Parallel universe
A parallel universe is a reality created when historical events diverge from the main timeline. Unlike alternate timelines, these occur naturally. Travel to parallel universes became impossible after the Last Great Time War. (DW: Rise of the Cybermen)
In the 1970s, the Doctor visited a parallel universe in which the United Kingdom was a fascist Republic ruled by an alternate Doctor. (DW: Inferno, NA: Timewyrm: Revelation)
- For full details see the article Parallel Earth (Inferno).
Circa 1979, the Doctor visited a universe in which the Roman Empire spanned the galaxy and was beginning to conquer other universes. (DWM: The Iron Legion)
One parallel universe was lifeless and empty due to the destruction of Logopolis in 1981. (PDA: The Quantum Archangel)
In the 1990s, Carbury was invaded by knights from a parallel universe which bore similarities to Arthurian legend. (DW: Battlefield)
- For full details see the article Arthur's World.
In 2007, the Doctor, Rose Tyler and Mickey Smith visited a universe in which Rose's father was still alive. (DW: Rise of the Cybermen)
- For full details see the article Pete's World.