"Is this an announcement of a fact, or of faith? If it is a fact how do scientists go about proving it? How real is something that may have existed billions of years ago?"
It is the statement of a conclusion derived from reasonable inference. No one has ever seen an electron. No one will ever see an electron. In science, by which I mean actual science and not the comic- book version promulgated by various religious authorities, "fact" does not imply "absolute certainty."
Instead "fact" means something so well supported by the existing evidence and models that it would be ridiculous to withhold at least tentative acceptance of it. The Earth is not flat; The Earth is not the center of the universe; electrons exist; objects at rest tend to stay at rest; objects in motion tend to stay in motion; it is gravitation and not angels which causes the orbits of planets about stars, of stars about stars, and of galaxies about each other; evolution has occurred and continues to occur; the entropy of an isolated system does not decrease; the earth's atmosphere is mostly nitrogen (even though no one has ever seen a nitrogen atom).
