We live in a very special universe. All sorts of things about our universe (like the strength of gravity) are perfectly tuned for the existence of life. If any of these universal qualities were even slightly changed life could not have arisen. Surely that suggests that the universe was tailored for the purpose of allowing life – presumably by some God?

The short answer is: No.

The Anthropic Principle
The more detailed answer is the Anthropic Principle. The Anthropic Principle is pretty cool and I plan on using it in some future posts so I thought I would explain it.

In short, the anthropic principle says that you shouldn’t read too much into a seemingly rare event if the only reason that you noticed the event is that it is rare.

Huh? – let’s have an example
Yeah, that did sound a little circular so lets have an example. Say you are flipping coins all day long. Eventually you’ll get 10 tails in a row – an event that in isolation has very low probability. The anthropic principle says that you shouldn’t read too much into it because the only reason you noticed was that it is rare. Most of the time nothing special was happening.

The chances of eventually getting 10 in a row are actually very high – don’t get excited when it eventually happens.

I had some friends who used to infer probabilities on the roulette table based on improbable strings of results. If they saw 5 reds in a row they inferred that black had to come up soon and bet black. The anthropic principle shows why this is madness (sorry guys). If you wait long enough you are guaranteed to eventually get a string of 5 reds, and when you do it has no bearing on the next spin.

It seems simple now, but I have had plenty of debates about this and I always find it tricky to get the point across.

So why isn’t our universe special?
The whole idea has it’s roots in cosmology. Cosmologists noticed that the universe appears to be finely tuned to creating an environment in which life can exist. It is easy to infer that God must have created it that way specially for us. However, the anthropic principle says that we shouldn’t read too much into the universe being so finely tuned. If the universe wasn’t “just right” for life then we wouldn’t be around to notice it!

The universe is special for other reasons – but it’s random luck that everything is set up to allow life.