the anthropic principle, redux

The oft-cited anthropic principle is a useless tautology.

Since I wrote a post about an astrophysics paper with potential tie-ins to the anthropic principle, I got a fair bit of feedback from readers who thought that I completely missed the point. All it means, they say, is that we shouldn't be surprised that the universe plays host to intelligent life because if it didn't, we wouldn't be here in the first place and the question being tackled was just a variant of the principle used by creationists and the intelligent design crowd.

This had me a bit confused because here we have a principle which actually seems to say nothing but a simple truism that if intelligent life couldn't exist in this universe, it wouldn't. So pardon me but where exactly is the principle? And what about the variants which insist that intelligent life has to evolve?

The big problem with trying to figure out just how hospitable the universe is to intelligent species is our lack of data about alien life and habitable planets. By this, I don't mean just carbon based life on a planet with liquid water orbiting around 1 AU from a type G star. Planets that can be habitable to some organisms which will be able to achieve something we could classify as intelligence if given enough time, also count.

But since we're just now developing the technology to detect the presence of potentially habitable planets and it will take us a while until we have the means to examine any aliens for signs of intelligence – unless it's made obvious to us by electronic signals or lights from vast hyper-cities on a planet's surface – we can't possibly start drawing up the statistical distribution of life in the universe and start making conclusions about it.

No matter what we ultimately find out, whether we find that intelligence is rare in the cosmos or it's as common as dirt, a variant of the principle will be satisfied in some way, shape or form.

And even more interesting, we could show that there's a wide range of physical laws which allow for life as we know it to come into existence and function, and we would be giving more proof to the variant of the principle which argues that we shouldn't be surprised life would eventually appear, while weakening the variant which predicts a universal fine-tuning.

Conversely, we could find a very significant restriction on the laws of physics or chemistry and do the opposite. And that makes me wonder why a single principle can be so contrary in its variations and remain a single principle. What exactly do you do with a theory that predicts something and its polar opposite at the same time?

How do you test it, especially when it gives no fixed data points and leaves itself wiggle room no matter what you find in an experiment or observation? How do you apply it? Should you bother with it at all? Is it just a cosmological tautology? I will make this correction to my original post; the paper was addressing a fine-turning variant of the principle which dealt with the realms of particle physics and quantum mechanics.

So, if you agree with the variant which says that we shouldn't be surprised by comfortable ranges in the laws of physics, it gives the principle more credence. If you're a fan of the fine-tuning idea born from theological musings on physics and chemistry, well you're out of luck in this case and have to now move the goalposts to accommodate for these ranges. But that brings us right back to the question of how one principle can have contrarian variants and be both reinforced and weakened at the same time…