There was nothing before the big-bang. Not nothing as in "the vacuum of space" but really nothing, not even the space for the vacuum to be empty in.
Without gravity, there is no time, so no "before" because time also started when matter existed
Wow Simon!! I think you just answered the age old question of how could God have ALWAYS existed. Based on your answer, there was no time until he created the first matter, hence he was always there since time didn't exist prior. haha