Re: Basic Science Question - "fabric" of space
General Relativity doesn't explain why gravitational mass curves space-time. It just describes how to calculate the effect based on a set of assumptions about how energy-momentum and space-time interact. Energy and momentum are seemingly joined at the hip just like space and time. Background-independent string theory or loop quantum gravity might eventually offer an insight why the Universe is the way it is, but they haven't as yet.
"Sans le canard de Vaucanson vous n'auriez rien qui fit ressouvenir de la gloire de la France." -- Voltaire -- Flip flap!