Greyness

According to the Book of Lies, a great empty greyness would fall over the universe in the far future. (PROSE: Unnatural History)

As part of his attempt to resolve the Rutan-Sontaran War, the Doctor took Sontar and a Rutan ten thousand years into their future with his TARDIS. He intended to show them that their fighting would end in the destruction of both sides; however, when he turned on the scanner, the display was simply grey. Opening the door confirmed that the universe was a sea of grey nothingness. Sontar described it as "grey mist".

The Doctor tested the greyness with his instruments, but there was nothing for him to interpret: it was completely empty, lacking even the miscellaneous virtual particles, photons, and ions present in the most desolate parts of the universe, and it continued forever. This horrified him. (PROSE: The Infinity Doctors)

"There's nothing left. No time, no space, no matter, no energy. The entire universe has gone."

- The Doctor

The Doctor theorised that the greyness had been caused either by the Effect or the Time Lords' reaction to it. (PROSE: The Infinity Doctors)

The boy indicated to the Eighth Doctor that Faction Paradox intended to hasten the onset of the greyness. (PROSE: Unnatural History)