The Big Picture

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The Big Picture Page 39

by Carroll, Sean M.


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  dict the laws of physics that we go astray.

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  If the world we see in our experiments is just a tiny part of a much bigger

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  reality, the rest of reality must somehow act upon the world we do see;

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  otherwise it doesn’t matter very much. And if it does act upon us, that im-

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  plies a necessary alteration in the laws of physics as we understand them.

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  Not only do we have no strong evidence in favor of such alterations; we

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  don’t even have any good proposals for what form they could possibly take.

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  The burden for naturalists, meanwhile, is to show that a purely physical

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  universe made of interacting quantum fields is actually able to account for

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  the macroscopic world of our experience. Can we understand how order

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  and complexity arise in a world without transcendent purpose, even in the

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  face of increasing disorder as implied by the second law of thermodynam-

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  ics? Can we make sense of consciousness and our inner experience without

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  appealing to substances or properties beyond the purely physical? Can we

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  bring meaning and morality to our lives, and speak sensibly about what is

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  right and what is wrong?

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  Let’s see if we can.

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  P A R t F O u R

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  COM Pl E x It y

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  The Universe in a Cup of Coffee

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  illiam Paley, a British clergyman writing at the turn of the

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  nineteenth century, invited you to imagine a walk through

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  one of Britain’s picturesque heaths. Suddenly your reverie is

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  interrupted when you stub your toe against a stone. You would be annoyed,

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  thought Paley, but what you wouldn’t do is start wondering where such a

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  stone could possibly have come from. Stones are the kinds of things one

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  naturally expects to come across while walking through fields.

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  Now imagine instead that you notice a pocket watch lying on the

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  ground during your walk. Here you have a puzzle— how did it get there?

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  Not a difficult puzzle, admittedly; presumably someone dropped it while

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  out on a walk similar to your own. Paley’s point was that you would never

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  imagine that the watch would just have been sitting there since time im-

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  memorial. A stone is a simple lump of material, but a watch is an intricate

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  and purposeful mechanism. It is clear that someone must have made it; a

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  watch implies a watchmaker.

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  And so it is, continues Paley, with so many things in nature. What

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  we observe in the form of living creatures in the natural world, he ar-

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  gued, is “every manifestation of design”— not only complexity but struc-

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  tures that are obviously attuned to some specific purpose. Nature, he

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  concluded, requires a watchmaker. A Designer, whom Paley identified

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  with God.

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  It’s an argument worth considering. If you found a watch lying on

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  the ground, you would indeed surmise that someone had designed it.

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  And there are specific mechanisms inside our bodies that, for example, help

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  us tell time. (Among them is a protein, cleverly named CLOCK, whose

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  production plays a crucial role in regulating our daily circadian rhythm.)

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  The human body is much more complex than a mechanical watch.

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  Concluding that biological organisms are designed doesn’t seem like much

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  of a leap.

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  We might be cautious about where exactly we should be leaping. David

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  Hume, in his Dialogues Concerning Natural Religion, argued fairly

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  compellingly— and even before Paley had popularized the “watchmaker

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  analogy” version of the argument from design— that there is a substantial

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  difference between “a designer” and our traditional notion of God. Paley’s

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  argument nevertheless has a good deal of persuasive power, and continues

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  to be popular today.

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  Immanuel Kant, writing in 1784, mused, “There will never be a Newton

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  for the blade of grass.” Sure, you can invent unbending mechanistic rules

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  governing the motions of planets and pendulums, but to account for the

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  living world, you need to go beyond mindless patterns. There must be some-

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  thing that accounts for the purposive nature of living creatures.

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  These days we know better. We even know who the Newton for the

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  blade of grass turned out to be: his name was Charles Darwin. In 1859,

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  Darwin published On the Origin of Species by Means of Natural Selection,

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  in which he laid out the basis for the modern theory of evolution. The great

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  triumph of Darwin’s theory was not only to account for the history of life

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  as revealed in the fossil record, but to do so without invoking any kind of

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  purpose or external guidance—“design without a designer,” as biologist

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  Francisco Ayala has labeled it.

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  Essentially every working professional biologist accepts the basic expla-

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  nation provided by Darwin for the existence of complex structures in bio-

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  logical organisms. In the famous words of Theodosius Dobzhansky,

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  “Nothing in biology makes sense except in the light of evolution.” But evo-

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  lution happens within a larger context. Darwin takes as his starting point

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  creatures that can survive, reproduce, and randomly evolve, and then shows

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  how natural selection can act on those random changes to produce the il-

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  lusion of design. So where did those creatures come from in the first place?

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  t h E u n I v E R S E I n A C u P OF C O F F E E

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  Our goal over the next few chapters is to address the origin of complex

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  structures— including, but not limited to, living creatures— in the context

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  of the big picture. The universe is a set of quantum fields obeying equations

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  that don’t even distinguish between past and future, much less embody any

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  long- term goals. How in the world did something as organized as a human

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  being ever come to be?

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  The short answer comes in two parts: entropy and emergence. Entropy

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  provides an arrow of time; emergence gives us a way of talking about collec-

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  tive structures that can live and evolve and have goals and desires. First we’ll

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  focus on entropy.

