good reasons (i.e., fitness benefits) for both kinds of circuit function. Just Google Scholar “lambda phage stochastic” for examples. My own bias is that this sort of stochastic understanding will play an important role in any good model of behavior/decision making/consciousness/free will/whatever-you-want-to-call-it (though this is still an open question). I agree that there is no need for biologists to call on QM directly, as yet, but the mathematics that underlie it may be useful (perhaps have already been used? I’m no expert here) for developing stochastic kinetic models.

  • Somite

    I agree. Stochastic yes. QM no. When I wrote indeterminacy I meant that of QM and now I realize I meant something like uncertainty.

  • Tom

    Hi, I’ve been following your blog for a while and I love it. I am not a physicist, just an avid follower of physics. This is my first time submitting a comment. Sorry it’s a bit off-topic, but maybe it’s something you could spend a future post on? I imagine many of your readers would have the same question.

    There’s something about many-worlds that I’ve always wondered: does it explain probabilities, and if so, how?

    If I imagine a 50:50 choice, like Schrodinger’s Cat, then it makes sense that (after opening the box) the wavefunction contains 2 pieces, and , and that I have a 50:50 chance of being part of either piece. One can certainly build up many rational-number probabilities with lots of 50:50 choices. However, I can change the setup so the probability is an irrational ratio, let’s say P():P() = 1:sqrt(2). How does many-worlds handle that case? The wavefunction still has two pieces, and . They have different amplitudes, but the “me” that is part of each feels just as real. Yet there must be some way in which “I” am more likely to be the “me” that is part of than . Does that arise out of the many-worlds program, or is it a further postulate, as in “My probability of existing in any branch of the wavefunction depends on the amplitudes at each branch.”

    • http://blogs.discovermagazine.com/cosmicvariance/sean/ Sean

      Tom– This is an excellent question, the subject of much current research. It is, at least, not perfectly obvious how to get probabilities out of the many-worlds interpretation. See e.g.


      There are promising approaches (e.g. from Deutsch, Wallace, Zurek, and others), but I don’t think there’s a consensus. Of course many other approaches “get” probability, essentially by putting it in by hand; MWI doesn’t have that freedom, since it’s just supposed to be the Schrodinger equation and nothing else.

  • Colin Bisset

    I used to argue about free will, but now I don’t. Whether the universe is deterministic or not is, as pointed out, pretty much irrelevant, because the possession of free will is a subjective state. You either feel free, or you don’t.
    It’s interesting to speculate on this though: If the universe is deterministic, then the conclusion from human behavior is that doing nothing is, evolutionarily speaking, advantageous. If choice is a non-concept, it follows that the time my ancestors spent making decisions, i.e., not doing anything when confronted with a stimulus, increased their reproductive success. This thought pleases me more than freedom.

  • https://twitter.com/#!/sprawld sprawld

    Bizarrely I was just reading David Wallace, a philosopher with Oxford Flu (symptoms include feeling you keep splitting into multiple copies). His entry in this years Oxford Handbook on Quantum Mechanics is a good look overview of some of these issues.


    He covers Many Worlds (Everett) generally, and the preferred basis problem, which he has a strong view on (spoiler alert: it’s emergent). For probability – which has been, and remains a hotly debated issue – he sketches out the main arguments on various sides.

    Probability is far from ‘solved’, but Deutsch, Wallace et al. have shown pretty convincingly that you can derive probability amplitudes (mod squared) from MWI + decision theory or symmetry arguments.

    To answer Tom’s question, branches are a continuum in Quantum Theory, so irrational weightings are just as easy as 50:50. The fact that probability amplitudes (the Born Rule) can be derived from Everett mean that no further postulates are required (if the derivation is valid of course!)

    As Sean pointed out (and Wallace agrees) there are a lot of questions with probability at determinacy, in Many Worlds or not. Arguably Deutsch’s derivation has put probability on a much firmer footing under Everett, than we had before. Giving a principled argument for uncertainty in a deterministic physics.

  • Katherine

    Regarding lawfulness and free will, does anyone have any thoughts on the following quote from Chapter One of Stephen Hawking’s “A Brief History of Time”:

    “Now, if you believe that the universe is not arbitrary, but governed by definite laws, you ultimately have to combine the partial theories into a complete unified theory that will describe everything in the universe. But there is a fundamental paradox in the search for such a complete unified theory. The ideas about scientific theories outlined above assume we are rational beings who are free to observe the universe as we want and to draw logical deductions from what we see. In such a scheme it is reasonable to suppose that we might progress ever closer toward the laws that govern the universe. Yet if there really is a complete unified theory, it would also presumably determine our actions. And so the theory itself would determine the outcome of our search for it! And why should it determine that we come to the right conclusions from the evidence? Might it not equally well determine that we draw the wrong conclusion? Or no conclusion at all?

    So that is Hawking’s fundamental paradox…how is science possible if we aren’t “free rational beings”?

