as the “crowning edifice” of this hierarchy. Subsequently, the daz-
16
zling success of physics at describing the microscopic world has flipped
17
things around in some people’s minds; they prefer to focus on the deepest,
18
most fundamental way of talking about reality. Ernest Rutherford, a New
19
Zealand– born experimental physicist who was as responsible as anyone for
20
discovering the structure of the atom, once remarked that “all of science is
21
either physics or stamp collecting.” It should come as no surprise that scien-
22
tists who are not physicists— the very large majority of scientists, in other
23
words— would beg to differ.
24
From the point of view of emergence, the question becomes: how new
25
and different are emergent phenomena? Is an emergent theory just a way of
26
repackaging the microscopic theory, or is it something truly novel? For that
27
matter, is the behavior of the emergent theory derivable, even in principle,
28
from the microscopic description, or does the underlying stuff literally act
29
differently in the macroscopic context? A more provocative way of putting
30
the same questions would be: are emergent phenomena real, or merely il-
31
lusory?
32
As you might imagine, these questions lie front and center when we
33
start talking about knotty issues such as the emergence of consciousness or
34
free will. Sure, you think you’re making a choice about whether to have that
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last slice of pizza or virtuously resist the temptation, but are you sure you
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really are? If the underlying laws of nature are deterministic, then isn’t your
02
volition simply an illusion?
03
But the independent reality of emergent phenomena is an important
04
issue even when we stick to physics. Philip Anderson won the Nobel Prize
05
in Physics in 1977 for his work on the electronic properties of materials. He
06
is a “condensed matter” physicist— someone who thinks about materials,
07
fluids, or other macroscopically tangible forms of matter here on Earth, as
08
opposed to an astrophysicist, atomic physicist, or particle physicist. In the
09
1990s, when the US Congress was contemplating the fate of the Supercon-
10
ducting Super Collider particle accelerator, Anderson was called to testify
11
as an expert in physics who was not directly involved in particle physics. He
12
told the committee that the new machine would doubtless do good work,
13
but any discoveries it would make would be utterly irrelevant to his own
14
research. That was honest, and accurate, if a bit frustrating to the particle
15
physicists who hoped the whole field would present a unified front. (Con-
16
gress canceled the SSC in 1993; a competing machine, the Large Hadron
17
Collider, was built in Europe, and went on to discover the Higgs boson
18
in 2012.)
19
Anderson’s comments were based on the fact that an emergent theory
20
can be completely independent of more fine- grained comprehensive de-
21
scriptions of the same system. The emergent theory is autonomous (it works
22
by itself, without reference to other theories) and multiply realizable (many
23
microscopic theories can lead to the same emergent behavior).
24
Anderson would be interested in questions about, for example, how cur-
25
rent flows through a particular kind of ceramic. We know that the material
26
is made of atoms, and we know the rules by which electricity and magne-
27
tism interact with those atoms. For the questions Anderson cares about,
28
that’s all we need to know. We can think of the theory of atoms, electrons,
29
and their interactions as the emergent theory, and anything more fine-
30
grained than that as a microscopic theory. The emergent theory has its own
31
rules, independent of any purported lower levels. And it may very well be
32
multiply realizable. Anderson doesn’t need to worry about the quarks zip-
33
ping about inside an atomic nucleus, or about the Higgs boson itself, and
34
certainly not about superstring theory or anything that tries to give a more
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comprehensive microscopic description of matter. (For much of his work,
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he doesn’t even need to know about atoms, as he is working at an even
01
higher level of coarse- graining.)
02
Given this situation, condensed- matter physicists have long argued that
03
we should think of emergent phenomena as truly new, not “merely”
04
smeared- out versions of some deeper description. In 1972 Anderson pub-
05
lished an influential article entitled “More Is Different,” arguing that every
06
one of the multiple overlapping stories we can tell about nature deserves to
07
be studied and appreciated for its own sake, rather than focusing primarily
08
on the most fundamental level. He has a point. A famous problem in
09
condensed- matter physics is to find a successful theory of high- temperature
10
superconductors, materials through which electrical current can flow with-
11
out resistance. Everyone working on the problem believes that such materi-
12
als are made out of ordinary atoms, obeying the ordinary microscopic rules;
13
knowing that has been of essentially zero help in guiding us toward an
14
understanding of why high- temperature superconductivity happens at all.
15
16
•
17
There are several different questions here, which are related to one another
18
but logically distinct.
19
20
1. Are the most fine- grained (microscopic, comprehensive)
21
stories the most interesting or important ones?
22
2. As a research program, is the best way to understand mac-
23
roscopic phenomena to first understand microscopic phe-
24
nomena, and then derive the emergent
description?
25
3. Is there something we learn by studying the emergent level
26
that we could not understand by studying the microscopic
27
level, even if we were as smart as Laplace’s Demon?
28
4. Is behavior at the macroscopic level incompatible— literally
29
inconsistent with— how we would expect the system to be-
30
have if we knew only the microscopic rules?
31
32
Regarding question 1, it’s obviously a subjective matter. If you’re inter-
33
ested in particle physics, and your friend is interested in biology, neither is
34
right or wrong; you’re just different. Question 2 is a bit more practical, and
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the answer is fairly obvious: no. In almost all cases of interest, we might
02
learn a little bit about higher levels by studying lower ones, but we’ll learn
03
more (and more quickly) by studying those higher levels themselves.
04
It’s at question 3 where things become contentious. One point of view
05
would say: if we completely understand the microscopic level, which has a
06
domain of applicability that strictly contains that of the emergent theory,
07
we know everything there is to know. Whatever question you have could,
08
in principle, be translated into the microscopic language and answered
09
there.
