Reasonable Dissent

Power in understanding the anthropic principle

The anthropic principle is an incredibly useful and powerful idea that I think is misunderstood by far too many people. I think the most likely reason is that it is somewhat like looking at an optical illusion that suddenly pops into the shape you’re supposed to see. Before you really get it, it’s not at all obvious what it’s really saying.

Not only that, but it’s easy to say it in an oversimplified way that sounds like it doesn’t solve anything. If I say, “If things weren’t like they are, we wouldn’t be here to ask why they are,” and you think that it’s a dodge of the question, read the rest of this, and then come back to that statement. Does it have a little more meaning now?

So I’ll dive right in. The anthropic principle comes in a few flavors. For the record, the one that I’m advocating is usually termed the Weak Anthropic Principle (not weak in the sense that it doesn’t stand up to itself well, but not as forceful as the others). I’ll start with the ones that I don’t advocate, because I don’t plan to spend much time on them. There is the Strong Anthropic Principle which says that the universe’s ultimate goal was to produce us, so it was fine-tuned to that purpose. Then, the Final Anthropic Principle tries to build on this by saying that if the universe intends to produce intelligent life, then it has a vested interest in intelligent life. Therefore, the universe not only must produce intelligent life, but once in existence, intelligent life will never die out. Wow, that’s quite a conclusion! As I said, I don’t like these. The vague relationship of the underlying ideas with the weak anthropic principle mean that they got to share the name, but it’s like grapes and grapefruit – the name may be the same, but one is delicious and the other is fit only for a madman.

The weak anthropic principle (I’ll drop the ‘weak’ from now on) goes like this. We look around us and see what seems to be huge amounts of order. The amount of chance events that would have to happen to end up where we are is staggering, and the probability of this is fantastically small. How then can we justify an impartial universe that seems perfectly tuned for our existence? The anthropic principle comes with this response: We are already biased to this universe/planet/whatever by our very existence. The fact that life has developed here means that this may not be such a common place, statistically speaking. Usually this is applied to cosmology and abiogenesis. I’ll borrow some ideas here from The God Delusion, and it’s worth the read, if you haven’t. One common issue people bring up with evolution is that it’s a great tool for explaining complexity from simplicity – but not from no life at all. It only applies after there is some start, which is apparently unlikely.

One of Dawkins’ arguments at this point is that, thanks to the anthropic principle, we can afford a somewhat greater degree of improbability in this first start, simply because it is only one event. We just need to get the chain started, and natural selection takes us the rest of the way easily. We seem to live in a very pleasant place, from the temperate climate of our planet and its orbit, to the star that we are around. Many things seem “just right” for us. But the anthropic principle is the idea that the very fact that we exist here means that this might just be exactly that special of a place. If it were not, who would be asking the question? It is conceivable that in different and uninhabitable-for-us  situations, an all together different kind of life would develop. They might ask the same things: why is this place so special? But it would be special to them, not us.  But the point is, the universe doesn’t necessarily have to have a temperate, life-supporting environment as the average. If this is a special place in the universe, this is exactly where we would show up. It’s not that surprising after all. We could then go into some probabilistic arguments based on the number of stars and planets to show that actually, even though it seems unlikely, the universe is so big that the fact that some places are ok for life like us is not that unlikely.

Maybe a resonable way to think of it is like the lottery. The odds against winning are incredible, and most people know this going in. But they also know that because of how many people are playing, the odds are reasonable that at least one of them could win. But in the cosmological case, losing isn’t as apparent as in the lottery. You don’t get bummed out and try again. You just simply aren’t. There aren’t life forms in uninhabitable parts of the universe to say “This is a terrible place to live,” you’re only aware because we won this lottery. And there were billions of years with billions of billions of stars and planets playing the lottery, and only once did we have to hit big. Just once, the right set of circumstances needed to come together to get life started, and the process of natural selection very logically produced what we see today.

So, if this is new to you, try that sentence again. “If things weren’t like they are, we wouldn’t be here to ask why they are.” Does it seem like a dodge still? If it does, let me know, because that means I failed at explaining it well too.

Tags: evolution, science