The Big Picture
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vironment in terms of its own molecular structure. The individual molecule
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has no idea it’s part of a snowflake, and could not care less.
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Something like downward causation is possible in principle, even if
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there’s no evidence for it in the real universe. We could imagine a possible
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world in which electrons and atoms obeyed the rules of the Core Theory in
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situations of very low numbers of particles, but started obeying different
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rules when the numbers became large (such as in a human being). Even
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then, the right way to think about the situation would not be “the larger
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structure is influencing the smaller particles”; it’s “the rules we thought
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were obeyed by particles were wrong.” In other words, we could discover
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that the domain of applicability of the Core Theory was smaller than we
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thought it was. There is no evidence that anything along those lines is true,
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and it would violate everything we know about effective quantum field
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theories— but many things are possible.
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The way we talk about human beings and their interactions is going to
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end up being less crisp and precise than our theories of elementary particles.
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It might be harmless, and even useful, to borrow terms from one story be-
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cause they are useful in another one—“diseases are caused by microscopic
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germs” being an obvious example. Drawing relations between different vo-
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cabularies, such as when Boltzmann suggested that the entropy of a gas was
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related to the number of indistinguishable arrangements of the molecules
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of which it was composed, can be extremely valuable and add important
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insights. But if a theory is any good, it has to be able to speak sensibly about
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the phenomena it purports to describe all by itself, without leaning on
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causes being exerted to or from theories at different levels of focus.
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Mental states are ways of talking about particular physical states. To say
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that a mental state causes a physical effect is precisely as legitimate as saying
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that any macroscopic physical situation is the cause of some macroscopic
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physical event. There is nothing incorrect about attributing your scratching
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to the existence of your itching; there’s simply more than one story we can
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legitimately tell about what’s going on.
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Freedom to Choose
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Once we see how mental states can exert physical effects, it’s irresist-
ible to ask, “Who is in charge of those mental states?” Am I, my
emergent self, actually making choices? Or am I simply a puppet,
pulled and pushed as my atoms jostle amongst themselves according to the
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laws of physics? Do I, at the end of the day, have free will?
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There’s a sense in which you do have free will. There’s also a sense in
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which you don’t. Which sense is the “right” one is an issue you’re welcome
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to decide for yourself (if you think you have the ability to make decisions).
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The usual argument against free will is straightforward: We are made of
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atoms, and those atoms follow the patterns we refer to as the laws of phys-
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ics. These laws serve to completely describe the evolution of a system, with-
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out any influences from outside the atomic description. If information
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is conserved through time, the entire future of the universe is already writ-
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ten, even if we don’t know it yet. Quantum mechanics predicts our future
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in terms of probabilities rather than certainties, but those probabilities
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themselves are absolutely fixed by the state of the universe right now. A
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quantum version of Laplace’s Demon could say with confidence what the
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probability of every future history will be, and no amount of human voli-
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tion would be able to change it. There is no room for human choice, so there
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is no such thing as free will. We are just material objects who obey the laws
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of nature.
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It’s not hard to see where that argument violates our rules. Of course
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there is no such notion as free will when we are choosing to describe human
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beings as collections of atoms or as a quantum wave function. But that says
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nothing about whether the concept nevertheless plays a useful role when we
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choose to describe human beings as people. Indeed, it pretty clearly does
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play a useful role. Even the most diehard anti– free will partisans are con-
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stantly speaking about choices that they and other people make in their
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daily activities, even if they afterward try to make light of it by adding,
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“Except of course the concept of choice doesn’t really exist.”
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The concept of choice does exist, and it would be difficult indeed to
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describe human beings without it. Imagine you’re a high school student
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who wants to go to college, and you’ve been accepted into several universi-
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ties. You look at their web pages, visit campuses, talk to students and fac-
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ulty at each place. Then you say yes to one of them, no to the others. What
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e best way to describe what just happened, the most useful vocabulary
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for talking about our human- scale world? It will inevitably involve some
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statements along the lines of “you made a choice,” and the reasons for that
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choice. If you had been a simplistic robot or a random- number generator,
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there might have been a better way of talking. But it is artificial and coun-
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terproductive to deny ourselves the vocabulary of choice when we talk
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about human beings, regardless of how well we understand the laws of
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physics. This stance is known in the philosophical literature as compatibil-
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ism, and refers to the compatibility between an underlying deterministic
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(or at least impersonal) scientific description and a macroscopic vocabulary
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of choice and volition. Compatibilism, which traces its roots back as far as
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John Locke in the seventeenth century, is the most popular way of thinking
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about free will among professional philosophers.