    Conway and Kochen raise a similar point in their paper, The Free Will Theorem:

    “It is hard to take science seriously in a universe that in fact controls all the choices experimenters think they make. Nature could be in an insidious conspiracy to ‘confirm’ laws by denying us the freedom to make the tests that would refute them. Physical induction, the primary tool of science, disappears if we are denied access to random samples.”


  • Rich

    Thanks to Matt for the clear explanation of why free will can’t be “hiding” in quantum probability. The necessity for such free will to leave a detectable signature in the distribution of results is indeed a strong constraint.

    I wonder however if we can still hide free will there if we assume that it exists only in the waveform and disappears when the wave is collapsed upon measurement. Uncollapsed waves still have a real effect on the world. If free will also disappeared upon measurement then it could not be detected in the distribution pattern.

  • Ray Gedaly

    If I learned there was no such thing as free will, I would live my life very differently. :)

  • Baby Bones

    I think that the idea of determinism is not well defined. Furthermore, the idea of randomness is even less well defined. On the other hand, I think that uncertainty is something that we can easily quantify, and we deal with it daily in many ways.

    One thing I hate to think of is a point particle. Or rather, I hate even more thinking of many point particles. The chance of two point particles colliding is precisely zero unless you assume that they are capable of attracting each other to an infinite extent. But that infinite extent makes points just as nasty as naked singularities. I can accept that there are point-like phenomena associated with a finite force field and that picture breaks down on some scale, but I think that any subsequent renormalization only confirms that the picture is going to be wrong on some scale.

    Another thing I hate to think of is plane waves that go on forever. I hate even wave packets that are clumpy but have to be defined way out at infinity to make the math work out right. It is really hard for me to think about how one bit of one real-world wave correlates with another bit of itself, but it must do so to some extent or else it wouldn’t be much of a wave. I bet that the extent is limited and that its limited nature shows up in detectors as imprecise arrival times of peaks and troughs (or imprecise photon arrival times that cannot be attributed to the source).

    What I find odd is that the hydrogen atom behaves in ways that suggest mathematical things like Hilbert Space or a space of all possibilities exist in some way. I am certain these things are useful mathematical tools but I fear that they are otherwise physical nonsense. They cannot exist in this world any more than a point particle can.

  • Physicalist

    does anyone have any thoughts on . . Hawking’s fundamental paradox…how is science possible if we aren’t “free rational beings”?

    My thoughts: There’s absolutely no reason to think that physicalism (or determinism) in any way implies that we aren’t free or rational.

    Hawking asks whither the laws of physics might “not equally well determine that we draw the wrong conclusion.”

    Sure, they might, in one sense. But only in the sense that the laws of physics might determine that a mouse will walk backwards to the edge of a cliff and leap backwards to its death. Such a process is physically possible — and it might be determined by the laws of physics — but as a matter of fact, it doesn’t fit with the emergent structure (e.g., biological structure and psychological structure) of the actual world.

    Rationality and freedom (of the compatibilist sort) are emergent physical features, and the development of these features makes it more likely that if we keep working at it, we’ll get an account of physics that’s more or less right.

  • marshall

    “The relevant point is that the behavior does follow the physical laws.”

    The thing about chaos (or, more generally, situations that are arbitrarily sensitive to initial conditions) is that you cannot show that, at least, not fully. I think that that is why it is improper to dismiss chaos here. (In other words, physics is at its heart about the prediction of consequences of initial actions. If the knowledge of the initial conditions is lost through chaotic evolution, so that you cannot calculate effect from cause, then you cannot be sure that that the physical law is in fact fully being followed. Maybe it is some other law, which also leads to a loss of knowledge of initial conditions.)

    Note that this is a fundamental failure. No matter how accurate your measurements are, and how many digits your calculations carry, I can make you lose all precision. If there is a “ghost in the machine,” I suspect that’s where it would enter in.

  • Mitchell Porter

    sprawld says

    “Deutsch, Wallace et al. have shown pretty convincingly that you can derive probability amplitudes (mod squared) from MWI + decision theory or symmetry arguments.”

    There seems to be a certain amount of credulous hype surrounding the decision-theory “derivation” of the Born rule for MWI. Sean Carroll describes it as “promising”, this commenter says it’s “convincing”. So I would like to point out a few things.

    First, if you are going to derive the Born rule from a multiverse theory, then the obvious thing to expect is that Born probabilities correspond to frequencies in the multiverse. If quantum mechanics says that outcome A is twice as probable as outcome B, that should mean that outcome A is twice as common in the multiverse, compared to outcome B.

    As things stand, MWI does not offer anything like this. Suppose we pick a basis and decompose the wavefunction, what do we get? *One* copy of each “world”, each of which has a complex number associated with it. If we decompose a reduced density matrix, instead of a full wavefunction, we at least get real numbers that look like probabilities, but so far, they’re still just numbers. Just because you now have a number 2/3 associated with the A-branch, and a number 1/3 associated with the B-branch, does not yet explain why we actually see outcome A twice as often as outcome B.

