Now you are talking about introducing extra energy. In the gravity creates gravity situation, where does that come from?
If you don't introduce energy nothing happens anywhere in the universe. You are a bit like the QM joke waiting for the girl to appear on your barstool
So lets do this again at a layman level, a flat empty section of vacuum of space is exactly that flat and empty. Virtual particles may briefly pop in and out of existence but on the whole the section remains flat and empty.
We can describe gravity as particles responding to the presence of spacetime curvature, or we can describe them as resulting from the exchange of virtual gravitons. It doesn't matter how we do it we need to introduce Energy into the section of spacetime to curve it and make them appear.
So lets slowly introduce some energy some way (say put some small energy there say an electron) enough energy to create a single graviton. Nothing exciting happens the graviton is our force carrier and the only thing it can exert a force on is thing that has our energy and so it gives mass to that thing.
The problem comes when we introduce a bit more energy and we get a second graviton. Now both our gravitons react with with whatever energy source we introduced but they will now also see each other as each graviton carries energy they react on each other. Nothing unusual there you would know it from electrons repels an electrons, protons repelling protons etc. The naive prediction would be that the two gravitons should therefore clump together creating even higher energy density at a specific point and given enough gravitons the whole thing could go into runaway with just the interaction of the gravitons creating more gravitons.
It's a horrible simplification but it will do for now. Pick the story up from there and explain your problem?
