One could in principle make the same second statement about anything
beyond one's immediate conscious awareness: (1) the universe before ten
billion years ago, (2) the earth before ten thousand years ago, (3) human
history before one hundred years ago, (4) one's experiences before ten minutes
ago, (5) other people, (6) the physical world beyond one's consciousness, etc.
Young earth creationists presumbly don't believe in the first two, solipsists
presumably don't believe in the third and fifth (Do any of you know any I could
actually interact with? I'd love to meet one, at least if he or she wouldn't
totally ignore me.), amnesiacs might not believe in the fourth, and some
idealists perhaps would not believe in the sixth (last) one (Any such idealists
out there willing to clarify your beliefs?). I myself could say that I don't
believe in a classical physical world and in spacetime in the most deeply
fundamental sense, because I believe that the physical world is quantum, and
that spacetime is just an appoximate concept with something more fundamental
underlying it that we don't yet understand. But certainly I would accept that
all of the six items above are, within their limitations, very good approximate
theoretical concepts, and I would be reluctant to say any of them are "facts"
without saying that they all are.