This question already has an answer here:
I'm looking for a probably short story (but I'm not 100% sure about it) where mankind got this huge achievement (probably immortality but might have been energy) through killing an inferior alien species.
Because of that, some kind of galactic/space alien counsel decided to punish mankind by extermination, which led to a war. What I can clearly remember (and the reason I'm looking for it) was the ending, where a bunch of humans escaped with a very fast ship, chased by an alien one. The ships were so fast that they bent time, and in the end, as the universe was crunching, the aliens sent a message by asking humans to let them catch them so that the whole thing would make sense.