Donna's World

Donna's World was a rewritten version of the timeline, created when Donna Noble turned right instead of left while deciding which of two different job interviews to attend. As a result, the Tenth Doctor never met Donna and died underneath the Thames Flood Barrier. He also never met Martha Jones. These events resulted in devastating effects for Earth and the universe.

History
While on the planet Shan Shen, Donna was unknowingly fitted with a time beetle, part of the Trickster's Brigade. A fortune teller selected a point in her life where making a seemingly random choice had enormous ramifications.

In June 2007, Donna had to make a choice between two jobs. The moment she chose between the jobs was at a junction. Her agency had offered her a contract with H.C. Clements, which while temporary, was posh and in the centre of London, which Donna enjoyed. Her mother, Sylvia Noble, had got her job opportunity to become the personal secretary of Jival Chowdry, owner of a photocopying business. Although this would be a permanent job, Donna found it less interesting.

While driving and in discussing the dilemma, Sylvia pressured her into turning right to stop by Jival Chowdry for a chat. While in the regular timeline Donna ignored her mother and turned left, in this timeline she turned right, resulting in her taking the PA job. (TV: Turn Left)

25 December 2007
The Tenth Doctor tracked down the Empress of the Racnoss to the Torchwood base underneath the Thames Flood Barrier and blew it up, which flooded the whole thing. (TV: The Runaway Bride) Although the Empress of the Racnoss and her offspring drowned, the Doctor was unable to escape and died too quickly to regenerate. Donna stumbled across Rose Tyler, who arrived on the scene too late to do anything. The Doctor's TARDIS was salvaged from under the Thames and sent to a UNIT base in Leeds. (TV: Turn Left)


 * In the original timeline, the Doctor met Donna Noble who saved his life when she told him to stop after the Doctor blew up the Torchwood base. Also, there was a hole drilled to the centre of the Earth so the hole may have been sealed off. Rose Tyler is not believed to have been present in this timeline. (TV: The Runaway Bride)

2008
The Judoon H2O scooped the Royal Hope Hospital to the Moon to find a Plasmavore criminal and her Slab accomplices. Although they found and killed the alien criminals, the Plasmavore had already armed the MRI. (TV: Smith and Jones) Sarah Jane Smith, Luke Smith, Maria Jackson, and Clyde Langer, who had been in the hospital when it was transported, disarmed it, but they died, along with the rest of the hospital, when their oxygen ran out. The only survivor was Oliver Morgenstern, who was passed the last oxygen tank by medical student Martha Jones, who gave up her life to save him. (TV: Turn Left)


 * In the original timeline, the Tenth Doctor investigated the hospital instead of Sarah Jane, Luke, Maria and Clyde under the alias "Mr Smith" and no one suffocated because he found the Plasmavore in time. Shortly after, he took on Martha Jones as a companion. (TV: Smith and Jones)


 * Also in the original timeline, the Doctor reunited with Jack Harkness, and awoke at the end of the Universe. Saxon stole the TARDIS, travelling to 21st century Earth. (TV: Utopia / The Sound of Drums) Saxon designed the Valiant and Archangel Network and used them to conquer the Earth. (TV: The Sound of Drums) With the help of Martha, the Doctor and Jack reversed this. (TV: Last of the Time Lords) Because those events hinged on the Doctor meeting Martha Jones, in this timeline, the events created by Harold Saxon also would never have occurred and the Archangel Network or the Valiant were never designed or built, among other changes such as Captain Jack Harkness never reuniting with the Doctor. The status of certain other events post-Thames Barrier such as the incident with the Weeping Angels (TV: Blink) remain unclear, especially in the aftermath of 25 December 2008 (see below) (although, in the case of Blink, that event also hinged on the Weeping Angels meeting the Doctor).

