> In 4.5 billion years, the Milky Way will collide with Andromeda. This presents us with a literal galactic-scale single-turn prisoner's dilemma: If intelligent

> In 4.5 billion years, the Milky Way will collide with Andromeda. This presents us with a literal galactic-scale single-turn prisoner's dilemma: If intelligent life exists in Andromeda, they may already be preparing to conquer the Milky Way. If they are, and we don't prepare to fight back, they will obviously win. We won't have any ability to communicate with Andromeda to find out their intentions until it's too late. The earlier we start preparing, the more likely we are to survive. I'm trying to imagine what to do now in preparation for a hostile encounter in 4.5 billion years that isn't already happening organically. By "organically", I mean both "in the course of gradual or natural development" and "w.r.t. living matter", given the time scale. Do you have ideas?