Dirac Sea

In Episode 16, Shinji is pulled down into the "shadow" (which is actually the body) of the Angel Leliel. Ritsuko describes this space as a Dirac Sea (ディラックの海).

Ritsuko: "It's six hundred eighty meters in diameter with a thickness of three nanometers. The ultra-thin space is supported by an inwardly-directed AT Field. The inside is an imaginary space, called a Sea of Dirac. I think it's probably connected to another universe."

This particular Sea of Dirac referred to in episode 16 exists presumably in three dimensions. Thus, when Ritsuko lists the dimensions as "680m x 3nm" the term "diameter" refers to both the length as well as the width (looking down on this Sea of Dirac one would thereby see a circle). For perspective, this would make the volume of said Sea of Dirac just about one cubic millimeter. Obviously, such a volume is nowhere near enough to hold an Evangelion, and based on the fact that Unit 01 emerged from this Sea of Dirac in normal scale it can be inferred that it was not compressed to fit this space. This actually proves that Ritsuko's theory of this Sea of Dirac leading to another dimension (also presented in episode 16) is correct, since Unit 01 would otherwise have had no space in which it could exist.

Essentially it is a pocket-dimension of sorts, from which escape is nearly impossible.

Notes

• "Dirac Sea" is a real scientific term (though it was not fully explained on-screen). It is a theoretical model of the vacuum as an infinite sea of particles possessing negative energy, that was invented by the British physicist Paul Dirac in 1930.

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