Alternate timelines are settings where an alternate history is occurring. Fictional alternate timelines generally exist in parallel with a main timeline and may be either stable or unstable and destined for collapse. Alternate timelines may be created by time travel, science experiment gone wrong, or may have always existed as an alternate dimension. Often they can be reached by portal, wormhole, time machine, superpower, or other means. They are home to time travelers, Nazis that never lost, and unimaginable horrors our own timeline was lucky to avoid.