I know a lot of people say water or carbon and some people even say fusion or gravity. I think these are just the building blocks we happen to find in our universe but I think life could exist without any of those things as long as the laws of physics of any particular universe allow for something like those things to exist. For me at least, it seems that nothing is the most important thing. Life really could not exist without a lot of vacuum in between the other stuff. We see this trend everywhere we look in our universe. The stuff between the stars and planets is mostly vacuum and even on the microscopic level most of the inside of atoms is vacuum. It would be impossible for life to exist in the instant after the big bang because there was so little vacuum that things were really hot. Even when our planet formed life could not exist until most of the asteroids were cleared up. It doesn't matter what sort of physical laws you have in your universe, a vacuum is always a vacuum (more or less once you start looking closely). So any universe that can harbor life must have a lot of nothing. So what do you guys think, what is the most important thing for life?