That isn't necessarily true. In a similar thread, it was shown that in quantum mechanical theory, randomness is integral, because the universe breaks down into probabilistic terms. Note Bell's Theorem (link
here and
here), for which I haven't found a non-mathematical/non-esoteric explanation, so I'll go ahead and simplify it here:
Assuming information doesn't travel faster than the speed of light (a trait which has been both theoretically and experimentally verified), then there exists no local hidden variable within space which effects any event. Bell's Theorem has already been verified many times experimentally.
Because of this, the most elementary properties of the universe are inherently random (since there is randomness in probability), and no prediction can be 100% true. Therefor, relating to a previous topic, if you were to go back in time one year and observe yourself up until the present, there is a chance that this reality is not the same as the reality you traveled from. This implies that the universe isn't deterministic, even though
in our scale it projects the illusion of determinism.