The Stuff Forever (or of nothing) that could no longer contain itself as a singularity, changing its form and 'banging' into a universe, obviously met a constraint that was being built up to in its wave form—since matter and spacetime came after the 'bang', as a low probability, but guaranteed (eventually), event, so we can go on to say about the only possible wave state of the Forever Something as the how and why of the 'bang', as well as the 'what' of the waves. Yes, it is a tall order, but we know that it could only do what it did, since all action is only from itself, there being no external directives possible for what is itself causeless. So, we expect to get 'lucky' in finding the only possible wave equation.