As humanity peers ever further into the lifeless void, we start to notice things. Long derelict world-ships on escape trajectories out of the galaxy, most having burnt through their fuel eons ago. We only found the first - the bussard scramjets - by virtue of their continued automated burns at low-g acceleration.

The first alcubierre warpship (or antimatter rocket, if you want to maintain the no-ftl rule) to arrive at the site of one of these world ships found nothing but voided computer banks and empty living quarters. The next, a sleeper ship, was found with similarly blank computers and millions of empty stasis pods.