> how do you know that gravity really exists?

Well you don't. All we got are models that are used to predict it's effects and they work pretty good.
I wonder what is meant when someone says 'Electricity exists'. We as a race know enough about nature
to build computers but does that imply that electricity exists?

> I stand by religion because it can be proven in a different way.

I think this site escpecially the thread "Scripture: History or Fantasy?" is evidence enough to
prove that proof is a contested word ;-) It is the goal of many to put forth proofs that god exists/
religion makes sense so it is proven and above criticism. Ironically many creationist argue
that Darwin just put forth a theory that could be wrong. A theory that can not be falsified is not
a good theory. If I say: "The word apple is red" then there is no way to falsify that claim. If
I say: "Apples are red" a single green apple will prove me wrong.