Aww, no alien empires yet

[Dalex]

Well there is one more disturbing possibility, we are really alone, but not because of Dawn hunters. Because this is a simulation, a virtual world.
Lets assume that you want to simulate our civilization, you don't really need to model things in great detail beyond certain point. Why add galaxy spanning civilizations when you care about one planet and it's development? Its wasteful, unnecessary, it increases complexity beyond what is required. So instead of that just leave rest of the universe blank. Use "normal" physics simulation and be done with it.