Paradox machine

The Paradox machine was a type of technology that was capable of creating a tear in space and time, and looping history back on itself. The Master used such a machine after he "cannibalised" the the Doctor's TARDIS in order to allow his army of Toclafane to invade Earth. The device created a tear in the sky, allowing millions of the sphere-like aliens to attack the planet and its populace. (DW: The Sound of Drums)

Although the TARDIS was heavily-modified by the Master, it still managed to ring its cloister bell as a sign of distress. Martha Jones also observed that it appeared to be "sick". It is not known exactly when the Master transformed the TARDIS but it is assumed he did it after he had taken Lucy to the end of the universe but before he became Prime Minister.

The device was designed to prevent a time paradox from occurring and The Master called it his "masterpiece". As the Toclafane were Humans from the future, any attacks on their ancestors would have prevented their existence, effectively erasing themselves from history. However, the use of the paradox machine prevented such an outcome, allowing the Toclafane to enslave Earth. The device was destroyed by Captain Jack Harkness, who opened fire on it with a machine gun. The destruction of the Paradox Machine reversed time to the point it was activated, undoing everything that had occurred since then. (DW: Last of the Time Lords)

The interior of the paradox machine was surrounded on all sides by an ominous red glow. The main console had gone under many modifications by the Master. The console itself was enclosed inside a metal cage, with various tubes and appendages attached to it. At the base of the console was a pipe connecting to another area of the TARDIS; on it was a dial showing a readout of the pressure build-up inside. It is unknown exactly how much of the TARDIS was cannibalised or whether any other rooms were lost or ejected. However, the paradox machine appeared to somehow use steam power and pressure as when it was activated it shot out steam in puffs from the console.


 * As the TARDIS was capable of preventing a paradox as long as the people creating the paradox stayed inside, the machine may have simply increased this power so that it could be used outside of the TARDIS.