>There would be no rational reason to do such a thing Have more imagination. We, as another intelligence species, could eventually evolve into a threat or comp

>There would be no rational reason to do such a thing Have more imagination. We, as another intelligence species, could eventually evolve into a threat or competition for resources. Such an ancient civilization probably has long term plans for outlasting through the heat death of the universe and beyond, they have a huge incentive to eliminate others. They might also have weird forms of morality and values so alien to us, we can't even speculate about it. They might come to earth to enforce their weird values on us, or just wipe us out and not deal with it. Then there is Paperclip Maximizers: http://wiki.lesswrong.com/wiki/Paperclip_maximizer http://wiki.lesswrong.com/wiki/Paperclip_maximizer Many people believe that most civilizations are eventually overtaken by AIs which are likely programmed with simple utility functions. E.g. and AI programmed with self preservation will make as many redundant copies of itself, store as much mass and energy to preserve through the heat death of the universe, destroy anything that has even a tiny probability of being a threat to it, etc. And you don't need relativistic weapons. A single self replicating nanobot would probably be sufficient. They don't need to go to any effort, if there is a tiny advantage to killing us then we are screwed. The universe is a terrifying place and it's quite possible the only reason we are alive is anthropic bias. Just by chance we happen to be far enough away from other civilizations to evolve to the state we are now. But at any moment another intelligence could expand into our space and wipe us out in the blink of an eye.