400 years is nothing. At this speed, all the Galaxy would have been colonized long ago. This subplot in the book is at least reasonable. Somehow aliens capable

400 years is nothing. At this speed, all the Galaxy would have been colonized long ago. This subplot in the book is at least reasonable. Somehow aliens capable of pico-scale engineering can't make a telescope to observe the nearby solar systems, but OK, whatever. Cultural blindness and all that. It's the later plot with the "dark forest" that makes no sense. There are ships capable of moving at relativistic velocities and spacetime-altering weapons.