Leibniz said the universe is built from infinite tiny substances that never interact

In his 1714 Monadology, Gottfried Leibniz argued reality is made of "monads," simple substances with no parts and, in his words, "no windows through which anything could come in or go out." Since nothing can causally affect a monad from outside, Leibniz proposed every monad instead unfolds in a pre-established harmony, a cosmic synchrony he credited to God winding up every clock to match from the start.

— Gottfried Wilhelm Leibniz, Monadology — 1714