    In my opinion, the logical thing to do would be to bite the bullet of duplicated worlds, and say that there are 2 copies of the A branch, and 1 copy of the B branch. You could get this by having an ontological axiom, that the coefficient of all branches must be equal, so a branch with coefficient 2/3 is actually a sum of two identical state vectors, each with a coefficient of 1/3. Finally this gives you a multiverse with the right multiplicities: outcome A now really does exist twice as often as outcome B.

    However, the ideology of MWI advocates is usually that “the wavefunction is everything”, “the theory interprets itself”, etc., so the idea of a special axiom to (1) define what a world is (2) make sure that multiverse frequencies do match the Born rule, is unappealing to them. I can only think of one version of MWI which explicitly talks about duplicated or near-duplicated worlds in order to obtain the Born rule, and that’s Robin Hanson’s “mangled worlds”. (Zurek seems to be edging close to this option, but he doesn’t want to sign on to MWI, instead taking the absurd line that “existence requires redundancy”, so something only exists if it exists several times over.) Hanson’s mangled worlds, as I understand it, involves a dynamically determined preferred basis in which the required multiplicities are obtained by treating a world that is e.g. 99% |dead cat> + 1% |live cat> as a “dead cat” world. So Hanson’s individual worlds are themselves superpositions; a solution to MWI’s problems which might itself be regarded as problematic.

    But returning to the mainstream of MWI – if mainstream is defined by public visibility and excited advocacy – that does appear to be defined by this “decision-theory derivation” of the Born rule. So allow me to point out what’s going on here. This perspective involves an explicit repudiation of the idea that Born probabilities correspond to multiverse frequencies. In one of his papers, David Wallace says there is just no answer to the question “how many copies of a given world are there?”

    Instead, probabilities are to be obtained from decision theory. Let me sketch how this works. A common decision-theoretic concept is that you are to maximize your expected utility – the benefit you can expect to obtain, given an action – and this is equal to a weighted sum over the various possible outcomes. Each outcome has an intrinsic benefit (its “utility”), and it also has a probability. Winning $1 million in the lottery would be highly beneficial to you, but also highly improbable, which is why buying lottery tickets is not a way to maximize your *expected* utility… Maximizing your expected utility, for a decision theorist, defines rational behavior. So here, finally, we reach how the Deutsch-Wallace derivation of the Born rule is supposed to work. We will examine *rational behavior in the multiverse*, e.g. we will look at quantum game theory. The prescription, be rational, will tell us how we should act in quantum games; we know the intrinsic utilities of the various outcomes; so if we “divide out” the rationality ranking by the intrinsic utilities, the probabilities of the outcomes will be left over, and here we will recover the Born rule.

    I fear that in describing this procedure, I have failed to convey the utter absurdity of it. So let’s go back to the big picture. MWI advocates have failed to find a satisfactory way to demonstrate that their multiverse contains two times as many copies of “A” as it does of “B”. So rather than conclude that there is a problem with their theory, they instead conclude that there is a problem with the concept of probability, and cleverly propose to do away with the idea that probabilities have something to do with how often an event occurs. Instead, they shall argue that being rational in the multiverse will require you to act *as if* A has twice the probability of B… I think I’m still not conveying how absurd and desperate a dodge this is.

    In any case, I see many people talking about how the Deutsch-Wallace “derivation” is “promising” or “convincing”, and yet I don’t think they really understand what is being proposed, at a fundamental level – this logical inversion which makes probability dependent on rationality, rather than vice versa. Hopefully I have managed to enlighten a few people as to what’s really going on in their arguments.

  • Physicalist

    @ 29. marshall: “. . . you cannot be sure that that the physical law is in fact fully being followed . . .

    Typically our reasons for thinking that we have the relevant laws in hand don’t rest on generating an absolutely precise prediction of a final state from an absolutely precise specification of an initial state. Instead, we get close enough, and run things many times, and we eventually decide that the best explanation of the data is the claim that the system follows certain simple laws.

    What is often most important for our deciding whether some physical law holds is our knowledge of the domain of applicability of those laws. (Sean has discussed this in several places, e.g., here.)

    This allows us to say that even though a system (e.g., a double pendulum) might be chaotic — thus making it impossible to predict its exact behavior — it nevertheless is obeying the laws of classical mechanics. (And the fact that the mechanics tells us that the behavior will be chaotic gives us all the more reason to believe that we’ve got the laws right.)

  • Arun

    The usual reason for wondering if there is free will, is that the common notion of morality requires it. If there is no free will, the argument goes, how can we hold people responsible for their actions?

    Of course, if there is no free will, then our choice of whether people can be held accountable for their actions also vanishes. Our choice, pro or con, is predetermined, and there is no point worrying about it.

  • Axel

    ** What happens to you in the future is a combination of choices you make and forces well beyond your control — make the best of it! **

    Forces beyond my control would be for example to die in an earthquake .. But that that happened to me was because I was born on earth .. That’s the point of view of Buddhists .. So control it and try to not be born (again) … 😉

  • Cosmonut

    Free will, in any real sense, is dead if you accept determinism.

