"Hyper-Tension!, Part 1 of 5: Big Bang Theory!"
When the JLA discover a dying Superboy who tells a story of the end of the world, they along with the real Superboy realize that the other Superboy is from another reality and is in possession of New God territory.
Superman and Batman theorize that the other Superboys jacket transcends Hypertime, however in order to enter Hypertime you need a massive amount of energy. So Superboy is strapped to an atomic missile and shot into space.
Superboy soon wakes up in the Batcave, where he meets a alternate Batman and a Superboy dressed as Robin.