Universe

For information on the Doctor Who Universe from a metafictional standpoint, see separate article.

A universe might have been considered as a space-time continuum, and the matter, energy, laws and biodata contained therein, such as it operated as a complete totality unto itself.

Cosmology

These universes existed within an expanse called the Void (DW: Army of Ghosts), an ur-space often conceptualised as an ocean in which they floated. (FP: The Book of the War)

A number of universes existed (DW: Inferno), but it is not known if that number was infinite or merely incalculably huge. (FP: The Book of the War) Prior to the Last Great Time War, the Time Vortex could have been used to access one another. Since the War, the pathways had closed, (DW: Rise of the Cybermen) and travel usually only occurred through a Void Ship or a reality bomb breaking down the fabric between universes. (DW: Army of Ghosts/Doomsday, The Stolen Earth/Journey's End)

Some existed 'sideways' or 'parallel' to each other (DW: Battlefield), although such spatial language must have been understood as simplification given that 'space' was a phenomenon confined to within individual universes. (FP: The Book of the War) Likewise, some existed 'before' (NA: All-Consuming Fire) or 'after' (MA: Millennial Rites) each other, although such temporal language must have been understood as simplification given that 'time' was a phenomenon also confined to within universes. (FP: The Book of the War)

Many universes developed a civilisation equivalent to that of the Time Lords - the first culture within a given reality to reach a level of sophistication which allowed them to tailor the laws of that universe to their own nature. (MA: Cold Fusion)

The composition of the universe consisted of galaxies which were made of stars which were orbited by planetary bodies. Earth, for example, lay in the Sol system of Mutter's Spiral, the galaxy closest to the Andromeda Galaxy.

Parallels

Most 'parallel' universes were exactly that: parallel. They ran alongside each other but existed independently. They may have shared many common features but did not 'diverge' or 'branch off' from each other at any specific point. (FP: The Cosmology of the Spiral Politic)

The countless worlds in which the Roman Empire never fell or in which the Nazis won World War II (FP: Warlords of Utopia) were not twigs off the branch of some 'main' universe or paths that had split off at some particular juncture, but were entirely separate creations that shared many, but not all, of the features of the familiar universe. (FP: The Cosmology of the Spiral Politic) The same would seem to have held true of Pete's World and Inferno Earth. (DW: Rise of the Cybermen, Inferno)

Those universes which shared the most features in common may have been considered as being located 'closest' to each other and those which shared the least features in common may have been considered as being 'furthest away' from each other. Although, again, the spatial terminology here is a simplification as 'space' only existed within universes. (FP: The Cosmology of the Spiral Politic)

It was, however, possible for complete new universes to have been formed by 'branching off' from specific points in another universe's history. The difficulty with this though is that it cut the lifespan of the original universe in half. (NA: Blood Heat)

A healthier way for a universe to reproduce was for it to have developed within it a species capable of 'engineering' a new universe from scratch. (FP: The Cosmology of the Spiral Politic) Although the Time Lords apparently never attained this level of accomplishment, an unpopular fringe theory on Gallifrey held that their own entire reality had been engineered in this way by the 21st century humanity of some other universe. (FP: The Book of the War)

History

"Before"

The so-called 'Pre-Universe' which existed prior to the Doctor's had a pink void, stars shaped like doughnuts and physical laws closer to what might be understood as magic. (MA: Millennial Rites)

Knowledge of this universe was a closely guarded secret, and was only in the Doctor's possession as a result of his connection to the Matrix during his time as Lord President. (MA: Millennial Rites, DW: The Invasion of Time) Even then, the knowledge would ultimately have proven temporary; in his sixth and seventh lives the Doctor was fully conversant with the details and specifics of this universe (NA: All-Consuming Fire, PDA: Synthespians™), but by his tenth life it was almost an article of religious faith to him that such a universe could not have existed. (DW: The Impossible Planet)

This universe's equivalent to the Time Lords were the Great Old Ones, who found a means by which to survive into the next. (NA: All-Consuming Fire, MA: Millennial Rites) The Beast claimed to have existed before the universe. (DW: The Impossible Planet) It was also speculated that the Ancient Lights came from the previous universe. (SJA: Secrets of the Stars)

"Current"

The universe of the Doctor and of the Time Lords, was known as N-Space, or Normal Space. It was in a state of constant expansion (DW: Genesis of the Daleks) and was created out of a continually existing black void roughly thirteen (SJA: Secrets of the Stars) or fourteen billion years BC in what was known as Event One. (DW: Castrovalva)

For more information on Event One, see corresponding article.

