I'm very bothered by the idea that the Universe may be infinite.
If the Universe is infinite, there must be an infinite number of galaxies. And so some of those galaxies must be like ours: some very much like ours, some having stars just like our sun, some of those suns having planets just like our Earth. And on some of those not-Earths, there will be intelligent beings, some of them very like us. Some of them exactly like us. And so somewhere, there's another intelligent not-human, who is exactly like a human, named Casey, sitting and writing a blog post about this very topic. And there isn't one world like this, but an infinite number. But that's not what bothers me.
In addition to the planets exactly like ours, there also must be many that are sort of like ours. Like one's where I'm not a scientist, but an engineer, a doctor, a hockey player, or play some other sport never heard of on our planet. Where I'm not writing this in a blog post, but on Facebook, or Myspace, or Friendster for some reason. And there's an infinite number of combinations, each one existing an infinite number of times. But that's not what bother me either.
But then, due to the laws of probability, there must be planets that are much like ours, but where nothing that happens makes the slightest bit of sense. Events occur that are not impossible, but are so improbable so as to seem so. And this happens over and over and over again, to the point where effects don't logically follow from causes. And the intelligent beings that populate these planets, rather than being used to this, are continually surprised, and live their lives expecting life to make some kind of sense and continually frustrated that it doesn't. And this is what bother me.
Because I realize that maybe those world do exist, and that maybe this is one of them.