During the Crisis on Infinite Earths, it was revealed how the existence of all parallel universes in the Multiverse came to be, including the positive matter multiverse and also the anti-matter universe, and how the Monitor and the Anti-Monitor came into existence; when the menace posed by the Anti-Monitor became apparent, several villains were sent back in time to stop him, but were defeated by Krona and the other Oans.[citation needed] In a final revision, it was established that it increased entropy in the universe, shortening its existence by a billion years (see heat death).[2] In any event, two beings were created, one on the moon of Oa and the other on the moon of Qward.