We don't know the ultimate source of gravitation, and the answers to your questions will have several Nobel Prizes attached to them. Regardless of what gravitation is or what produces it, we know very well by now how it works. As many others have mentioned already, GR is our most advanced and...
Here goes nothing...
Hilbert space is a vector space.
A vector space is an algebraic structure that contains objects called vectors (in quantum mechanics, these become the wavefunctions), which display the properties of vector addition and scalar multiplication.
An algebraic structure...