Another unasked question is, "Into what did the expansion go?" If the speck that was to become the universe (singularity) exploded and expanded, it had to expand into some larger space--- something outside of the universe. As with theories about infinite regression (everything came from something else and there was no true beginning), it answers nothing but simply moves the goal posts to places and times that cannot be observed. Thus, by definition, it cannot be a scientific theory.