Multiverse

The multiverse is a concept that refers to the existence of infinite universes that comprise everything that is. Each universe within the multiverse is referred to as a different "Earth", and each vibrates at a different frequency so that they cannot normally interact with or be seen by each other. If one is able to travel fast enough it is possible to breach the laws of physics and travel between these Earths.

History
In early 2388, Barry Allen and the rest of Team Flash accidentally opened a singularity above Central City; though they succeeded in closing it, a series of 52 breaches between Earths One and Two were opened throughout the city as a result of their actions.

Between mid to late 2388 and early 2389, an Earth Two speedster known as Hunter Zolomon began exploring the Multiverse before using the breaches to launch an assault on Earth One's Central City in an attempt to steal The Flash's speed. Numerous meta-humans were sent through the breaches, each tasked with killing The Flash, but none succeeded. Team Flash, in an effort to stop Zoom's onslaught, systematically sealed each of the breaches, leaving only one open on a lower level inside S.T.A.R. Labs. Barry, Cisco Ramon, and Harrison Wells used the breach to travel to Earth Two in order to rescue Jesse Quick, sealing the breach upon their return.

Attempting to increase his speed, Barry Allen used a tachyon device, which in turn caused him to run too fast and accidentally create a breach between Earth One and an Unnamed Earth, the parallel world that is the home of Supergirl.

During his travels, Zolomon discovered that Earth One happened to be in the center of the entire Multiverse, and that from there one could travel to any of the other infinite number of Earths. Enthralled by the idea of conquering all of existence, in May of 2016 he attempted to use the Mercury Labs Magnetar to instantaneously destroy every Earth in the Multiverse besides Earth One, using its central location as a means of targeting every other universe at the same time. Through the sacrifice of his own time remnant, Barry Allen was able to stop the device moments before it destroyed the Multiverse, and also managed to defeat Zolomon in the process.

Known parallel worlds

 * Earth One
 * Earth Two
 * Earth Three
 * An unnamed Earth (home to Supergirl)
 * An unnamed Earth (home to CBS' The Flash)