Big Picture

One of a series of quick posts on the six sections of my book The Big Picture — Cosmos, Understanding, Essence, Complexity, Thinking, Caring.

Chapters in Part Two, Understanding:

• 9. Learning About the World
• 10. Updating Our Knowledge
• 11. Is It Okay to Doubt Everything?
• 12. Reality Emerges
• 13. What Exists, and What Is Illusion?
• 14. Planets of Belief
• 15. Accepting Uncertainty
• 16. What Can We Know About the Universe Without Looking at It?
• 17. Who Am I?
• 18. Abducting God

If, as a naturalist, you want to seriously engage with people who might not agree with you already, you’re going to have to talk a bit about epistemology — how we know what we know. It’s common for non-naturalists to level the accusation (perhaps sincerely felt) that naturalists simply assume their conclusion, and use methodologies that are not sensitive to the possibility of something outside the natural world.

I don’t agree, so in The Big Picture I spend a decent amount of time talking about how we actually go about the task of understanding the world. In particular, science doesn’t presume naturalism, it concludes that it’s the best explanation for the world we experience. Provisionally, of course — science never “proves” anything in the logical sense, so we should always be open to changing our minds in the face of new evidence. I talk a good deal (maybe too much) about Bayesian reasoning and how to update our beliefs.

As an extremely simple — but usefully illustrative — example of this philosophy in action, I concocted a straw-man example of theory choice:

Simplicity is sometimes easy to gauge, sometimes it is less so. Consider three competing theories. One says that the motion of planets and moons in the Solar System is governed, at least to a pretty good approximation, by Isaac Newton’s theories of gravity and motion. Another says that Newtonian physics doesn’t apply at all, and that instead every celestial body has an angel assigned to it, and these angels guide the planets and moons in their motions through space, along paths that just coincidentally match those that Newton would have predicted.

Most of us would probably think that the first theory is simpler than the second — you get the same predictions out, without needing to invoke vaguely-defined angelic entities. But the third theory is that Newtonian gravity is responsible for the motions of everything in the Solar System except for the Moon, which is guided by an angel, and that angel simply chooses to follow the trajectory that would have been predicted by Newton. It is fairly uncontroversial to say that, whatever your opinion about the first two theories, the third theory is certainly less simple than either of them. It involves all of the machinery of both, without any discernible difference in empirical predictions. We are therefore justified in assigning it a very low prior credence. (This example seems frivolous, but analogous moves become common when we start talking about the progress of biological evolution or the nature of consciousness.)

Some people don’t like the Bayesian emphasis on priors, because they seem subjective rather than objective. And that’s right — they are. It can’t be helped; we have to start somewhere. On the other hand, ideally the likelihoods of making certain observations can be objectively determined. If you have a certain theory about the world, and that theory is precise and well-defined, you can say with confidence what the chances are of observing various bits of data under the assumption that your theory is correct. In realistic circumstances, we are often stuck trying to evaluate theories that aren’t so rigorously defined in the first place. (“Consciousness transcends the physical” is a legitimate proposition, but it’s not sufficiently precise to make quantitative predictions.) Nevertheless, it’s our job to try to make our propositions as well-defined as possible, to the point where we can use them to objectively establish the likelihoods of different observations.

Everyone’s entitled to their own priors, but not to their own likelihoods.

Sadly, as much as we might aspire to be, we humans are not always completely rational. One concept I talk about is that of a “planet of belief” — rather than grounding our beliefs on an unshakeable foundation, we assemble a collection of beliefs that hold together under a mutual epistemological attraction. That’s not a mistake, it’s the best we can do. The secret is not to grow so attached to our planets that we equip them with impregnable defense systems, so that they can never be altered no matter what new things we learn.

Here we see some representative components of three plausible planets of belief. Can you figure out what kind of person each might belong to?

One of a series of quick posts on the six sections of my book The Big Picture — Cosmos, Understanding, Essence, Complexity, Thinking, Caring.

Chapters in Part One, Cosmos:

• 1. The Fundamental Nature of Reality
• 2. Poetic Naturalism
• 3. The World Moves By Itself
• 4. What Determines What Will Happen Next?
• 5. Reasons Why
• 6. Our Universe
• 7. Time’s Arrow
• 8. Memories and Causes

It wasn’t easy to settle on how to organize all the material in The Big Picture. Ultimately I decided to start with the universe — a bit of cosmology, yes, but also some basic features of how the universe physically operates. Features that played a crucial role in the transition from an ancient view of the world, which still lingers on in our informal “manifest image” of how things work, to our modern scientific view.

