This image from the Hubble Space Telescope shows two distant galaxies "grazing" each other, coming within a few thousand light years--a fantastic distance to you and me, but a close shave by interstellar standards. Galaxies in our part of the present universe are almost unfathomably far apart: Andromeda, the closest major galaxy to our Milky Way, is about 1.5 million light-years distant. And the distance between galaxies increases daily as the universe continues to expand, everything constantly getting farther away from everything else in the same way that dots on the surface of a balloon get farther and farther apart as the balloon is blown up.

Perhaps intergalactic distance is simply the result of physics, or perhaps it reflects preternatural logic. Assuming (as scientists currently do) that there cannot be faster-than-light travel, galaxies separated by distances in the millions of light-years will never be able to have any form of intercourse with each other: no weapon one could make could strike the other, and no invasion could ever be launched.

Considering the track record of mutual hostility and misunderstanding in our world alone, where there is but a single species, imagine the havoc if intelligent races from across the galaxies could war on one another. Because of the sheer expanse of intergalactic space, conflict between regions of the cosmos may simply always be impossible, leaving each galaxy to the fate that its own inhabitants determine - not necessarily such a bad arrangement if you're building a universe.