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