Whats the word for the belief in a rational universe?

Is there a word for the belief that the universe is rational/ordered/able to have things known about it/not things happening randomly? Sorry for the slashes, but if I could phrase this concisely, I’d tack an -ist onto it and answer my own question.

Deterministic.

Whats the word for the belief in a rational universe?

Oxymoron?

Optimism.

Scientism?

Unrealistic? BwaHaHaHa, I kill me! (no, not really)

Um, I’ll go with Determinism also: (From Merriam-Webster online)

Rationalism would seem to fit the bill.