if the universe is infinite ...., page-138

Your first point is so true - we have hardly scratched the surface. It's amazing to hear some people say we know all there is to know - what utter nonsense. More accurately we have many theories about the Universe and beyond. Those theories inside our Universe can and are being tested. For example the Planck satellite being developed by ESA may solve some of the mysteries.

Re your 2nd point about what was there before the big bang? It's yet another "meanigless" question like the one about what's the Universe expanding into. All physics, space, time as we know it cease to exist and so we can't possibly comprehend what was or is there, let alone devise experiments to test any theory. We can only test theories in our Universe, at least until we enter hyperdimensional space. Trouble with that time might not exist so how does one "live" there? All philosophical or metaphysical.

Anyway, the current explanation to how the big bang started is it started from an Inflation Universe. Here the Universe starts out as a rapidly expanding bubble of pure vacuum energy. During the rapid cooling process, the potential energy in the vacuum is converted to highly energetic matter and radiation. The Universe heats up quickly and the big bang happens.