This upper limit, of earth at our feet is visible and touches the air, but below it reaches to infinity
XenophanesThe Gods did not reveal, from the beginning, all things to us, but in the course of time through seeking we may learn & know things better. But as for certain truth no man knows it, nor shall he know it, neither of the Gods nor yet of all things that I speak. For even if by chance he were to utter The Final Truth, he would himself not know it: for all is but a woven web of guesses.
Xenophanes