commonplace book redux

List of passages I highlighted in “The Big Picture”.

On ontology:

We will see how our best approach to describing the universe is not a single, unified story but an interconnected series of models appropriate at different levels. Each model has a domain in which it is applicable, and the ideas that appear as essential parts of each story have every right to be thought of as “real.” […]

While there is one world, there are many ways of talking about it. We refer to these ways as “models” or “theories” or “vocabularies” or “stories”; it doesn’t matter. Aristotle and his contemporaries weren’t just making things up; they told a reasonable story about the world they actually observed. Science has discovered another set of stories, harder to perceive but of greater precision and wider applicability. It’s not good enough that the stories succeed individually; they have to fit together. […]

The different stories or theories use utterly different vocabularies; they are different ontologies, despite describing the same underlying reality. In one we talk about the density, pressure, and viscosity of the fluid; in the other we talk about the position and velocity of all the individual molecules. […]

One theory can directly be obtained from the other by a process known as coarse-graining. […]

The case of fluid dynamics emerging from molecules is as simple as it gets. One theory can directly be obtained from the other by a process known as coarse-graining. […]

Typically—though not necessarily—the theory that has a wider domain of applicability will also be the one that is more computationally cumbersome. There tends to be a trade-off between comprehensiveness of a theory and its practicality. […]

There are several different questions here, which are related to one another but logically distinct. Are the most fine-grained (microscopic, comprehensive) stories the most interesting or important ones? As a research program, is the best way to understand macroscopic phenomena to first understand microscopic phenomena, and then derive the emergent description? Is there something we learn by studying the emergent level that we could not understand by studying the microscopic level, even if we were as smart as Laplace’s Demon? Is behavior at the macroscopic level incompatible—literally inconsistent with—how we would expect the system to behave if we knew only the microscopic rules? […]

(A similar view was put forward by Stephen Hawking and Leonard Mlodinow, under the label “model-dependent realism.”) […]

To evaluate a model of the world, the questions we need to ask include “Is it internally consistent?,” “Is it well-defined?,” and “Does it fit the data?” When we have multiple distinct theories that overlap in some regime, they had better be compatible with one another; otherwise they couldn’t both fit the data at the same time. The theories may involve utterly different kinds of concepts; one may have particles and forces obeying differential equations, and another may have human agents making choices. That’s fine, as long as the predictions of the theories line up in their overlapping domains of applicability. The success of one theory doesn’t mean that another one is wrong; that only happens when a theory turns out to be internally incoherent, or when it does a bad job at describing the observed phenomena. […]

“Causation,” which after all is itself a derived notion rather than a fundamental one, is best thought of as acting within individual theories that rely on the concept. Thinking of behavior in one theory as causing behavior in a completely different theory is the first step toward a morass of confusion from which it is difficult to extract ourselves. […]

The way we talk about human beings and their interactions is going to end up being less crisp and precise than our theories of elementary particles. It might be harmless, and even useful, to borrow terms from one story because they are useful in another one—“diseases are caused by microscopic germs” being an obvious example. Drawing relations between different vocabularies, such as when Boltzmann suggested that the entropy of a gas was related to the number of indistinguishable arrangements of the molecules of which it was composed, can be extremely valuable and add important insights. But if a theory is any good, it has to be able to speak sensibly about the phenomena it purports to describe all by itself, without leaning on causes being exerted to or from theories at different levels of focus. […]

On reductionism:

Galileo observed that Jupiter has moons, implying that it is a gravitating body just like the Earth. Isaac Newton showed that the force of gravity is universal, underlying both the motion of the planets and the way that apples fall from trees. John Dalton demonstrated how different chemical compounds could be thought of as combinations of basic building blocks called atoms. Charles Darwin established the unity of life from common ancestors. James Clerk Maxwell and other physicists brought together such disparate phenomena as lightning, radiation, and magnets under the single rubric of “electromagnetism.” Close analysis of starlight revealed that stars are made of the same kinds of atoms as we find here on Earth, with Cecilia Payne-Gaposchkin eventually proving that they are mostly hydrogen and helium. Albert Einstein unified space and time, joining together matter and energy along the way. Particle physics has taught us that every atom in the periodic table of the elements is an arrangement of just three basic particles: protons, neutrons, and electrons. Every object you have ever seen or bumped into in your life is made of just those three particles. We’re left with a very different view of reality from where we started. At a fundamental level, there aren’t separate “living things” and “nonliving things,” “things here on Earth” and “things up in the sky,” “matter” and “spirit.” There is just the basic stuff of reality, appearing to us in many different forms. How far will this process of unification and simplification go? It’s impossible to say for sure. But we have a reasonable guess, based on our progress thus far: it will go all the way. We will ultimately understand the world as a single, unified reality, not caused or sustained or influenced by anything outside itself. That’s a big deal. […]

On truth and falsity of models:

