When we talk about something so big that it might as well be infinite, we call it "astronomical". We've all heard the awesome facts: we know we're an invisible dot in our town; we know the town is an invisible dot on the planet; we know the planet is an invisible dot in the solar system; we know the solar system is an invisible dot in the galaxy; we know the galaxy is an invisible dot in the universe.

But, as impressive as that all sounds, that's describing scale with exponential growth, but exponential growth pales in comparison to combinatoric growth.

The number of ways you can arrange 100 people is far greater than the number of estimated atoms in the universe. And not _just_ greater, greater in a way that is difficult to explain. A drop in a bucket? No. A drop in the ocean? No. All our metaphors are physical, and so they're inadequate, but let's just it's beyond all that.

Of course, that doesn't mean the probability of other intelligent life is best assumed to be of a combinatoric nature, but let's get ahead of ourselves and let our awe of the universe's size cloud our judgement. It's far from infinite, and silly to assume intelligent life is certain.