One important step in that transition was the seemingly-innocuous realization that momentum is conserved. In Aristotle’s physics, to keep something moving you had to keep pushing it. That’s a very sensible thing to believe, since it’s absolutely true in our everyday experience. It took many centuries of thinking by very smart people (including Persian polymath Ibn Sina, right) to realize that things tend to move by themselves, and are only slowed down by external forces such as friction. That’s important for physics, of course, but there is a deeper implication for our picture of what kinds of things we need to invoke to explain the universe. As I put it in the book:

Aristotle’s argument for an unmoved mover rests on his idea that motions require causes. Once we know about conservation of momentum, that idea loses its steam. We can quibble over the details — I have no doubt Aristotle would have been able to come up with an ingenious way of accounting for objects on frictionless surfaces moving at constant velocity. What matters is that the new physics of Galileo and his friends implied an entirely new ontology, a deep shift in how we thought about the nature of reality. “Causes” didn’t have the central role that they once did. The universe doesn’t need a push; it can just keep going.

It’s hard to over-emphasize the importance of this shift. Of course, even today, we talk about causes and effects all the time. But if you open the contemporary equivalent of Aristotle’s Physics — a textbook on quantum field theory, for example — words like that are nowhere to be found. We sometimes talk about causes, but they’re no longer part of our best fundamental ontology.

What we’re seeing is a manifestation of the layered nature of our descriptions of reality. At the deepest level we currently know about, the basic notions are things like “spacetime,” “quantum fields,” “equations of motions,” and “interactions.” No causes, whether material, formal, efficient, or final. But there are levels on top of that, where the vocabulary changes. Indeed, it’s possible to recover pieces of Aristotle’s physics quantitatively, as limits of Newtonian mechanics in an appropriate regime, where dissipation and friction are central. (Coffee cups do come to a stop, after all.) In the same way, it’s possible to understand why it’s so useful to refer to causes and effects in our everyday experience, even if they’re not present in the underlying equations. There are many different useful stories we have to tell about reality to get along in the world.

The idea that “cause and effect” isn’t fundamental to the workings of the universe hasn’t spread as widely as it should have, despite the efforts of smart people such as Bertrand Russell. In this first section of the book I sketch how we moved from a picture of the universe animated by causes and reasons to one that obeys patterns, without the need for anything to cause it or sustain it. Of course the idea of causality is still crucial to our everyday lives, so I talk a bit about how cause-and-effect relations are emergent phenomena in a macroscopic world with a pronounced arrow of time.

Many years ago I had the pleasure of attending a public lecture on cosmology by Martin Rees, one of the leading theoretical astrophysicists of our time and a wonderful speaker. For the most part his choice of material was unimpeachably conventional, but somewhere in the middle of explaining the evolution of the universe he suddenly started talking about the possibility of life on other planets. You could sense the few scientists in the room squirming uncomfortably — this wasn’t cosmology at all! But the actual public, to whom the talk was addressed, loved it. They didn’t care about fussy academic boundary enforcement; they thought these questions were interesting, and were curious about how it all fit together.

Since then, following Martin’s example, I have occasionally slipped into my own talks some discussion of how the particular bit of science I was discussing fit into a larger context. What are the implications of quantum mechanics for free will, or entropy for aging and death, or the multiverse for morality? To (what should be) nobody’s surprise, those are often what people want to follow up on in questions after the talk. Professional scientists will feel an urge to correct them, arguing that those aren’t the questions they should be asking about. But I think it’s okay. Science isn’t just about solving this or that puzzle; it’s about understanding how the world works. The whole world, from the vastness of the cosmos to the particularity of an individual human life. It’s worth thinking about how all the different ways we have to talk about the world manage to fit together.

That idea is one of the motivating considerations behind my new book, The Big Picture: On the Origins of Life, Meaning, and the Universe Itself, which is being released next week (Tuesday May 10 — I may be visiting your area). It’s a big book, covering a lot of things, so over the next few days I’m going to put up some posts containing small excerpts that give a flavor what what’s inside. You can get a general feeling from glancing at the table of contents. I also can’t resist pointing you to check out the amazing blurbs that so many generous people were thoughtful enough to contribute — Elizabeth Kolbert, Neil Shubin, Deborah Blum, Alan Lightman, Sabine Hossenfelder, Michael Gazzaniga, Carlo Rovelli, and Neil deGrasse Tyson.

