Doing cosmology with a brain

A favourite XKCD:

Made out of Meat

Here’s a few idle, Friday afternoon thoughts. I study distant galaxies. I use mathematical models of the laws of nature (and a supercomputer) to try to predict the properties of light emitted by and scattered through swirling vortices of matter, each containing a thousand trillion trillion trillion tons of stars, gas and dark matter, almost a trillion trillion kilometers away. My discipline – cosmology – has taken as its object of study the universe as a whole. And we’re doing pretty well, thanks for asking. I’d like to think that I am an evidence collecting, theory discovering, model investigating, equation solving (with a little help from my computer) machine.

And then I hear a talk from a biologist. I am reminded that I’m a fighting, fleeing, feeding, and reproducing machine. The lump of stuff in my head was produced by causes that “see” survival and reproduction. My brain is the control centre of a biological organism, and there seems to be precious little overlap between survival, reproduction and astrophysical ability. (Unless my astrophysical brain has made me so attractive to the ladies that it significantly increases my chances of reproduction. I’ll ask my wife.) An accurate mental picture of the world, formed using mostly reliable senses and the ability to reason logically, creatively and flexibly, seems useful to survival. But to use a brain to do cosmology? Really? (If you haven’t read Terry Bisson’s wonderful short essay “They’re made out of meat“, then do it now: “Thinking meat! You’re asking me to believe in thinking meat!”.)

A parable. Suppose I call Toyota customer services.

Me: Hi there. I own a 1993 Toyota Camry. I have a question.

Toyota: Certainly, sir. Is the car running well, getting you from A to B in comfort?

Me: Sure. It’s doing all that nicely. I was thinking about using it to drive to the moon.

Toyota: … Right … Wouldn’t recommend that, Mr Barnes. No … uh … not really in the user manual, I’m afraid. Not what it’s made for.

Suppose I find a customer support label on the back of my brain.

Me: Hi there. I own and operate one of your brains. I have a question.

Support: Certainly, sir. Is it operating your body, correctly? Are you getting enough food? Have you found a mate?

Me: Sure. It’s doing all that nicely. I was thinking about using it to do theoretical physics, discover the fundamental laws of the universe and use them to understand the structure and evolution of the universe and all its contents.

Support: … Right … Wouldn’t recommend that, Mr Barnes. No … uh … not really in the user manual, I’m afraid. Not what it’s made for.

Let’s be clear about the point I’m making here. I don’t doubt that physicists in general and cosmologists in particular have discovered true facts about the universe. It’s just a tad amazing that we can do that sort of things with our brains. (We use computers and telescopes as well, of course, but they too are the products of human brains). To extend the analogy, it’s as if I find myself standing on the moon, wondering how I got there. And as I look around, all I can see is a 1993 Toyota Camry. It’s not that I doubt where I am; I’m wondering how I got here in that! I’m not asking: how do I know that our investigation of the universe is successful? I’m asking: why is our investigation of the universe successful? How does fighting/fleeing/feeding/reproducing machine manage to do theoretical physics?

Perhaps the boring answer is the right one: we do it bit by bit. If we view science as extended and refined common sense, then maybe we can understand how a brain “made for” understanding local terrestrial environments is able to understand the universe. We don’t directly grasp the universe, of course. We rely on mental pictures and analogies. Mathematical models of the universe are perhaps analogies with equations. Having a mental picture of the world is useful. Just add curiosity and get practicing.

It seems like the same problem arises for mathematics – how does a brain manage to investigate such abstract ideas as those of pure mathematics? The same answer suggests itself: abstract thinking is useful. Just add curiosity and get practicing.

The universe is easy

We seem to need another ingredient in this explanation. That a brain can do theoretical physics and cosmology suggests not only that it is a remarkably adaptable, programmable thing, but also that the universe is an easier problem than we might have expected. A great example of this is the so-called cosmological principle. (I discuss this in more detail in my Australian Physics article here.)

That the universe is rationally analysable at all, that there is order and reason waiting for us in the mathematical structure of the universe, is a remarkable fact. The intellectual problem we are presented with in nature is, in a very real and precise sense, solvable.  It is one thing that the universe exemplifies such beautiful mathematics as Lagrangian dynamics; it is another, a fortiori, that the Lagrangians that describe our universe display numerous and deep symmetries. The universe is a complicated place, and the mathematics that describes it must be complicated at some level. The remarkable thing is that the complication is on top; there is simplicity underneath. To be more precise, the laws of nature are simple, their solutions can be complicated. Newton’s law of gravitation is simple, but for even three bodies, its solution cannot be written down analytically.

In physics’s search for the ultimate laws of nature, many physicists wouldn’t accept a proposed fundamental theory unless it were simple, elegant, and beautiful. Paul Dirac went so far as to say that “it is more important to have beauty in one’s equations than to have them fit experiment”. It follows that physics cannot explain why the laws of nature are simple, elegant, and beautiful. Now there’s a thought for the weekend.