I am in bewilderment with the first law of thermodynamics. I am not doubting its validity but my conscience feels a bit hazy about it.
Energy is equivalence of mass. E=mc^2. According to Big Bang theory, the was millions millions millions millions tumss mass was packed in a volume of about your fist or maybe less than it. So as it exolodex mass and energy gets discreted and we don't know yet how big bang started.