Why did Aleister create the Science Side? Do we actually know?
Reality Warper: He is capable of omnipresence and other tricks. Confirmed when it is revealed at the end of New Testament volume 11 that he possesses something called the Archetype Controller, which can basically create or destroy Jungian archetypes, which would be like the equivalent of controlling tropes, in a way. It is revealed that, using this power, he literally created the entire concept of a "Science side", and made Academy City and its espers part of the archetype of "mankind’s worship of science".