Multiverse

The Multiverse consists of parellel versions of the universe existing in the same physical space, but separated from each other by their vibrational resonances.

The Original Multiverse was created as the result of interference in the Big Bang by Krona. It was destroyed by the Crisis on Infinite Earths when, at the crisis' conclusion, all of the dimensions cascaded into one single dimension until an Interregnum Multiverse was created by Alexander Luthor during Infinite Crisis. After the events of Infinite Crisis, the remaining Earths created collapsed back together, combining historical remnants to form one New Earth. However, the single universe was too small to contain the energy inside it and it began replicating into 52 identical Universes, the 52 Multiverse. These alternate Earths were originally identical until the meddling of Mr Mind caused them to differ from each other in various ways.

The parallel realities were separated by an an interdimensional sub-reality barrier called The Bleed. The Bleed was also spatially connected with the Source Wall, the Multiversal Nexus and the Nanoverse. The Bleed was completely collapsed in the Final Crisis event by Nix Uotan.

The Source Wall and the Anti-Life Equation exist between each matter universe. It is thought that knowledge and control of the Anti-Life Equation, the Speed Force, and quantum mechanics were needed to travel between universes, but have managed to do so without them.

History
Krona (a member of the ancient race that would be later known as Oans; masters and creators of the Green Lantern Corps) was a scientist obsessed with observing the creation of the universe, despite an Oan legend that said discovering that secret would cause a great calamity. Krona created a machine that allowed him to see into the moment of creation. Somehow, his experiment disrupted the process of creation, causing the creation of not a single universe, but the generation of an infinite number of universes.

From the perspective of the Earth-One universe, the first travel to another parallel universe occured when Flash (Barry Allen) accidently changed his vibrational frequency to match that of Earth-Two, where he met Flash (Jay Garrick). That meeting resulted in years of interaction between the Earth-Two superhero team, The Justice Society of America, and their Earth-One counterparts, The Justice League of America.

As Barry Allen was the first traveller, the honor of naming the two Earths fell to him - his universe's Earth was called Earth-One, Jay Garrick's became Earth-Two. As noted years later by Earth-Two's Superman, the JSA were too polite to mention that they were around first.

After Earth-Two, the next parallel world encountered by the JLA was that of Earth-Three, a partially "reversed" Earth populated by their evil "opposites", the Crime Syndicate of America. However the general populace of Earth-Three reflected a society based on laws and good values, despite the majority of their super powered beings having an evil nature. The Syndicate would eventually be imprisoned by the JLA and JSA, escaping at various times throughout the years to cause trouble.

It was eventually discovered that the Universes co-existed with an Antimatter Universe. These Universes were each overseen by a Monitor, however the Anti-Monitor, the Monitor of the Antimatter Universe, caused a wave of antimatter to sweep across the infinite universes in an effort to gain absolute power and remake existence to his liking. This crisis would become known as the Crisis on Infinite Earths.

The battle against the Antimonitor would continue until, with five universes remaining, the remaining heroes of the Multiverse, at the Spectre's urging, pooled their resources and traveled back to the Dawn of Time where they confronted the Anti-Monitor while the villains, meanwhile, traveled to Oa to try to stop Krona from peering back in time and creating the Multiverse.

Despite the heroes having arrived into a trap, the Spectre, aided by Earths' mightiest sorcerors, managed to defeat the Anti-Monitor. The histories and peoples of the remaining five universes (Earth-One, Earth-Two, Earth-Four, Earth-S, and Earth-X) were effectively merged to form one composite universe, the Post-Crisis Earth.

Years would pass until the forgotten survivors of the Crisis on Infinite Earths (Superman (Kal-L), Superboy Prime, Lois Lane (Earth Two) and Alexander Luthor) would re-enter the Post-Crisis dimension in an attempt to create their own version of the "Perfect Earth". This crisis would become known as the Infinite Crisis and would see the partial recreation of the Original Multiverse through the creation of the Alexander Luthor's Interregnum Multiverse. However this Multiverse was only temporary as the Earths couldn't sustain themselves and cascaded back into a singular entity. However this state was also temporary as the Earths slowly replicated to form 52 seperate versons of itself; becoming known as the 52 Multiverse, and along with them, 52 individual Monitors.

The Monitors charging themselves with keeping order between the alternate dimensions and began hunting down what they would consider "Multiverse Anomalies", such as individuals living in the wrong dimension, living when they should be dead, or cross-dimensional travelers. Their efforts, coupled with those made by a now insane Superboy-Prime, the Monarch, and specifically when Darkseid rediscovered the Anti-Life Equation saw the new 52 Multiverse come under threat yet again, this crisis becoming known as the Final Crisis and was only won through the defeat of Darkseid and the complete reset of reality through a Miracle Machine created by Superman.

