[CraigS]

Originally Posted by renormalised

Since the curvature of spacetime in our Hubble sphere is zero (flat), or as close to as it gets, GR is our main concern.

Yes...SR is considered a local theory, whereas GR is a global theory.

Here's a little conundrum for you....according to Einstein, gravity is nothing more than the curvature of space due to the presence of matter.

Err… shouldn't this read: "curvature of spacetime" ?

Originally Posted by renormalised

But how is that matter curving spacetime and producing gravity??

At 'micro-scales', spacetime in our Hubble sphere is thought of as curved within the vicinity of dense matter … how else would we explain the observed effects of gravity in the form of things like lensing, the Shapiro effect, etc ?

If you are really asking what causes gravity, I would require a Nobel Prize for the answer. Are you up for it ?


Cheers