If the Universe is flat and the total energy of the universe can be zero (we don't know if it is, but it can be) then is it possible that all matter in the universe could have emerged from nothing? If so, that what is the positive energy of the matter compensated by to yield a total of 0 in result, and why does is contradict the human logic so much. I know, matter can appear and annihilate in quantum fluctuations and all... but even this thing is kinda brain-crashing when you try to grasp it, to say nothing about applying the same idea to the whole universe.
Just in case, sorry for my english, it's not the native language for me. Thanks to all in advance.
Edit: wanted to add 'cosmology' and 'universe' tag, but there are no such (( this is so emarrasing for this kind of Q&A site.