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The year 100,000,000,000,000 marked the end of the universe and end of all ages, and was further than even the Time Lords had travelled. By this time, most of the galaxies in the universe had collapsed as stars had burnt away, and most life had become extinct.

It was in this year that the last remnants of humanity flew to Utopia from the planet Malcassairo (despite hazards such as the Futurekind) thanks to the efforts of Professor Yana and the Tenth Doctor. Yana realised he was the Master and stole the TARDIS, stranding the Doctor, Martha Jones and Jack Harkness there. (DW: Utopia) At some point afterwards, the Doctor was able to get Jack's vortex manipulator to function and the three returned to the early 21st century. The Master, meanwhile, later returned to approximately 100,000,000,000,000 and rendezvoused with the remnants of humanity, transforming them into the Toclafane. (DW: The Sound of Drums/Last of the Time Lords)

By this late stage of its existence, humanity had come "full circle" after spending aeons evolving into other forms, returning to a form similar to that of the 21st century and surrounding eras: bipedal, with traditional language skills and no apparently differences in physical make up. The related species, Futurekind, had developed some differences, but were still recognisable as humanoid.

At some point in the Doctor's personal timeline, River Song travelled with him to "the end of the universe". This could be the year 100,000,000,000,000, though she could have been referring to the Universe ending on 26th June 2010 due to the cracks in Time. (DW: Forest of the Dead, The Pandorica Opens, The Big Bang)