Question:
What causes gravity? I know about Universal Gravitation, but
what, other than a formula, really makes two things attract each other?

Replies:
Your question is very profound. We simply do not know the cause.
What we know is that the Gravitational constant G that appears in the
gravitational force equation is fundamental. We have no theory that gives us
its value. Aside from the actual size of the gravitational forces, the fact
that a mass distorts the space around itself by producing a field at points
distant from it is one of most profound assumptions of modern science. The
electric and magnetic fields are the other familiar fields. With these we
have detected the quanta of radiation and have measured their propagation in
space. We have not yet detected the graviton for gravity, so we do not yet
know how it is propagated in detail. We know in some detail how gravity
works, but we do not have a clue about what causes it. For that we would need
some theory that would predict at least the value of G.

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