Relative dimension
The acronym "TARDIS" came from the phrase "Time And Relative Dimension In Space". (TV: An Unearthly Child) Other accounts indicated there were multiple relative dimensions. (TV: The Time Meddler, et al.) Indeed, the First Doctor claimed that the TARDIS was used for "investigating time and relative dimensions in space" (TV: "The Feast of Steven") and "travelling through time and relative dimensions in space". (TV: "Bell of Doom") According to some accounts, time only became "relative" with the end of the golden age and beginning of time travel. (PROSE: The Infinity Doctors, Mr Saldaamir)
When reciting the acronym, the singular dimension was used by Susan Foreman, (TV: An Unearthly Child) the Fourth Doctor, (TV: Frontios) the Ninth Doctor, (TV: Rose) the Tenth Doctor, (TV: Smith and Jones) Rose Tyler, (TV: Turn Left) Idris, (TV: The Doctor's Wife) the Twelfth Doctor, (TV: The Pilot) and the Fugitive Doctor. (TV: Fugitive of the Judoon) The multiple "dimensions" was used by Vicki Pallister, (TV: "The Watcher") WOTAN, (TV: The War Machines) the Second Doctor, (TV: The Wheel in Space) Zoe Heriot, (TV: The War Games) K9 Mark II, (TV: The Creature from the Pit) Adric, (TV: Four to Doomsday) and the Seventh Doctor. (TV: Delta and the Bannermen)
Some accounts indicated the relative dimensions included Imagination, (PROSE: Cat's Cradle: Time's Crucible, AUDIO: Auld Mortality) Inner Space-Time, (PROSE: Cat's Cradle: Time's Crucible) and possibility theory. (AUDIO: Auld Mortality)
Marnal believed that the term "relative dimensions" referred to the five dimensions in which time travel occurred, and how time travellers shared a relative present in overtime no matter which point in time they visited. (PROSE: The Gallifrey Chronicles) To a Time Lord, the phrase "time is relative" referred to the fact that a TARDIS could travel to the past and future, but not its own past and future. (PROSE: The Gallifrey Chronicles, The Infinity Doctors) This state of subjectivity was created in the destruction of the objective linear timeline via the invention of time travel, with Omega knowing in advance that the Eye of Harmony would make time relative. (PROSE: The Infinity Doctors)
The Second Doctor explained the TARDIS's dimensionally transcendental interior to the Brigadier as "relative dimensions and all that." (TV: The Three Doctors) When Sarah Jane Smith asked how big the TARDIS was, the Fourth Doctor answered:
Well, how big's big? Relative dimensions, you see. No constant.
When Sarah was not satisfied by this answer, the Doctor explained that there were no measurements in infinity before lamenting that humans had "such limited little minds. (TV: The Masque of Mandragora)
Professor Hayter, a human scientist, upon hearing that a TARDIS was bigger on the inside, told the Fifth Doctor that this would revolutionise "the whole concept of relative dimension" and wished that he had the time to make use of the Doctor's knowledge. (TV: Time-Flight)
When a TARDIS was destroyed, its relative dimensions would evaporate. (PROSE: The Quantum Archangel)
