vironment in terms of its own molecular structure. The individual molecule
11
has no idea it’s part of a snowflake, and could not care less.
12
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
15
situations of very low numbers of particles, but started obeying different
16
rules when the numbers became large (such as in a human being). Even
17
then, the right way to think about the situation would not be “the larger
18
structure is influencing the smaller particles”; it’s “the rules we thought
19
were obeyed by particles were wrong.” In other words, we could discover
20
that the domain of applicability of the Core Theory was smaller than we
21
thought it was. There is no evidence that anything along those lines is true,
22
and it would violate everything we know about effective quantum field
23
theories— but many things are possible.
24
The way we talk about human beings and their interactions is going to
25
end up being less crisp and precise than our theories of elementary particles.
26
It might be harmless, and even useful, to borrow terms from one story be-
27
cause they are useful in another one—“diseases are caused by microscopic
28
germs” being an obvious example. Drawing relations between different vo-
29
cabularies, such as when Boltzmann suggested that the entropy of a gas was
30
related to the number of indistinguishable arrangements of the molecules
31
of which it was composed, can be extremely valuable and add important
32
insights. But if a theory is any good, it has to be able to speak sensibly about
33
the phenomena it purports to describe all by itself, without leaning on
34
causes being exerted to or from theories at different levels of focus.
35S
Mental states are ways of talking about particular physical states. To say
36N
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that a mental state causes a physical effect is precisely as legitimate as saying
01
that any macroscopic physical situation is the cause of some macroscopic
02
physical event. There is nothing incorrect about attributing your scratching
03
to the existence of your itching; there’s simply more than one story we can
04
legitimately tell about what’s going on.
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01
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44
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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
18
laws of physics? Do I, at the end of the day, have free will?
19
There’s a sense in which you do have free will. There’s also a sense in
20
which you don’t. Which sense is the “right” one is an issue you’re welcome
21
to decide for yourself (if you think you have the ability to make decisions).
22
The usual argument against free will is straightforward: We are made of
23
atoms, and those atoms follow the patterns we refer to as the laws of phys-
24
ics. These laws serve to completely describe the evolution of a system, with-
25
out any influences from outside the atomic description. If information
26
is conserved through time, the entire future of the universe is already writ-
27
ten, even if we don’t know it yet. Quantum mechanics predicts our future
28
in terms of probabilities rather than certainties, but those probabilities
29
themselves are absolutely fixed by the state of the universe right now. A
30
quantum version of Laplace’s Demon could say with confidence what the
31
probability of every future history will be, and no amount of human voli-
32
tion would be able to change it. There is no room for human choice, so there
33
is no such thing as free will. We are just material objects who obey the laws
34
of nature.
35S
It’s not hard to see where that argument violates our rules. Of course
36N
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
01
nothing about whether the concept nevertheless plays a useful role when we
02
choose to describe human beings as people. Indeed, it pretty clearly does
03
play a useful role. Even the most diehard anti– free will partisans are con-
04
stantly speaking about choices that they and other people make in their
05
daily activities, even if they afterward try to make light of it by adding,
06
“Except of course the concept of choice doesn’t really exist.”
07
The concept of choice does exist, and it would be difficult indeed to
08
describe human beings without it. Imagine you’re a high school student
09
who wants to go to college, and you’ve been accepted into several universi-
10
ties. You look at their web pages, visit campuses, talk to students and fac-
11
ulty at each place. Then you say yes to one of them, no to the others. What
12
is th
e best way to describe what just happened, the most useful vocabulary
13
for talking about our human- scale world? It will inevitably involve some
14
statements along the lines of “you made a choice,” and the reasons for that
15
choice. If you had been a simplistic robot or a random- number generator,
16
there might have been a better way of talking. But it is artificial and coun-
17
terproductive to deny ourselves the vocabulary of choice when we talk
18
about human beings, regardless of how well we understand the laws of
19
physics. This stance is known in the philosophical literature as compatibil-
20
ism, and refers to the compatibility between an underlying deterministic
21
(or at least impersonal) scientific description and a macroscopic vocabulary
22
of choice and volition. Compatibilism, which traces its roots back as far as
23
John Locke in the seventeenth century, is the most popular way of thinking
24
about free will among professional philosophers.
25
From this perspective, the mistake made by free- will skeptics is to care-
26
lessly switch between incompatible vocabularies. You step out of the shower
27
in the morning, walk to your closet, and wonder whether you should put
28
on the black shirt or the blue shirt. That’s a decision that you have to make;
29
you can’t just say, “I’ll do whatever the atoms in my body were going to
30
deterministically do anyway.” The atoms are going to do whatever they were
31
going to do; but you don’t know what that is, and it’s irrelevant to the ques-
32
tion of which decision you should make. Once you frame the question in
33
terms of you and your choice, you can’t also start talking about your atoms
34
and the laws of physics. Either vocabulary is perfectly legitimate, but mix-
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ing them leads to nonsense.
