True, we don't know how to make a photon drive that is very strong except by using antimatter. But, if we could make enough matter to matter it will probably be half antimatter, and the problem is solved.
"What you're missing is that mass and energy are the same thing. E=mc<sup>2</sup>. If you could somehow convert matter 100% into energy (That's going to be photons—and the only way we know to do this is to combine matter…"
"A photon drive works only by radiation pressure. That's very weak. Using energy to create particles which have mass would theoretically enable a much stronger thrust. Unless I've missed something fundamental, that should allow a much…"