Universe

A Universe may be considered as a space-time continuum, and the matter, energy, laws and biodata contained therein, such as it operates as a complete totality unto itself.

They exist within an expanse called the Void (DW: Army of Ghosts), an ur-space often conceptualised as an ocean in which they float (FP: Dead Romance 2nd Ed.: A Cosmology of the Spiral Politic).

A number of universes exist (DW: Inferno), but it is not known if that number is infinite or merely incalculably huge (FP: Dead Romance 2nd Ed.: A Cosmology of the Spiral Politic).

Some exist 'sideways' or 'parallel' to each other (DW: Battlefield), although such spacial language must be understood as simplification given that 'space' is a phenomenon local to within universes (FP: Dead Romance 2nd Ed.: A Cosmology of the Spiral Politic).

Some exist 'before' (NA: All-Consuming Fire) or 'after' (MA: Millennial Rites) each other, although such temporal language must be understood as simplification given that 'time' is a phenomenon local to within universes (FP: Dead Romance 2nd Ed.: A Cosmology of the Spiral Politic).

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

The Doctor's Universe
The universe which produced The Doctor is the site of the majority of his adventures.

Infinite in space and constantly expanding (DW: Genesis of the Daleks), it was created roughly fourteen billion years ago as a consequence of the Big Bang. The Time Lords refer to this as 'Event One' (DW: Castrovalva).

'Event Two' signifies the end of the universe (PDA: The Infinity Doctors), which has variously been projected to occur in 60, 000,000,000 AD (BFA: Zagreus), 100,000,000,000,000 AD (DW: Utopia) or 100, 000, 000, 000, 000, 000, 000, 000, 000, 000, 000 AD (PDA: The Infinity Doctors). As discussed below, there may be good reason for the discrepancy.

The universe passed the point where it should have succumbed to heat death long before any of these dates, but vented most of its entropy into E-Space. (DW: Logopolis)

The Time Lords of Gallifrey were, as the first sentient culture to develop within this universe (NA: Lucifer Rising), responsible for setting the parameters within which the universe operates (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 favour the development of humanoid life. They established the Web of Time which guaranteed the universe a stable, linear, history (BFA: Neverland, FP:The Book of the War).

With the Time Lords now lost to the Last Great Time War, this particular universe has become a more uncertain and dangerous place.

'Before'
The so-called 'Pre-Universe' which existed prior to the Doctor's had green space, 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 possesion 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 prove temporary; In his seventh life the Doctor was fully conversant with the details and specifics of this universe (NA: All-Consuming Fire), wheras by his tenth it would almost be 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 Old Ones, who found a means by which to survive into the next (NA: All-Consuming Fire, MA: Millennial Rites) The Beast's claims would also suggest he originated in this cosmos (DW: The Impossible Planet).

'After'
The universe that followed the Doctor's would be a pink void, interspersed with green mists of orbiting plankton (MA: Millennial Rites).

The City of the Saved existed 'inbetween' the end of the Doctor's universe and the start of this one (FP: Of the City of the Saved...).

Saraquazel would become this universe's equivalent of a Time Lord (MA: Millennial Rites).

The inhabitants of the City of the Saved once belived they had penetrated into this universe and established a colony there, but in fact they were deceived and had in fact only reached a simulated enviroment inside the hostile TARDIS known as Antipathy (FP: Of the City of the Saved...).

'Sideways'
Most 'parallel' universes are exactly that; parallel. They run alongside each other but have an independant existence. They may share many common features but do not 'diverge' or 'branch off' from each other at any specific point (FP: Dead Romance 2nd Ed.: A Cosmology of the Spiral Politic).

The countless worlds in which the Roman Empire never fell or in which the Nazis won World War II (DWM: The Iron Legion,FP: Warlords of Utopia) are not twigs off the branch of some 'main' universe or paths that have split off at some particular juncture. They are entirely seperate creations that share many, but not all, of the features of the familiar universe (FP: Dead Romance 2nd Ed.: A Cosmology of the Spiral Politic). The same would seem to hold true of Pete's World and Inferno Earth (DW: Rise of the Cybermen,''Inferno').

Those universes which share the most features in common may be considered as being located 'closest' to each other and those which share the least features in common may be considered as being 'furthest away' from each other. Although, again, the spacial terminology here is a simplification as 'space' only exists within universes (FP: Dead Romance 2nd Ed.: A Cosmology of the Spiral Politic).

It is however possible for complete new universes to be formed by 'branching off' from specific points in another universe's history. The difficulty with this though is that it cuts the lifespan of the original universe in half (NA: Blood Heat). This process may account for the radically fluctuating lifespan of the Doctor's universe.

A healthier way for a universe to reproduce is for it to develop within it a species capable of 'engineering' a new universe from scratch (FP: Dead Romance 2nd Ed.: A Cosmology of the Spiral Politic).

The Time Lords never apparently attained this level of accomplishment. However an unpopular fringe theory on Gallifrey held that their own entite reality had been engineered in this way by the 21st Century Humanity of some other universe (FP: The Book of the War).