    Regardless of whether you can *predict* the future or not, the path of your life and the fate of humanity, is already laid out as surely as the orbit of the moon around the earth.

    You can *pretend* that you are making free choices that determine your future, but what choices you make are also determined by the laws of physics, as well as their consequences.

  • http://jbg.f2s.com/quantum2.txt James Gallagher

    Thanks to Mitchell Porter (#30) for the critique of the (attempted) Decision Theory based derivation of probability in MWI. Personally I think that any such derivation is doomed, for the simple reason that you cannot get (fundamental) probabilities out of a model unless you put (fundamental) probabilities in. This seems so trivially obvious that I am amazed that so many educated people believe the purely deterministic MWI is a sensible idea, unless they really believe in a (super)deterministic universe – and in that case it is not even possible to conclude that logic is correct – so the whole scientific enterprise would be pointless.

    But I think this debate always starts with the wrong emphasis – that determinism seems natural (due to Laplace argument etc) – whereas I would say it’s actually much more reasonable to accept that free-will is an obvious feature of the universe, at least since conscious life evolved. Is it not so staggeringly obvious that the behaviour of physical things on our planet is different from the deterministic behaviour on lifeless planets? A Poincaré recurrence cycle of the entire universe would probably happen more often than the Schrödinger equation would produce the works of Shakespeare.

    (Super)Determinism is clearly not how the universe works once conscious beings have evolved, and I don’t need an intensive study of tedious theological or philosophical works to deduce that (although I have been unfortunate enough to have wasted time studying some of these in the past)

  • http://www.naturalism.org Tom Clark

    “What happens to you in the future is a combination of choices you make and forces well beyond your control — make the best of it!”

    On the block universe view, which I think you accept, the future (like the past and present) is fixed in 4D spacetime. I imagine many folks would suppose the block universe obviates any notion of real choice, since choices too are equally fixed in spacetime. “Real” choices, “real” freedom, they might suppose, require us to exist outside spacetime, exerting control over it. But since we exist within spacetime, freedom and control can only consist in our participating in certain sorts of fixed patterns in the block universe, those in which the outcomes we want follow from the actions we take in service to our desires. This gets elaborated at http://www.naturalism.org/spacetime.htm but I’d be interested to get your take on it.

  • Dave

    I think you are a little bit too hasty in dismissing the idea of simple robust future boundary conditions applying to our universe affecting the fate of “rational” agents.

  • Richard D. Morey

    How is free will “a useful theory of macroscopic human behavior models people as rational agents capable of making choices”? What constraint does free will make on predictions of behavior? Actually, free will is not a theory of behavior at all, since it (by definition) has no constraint. Unless you are using the words “useful” and “theory” in ways that they are not typically used in science, I see no way that your claim can be true.

    And if it were true, why not describe other complex systems as having “free will”, like say, the weather? Certainly the ancients thought the weather was driven by will. Why are humans any different than any other complex system that makes “free will” a “useful theory”?

    “It wanted to rain today, but it couldn’t quite make the decision. Weather here is so indecisive.”

  • Physicalist

    Actually, free will is not a theory of behavior at all, since it (by definition) has no constraint.

    You’re assuming a libertarian notion of freedom, which is rejected by Sean (and by the majority of people who have thought carefully about this topic). What Sean is advocating is a compatibilist account of freedom, which can indeed be seen a result of constraints.

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  • gr8hands

    Cosmonut @34 is correct to point out that if hard determinism is correct, then all of existence is as pre-determined as a movie on a DVD — from any frame of the movie, there is only one possible next frame. No choices are possible.

    I believe free will (and consciousness) is an emergent property — like “solid”. You can’t show me under the microscope anything solid. In fact, the better the microscope, the less “solid” something is. Yet, you will hurt yourself walking into the wall trying to act on the knowledge that it is 99.999999999+% unsolid.

  • Richard D. Morey

    “You’re assuming a libertarian notion of freedom, which is rejected by Sean (and by the majority of people who have thought carefully about this topic). ”

    No, I’m not. Free will has no constraint. That doesn’t mean that it isn’t *compatible* with constraint (which is the compatibilist position) but rather that it doesn’t, as a “theory” *offer* any constraint, which means it cannot be a useful theory of human behavior.

  • Physicalist

    Re: 42
    The compatibilist account of freedom usually claims that actions are free just in case they are caused by an agents desires, commitments, personality, etc. and they are not the result of external coercion or force. I don’t see that as a “theory of behavior” this differs importantly from other psychological features.

  • Richard D. Morey

    Re: 43

    That is not a useful theory of behavior, that is a definition.

  • Chris W.

    Katherine (#24),

    From pretty early on in his career, the philosopher of science Karl Popper emphasized precisely this point. (I’ll ignore Conway and Kochen’s use of the term “induction”. :) ) It is a deep issue; I would argue that it is the central issue. Another way of putting it is this: Does the notion of seeking and discovering (usually provisional) solutions to problems really mean anything in a universe that allows no room for making choices that are not predetermined by its past state plus the laws of physics?

