The Big Picture

Physics is, by far, the simplest science. It doesn’t seem that way, because we know so much about it, and the required knowledge often seems esoteric and technical. But it is blessed by this amazing feature: we can very often make ludicrous simplifications—frictionless surfaces, perfectly spherical bodies—ignoring all manner of ancillary effects, and nevertheless get results that are unreasonably good. For most interesting problems in other sciences, from biology to psychology to economics, if you modeled one tiny aspect of a system while pretending all the others didn’t exist, you would just end up getting nonsense.

The world exists; beauty and goodness are things that we bring to it.

The move from description to prescription, from saying what happens to passing judgment on what should happen, is a creative one, a fundamentally human act.

Within poetic naturalism we can distinguish among three different kinds of stories we can tell about the world. There is the deepest, most fundamental description we can imagine—the whole universe, exactly described in every microscopic detail. Modern science doesn’t know what that description actually is right now, but we presume that there at least is such an underlying reality. Then there are “emergent” or “effective” descriptions, valid within some limited domain. That’s where we talk about ships and people, macroscopic collections of stuff that we group into individual entities as part of this higher-level vocabulary. Finally, there are values: concepts of right and wrong, purpose and duty, or beauty and ugliness. Unlike higher-level scientific descriptions, these are not determined by the scientific goal of fitting the data. We have other goals: we want to be good people, get along with others, and find meaning in our lives. Figuring out the best way to talk about the world is an important part of working toward those goals.

Naturalism comes down to three things:
There is only one world, the natural world.
The world evolves according to unbroken patterns, the laws of nature.
The only reliable way of learning about the world is by observing it.

All good philosophical fun and games of course, but without much relevance to the real world, at least not at our current level of technology. Or maybe not. There’s an older thought experiment called the Ship of Theseus that raises some of the same issues. Theseus, the legendary founder of Athens, had an impressive ship in which he had fought numerous battles. To honor him, the citizens of Athens preserved his ship in their port. Occasionally a plank or part of the mast would decay beyond repair, and at some point that piece would have to be replaced to keep the ship in good order. Once again we have a question of identity: is it the same ship after we’ve replaced one of the planks? If you think it is, what about after we’ve replaced all of the planks, one by one? And (as Thomas Hobbes went on to ask), what if we then took all the old planks and built a ship out of them? Would that one then suddenly become the Ship of Theseus?

We’re going to have to be both smart and courageous as we work to get this right.

As a physicist, I know it doesn’t violate any laws of nature to imagine living beings lasting for millions or even billions of years, so I have no objection there. But eventually all of the stars will have exhausted their nuclear fuel, their cold remnants will fall into black holes, and those black holes will gradually evaporate into a thin gruel of elementary particles in a dark and empty universe. We won’t really live forever, no matter how clever biologists get to be.
Everybody dies. Life is not a substance, like water or rock; it’s a process, like fire or a wave crashing on the shore. It’s a process that begins, lasts for a while, and ultimately ends. Long or short, our moments are brief against the expanse of eternity.

What we can’t do is demand that the universe scratch our explanatory itches. Curiosity is a virtue, and it’s good to look for answers to “Why?” questions whenever we might be able to find them, or when we think that asking such questions might help us to understand things better. But we
should be at peace with the possibility that, for some questions, the answer doesn’t go any deeper than “That’s what it is.” We’re not used to that—our intuition assures us that every event can be explained in terms of some reason why. To understand why we have that impression, we need to dig more deeply into how our actual universe has evolved.

The observable universe around us isn’t just an arbitrary collection of stuff obeying the laws of physics—it’s stuff that starts out in a very particular kind of arrangement, and obeys the laws of physics thereafter. By “starts out” we are referring to conditions near the Big Bang, a moment about 14 billion years ago. We don’t know whether the Big Bang was the actual beginning of time, but it was a moment in time beyond which we can’t see any further into the past, so it’s the beginning of our observable part of the
cosmos.