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01
•
02
03
You may be willing to accept that oceans and temperature are real, even
04
though they are nowhere to be found among the fundamental ingredients
05
of the Core Theory, but feel unwilling to apply the same logic to free will.
06
After all, the ability to make choices isn’t just a macroscopic collection of
07
many microscopic pieces; it’s an entirely different kind of thing. If it’s not
08
there in our best comprehensive description of nature, why is it helpful to
09
act like it’s there in our human- scale vocabulary?
10
The answer comes down to the arrow of time. In chapter 8 we talked
11
about how we have epistemic access to the past— memories— that we don’t
12
have when it comes to the future. That’s because there is a special boundary
13
condition, the Past Hypothesis, according to which entropy was very low
14
near the Big Bang. That’s a powerful bit of information about the past,
15
which enables us to pin it down in a way that we can’t pin down the future.
16
This temporal asymmetry arises only because of the distribution of matter
17
in the universe on macroscopic scales; there is no analogue of it in the Core
18
Theory itself.
19
There is a crucial role played by the leverage that features of our current
20
state exert over our knowledge of events in the past or future. When a fea-
21
ture of our current state implies (given the Past Hypothesis, and all else
22
being equal) something about the past, that’s a memory; when a feature of
23
our current state implies something about the future, that’s a cause of some
24
future effect. The small differences in a person’s brain state that correlate
25
with different bodily actions typically have negligible correlations with the
26
past state of the universe, but they can be correlated with substantially dif-
27
ferent future evolutions. That’s why our best human- sized conception of the
28
world treats the past and future so differently. We remember the past, and
29
our choices affect the future.
30
Laplace’s Demon discerns no such imbalance; he sees the whole history
31
of the world with perfect clarity. But none of us is Laplace’s Demon. None
32
of us knows the exact state of the universe, or has the calculational power
33
to predict the future even if we did. The unavoidable reality of our incom-
34
plete knowledge is responsible for why we find it useful to talk about the
35S
future using a language of choice and causation.
36N
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
01
there is no such ability. Given the quantum state of the elementary particles
02
that make up me and my environment, the future is governed by the laws
03
of physics. But in the real world, we are not given that quantum state. We
04
have incomplete information; we know about the rough configuration of
05
our bodies and we have some idea of our mental states. Given only that
06
incomplete information— the information we actually have— it’s com-
07
pletely conceivable that we could have acted differently.
08
09
•
10
This is the point at which free- will doubters will object that the stance
11
we’ve defended here isn’t really free will at all. All we’ve done is redefine the
12
notion to mean something completely different, presumably because we are
13
too cowardly to face up to the desolate reality of an impersonal cosmos.
14
I have no problem with the desolate reality of an impersonal cosmos.
15
But it’s important to explore the most accurate and useful ways of talking
16
about the world, on all relevant levels.
17
Admittedly, some formulations of “free will” go well beyond anything
18
that a poetic naturalist would be willing to countenance. There is what is
19
called libertarian freedom. This has nothing to do with the political free-
20
market idea of libertarianism. Rather, it’s the position that human agency
21
introduces an element of indeterminacy into the universe; people are not
22
governed by the impersonal laws of physics; they have a distinct ability to
23
shape their own futures. It’s a denial that there could be anything like La-
24
place’s Demon, who could know the future before it happened.
25
There’s no reason to accept libertarian freedom as part of the real world.
26
There is no direct evidence for it, and it violates everything we know about
27
the laws of nature. In order for libertarian freedom to exist, it would have
28
to be possible for human beings to overcome the laws of physics just by
29
thinking.
30
A poetic naturalist says that we can have two very different- sounding
31
ways of describing the world, a physics- level story and a human- level story,
32
which invoke separate sets of concepts and yet end up being compatible in
33
their predictions concerning what happens in the world. A libertarian
34
thinks that the right way to talk about human beings ends up making pre-
S35
dictions that are incompatible with the known laws of physics. We don’t
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01
need to do such dramatic violence to our understanding of reality just to
02
make peace with the fact that we make choices as we go through the day.
03
In a famous experiment in the 1980s, physiologist Benjamin Libet mea-
04
sured brain activity in subjects as they decided to move their hands. The
05
volunteers were also observing a clock, and could report precisely when they
06
made their decisions. Libet’s results seemed to indicate that there was a
07
telltale pulse of brain activity before the subjects became consciously aware
08
of their decision. To put it dramatically: part of their brain had seemingly
09
made the decision before the people themselves became aware of it.
10
Libet’s experiment, and various follow- ups, have become controversial.
11
Some claim that they are evidence against the existence of free will, since
12
obviously our consciousness is a bit behind the curve when it comes to
13
decision making. Others have raised technical concerns about whether the
14
signal Libet measured is truly a sign of a decision having been made, and
15
whether the subjects were reliable in reporting when their decisions oc-
The Big Picture Page 64