  • Eric Smith

    Obviously as physical beings our actions are “determined” by the laws of physics. Nevertheless I would argue that we have free will in any practical sense, namely:

    (1) Given a choice between two alternatives, we are in fact capable of choosing either one; and
    (2) No outside observer is able to predict with 100% confidence which of the alternatives we will choose.

    As evidence I offer the following experiment, which you can do yourself: prepare two breakfast beverages (for convenience we will label them T and C). Also prepare some quantum mechanical system so that it is in a superposition with two equally likely outcomes upon measurement (e.g. an electron in a superposition of spin up and spin down). Perform the measurement in secret, and based upon the result drink one of the beverages (e.g. if the measurement shows spin up, drink T, otherwise drink C).

    At first blush this doesn’t seem to say much about free will, since you’re letting an outside event (the state of the electron) “determine” your choice. If you prefer, you can consider the system (you + electron) to be the agent, In any case, if you perform the experiment you do show that property (1) is true, namely that you are in fact capable of choosing either alternative. Moreover, if the measurement is secret and if our current understanding of quantum mechanics is correct, no outside observer can predict which beverage you will drink, so property (2) is also true. One can argue the metaphysics either way, but I think properties (1) and (2) together amount to free will in any practical sense.

  • Richard D. Morey

    Eric, your definition of free will is circular, given that you used the concept of “choosing” in point 1. Or perhaps you should clarify what “choose” means – can you define it in such a way that it doesn’t apply equally well to the quantum system you’ve described in your thought experiment? Does that system “choose” the state?

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  • Eric Smith

    Re: 47

    You bring up a good point. I don’t see any circularity in the definition, but I can see that one might think the word “choose” implies more than it ought to. I simply meant that of the two possible outcomes (I drink C) or (I drink T), either outcome is possible. Yes I see that could also equally well apply to a quantum system, so it’s probably not a good choice (:-)) of words. Perhaps “choice” = “outcome” + “consciousness”.

    I have no problem with materialism, and am perfectly happy to agree that my “choices” are the product of the states and transitions of all the particles that make up my brain. Nevertheless I think it is an interesting thing that “I” (some system of particles) can act in very complicated ways which seem not to be predictable even in principle. I know that some people prefer to avoid the term “free will” because it seems to imply dualism, but we already have the perfectly good words “materialism” and “dualism”, and I’d hate to simply define “determinism” as “materialism”.

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  • http://n/a Frank Williams

    I am curious why nowhere in the several discussions of determinism & freewill is there any consideration of the idea that if all our behavior, including our thoughts, are the result of determinism – i.e. are predetermined to be whatever they are by brain structure, evolution, whatever – then all our reasoning pro and con about determinism or anything else is pointless, because we then think whatever we think not because we have correctly (or incorrectly) judged evidence etc., but merely because we are predetermined to think whatever we think. Seems to me that this means that IF determinism is true, then all reasoning is illusory. This doesn’t show that determinism is wrong – only that IF it is true, then we can’t have good reasons for anything (including determism).

  • http://qpr.ca/blog/ Alan Cooper

    Frank of#52, I think the Katherine’s quote from Stephen Hawking in #24 is an example of something pretty close to what you say is missing.

  • Chris W.

    Re #52, 53: Also see comment #45.

  • Richard D. Morey

    Re: 50

    ‘Perhaps “choice” = “outcome” + “consciousness”’

    If consciousness is only observing the outcome after the fact, as some of the neuroscientific evidence suggests in at least some cases, it seems strange to call it a “choice”. After all, I can observe other peoples’ actions after the fact too (or the measurement of the spin of an election, after the fact) but that doesn’t mean I had any “choice” about these outcomes.

    So, consciousness of an outcome would not seem to be sufficient, unless your are comfortable in calling everything you observe the result of your “choices”. One might object that there’s something special about the fact that you’re observing yourself, but I’d argue that’s just an illusion; consciousness is just one part of a complex system “observing” the other parts. There seems to be no particular reason why this couldn’t just as well be said about any of the other complex systems we are a part of (such as social, or physical).

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  • Haelfix

    Suppose I were to tell you that right now, I decided to post on this website, b/c my photomultiplier (with a very high filter) just clicked! Chances are, it was going to click at least once in the next 10 seconds, but I decided I would post if it was anytime in the next 5 seconds starting now.

    Now, it is completely clear that this isn’t just about classical Poisson statistics, even though I have no detailed knowledge about the state of the system emmitting the photon and how my measuring apparatus observed the state. The experiments have been done in full detail, and there is a irreducible measure of probability within such a system that is simply due to the nature of quantum mechanics

    The point is, it is very easy to make an arbitrarily large macroscopic change (posting or not posting on a website), based upon the details of a microscopic experiment, where we have reduced to a minimum all classical notions of measurement error.

