Dave, how many times do we have to show you that gravity does exist, and it's measurable. We can measure the force of gravity to levels Newton could never have dreamed of.
By the way, have we mentioned that Newton was a creationist Christian?
Dave, gravity only pulls (as far as we can tell, currently), it doesn't push. And celestial bodies (well, everything, for that matter) has inertia (which has nothing to do with gravity). Remember "an object in motion tends to stay in motion, and an object at rest tends to stay at rest"? That's practically the definition of inertia.
Stars, galaxies, nebulae, black holes, all continue in the paths they are traveling on because of inertia. Galaxies are billions of stars orbiting around a central point of gravity, (usually believed to be a black hole, but scientists still aren't 100% sure that's the case for all galaxies, as the centers of galaxies are so bright we can't see into them, typically) which keeps them from continuing in a straight line away from all the other stars. Gravity is what keeps them in orbit around a central point, just like the moon orbits the earth, the earth orbits the sun, and the sun orbits the center of the Milky Way.
There's a topic I want to discuss, but I won't just yet until I see that you can distinguish better between secular and Creationist cosmologies.