Empty Nest Syndrome
We started building colony ships in the 2050s. They weren’t exactly visually impressive: the main bulk was the industrial nanofab, resembling a dull grey quonset hut. Also on-board: some rad-shielding, some primitive AI navigation and replication-bootstrapping routines, two kilos of antimatter, 12,182 frozen human embryos. That number is “optimal for an initial settlement on a new world,” said some report that no one read.
The idea was to land these things on all “potentially habitable” exoplanets within 50 light years. Eventually, they’d make their own ships and launch them, et cetera et cetera, kickstarting our expansion into the entire galaxy. At the modest 13% of the speed of light afforded by the antimatter engines, it would take us less than a million years.
Initial reports received from the planets were extremely promising. Mining machines and reactors and robots were manufactured exactly as planned.
We later discovered that every ship had dumped its human cargo before even reaching the Kuiper belt.