TLDR; A time traveller, named Besso, came back to push Einstein to formulate his theory General Relativity earlier than he would have done on his own. This acce

TLDR; A time traveller, named Besso, came back to push Einstein to formulate his theory General Relativity earlier than he would have done on his own. This accelerated the technological growth of humanity over the next two centuries to such a degree that they were ready for the alien invasion in the year 2122.