Heat death

Heat death was the result of entropy in the universe increasing to the maximum amount possible to exist. Long ago, the universe passed the point into total collapse. The Logopolitans created CVEs to postpone the time until heat death occured while their Advanced Research Project would formulate a more permanent solution. Due to interference caused by The Master the CVEs closed prematurely, causing entropy to build up much faster than normal. As entropy built up, it destroyed the Logopolitans, including The Monitor, and caused their planet to crumble to dust. The entropy quickly built up and formed an entropy wave which caused heat death at any point it reached, reducing that part of the universe to nothing. The heat death caused by the wave destroyed planets and other astronomical objects in its path. Heat death in N-Space accounted for the destruction of Traken Union and much of everything else in the universe. The Fourth Doctor prevented the total destruction of N-Space due to heat death by redirecting this entropy into other universes, such as E-Space, through a CVE. (TV: Logopolis)

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