TEXT:“Metaphysical Biology Research Room 1 Fuyutsuki”
Dr. Nick: A GIGANTIC plot point is understatedly spelled out: this is the made-up science that makes NGE's plot happen. In that sense, it's somewhat comparable to Minovsky physics in the original Gundam.
The basics of Evangelion's soul science are of course recycled from another Tomino series, Space Runaway Ideon, wherein a temperamental hivesoul called the Ide resides within the titular robot and serves as the all-powerful cosmic horror macguffin over which the two factions fight. Anno puts his prequelist spin to this, with the Third Impact being an event that can potentially create such a cosmic being.
Additional Commentary
Dr. Nick: Ideon, in turn, gets a big chunk of its metaphysics from - believe it or not - the 1956 scifi classic Forbidden Planet. The movie is of course one of those ur-influence texts whose DNA can be found in basically every single work of pop science fiction that came after it, but in Ideon's case the things borrowed are remarkably specific. This goes even for the name of the hivesoul: turns out IDE isn't just a cheeky anagram for DIE.