"Nothingness" as you put it...is what? Empty space, correct? Well space is mainly, as you so blatantly put it, nothingness. The universe is made up of empty space and matter, but the question is, what is at the ends of the universe? Most likely more empty space, but where does it end? I just can't get through my head how the universe could be continuous in all directions with no ends...boggles my mind…It’s basically like San Andreas, if you keep flying further and further out over the ocean…you just keep going and going…like the energizer bunny.
Space is not nothingness, it contains matter therefore it contains something. The fundamental difference between ordinary space inside the universe and outside is on average about 3 particles. It's a fundamental difference, space isn't empty, it's what's outside the universe (and thus outside space) which is empty. The end of the universe is merely the edge of matter, as light travels (and other matter) outwards, its very prescence is expanding the universe. You may want to imagine the universe as a gas spreading out in vacuum, the end of the gas is spreading out, and outside the gas is nothing, therefore as the gas spreads out, what can be construed as the gas is essentially expanding. Hope this clears things up