Aliens visit earth and leave again, as if they were just stopping for a picnic along the way to somewhere more interesting. The people living near the visited sites (Zones) find all sorts of mysterious and often dangerous things left behind that shatter our concepts of physics and the possibilities of life. Scientists are no better off than anyone else tring to understand them. And that's the crux of it - when humans are so insignificant, so far away from understanding reality, there is really very little separating us. I've typed and deleted a few more things but felt like it cheapened the book's themes because ultimately I think they are affective rather than ideological. So I'll just keep them to myself.