    Thus, I mantain the case is pretty clear, nature is nondeterministic unless you believe in something like hidden variables (which are almost ruled out entirely)

  • Eric Smith

    Re: 50

    We often use the word “choice” in contexts where free will or consciousness aren’t an issue, e.g. we will say that a computer playing chess will “choose” to make a particular move, or will “choose” a particular element of a set in a sorting algorithm. I didn’t mean anything more by “choose” than that.


  • Richard D. Morey

    Re: 58

    Then you didn’t mean ‘Perhaps “choice” = “outcome” + “consciousness”’, but rather, ‘Perhaps “choice” = “outcome”’?

  • http://jbg.f2s.com/quantum2.txt James Gallagher

    #46 Eric

    I don’t think that demonstrates free-will, since in a large sequence of “trials” you would drink T 50% of time, free-will would be more illustrated by you drinking T 100% of the time even when it seems (to an outsider) that either T or C could be drunk with equal probability.

    The signature of free-will is the regular appearance of statistically unlikely outcomes. So if you found the works of Shakespeare in written form on Mars you could conclude that it was put there by something exercising free-will – since the statistical likelihood of macroscopic pages forming with written text by random is so unlikely as to not be expected to occur in several lifetimes of the universe.

    In the very unlikely event that such a ‘miracle’ occurs – then unlucky us we may make a false attribution of free-will, but it is so unlikely as not to concern proper scientifically minded people.
    (In the same way poincare recurrence doesn’t contradict the 2nd law of thermodynamics in any scientifically relevant way)

  • Jon H

    “If consciousness is only observing the outcome after the fact, as some of the neuroscientific evidence suggests in at least some cases, it seems strange to call it a “choice”.”

    I don’t see any reason to assume awareness would be instantaneous. When a computer CPU makes a “decision”, that isn’t instantly reflected outside of the CPU (on the screen, in RAM, etc). That’d take few more nanoseconds.

    After all, in the brain the decision would be made probably by some process of weighing alternative activation patterns, in a manner that isn’t necessarily tied into the verbal or visual centers. If that’s the case, it’d make sense for there to be a slight delay while the decision result was translated into language, or into a visualized image, or into an action.

    The mind may not be dualistic in the mind/body sense, but there’s also no reason to assume that it all works together as an atomic unit, with a decision being instantly reflected throughout the brain and available to be expressed.

  • Richard D. Morey

    Re: 61

    “If that’s the case, it’d make sense for there to be a slight delay while the decision result was translated into language, or into a visualized image, or into an action.”

    As an experimental psychologist, I can tell you that 300ms is an eternity in behavioral response time studies. If it really took 300ms to turn a decision into a verbal response, then it would be really hard to get verbal responses in any paradigm less than, say, 350ms. But that’s not the case. You can’t wave it away that simply.

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  • http://knotsinmythinking.wordpress.com/ Tom, Knots

    Is it possible that this is a discussion about whether physics can (even in theory) understand human freedom?

    It just seems to me that, within the context of the argument, what would resolve the issue in favour of the existence of free will would be a theory that explains it. Wouldn’t genuinely self-determined behaviour be exactly not this, ie not anything that you could explain, that wouldn’t conform to laws, that wouldn’t look like any form of behaviour in the inert universe.

    I think the argument over Free Will is actually an argument over the limits of the scientific method. The reason it continues to go around and around is that it is impossible for physics and biology to explain the human capacity for voluntary action, and yet that thought means science cannot answer every question, and that is unthinkable (from within the system) so it returns to the begining again. These endless iterations leave plenty of time for coming up with quasi-technical terms that make it all look like a very important discussion.

    As far as I’m concerned, we learn how to be free. You can’t learn a law of physics. Therefore, human freedom doesn’t have anything to do with physics.


  • David

    I would really like to see Sean respond to Mitchell Porter’s post about the deep problem of probability in MWI

  • Maurice

    Actually, this argument of determinism and free will is almost exactly analogous to a theological discussion stirred up by John Calvin in the 16th Century. His issue was with the apparent contradiction between the omniscience of a Christian god (his Laplace’s Demon) and the claim that human beings have free will (absence of predestination).

    The ensuing discussion about predeterminism, predestination and whether or not these contradict free will, were fascinating anticipations of Laplace’s dilemma, and ahead of their time philosophically. A key revelation from these discussions is (as indeed you observe) that it is possible for an omniscient being (or supercomputer) to be able to predetermine the outcome of a person’s choices without violating their free will (i.e. there is no predestination). This was the view held by the Catholic Church and opposed by Calvin (who concluded that there must be predestination). It appears that this makes one philosophical point on which you, Sean, and the Catholic church’s agree — even if you disagree that the existence of the Church’s particular “Laplace Demon” 😉

  • steven johnson

    Is there really any meaning to the word determinism that does not imply that whatever is being determined takes some particular value? I don’t think so. Thus, if the free will is not determined by something else, it doesn’t have any particular values. In coin tosses, the values are either heads or tails, and in physics there are measurable observables. It’s not quite certain what a will, free or otherwise consists on, but if whatever it is made of has no values, it is doubtful we can meaningfully say it exists. If it has self-determined values, we are positing a metaphysical entity which is pretty much indistinguishable from the soul.