Current 52 Universes
Earth Prime: Earth based closest on the real world Earth, with only Superboy-Prime as its sole existing hero.

Earth-0 (New Earth): The Earth existing in the primary reality following the Infinite Crisis and Final Crisis events. As all other universes are based and dependant on this Earth if this Earth is destroyed the entire multiverse will be destroyed.

Earth-1: This Earth is defended by characters of the graphic novels Superman: Earth One and Batman: Earth One.

Earth-2: A slightly altered version of the JSA fight the Axis powers in WWII. This Earth is later defended by Justice Society Infinity, a successive version of the JSA whose members include Batman's daughter, the Huntress, and an older Robin. Reminiscent of Pre-Crisis Earth-Two.

Earth-3: On this moral mirror image of New Earth, the Crime Society of Ultraman (Superman), Owlman (Batman), Superwoman (Lois Lane), Power Ring (Green Lantern) and Johnny Quick (Flash) rule with an iron hand, while rogue do-gooders like the Jokester (Joker) fight for freedom. The Joker’s Daughter came from this universe.

Earth-4: Blue Beetle, Captain Atom, Judomaster, Nightshade, the Peacemaker and the Question are the heroes of this Earth. Reminiscent of Pre-Crisis Earth-Four.

Earth-5: The Marvel Family are this Earth's main heroes in a bright, sunny world of magic. Reminiscent of Pre-Crisis Earth-S.

Earth-6: World including version of Ray Palmer who becomes The Ray. This Earth contains heroes similar to those of Marvel Comics. This universe is overseen by the Monitor Weeja Dell.

Earth-7: World including version of Courtney Whitmore who becomes known as Starwoman.

Earth-8: Home world of Lord Havok and the Extremists with no hero analogues. Earth is called Angor, home of Lord Havok's Extremists. Modeled after the Marvel universe, and of the planet Angor on New Earth, home of the original Extremists and Justifiers. This universe is overseen by the Monitor Solomon.

Earth-9: Tangent Universe. Heroes bare familiar names, but the similarities end there. Here, Superman is Harvey Dent and takes over the entire planet.

Earth-10: In the Earth Adolph Hitler achieved victory in World War II and conquered the planet. Alternate versions of Uncle Sam and the Freedom Fighters plot to end his reign while fighting Nazi counterparts of the JLA.

Earth-11: A reverse gender Earth.

Earth-12: The Timmverse; a universe filled with parallel versions of Earth’s heroes whose adventures are advertised in numerous animated shows (Batman: The Animated Series, Superman: The Animated Series, The New Adventures of Batman and Robin, Justice League, Justice League Unlimited, Batman Beyond, etc).

Earth-13: World of dark and arcane heroes.

Earth-14: unknown

Earth-15: A Earth whose people have evolved to become 'nearly perfect beings' of their own personal development. Heroes included Jason Todd as Batman, Jessica Palmer as the Atom, Donna Troy as Wonder Woman and Zod and Christopher Kent as dual Supermen. Earth-15 was completely destroyed by Kal-El (Earth-Prime). The source dimension and other inhabited planets of that dimension continue to exist.

Earth-16: Home of the Super-Sons. Source Earth of Christopher Kent the alternate Superman. Once designated to be the Source Earth of the 52 multiverse version of The Supersons, but is has been revealed that there are no other Kryptonian relatives to Christopher Kent in this reality. Also the home of the Young Justice animated series and its comic counterpart.

Earth-17: A post-apocalyptic world where the Atomic Knights protect the last signs of life. On this Earth, science and magic apparently co-exist - this Earth's greatest hero is Superdemon

Earth-18: A world where the JLA are a group of lawmen who ride the Wild West.

Earth-19: Gotham by Gaslight reality; Batman fights Jack the Ripper among other villains in this Victorian-era Gotham lit by gaslight in the closing decades of the 19th century.

Earth-20: Home to a group of pulp-inspired heroes, the Society of Super-Heroes, led by Doc Fate

Earth-21: The New Frontier reality; a world where the Cold War has recently ended and a new age of heroes has begun. This Earth is where the core heroes became famous during the 1950’s and 60’s.

Earth-22: The Kingdom Come reality; A near-future world brought to the brink of apocalypse by warring superheroes. Starman confirms that before he came back to the 21st Century during the Lightning Saga, he was accidently shunted to Earth-22. Superman from this world now lives on New Earth and is a member of the JSA. He claims that his world was destroyed.

