Parallel universe of the Cla'tac'teth

The parallel universe of the Cla'tac'teth, also called the "realm of the Cla'tac'teth" and the "Cla'tac'teth reality," was an alternate universe that reached the point of heat death and the entropy wave was not stopped by the Fourth Doctor and the Master in 1981. However, the Sixth Doctor believed the Cla'tac'teth reality had millions of years of divergence from the primary reality.

In this realm, matter and energy were infected with the entropy virus, which created emerald green waste products, and reduced all of creation to a dull red glow. It was, presumably, only inhabited by the Cla'tac'teth who, in the main universe, lived just before the heat death of the universe, their home a neutron star orbiting the Great Attractor.

The co-ordinates for this universe were programmed into the Master's TARDIS which, linked with the Doctor's TARDIS, enabled both ships to pass through the sidereal barrier between universes and enter the Cla'tac'teth reality briefly, before returning to the Great Attractor of the prime reality to defeat the Quantum Archangel. (PROSE: The Quantum Archangel)