This book is a culmination of things I’ve been thinking about for a long time. I’ve loved physics from a young age, but I’ve also been interested in all sorts of “big” questions, from philosophy to evolution and neuroscience. And what these separate fields have in common is that they all aim to capture certain aspects of the same underlying universe. Therefore, while they are indisputably separate fields of endeavor — you don’t need to understand particle physics to be a world-class biologist — they must nevertheless be compatible with each other — if your theory of biology relies on forces that are not part of the Standard Model, it’s probably a non-starter. That’s more of a constraint than you might imagine. For example, it implies that there is no such thing as life after death. Your memories and other pieces of mental information are encoded in the arrangement of atoms in your brain, and there’s no way for that information to escape your body when you die.

More generally, ontology matters. What we believe about the fundamental nature of reality affects how we look at the world and how we choose to live our lives. We should work to get it right.

The viewpoint I advocate in TBP is poetic naturalism. “Naturalism” being the idea that there is only one world, the natural world, that follows the laws of nature and can be investigated using the methods of science. “Poetic” emphasizes the fact that there are many ways of talking about that world, and that different stories we tell can be simultaneously valid in their own domains of applicability. It is therefore distinguished from a hardcore, eliminativist naturalism that says the only things that really exist are the fundamental particles and forces, and also from various varieties of augmented naturalism that, unsatisfied with the physical world by itself, add extra categories such as mental properties or objective moral values into the mix.

Along the way, we meet a lot of fun ideas — conservation of momentum and information, emergent purpose and causality, Bayesian inference, skepticism, planets of belief, effective field theory, the Core Theory, the origin of the universe, the relationship between entropy and complexity, free energy and the purpose of life, metabolism-first and replication-first theories of abiogenesis, the fine-tuning argument, consciousness and philosophical zombies, panpsychism, Humean constructivism, and the basic finitude of our lives.

Not everyone agrees with my point of view on these matters, of course. (It’s possible that literally nobody agrees with me about every single stance I take.) That’s good! Bring it on, I say. Maybe I will learn something and change my mind. There are plenty of things I talk about in the book on which respectable good-faith disagreement is quite possible — finer points of epistemology and metaphysics, the connections between different manifestations of the arrow of time, how to confront radically skeptical scenarios, the robustness of the Core Theory, approaches to the mind-body problem, interpretations of quantum mechanics, the best way to think about complexity and evolution, the role of purposes and causes in our ontology, free will, moral realism vs, anti-realism, and so on.

The point of the book is not to stride confidently into multiple ongoing debates and proclaim that I have it All Figured Out. Quite the opposite: while the subtitle correctly implies that I talk about the origins of life, meaning, and the universe itself, the truth is that I don’t know how life began, what the meaning of it all is, or why the universe exists. What I try to advocate is a particular framework in which these kinds of questions can be addressed. Not everyone will agree even with that framework, but it is very explicitly just a starting point for thinking about some of these grand issues, not the final answers to them.

There will inevitably be complaints that I’m writing about things — biology, neuroscience, philosophy — on which I am not an academic expert. Very true! I’m pretty sure nobody in the world is an expert on absolutely everything I talk about here. But I’m just as sure that different kinds of experts need to occasionally wander outside of their intellectual comfort zones to discuss how all of these pieces fit together. My primary hope in TBP is not to put forward some dramatically original view of the universe, but to work toward a synthesis of a wide variety of ideas that have been developed by smart people of the course of centuries. It is at best a small step, but if it helps spark ongoing conversation, I’ll consider the book a great success.

So from people who don’t read the book very carefully, I’ll no doubt get it from both sides: “Knowing physics doesn’t make you an expert on the meaning of life, how dare he presume?” and “I read the whole book and he didn’t tell me what the meaning of life is, what a cheat!” So be it.

One thing that I meant to include in the Acknowledgements section of the book, but unfortunately it slipped my mind at the last minute: I should have mentioned how much my ideas about many of these topics have been shaped and sharpened by interacting with commenters on this very blog. Longtime readers will recognize many of the themes, even if the book presents them in a different way. I’ve definitely learned a lot from questions and arguments in the comment sections here (even if I’m usually too busy to participate very much myself). So — thank you, and I hope you enjoy the book!