    But if we postulate the will is not an entity but a process, we are left either with deterministic processess or interministic, i.e., probabilistic ones. By definition a deterministic process forming the “will” is unfree. But a probabilistic process means that the will is random. It seems inescapable to me that there’s a real problem in associating freedom of the will with the randomness of the will.

    You could get around this by treating probabilistic processes as determinate, while acknowledging the plain truth that individual trials are not. Fair coins come up heads 50% of the time, a very specific value, which as the opening question highlighted, is in fact a key aspect to determinism. (I like to think of determinism coming in three varieties: mechanism, stochasm and history.) But it sppears this is not an option. This seems to be a shame, because if any individual act of will is an outcome of a probabilistic process, the peculiar determinateness of probabilistic processes can provide the bias predictability we associate with personal character, while the inherently probabilistic nature of individual outcomes, specific acts, account for the equally real unpredictability.

    If the many clauses of the last sentence left it too obscure, think of it this way. The will plainly cannot be unconstrained. If Sean has an embarrassing need for latex for sexual fulfillment, he cannot will that he will be aroused in more socially acceptable. This is not reflection on Sean. I myself cannot reliably will myself to remember facts that I know! For both of us, I suppose exercising the will to decide to cultivate good habits would constitute freedom of the will, while the subsequent habits (should we be so fortunate as to succeed in our endeavors,) would not constitute will, but, well, habit. And for both of us, delaying gratification is in no sense a defiance of needs or desires imposed upon us by deterministic processes, even though it is entirely volitional.

    As for alarm at the notion that a scientific understanding of the mind will leave old ideals of morality shamed, I’d say that’s because it’s true. On the one hand, miscreants who would simply be condemned as bad stand relieved of full responsibility. The insistence upon treating them as sinners would not just seem, but be, barbarous. And those of us fortunate to have met social expectations (publicly, anyhow) could not honestly congratulate ourselves upon our probity. All this would change society and undermine religion of course. The old joke is that hell was created so that heaven would have some entertainment. How could we be religious when delight in God’s justice is philistine backwardness?

  • BobC

    I made it all the way through the comments! Clearly, an act of free will.

    Does free will exist if there is no brain to ponder it? Free will would seem to require life, minds, intelligence, and probably more than a single instance (to encourage interaction, socialization, the creation of civilization, culture, philosophical thought, science, and science blogs with comments). Epistemology and existentialism, anyone?

    Let’s assume free will does exist. Did it always exist? If not, then when, why and how did it come into existence?

    What manner of things possess free will? Does a chimp have free will? A snake? A fruit fly? A worm? A nematode? An amoeba? Does free will require a complex nervous system? Or self-awareness?

    Consider entropy and Time’s Arrow. Our own limited existence, including our free will, is merely an eddy of local, temporary order in the rush toward the heat death of the universe. It is highly localized, extremely constrained.

    What is free will within the context of the evolution of the universe? Is it nothing more than an temporary emergent property, possessed by only an insignificant number of small clumps of matter?

    Is free will nothing other than a rounding error in the statistics of the universe?

    My brain hurts. Can we stop now?

  • http://juanrga.com Juan Ramón González Álvarez

    It is truly fascinating how early non-scientific ideas of Laplace (who apparently never fully understood classical dynamics) are being re-branded for forcing a fabulous fitting into many-worlds and similar post-modern metaphysical stuff.

    First, many-worlds is not another interpretation of QM, as one reads sometimes, but a well-known misunderstanding of QM that cannot reproduce what we observe at our labs

    Against Many-Worlds Interpretations 1990: Int. J. Mod. Phys. A 5, 1745–1762 by Kent, Adrian.

    see also


    Note that Kent article is titled Interpretations, in plural, because there is not one MWI but a collection of mutually contradictory MWIs. The MWI by Deutsch (who you cite) is not the same than MWI by Everett, which is not the same than MWI by Hartle…

    Second, science is an enterprise with no room for the kind of supernatural observers G introduced in many-worlds for justifying the kind of metaphysical process associated to deterministic knowledge


    Therefore it would be a good idea to keep in mind the limits of the scope of science when discussing about science.

    and third, I am not surprised that when you write about chaos you only cite deterministic chaos (where uncertainty of final states is due to our a small uncertainty in our knowledge of the initial state of a deterministic system), whereas you omit to cite the case of nondeterministic chaos, where the uncertainty about the system remains although you know the initial state with infinite precision.

    This omission of fundamental results is still more glaring when a famous Nobel laureate wrote several popular books (including bestsellers) about the current state of the science of chaos.