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From this perspective, the mistake made by free- will skeptics is to care-
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lessly switch between incompatible vocabularies. You step out of the shower
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in the morning, walk to your closet, and wonder whether you should put
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on the black shirt or the blue shirt. That’s a decision that you have to make;
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you can’t just say, “I’ll do whatever the atoms in my body were going to
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deterministically do anyway.” The atoms are going to do whatever they were
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going to do; but you don’t know what that is, and it’s irrelevant to the ques-
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tion of which decision you should make. Once you frame the question in
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terms of you and your choice, you can’t also start talking about your atoms
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and the laws of physics. Either vocabulary is perfectly legitimate, but mix-
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You may be willing to accept that oceans and temperature are real, even
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though they are nowhere to be found among the fundamental ingredients
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of the Core Theory, but feel unwilling to apply the same logic to free will.
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After all, the ability to make choices isn’t just a macroscopic collection of
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many microscopic pieces; it’s an entirely different kind of thing. If it’s not
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there in our best comprehensive description of nature, why is it helpful to
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act like it’s there in our human- scale vocabulary?
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The answer comes down to the arrow of time. In chapter 8 we talked
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about how we have epistemic access to the past— memories— that we don’t
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have when it comes to the future. That’s because there is a special boundary
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condition, the Past Hypothesis, according to which entropy was very low
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near the Big Bang. That’s a powerful bit of information about the past,
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which enables us to pin it down in a way that we can’t pin down the future.
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This temporal asymmetry arises only because of the distribution of matter
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in the universe on macroscopic scales; there is no analogue of it in the Core
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Theory itself.
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There is a crucial role played by the leverage that features of our current
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state exert over our knowledge of events in the past or future. When a fea-
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ture of our current state implies (given the Past Hypothesis, and all else
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being equal) something about the past, that’s a memory; when a feature of
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our current state implies something about the future, that’s a cause of some
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future effect. The small differences in a person’s brain state that correlate
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with different bodily actions typically have negligible correlations with the
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past state of the universe, but they can be correlated with substantially dif-
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ferent future evolutions. That’s why our best human- sized conception of the
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world treats the past and future so differently. We remember the past, and
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our choices affect the future.
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Laplace’s Demon discerns no such imbalance; he sees the whole history
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of the world with perfect clarity. But none of us is Laplace’s Demon. None
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of us knows the exact state of the universe, or has the calculational power
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to predict the future even if we did. The unavoidable reality of our incom-
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plete knowledge is responsible for why we find it useful to talk about the
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future using a language of choice and causation.
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One popular definition of free will is “the ability to have acted
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differently.” In a world governed by impersonal laws, one can argue that
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there is no such ability. Given the quantum state of the elementary particles
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that make up me and my environment, the future is governed by the laws
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of physics. But in the real world, we are not given that quantum state. We
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have incomplete information; we know about the rough configuration of
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our bodies and we have some idea of our mental states. Given only that
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incomplete information— the information we actually have— it’s com-
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pletely conceivable that we could have acted differently.
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This is the point at which free- will doubters will object that the stance
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we’ve defended here isn’t really free will at all. All we’ve done is redefine the
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notion to mean something completely different, presumably because we are
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too cowardly to face up to the desolate reality of an impersonal cosmos.
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I have no problem with the desolate reality of an impersonal cosmos.
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But it’s important to explore the most accurate and useful ways of talking
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about the world, on all relevant levels.
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Admittedly, some formulations of “free will” go well beyond anything
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that a poetic naturalist would be willing to countenance. There is what is
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called libertarian freedom. This has nothing to do with the political free-
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market idea of libertarianism. Rather, it’s the position that human agency
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introduces an element of indeterminacy into the universe; people are not
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governed by the impersonal laws of physics; they have a distinct ability to
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shape their own futures. It’s a denial that there could be anything like La-
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place’s Demon, who could know the future before it happened.
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There’s no reason to accept libertarian freedom as part of the real world.
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There is no direct evidence for it, and it violates everything we know about
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the laws of nature. In order for libertarian freedom to exist, it would have
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to be possible for human beings to overcome the laws of physics just by
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thinking.
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A poetic naturalist says that we can have two very different- sounding
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ways of describing the world, a physics- level story and a human- level story,
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which invoke separate sets of concepts and yet end up being compatible in
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their predictions concerning what happens in the world. A libertarian
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thinks that the right way to talk about human beings ends up making pre-
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dictions that are incompatible with the known laws of physics. We don’t
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need to do such dramatic violence to our understanding of reality just to
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make peace with the fact that we make choices as we go through the day.
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In a famous experiment in the 1980s, physiologist Benjamin Libet mea-
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sured brain activity in subjects as they decided to move their hands. The
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volunteers were also observing a clock, and could report precisely when they
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made their decisions. Libet’s results seemed to indicate that there was a
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telltale pulse of brain activity before the subjects became consciously aware
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of their decision. To put it dramatically: part of their brain had seemingly
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made the decision before the people themselves became aware of it.
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Libet’s experiment, and various follow- ups, have become controversial.
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Some claim that they are evidence against the existence of free will, since
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obviously our consciousness is a bit behind the curve when it comes to
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decision making. Others have raised technical concerns about whether the
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signal Libet measured is truly a sign of a decision having been made, and
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whether the subjects were reliable in reporting when their decisions oc-