This is an important topic that bleeds over into epistemology / canonics, but given how closely it is related to atomism it needs a thread here. I will try to go through the forum and crossreference threads to Democritus' statement about "....in reality, only atoms and void..." and why Epicurus would not have accepted this viewpoint. At the moment, one of the best discussions of this is in David Sedley's "Epicurus's Refutation of Determinism.
Hard to overstate how critical this paragraph is:
As Sedley says, Epicurus rejects "reductionist atomism," in favor of the common sense perspective: "that there are truths at the microscopic level of elementary particles, and further very different truths at the phenomenal level; that the former must be capable of explaining the latter, but that neither level of description has a monopoly of truth.'