Spacetime

According to Doom (2016) the DOOM Marine has traveled between worlds and through time suggesting not only an interdimensional element to the new game's story, but also time travel.

In addition the new series seems to introduct even more 'worlds' besides the Earth universe, and Hell universe  but also a former elemental plane referred to as Argent D'Nur former home of the Elemental Wraiths, and guarded by Night Sentinels. There is also reference to a Seriphimn race (though perphaps they are tied to the elemental wraiths). It is all enigmatic and mysterious but the the reference could be meta in such a way that the DOOM Marine himself might have travelled between parallel DOOM universes as well, to a universe where an Earth has attempted to religiously exploit or inadvertantly opened passages to hell into multiple 'worlds', if not part of a single timeline (it does seem to be one of the game's way of acknowleding the many iterations of DOOM that has come before).



Some fans theorize that DOOM Marine is the same Marine from the original DOOM series and DOOM 64, following DOOM64's ending in which the Marine choose to remain in Hell to insure it would never arise again. In some versions of these theories the original Doom universe is parallel to the Doom 2016 universe, and that he has been pulled into a seperate universe.