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  The role of entropy in the development of complexity seems counterin-

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  tuitive at first. The second law of thermodynamics says that the entropy of

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  isolated systems increases over time. Ludwig Boltzmann explained entropy

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  to us: it’s a way of counting how many possible microscopic arrangements

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  of the stuff in a system would look indistinguishable from a macroscopic

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  point of view. If there are many ways to rearrange the particles in a system

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  without changing its basic appearance, it’s high- entropy; if there are a rela-

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  tively small number, it’s low- entropy. The Past Hypothesis says that our

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  observable universe started in a very low- entropy state. From there, the

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  second law is easy to see: as time goes on, the universe goes from being low-

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  entropy to high- entropy, simply because there are more ways that entropy

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  can be high.

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  Increasing entropy isn’t incompatible with increasing complexity,

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  but it can seem that way because of how we sometimes translate the techni-

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  cal terms into informal speech. We say that entropy is “disorderliness” or

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  “randomness,” and that it always increases in isolated systems (such as

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  the universe). If the general tendency of stuff is to grow more random

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  and disorganized, it might seem strange that highly organized subsys-

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  tems come into being without any guiding force working behind the

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  scenes.

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  There’s a common response to this worry, which is perfectly correct but

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  doesn’t quite get at the underlying concern. It goes like this: “The second

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  law is a statement about the growth of entropy in isolated systems, ones that

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  don’t interact with an external environment. In open systems, exchanging

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  energy and information with the outside world, of course entropy can go

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  down. The entropy of a bottle of wine goes down when you put it in a re-

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  frigerator because its temperature goes down, and the entropy of your room

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  goes down when you clean it up. None of that violates the laws of physics,

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  since the total entropy is still going up— refrigerators expel heat from the

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  back, and human beings sweat and grunt and radiate as they clean up a

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  room.”

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  While it addresses the letter of the concern, this response sidesteps

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  its spirit. The emergence of complex structures on a place like the surface

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  of the Earth is completely compatible with the second law, and it is silly

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  to suggest otherwise. The Earth is an extremely open system, radiating

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  into the universe and increasing its total entropy all the time. The prob-

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  lem is, while that explains why organized systems can come into being

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  here on Earth, it doesn’t explain why they actually do. A refrigerator low-

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  ers the entropy of its contents, but only by making them colder, not by

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  making them more intricate or complex. And rooms can be cleaned,

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  but in our experience it seems to require exactly what Paley was talk-

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  ing about: an external intelligence to do the work. Rooms don’t spontane-

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  ously clean themselves, even if we allow them to interact with the

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  environment.

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  We still need to understand how and why the laws of physics brought

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  about complex, adaptive, intelligent, responsive, evolving, caring creatures

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  like you and me.

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  What do we mean by “simple” or “complex,” and how do they relate to en-

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  tropy? Intuitively, we associate complexity with low entropy, and simplicity

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  with high entropy. After all, if entropy is “randomness” or “disorganiza-

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  tion,” that sounds like the opposite of how we think about the intricate

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  mechanisms we find in a wristwatch or an armadillo.

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  Our intuition here is a bit off. Think of mixing cream into coffee, inside

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  a glass mug. Since we’re doing a physics experiment rather than a morning

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  ritual, let’s do it first by gently putting the cream on top of the coffee, and

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  only then mixing them together with a spoon. (The spoon is an external

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  influence, but not a guided or intelligent one.)

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  At the beginning, the system is low- entropy. There are relatively few

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  ways to rearrange the atoms in the cream and coffee without changing its

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  macroscopic appearance; we could swap individual cream molecules

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  amongst themselves, or individual molecules in the coffee, but once we

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  started exchanging cream with coffee, our glass mug would look different.

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  At the end, everything is mixed together and the entropy is relatively high.

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  We could exchange any bit of the mixture with any other bit and the system

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  would look essentially the same. Entropy has gone up throughout the pro-

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  cess, just as the second law would lead us to expect.

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  Mixing cream into coffee. The initial state is low- entropy and simple. The final state is 25

  high- entropy and simple. The intermediate, medium- entropy state exhibits interesting 26

  complexity.

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  But it’s not true that complexity has gone down as entropy has gone up.

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  Consider the first configuration, with cream and coffee totally separate; it’s

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  low- entropy, but it’s also manifestly simple. Cream on top, coffee on bot-

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  tom, nothing else going on. The final configuration, with everything mixed

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  together, is also quite simple. It’s completely characterized by saying “every-

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  thing is mixed together.” It’s the intermediate stage, in between low entropy

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  and high entropy, where things look complex. Tendrils of cream reach into

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  the coffee in intricate and beautiful ways.

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  The cream- and- coffee system exhibits behavior that is very different

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  from a naïve identification of “increasing entropy” with “decreasing com-

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  plexity.” Entropy goes up, as the second law says it should; but complexity

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  first goes up, then goes down.

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  At least, that’s the way it looks. We haven’t yet given a precise definition

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  of what we mean by “complexity,” as we were able to do for entropy. Partly

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  that’s because there is no one definition that works for every circumstance—

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  different systems can exhibit complexity in different ways. That’s a feature,

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  not a bug; complexity comes in many forms. We can ask about the complex-

 

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