Perhaps I should have thought about this years ago – when I was surrounded by physicists and cosmologists and the like, and so could have got an answer: but I didn’t – until I started reading Lee Smolin‘s Time Reborn: From the Crisis in Physics to the Future of the Universe.
Here’s the issue: as Smolin states, nothing stops gravity. You cannot muffle it or block it.
Then let us think of an object with mass – it sends out “gravitons” (we assume – these have never been detected of course) and these exert a force on every object they meet. If we go one step further and suggest that the universe is infinite, do we not end up with our massive body being the source of an infinite amount of force and hence an infinite amount of energy?
Getting into murky waters here – but as I understand it, physics gets round this with something of an accounting trick: bodies with gravitational potential energy are deemed to have negative energy and so all that happens is that our massive body converts this negative energy into a positive energy and the total amount of energy in the universe is unchanged.
Is that really it?