The universe is a big place. But not nearly as big as the multiverse. By some accounts, there are as many Earths as there are atoms in the planet Earth. In a less organized multiverse, these universes would be falling all over each other, but in the Wildstorm multiverse, each Earth is secure within The Bleed. Reasonably secure, anyway.
As perceived by humans, The Bleed is a red, swirling maelstrom, and the image is apt. The Bleed is not a pleasant place, and not safe for the average traveler. There are entities living in The Bleed what hate and despise the billions of Earths. Every human incursion in The Bleed has repercussions and echoes, so traveling there without a specially designed Bleed Ship is not a good idea.
There are two Bleed Ships currently known. One is The Carrier, which is operated by The Authority. The other is operated by Jim Wilder and metahuman descendants of Science City Zero. Thanks to Kherubim Technology, some Kherubim ships are able to travel The Bleed also. These ships aren't built just for The Bleed though, that is more of a secondary function. These ships can enter and leave The Bleed at will, moving between universes.
In 1945, a group of adventurers led by Dr. Axel Brass built a computer capable of mapping the multiverse, which allowed for a Bleed incursion. All of Brass' teammates died closing the rift. Nearly sixty years later, a disgruntled employee of *Planetary* opened a second rift, nearly overrunning the Earth with self-replicating destroyer robots. They were stopped by Planetary and The Authority.
Since the combining of the WSU and the DCU, Wildstorm Earth has become one of the 52 Earths in the multiverse but the exact nature of the Bleed (and worlds seen through it) is unknown. According to the Guardians Of The Universe, the Bleed lies beyond the Source Wall, but no other information was given.