The universe passed the point where it should have succumbed to heat death by the 20th century, but vented most of its entropy into E-Space. (DW: Logopolis)

The universe was replete with pocket universes and other realms or domains discrete from the wider continuum. Some of these existed in exotic special dimensions such as Calabi-Yau Space (PDA: The Quantum Archangel), some folded into quirks of perceptual history such as the Eleven-Day Empire (EDA: Interference - Book One) and others, such as Mictlan, had no measurable existence beyond the purely conceptual. (EDA: Alien Bodies)

When the Olympian Prometheus stole life spores from the planet Olympus and let them go across the universe, he created life. This angered Zeus, who chained Prometheus to a mountain on an unknown planet for his actions. (DWM: The Life Bringer) Greyjan the Sane, on the other hand, stated that life evolved from a single ancestor cell. This didn't include more exotic lifeforms, which came into being soon after the creation of the universe. (EDA: The Ancestor Cell)

It is possible both sources were true, with life spores being another name for the ancestor cell.

The Time Lords of Gallifrey, as the first sentient culture to develop within their universe (NA: Lucifer Rising), were responsible for setting the parameters within which the universe operated. (NA: Sky Pirates!) They expunged magic in favour of science as the basic governing principle. (NA: Cat's Cradle: Time's Crucible, Christmas on a Rational Planet) They established the morphic field that would seem to have favoured the development of humanoid life. (NA: Lucifer Rising) They established the Web of Time which guaranteed the universe a stable, linear history. (BFA: Neverland, FP: The Book of the War)

After the Time Lords were lost to the Last Great Time War, the universe became a more uncertain and dangerous place. Travel to other universes became impossible (DW: Rise of the Cybermen) and the creation of time paradoxes had a much more dangerous effect. (DW: Father's Day)

The destruction of the Doctor's TARDIS created cracks in time throughout time and space which began erasing the universe. By piloting the Pandorica (which basically contained a blueprint for the universe) into the heart of the TARDIS explosion (which was happening at all points in space and time), the Eleventh Doctor rebooted the universe, restoring it to its original state. It is unclear, however, if everything erased by the cracks were restored. Amy Pond's parents, her husband Rory and the Doctor were all restored, but this was only due to her specifically remembering them and the influence of one of the cracks on her life for years. In the case of the Doctor, she had to actively remember him in order to restore him after he was erased by the cracks while restoring the universe, so everything else erased, such as the Weeping Angels, may not have been restored. (DW: The Pandorica Opens, The Big Bang)

"After"

The end of the Universe, also known as Event Two (PDA: The Infinity Doctors), was variously projected to have occurred in 60 billion AD (BFA: Zagreus), 100 trillion AD (DW: Utopia) or 100,000,000,000,000,000,000,000,000,000,000 AD. (PDA: The Infinity Doctors)

Though the Tenth Doctor denied the existence of a universe before his own (DW: The Impossible Planet), he remained aware that the death of his universe would have been followed by the birth of another. (DW: Army of Ghosts) Many time travellers killed themselves at the end of the universe in the Institute of Time because they feared the universe's heat death. (ST: The End)

The Doctor may have come to the rationale of there being a next universe after learning about the existence of a pre-universe. At the time he mentioned the start of the next universe, he was also referring to a ship he assumed was only theoretical.

The City of the Saved existed 'in between' the end of the Doctor's universe and the start of the next one. The inhabitants of the City once believed they had penetrated into that universe and established a colony there, but in fact they were deceived and had only reached a simulated environment inside the hostile TARDIS known as Antipathy. (FP: Of the City of the Saved...)

The After-Universe was a green void interspersed with yellow mists of orbiting plankton and Saraquazel, who became its equivalent of a Time Lord. (MA: Millennial Rites) The Zytragupten also inhabited this universe. (DWM: The Stockbridge Child)