The definition of total nothingness is necessary for the "theory" of existence, because there is the necessary requirement for the explanation of causality. "Before and after". Cause and effect.
Exactly what is nothingness if reality i.e. the universe, started to exist at the point in spacetime t=0 ?
Since "before" is a state of existence and there was no existence "before" reality, reality must have created itself.
Time could be a sequence of "states" of existence. In accordance with the "syntax" of reality. Superposition and actuality, with every moment in immediate contact with every other moment.
Deterministic constraints juxtaposed with self configurative freedom.
Russ