Interesting thread. I came to it and this forum because I wanted to know if the question ( 'WHY or HOW mass/energy curves space-time?') had ever been answered. And, it appears not, though this is only the beginning of my search.
I'd just watched a fascinating talk by Noam Chomsky, which amazingly had nothing to do with politics. He addresses the limits of human knowledge and discovery and concludes that what we know of nature, which - though quite 'useful' to us - is nontheless only a fraction of 'reality' and that there are certain 'things' we will never understand because it is simply outside our capacity. Kind of like we'll never be able to 'see' 4 + dimensions of space.
I immediately objected and siezed upon the fact that Einstien explained what gravity 'is' after Newton explained what gravity 'does'. Newton left the former question in the hands of God and was convinced it was unknowable. He didn't or couldn't anticipate General Relativity. But, now that we know what gravity does and what it is: the curvature of space-time by energy/mass. The next question, 'why does space time react thus in the presence of mass/energy?'; tries to dig a bit deeper.
And so, I wonder if this is one of those things that falls outside the capacity of human understanding, knowledge, discovery etc.
Then again maybe the answer is as simple as imagining someone pushing there way into a crowded elevator. Their very presence upsets or warps the configuration of passengers already present. (!?) But then the question becomes what is the 'fabric' of space-time or, sticking with the metaphor, who/what are the 'passengers'?
