On September 15th, 2014, /u/mateogg asked the following on /r/DCcomics:
How does the Anti-Matter universe fit in the multiverse? is it just one of the 52? or is the Matter-Antimatter pair one universe from this perspective?
It has nothing to do with the Earth-3 universe, right?
Crime Syndicate of Amerika
Oh man, I love this question. OK kids, this is where it gets complicated…
Originally the antimatter universe was created billions of years ago by Krona, basically a renegade Gaurdian from before they were the Gaurdians who’s been screwing stuff up since, including in Brightest Day. Anyway:
Billions of years ago, a Maltusian scientist named Krona, performed a forbidden experiment in an effort to see the origin of the universe. His irresponsible actions disrupted the process of cosmic creation, resulting in an additional, opposite universe.