10
But “in principle” covers a multitude of sins here, or at least one very big
11
sin. This perspective amounts to saying “You want to know if it will rain
12
tomorrow? Just tell me the position and velocity of all the molecules in the
13
Earth’s atmosphere, and I’ll get to calculating.” Not only is that wildly un-
14
realistic; it’s also ignoring the fact that the emergent theory describes true
15
features of the system that might be completely hidden from the micro-
16
scopic point of view. You might have a self- contained and comprehensive
17
theory of how things behave, but that doesn’t mean you know everything;
18
in particular, you don’t know all of the useful ways of talking about the
19
system. (Even if you know how every atom in a box of gas behaves, you
20
might be blind to the important fact that the system can also be described
21
as a fluid.) From that perspective— the correct one— we really do learn
22
something new by studying emergent theories for their own sakes, even if
23
all the theories are utterly compatible.
24
Then we have question 4, where all hell breaks loose.
25
•
26
27
We’re now entering into the realm known as strong emergence. So far we’ve
28
been discussing “weak emergence”: even if the emergent theory gives you
29
new understanding and an enormous increase in practicality in terms of
30
calculations, in principle you could put the microscopic theory on a com-
31
puter and simulate it, thereby finding out exactly how the system would
32
behave. In strong emergence— if such a thing actually exists— that wouldn’t
33
be possible. When many parts come together to make a whole, in this view,
34
not only should we be on the lookout for new knowledge in the form of bet-
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ter ways to describe the system, but we should contemplate new behavior. In
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strong emergence, the behavior of a system with many parts is not reducible
01
to the aggregate behavior of all those parts, even in principle.
02
The notion of strong emergence is a bit puzzling, on the face of it. It
03
starts by admitting that there is a sense in which a big macroscopic object,
04
such as a person, is made up of smaller constituents, such as atoms. (In
05
quantum mechanics, remember, this division into constituents isn’t always
06
possible, but that’s not the subtlety that strong emergentists usually have in
07
mind.) It further admits that there is a microscopic theory, one that will tell
08
you how an atom will behave in any particular circumstance. But then it
09
claims that there is an effect on that atom by the larger system of which it
10
is a part— an effect that cannot be thought of as arising from all of the other
11
atoms individually. The only way to think of it is as an effect of the whole
12
on the individual parts.
13
I can imagine focusing on one particular atom that currently resides as
14
part of the skin on the tip of my finger. Ordinarily, using the rules of atomic
15
physics, I would think that I could predict the behavior of that atom using
16
the laws of nature and some specification of the conditions in its
17
surroundings— the other atoms, the electric and magnetic fields, the force
18
due to gravity, and so on. A strong emergentist will say: No, you can’t do
19
that. That atom is part of you, a person, and you can’t predict the behavior
20
of that atom without understanding something about the bigger person-
21
system. Knowing about the atom and its surroundings is not enough.
22
That is certainly a way the world could work. If it’s how the world actually
23
does work, then our purported microscopic theory of the atom is simply
24
wrong. The nice thing about theories in physics is that they are very clear
25
about what information is needed to predict the behavior of an object, and
26
also clear about what the predicted behavior actually is. There’s no ambigu-
27
ity in what that atom is supposed to do, according to our best theory of
28
physics. If there are situations in which the atom behaves otherwise, such
29
as when it’s part of the tip of my finger, then our theory is wrong and we
30
have to do better.
31
Which is completely possible, of course. (Many things are possible.) In
32
chapters 22 to 24 we’ll dive more deeply into how our best theories of phys-
33
ics work, including the remarkably successful and unforgiving frame
work
34
of quantum field theory. Within quantum field theory, there is no way for
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new forces or influences to play an important role in what atoms do in my
02
body— or, more precisely, all of the possible ways this could happen have
03
been ruled out by experiments. But it’s always conceivable that quantum
04
field theory itself is just wrong. There’s no evidence that it’s wrong, however,
05
and very powerful experimental and theoretical reasons to think it’s right,
06
within a very wide domain of applicability. So we’re allowed to contemplate
07
alterations in this basic paradigm of physics— but we should be aware of
08
how dramatically we are changing our best theories of the world, just in
09
order to account for a phenomenon (human behavior) that is manifestly
10
extremely complex and hard to understand.
11
•
12
13
We may or may not need to bite the bullet of strong emergence in order to
14
understand the relationship between the atoms of which we are made and
15
the consciousness we all experience. But it’s our duty to figure out how they
16
are related, given that both atoms and consciousness exist in the real world.
17
Or do they?
18
There is a continuum of possible stances toward the way that the differ-
19
ent stories of reality fit together, with “strong emergence” (all stories are
20
autonomous, even incompatible) on one end and “strong reductionism” (all
21
stories reduce to one fundamental one) on the other. A strong reductionist
22
would be someone who not only wants to relate macroscopic features of the
23
world to some underlying fundamental description but also wants to go
24
further by denying that elements of the emergent ontology even exist, under
25
some appropriate definition of “exist.” The real problem with consciousness,
26
according to this school of thought, would be that there’s no such thing.
27
Consciousness is merely an illusion; it doesn’t really exist. In the context of
28
philosophy of mind, this hard-core flavor of reductionism is known as elim-
29
inativism, since its proponents want to eliminate talk of mental states en-
30
tirely. (Naturally, there is a rich zoo of different types of eliminativism, each
The Big Picture Page 19