It seems that bandying mathematical formulae about gets nowhere significant.
Here is a non-mathematical suggestion:

At the time of the Big Bang we are told that all the matter and energy of the Universe occupied a very small area. The energy of the BB forced this matter and energy to expand. GPE is simply the equal and opposite force which, provided there were no "interference", would tend to bring everything back together.

Of course, this implies acceptance of the BB, the expanding Universe and equal and opposite forces, but, heck, where would we be without a little "faith"?

BTW, preearth, it's good to see you haven't deserted us. It's been very quite around here, and you do tend to liven things up. smile

There never was nothing.