Rose Tyler visited Donna and advised her to persuade her family to spend Christmas some place other than London. (TV: Turn Left)

25 December 2008
A replica of the Titanic crash-landed onto Buckingham Palace. It destroyed the Greater London Area and flooded the whole of Southern England with radiation. Donna's family, who did decide not to stay in London for the holidays, having won a luxury getaway in a raffle, watched the events on television and were able to see the mushroom cloud of the explosion from a distance. (TV: Turn Left)
 * In the original timeline, this crisis was averted thanks to the Doctor. Although the city was nearly abandoned in the main timeline, this seems not to be the case here. Also, both the Doctor and Max Capricorn had stated that if the Titanic crash-landed on Earth, it would wipe out all life, but it appears they were mistaken or exaggerating, as only southern England was affected directly. (TV: Voyage of the Damned)

2009
Britain went under martial law in order to deal with the crisis caused by the nuclear explosion. Many citizens fled to France, until France closed its borders. The United States promised fifty billion pounds in financial help for Great Britain but this plan was abandoned when sixty million Americans were fully converted into Adipose children. (TV: Turn Left) Miss Foster's (TV: Partners in Crime) plan was not only successful, but sixty times as successful as was planned in the original timeline. (TV: Turn Left)


 * In the original timeline, the Adipose plan targeted Great Britain and was stopped before it was put in full swing thanks to the Doctor and Donna Noble. (TV: Partners in Crime) The change in location was due to Britain no longer being viable for breeding due to the nuclear disaster.

The Sontarans activated the ATMOS devices in the cars to convert Earth into a breeding ground. (TV: The Sontaran Stratagem / The Poison Sky) The surviving members of the Torchwood 3 team worked to stop the scheme. The team destroyed the Sontaran flagship and successfully reverted the atmosphere to its previous state, but Gwen Cooper and Ianto Jones died in the attempt; Jack Harkness, being immortal, survived and was captured by the Sontarans and transported to Sontar as a prisoner. Britain was largely unaffected due to its poverty and hence its lack of vehicles with ATMOS devices. Rose Tyler once more appeared to Donna to try to persuade her to help change back the timeline. (TV: Turn Left)


 * Without "Harold Saxon" to design it, the UNIT vessel the Valiant, which helped turn the tide against the Sontarans in the original timeline, was never built. In the original timeline, the Sontaran invasion of Earth was prevented by the Doctor, Donna, Luke Rattigan and UNIT. The Doctor was able to clear the atmosphere without the assistance (or sacrifice) of any Torchwood members. In this timeline, Rose implied that the destruction of the Sontaran ship was what repaired the atmosphere, but in the original timeline, the clearing of the air and the flagship's destruction were two separate events, though both involved the Atmospheric Converter. (TV: The Poison Sky)

Roughly three weeks after the Sontaran invasion, the British government made a new law ("England for the English") forcing all non-British citizens in Britain to go to "labour camps". Donna's grandfather lamented that "he never thought he would see this happen again", and when Donna chided him, saying that they are just relocation camps, he replies that "that's what they said last time". Soon afterwards, the stars began going out. (TV: Turn Left)


 * After the timeline was corrected, the stars' fading was discovered to be an effect of the reality bomb, breaking through the Medusa Cascade into Donna's parallel world. (TV: Journey's End)

Rose Tyler, through methods and reasoning unknown, was working with UNIT on reverse-engineering the TARDIS, creating a time machine with which Rose hoped to restore the timeline. (TV: Turn Left)


 * Rose's relationship with UNIT was unique to this timeline, as there's no indication that she ever worked with the UNIT of the normal timeline.

Negation
UNIT and Rose Tyler sent Donna back to the point where the timelines diverged. According to Rose, in order to restore the timeline, Donna had to make her past self turn left instead of right at the point where she decided whether to follow her mother's advice or her own instincts. Donna arrived in 2007, but too far away from her past self to directly influence her; instead, she orchestrated an accident by stepping out in front of a lorry, which blocked traffic and forced the earlier Donna to turn left. Just before her death, Rose Tyler appeared and whispers a message for her to give the Doctor when the timeline was fully restored. (TV: Turn Left)

Behind the scenes

 * It is not actually a parallel world since the walls between realities were sealed in TV: Doomsday. This was made explicit by the production team. Rather it is an altered version of the Doctor's world. According to quantum physics, every decision we make creates multiple realities - one for each option of that decision. This theory implies that, despite the timeline being restored, the Donna's World reality still continued to exist in some form.