With Star Trek: Discovery (DSC) visiting the “Mirror Universe” in their current story arc a quick review of Star Trek’s parallel universes and time travel is in order. This plot device has allowed Star Trek to explore a number of alternate realities, most notably the “Mirror Universe”. The crew of the NCC-1701 a year earlier, in the episode “Mirror, Mirror”, had direct experience with the “Mirror Universe” alternate reality when during a transporter accident Captain James T. Kirk, and three other members of the crew were swapped out with their counterparts from there. The origins of the Terran Empire are unclear, with the first precise difference seen in the Star Trek: Enterprise (ENT) episode “In a Mirror, Darkly”. In “Mirror, Mirror”, for example, the NCC-1701’s Captain Kirk, Chief Engineer Montgomery Scott, Dr. Leonard McCoy, and Communications Officer Nyota Uhura are members of the landing party on the Halkan homeworld in both universes.

Source: Huffington Post January 13, 2018 21:00 UTC