Science is not theology: ideas must be tested against reality. We thought antimatter would fall down, but it's been very hard to test (since gravity is so weak

Science is not theology: ideas must be tested against reality. We thought antimatter would fall down, but it's been very hard to test (since gravity is so weak). In particular, antimatter tends to form as fast-moving charged particles, whose gravitational behaviour is drowned-out by other forces like electromagnetism. Hence we need to form neutral particles, like atoms of anti-hydrogen; and that requires slowing the particles down. Even then, measuring the gravitational effect on such tiny scales requires incredible precision!