We say that spacetime is warped by the presence of mass and momentum because the actual measured geometrical features don't match the properties of Euclidean space with location-independent clocks. That's more complicated than our intuition would suggest, but the results still fit a precise coherent picture, General Relativity.
It might be easy to say that matter expands outwards, but it's frequently false. Gravity pulls things together. So the tendency for non-interacting things to expand, implied by the Second Law of Thermodynamics, is definitely
not what accounts for gravity, in fact it has the opposite effect. Gravity+the 2
nd law actually is what accounts for the clumpiness of things, since the energy released as things clump makes more entropy than is lost in the clumping.
Mike W.
(published on 08/17/2009)
