Leliel: Leliel seems to appear out of nowhere over Tokyo 3 as a three dimentional black-and-white sphere, that is a positive energy object and has a two dimentional shadow, a "Dirac Sea" that swallows everything above it. So the Angel, made of negative mass, is two dimentional and casts a shadow into three dimentions. Not really scientific, but we're talking about Eva here. Shinji in Unit 01 is enveloped in this area, left alone to contemplate his existence for sixteen lonely hours. The Eva breaks out, destroying the angel and freeing himself at the same time.

Also the Dirac Sea is named after the physicist Dirac who more or less invented quantum physics. The Dirac Sea was a theory he constructed to explain some of the odder results of his equations. I won't go into the deep quantum mechanics involved, but essentially a Dirac sea is an area full of electrons with negative energy. Negative energy means they have negative mass (figure that one out!), which means they're basically producing antigravity. Obviously we have no proof that such things even exist, and the idea of the Dirac sea is rather out of use.