Big Bang Two

The Big Bang Two refers to the explosion caused by the Doctor "rebooting" the universe after its destruction.

History
In 1996, all stars in the universe had gone supernova due to the unique circumstances of the TARDIS's destruction. The entire universe was destroyed except for the Earth and its moon. The TARDIS's continuing explosion, which, like the resultant destruction of the universe, was happening "at every point in history", acted as a replacement for the sun, keeping Humanity alive.

When the Pandorica opened in 1996, it contained billions of atoms from the universe as it should have been. Some of these were the final traces of whole races that had been un-made by the cracks in the universe. As "the perfect prison", the Pandorica was also designed to emit a Restoration field which would preserve or restore whatever was inside it. This combination of pre-collapse atoms and the restoration field, had a restorative effect on a fossilised Dalek. This was thought impossible, because the Daleks had never existed, having been wiped from history, so there should have been nothing to resurrect. Upon working this out, the Doctor reasoned that if the restoration field could be transmitted to the entire universe, it would recreate it.

The Doctor used a vortex manipulator to fly the Pandorica directly into the heart of the TARDIS's eternal explosion. Since the TARDIS was exploding at all points in history, the particles and restoration field were scattered at every point in time. A new universe was created based on the old one, but with the Doctor having never existed. "Rebooting" the universe caused this new universe to proceed undamaged, because the TARDIS had not exploded. Thanks to the ability the crack in her room gave her to recall things erased by remembering them, Amy Pond was able to bring back, at least, her parents and Rory, and later the Doctor after she remembered who he was and focused on calling him back.

Behind the scenes

 * Because this new universe's survival hinged on certain omissions when compared to the history of the prior universe, it is unclear whether any previous Doctor Who adventures ever took place. It is somewhat likely that all prior stories were remembered back into existence alongside the Doctor himself, however, this would conflict with removing the cracks. The opposite alternative would be if no prior adventures took place, which would drastically alter history and the status of many characters and factions. It is also possible that the other things erased remained that way as Amy had to focus on Rory and her parents for them to be brought back and she had to focus on the Doctor to bring him back as well. Another theory is that the events of Series 5 happened, but only in the memories of those involved - except for The Pandorica Opens\The Big Bang, where only the Doctor, Amy, Rory and River remembered.


 * Viewers are probably expected to Hand Wave it.