  • Justin Loe

    I simply don’t believe free will is a tractable problem, scientifically (at this time). From an everyday standpoint we all act as if free will is true, whether it is or not. In the same fashion, our everyday actions and ambitions are based on the sense that they are meaningful.

    Just as we cannot know scientifically (at this time) whether our lives are meaningful, in my opinion, we cannot know whether free will exists or not based on current science. Arguably, we’re no closer to resolving the free will debate than we were 100 years ago or in the time of Newton.

    Most of us act, then, on the assumption that we have free will.

    Whether we can answer that definitively, at some future time, remains to be seen.

  • http://protagoras.typepad.com Aaron Boyden

    I’m quite astonished that nobody has clearly made what seems like the most relevant point here; if determinism rules out freedom, indeterminism almost certainly does as well. At least, randomness is no help at all; how can a roll of the dice constitute an exercise of agency, a person choosing for themselves what to do? But the interpretations of physics are only arguing about whether there are dice, so they aren’t talking about anything that’s relevant to the real questions of freedom.

  • http://theoperspectives.blogspot.com/ James Goetz

    Regardless of free will or no free will, if determinism is true, then all scientific theories based on empirical observation of cause and stochastic effect are illusionary. Determinism would ultimately invalidate most science, and it would be completely ridiculous then to appeal to scientific discoveries to support determinism. Nobody can disprove determinism, but accepting it is an implicit rejection of most empirical observation.


    James Goetz

  • Mitchell Porter

    James, you seem to be assuming that cause and effect in the intellectual sphere is necessarily our enemy – that it can only have the role of forcing our thoughts down a path which has no a-priori relationship to the truth. But reasoning is itself a causal process; being caused is part of why it works.

    Natural selection – or even just the simpler truth that survival is not guaranteed – dictates that the intellectual processes of an organism must have some capacity to represent the world correctly, or else it will swiftly die. Meanwhile, the modern theory of computation (due to people like Turing) tells us that a relatively simple set of symbol manipulations is “computationally universal”, capable of doing anything that a modern computer can do. So above a very elementary threshold of computational ability, cognitive dispositions selected merely for compatibility with survival will also give rise to open-ended powers of rationality, bounded only by restrictions on memory, sensory bandwidth, etc.

    In other words, the argument is:

    1) The need to survive dictates that cognitive processes have some fidelity to reality.

    2) Turing universality tells us that it’s a short step from “cognition with some fidelity to reality” to “cognition with an open-ended capacity to analyse data and draw correct conclusions”.

    It is absolutely true that we may be caused to make mistakes. I mean, I believe in cause and effect, and I believe that people make many mistakes, therefore I believe those mistakes have causes! But I don’t believe that determinism implies the uselessness of science or of thought. Cause and effect can be our epistemic ally too.

  • http://juanrga.com Juan Ramón González Álvarez

    I understand James point, if determinism ruled universe, then giving people Nobel Prizes would be as giving gifts to a rock when falling from a terrace roof. Both the Nobel laureate and the rock would be merely following rules (deterministic laws) established even before them existed, without any fundamental difference.

    In a purely deterministic world, fraudulent scientists would have the same respect than Nobel Prize winners. Because none of them would have the most minimum possibility to chose their own actions (good or bad).

    In a world where a nondeterministic evolution is possible, we would be giving Prizes to people, because the creation of a scientific theory is not a deterministic process, but the outcome of a wise mixture of human intelligence, perseverance, and personal choices; whereas no prize would be given to a falling rock, because the rock is merely following a law in a passive way. We would recriminate fraudulent scientists, because they had the option to chose their actions and decided to make the fraud.

  • http://www.cthisspace.com Claire C Smith

    No chaos, only random chance?

  • Doc-2

    Gee, when free will was passed out, no one asked me if I wanted it or not!..at least in this MWI…

  • martenvandijk

    There is no space for determinism in the universe.

  • Pingback: Ontological Determinism, Epistemological Indeterminism, Laplace’s Demon « Ramblings()

  • Chinahand

    I realize this thread is now very old and so this question will probably never get answered, but when Dr Carroll says:

    “in a classical deterministic system, with perfect information and arbitrary computing power you can predict the future in principle, but not in practice”

    Does that mean you will be able to predict if any given Turing Machine will halt or not?

    Does this lead to a contradiction?

  • Gene Venable

    Well anyway, I think we don’t have more free will than a flipping coin does, but we certainly don’t know the ultimitate consequences of any action we take, so we can’t very well pat ourselves on the backs for taking actions that have ‘good’ results, can we?

  • Bangar

    when I was passed out, Free Will didn’t ask me if I “wanted it…” :(


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Cosmic Variance

Random samplings from a universe of ideas.

About Sean Carroll

Sean Carroll is a Senior Research Associate in the Department of Physics at the California Institute of Technology. His research interests include theoretical aspects of cosmology, field theory, and gravitation. His most recent book is The Particle at the End of the Universe, about the Large Hadron Collider and the search for the Higgs boson. Here are some of his favorite blog posts, home page, and email: carroll [at] cosmicvariance.com .


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