I’ve posted this before, but it’s worth seeing again in light of the Earth-sized planets Kepler just found.
A less-strong version of the Weak Anthropic Principle suggests that we’re here to see this universe because it has the properties to sustain us — this is not a tautology, though it sounds like one. It escapes that label only in that it implies the possibility of multiple universes. It means that if there are multiple universes with infinite ways to arrange the cosmological constants, we are here because this is one of them that fits the “goldilocks zones” for those properties, throwing the fine-tuning argument right out the window.
It’s not an argument that this universe was built around the necessity for our existence, though the two more popular versions of the postulate suggest as much. It is an admission that we don’t know how many rolls of the dice the potential multiverse (or infinite cycles of the universe) has had to get things exactly right to produce us. A corollary of this argument is that we also don’t know how many rolls of the dice this universe has had to create life — how many planets we’re finding that have the right makeup, size, and distance from their stars to have liquid water and organic chemicals all the other prerequisites for abiogenesis. If this universe is as replete with planets that failed to produce life as we suspect, perhaps we are unique in this universe — but it seems unlikely. It seems far more likely that life exists somewhere, given how many planets there are.