The force of gravity is defined by Newton's formula:
In this formula, F is the force of gravity, G is a constant (the Gravitational Constant) which can be measured, m1 and m2 are the masses of the two objects in question, and d is the distance between them. And there you can see that gravity follows the inverse square law. Nice!
Okay, now the brilliant Stephen Hawking has just been quoted as saying, "Because there is a law such as gravity, the universe can and will create itself from nothing." Clear enough. So we have gravity (given) and we have nothing (given), so let's put it in the formula and see what we get.
F=((6.67300 × 10-11 m3 kg-1 s-2) x 0 x 0)/0. The answer? Yeah, I don't think we need a calculator to figure that out. Not so brilliant!