Change of the World

A prophesied great cataclysm that will utterly change the form of the world. References to the Change of the World are somewhat oblique, so that the meaning of the term is not completely sure, but it appears to refer to the foretold remaking of Arda after the return of Melkor and the Last Battle. Specifically, we're told the Valar reckoned time by the passing of the Sun until the Change of the World, and that those trapped by the Enchanted Isles would sleep until the Change came.

An alternative reading is that the Change of the World relates to the events surrounding the Downfall of Númenor of II 3319, in which Aman was taken out of the world and made unreachable for Mortals. This seems a rather less likely interpretation (especially given that the Change of the World implies the ending of the Sun, which certainly did not happen in the Downfall), and the more plausible reading has the Change of the World after the Dagor Dagorath at some point in the far future.