Earth-23: unknown 

Earth-24: unknown 

Earth-25: unknown 

Earth-26: Home of the cartoon animal superheroes Captain Carrot & The Zoo Crew.

Earth-27: In this universe, Clark Kent tells Lex Luthor of his powers early in their friendship. With their relationship built on trust, they become the best of friends. The two confide in each other and because Clark is able to have such a positive influence over Lex, the two of them work together to save the world. Clark also tells a small group of his friends about his origins, and they all accept him for who he is. Clark marries his first love, Lana Lang, and have children that share Clarks powers. In this universe, Clark, as Superman, along with his family and Lex Luthor protect the world against evils.

Earth-28: unknown 

Earth-29: unknown 

Earth-30: The Red Son reality; where baby Kal-El landed in the Soviet Union during the Cold War of the 1950’s. A champion of Soviet Russia Superman helps Russia to dominate the globe.

Earth-31: The Millerverse; Earth’s heroes are led by a pro-government, all-American Superman and a violent Batman. Wonder Woman is also an extremely anti-male feminist.

Earth-32: Bruce Wayne becomes Green Lantern instead of Hal Jordan.

Earth-33: A mystical earth where all of the heroes have magic-based powers, including Bat-Mage, and Kal-El, wielder of Kryptonian Magicks. Ruled by the multiversal seer Oracle.

Earth-34: The Amazonia reality; Princess Diana is kidnapped from Paradise Island by Captain Steven Trevor and the Royal Marines before becoming a hero, Wonder Woman, in 19th century London and frees Britain from male-dominant oppression under the reign of King Jack (Jack the Ripper).

Earth-35: unknown 

Earth-36: unknown 

Earth-37: Thrillkiller Universe. Barbara Gordon becomes Gotham's foremost costumed protector, and Bruce Wayne is a cop. Its Captain Atom was Quantum-Storm.

Earth-38: Homeworld to a Captain Atom who leads the Atomic Knights.

Earth-39: Homeworld of Daniel Garrett who became Blue Beetle the same way as Jamie Reyes.

Earth-40: The Liberty Files world, where costumed heroes and villains have joined World War II.

Earth-41: unknown 

Earth-42: unknown 

Earth-43: Batman Vampire, Red Rain universe; A world of vampires and the supernatural, inhabited by a vampire Batman. Dick Grayson tried to take him down, but succumbed to Batman's contagion and is now, too, a vampire. Barbara Gordon was also transformed, but killed by Grayson.

Earth-44: Unknown, but it's main heroes were a group of robots called the Metal Men, led by "Doc Tornado"

Earth-45: unknown 

Earth-46: unknown 

Earth-47: unknown 

Earth-48: This universes Earth is used as a neutral warring ground for Martians, Venusians and other alien species in the solar system. The cross-bred survivors of Earth have evolved to become the Forerunners; elite killing machines in the service of the Monitors. This universe's counterpart of J'onn J'onzz is a general in the Martian army.

Earth-49: An Earth who's sun has been turned into a Red Sun by Firestorm. Superman, Supergirl and other heroes that need the sun's yellow rays must wear suits identical to Superboy-Prime's.

Earth-50: The Wildstorm Universe. Heroes include WildC.A.T.S., the Authority and Gen13.

Earth-51: Due to this Earth's Batman secretly killing irredeemable villains after the death of Jason Todd, this Earth is described as a near perfect world. With no mention of crime, war, poverty or disease. Now home of the former gods of New Genesis and Kamandi (Jack Kirby's Earth). This Earth began very similar to Earth-0. The Justice League eventually triumphed over all evil and created a peaceful society. Most of them retired. When the Atom of Earth-0 came across his Earth-51 counterpart, he witnessed the latter's death. Earth-0 Ray decided to take up Ray-51's life, which included a happy marriage to Jean Loring, and a science project that would allow him to travel across the multiverse. All life on this world was destroyed when Superboy Prime breached Monarch's containment suit (Countdown #13). Afterwards, its monitor, Nix Uotan, remade humanity. But it was doomed again, as the site of the "Great Disaster." Brother Eye came to Earth-51 and unleashed the Morticoccus virus (also spread by Karate Kid). The only human survivors were Buddy Blank and his grandson, the "last boy on Earth," who becomes Kamandi. This is the setting for DC's 1970s titles OMAC and Kamandi.

Trivia

 * The key to each Multiverse universe is that universe's Earth, from which the origin of each universe originates from.
 * Brainiac's purpose for obtaining the Earth is so that he can unlock the secrets of accessing the Multiverse.