One afternoon some years ago, I was walking through the snow thinking about other universes. More specifically, I was turning over in my mind the fact that the hospitality provided by our universe depends on many extremely special things. For example, if the electric repulsion between protons in the nuclei of atoms were just a bit stronger, then those atoms, and hence chemistry, and hence life itself, could not apparently exist. And there are many other such “coincidences.”
I had convinced myself that there were four—and pretty much only four—possible explanations for the fact that the laws of physics seem to be carefully chosen to allow us living, conscious beings to be here.
First, perhaps the laws of physics really were designed for us: when the universe began, it (or some superbeing that created it) had us—or at least life—in mind. Second, perhaps it was just an immense coincidence: there was one “roll of the dice” that specified, among other things, the force between protons, and we just got colossally lucky. Third, it could be that many “universes” exist with different laws of physics, and we are perforce in one of the universes that allow life. Fourth, perhaps the coincidences are illusory: perhaps life would somehow find a way to arise in any universe, with any possible set of physics.