Consider a coffee cup sitting at rest on a table. It is in its natural state, in this case at rest. (Unless we were to pull the table out from beneath it, in which case it would naturally fall, but let’s not do that.) Now imagine we exert a violent motion, pushing the cup across the table. As we push it, it moves; when we stop, it returns to its natural state of rest. In order to keep it moving, we would have to keep pushing on it. As Aristotle says, “Everything that is in motion must be moved by something.” This is manifestly how coffee cups do behave in the real world. The difference between Galileo and Aristotle wasn’t that one was saying true things and the other was saying false things; it’s that the things Galileo chose to focus on turned out to be a useful basis for a more rigorous and complete understanding of phenomena beyond the original set of examples, in a way that Aristotle’s did not. […]

On simluation:

To simulate the entire universe with good accuracy, you basically have to be the universe. […]

On the arrow of time:

When a later event has great leverage over an earlier one, we call the latter a “record” of the former; when the earlier event has great leverage over a later one, we call the latter a “cause” of the former. […]

On quantum mechanics:

Physicists were forced to throw out what we mean by the “state” of a physical system—the complete description of its current situation—and replace it with something utterly different. What is worse, we had to reinvent an idea we thought was pretty straightforward: the concept of a measurement or observation. […]

On cells:

Keeping the cell membrane intact and robust turns out to be a kind of Bayesian reasoning. […]

On information:

As the universe evolves from this very specific configuration to increasingly generic ones, correlations between different parts of the universe develop very naturally. It becomes useful to say that one part carries information about another part. It’s just one of the many helpful ways we have of talking about the world at an emergent, macroscopic level. […]

On fine-tuning:

The fine-tuning argument plays by the rules of how we come to learn about the world. It takes two theories, naturalism and theism, and then tests them by making predictions and going out and looking at the world to test which prediction comes true. It’s the best argument we have for God’s existence. […]

naturalists need to face fine-tuning head-on. That means understanding what the universe is predicted to look like under both theism and naturalism, so that we can legitimately compare how our observations affect our credences. We’ll see that the existence of life provides, at best, a small boost to the probability that theism is true—while related features of the universe provide an extremely large boost for naturalism. […]

On the evolution of higher intelligence:

If you’ve spent much time swimming or diving, you know that you can’t see as far underwater as you can in air. The attenuation length—the distance past which light is mostly absorbed by the medium you are looking through—is tens of meters through clear water, while in air it’s practically infinite. (We have no trouble seeing the moon, or distant objects on our horizon.) What you can see has a dramatic effect on how you think. If you’re a fish, you move through the water at a meter or two per second, and you see some tens of meters in front of you. Every few seconds you are entering a new perceptual environment. As something new looms into your view, you have only a very brief amount of time in which to evaluate how to react to it. Is it friendly, fearsome, or foodlike? Under those conditions, there is enormous evolutionary pressure to think fast. See something, respond almost immediately. A fish brain is going to be optimized to do just that. Quick reaction, not leisurely contemplation, is the name of the game. Now imagine you’ve climbed up onto land. Suddenly your sensory horizon expands enormously. Surrounded by clear air, you can see for kilometers—much farther than you can travel in a couple of seconds. At first, there wasn’t much to see, since there weren’t any other animals up there with you. But there is food of different varieties, obstacles like rocks and trees, not to mention the occasional geological eruption. And before you know it, you are joined by other kinds of locomotive creatures. Some friendly, some tasty, some simply to be avoided. Now the selection pressures have shifted dramatically. Being simple-minded and reactive might be okay in some circumstances, but it’s not the best strategy on land. When you can see what’s coming long before you are forced to react, you have the time to contemplate different possible actions, and weigh the pros and cons of each. You can even be ingenious, putting some of your cognitive resources into inventing plans of action other than those that are immediately obvious. Out in the clear air, it pays to use your imagination. […]

On our righteous minds:

Kahneman compares System 2 to “a supporting character who believes herself to be the lead actor and often has little idea of what’s going on.” […]

On cognitive science:

The study of how we think and feel, not to mention how to think about who we are, is in its relative infancy. As neuroscientist and philosopher Patricia Churchland has put it, “We’re pre-Newton, pre-Kepler. We’re still sussing out that there are moons around Jupiter.” […]

On philosophy of mind:

Frank Jackson himself has subsequently repudiated the original conclusion of the knowledge argument. Like most philosophers, he now accepts that consciousness arises from purely physical processes: “Although I once dissented from the majority, I have capitulated,” he writes. Jackson believes that Mary the Color Scientist helps pinpoint our intuition about why conscious experience can’t be purely physical, but that this isn’t enough to qualify as a compelling argument for such a conclusion. The interesting task is to show how our intuition has led us astray—as, science keeps reminding us, it so often does. […]

Sean Caroll, The Big Picture: On the Origins of Life, Meaning, and the Universe Itself Hardcover, 2016