Because it can be demonstrated that in the real world 2+2=4. That's the only reason we know it's true. If I say the stove top is hot, and you don't believe me, touch it! And you will know.
You can't "prove" the entire creation wasn't created 5 minutes ago with everyone's memories created as the now are
That's right. I can't prove it and neither can you prove that the world was created, let alone by something you call God.
We can't "prove" any of the basic axioms of logic or the basic axioms of Euclidian geometry. But we accept them as true.
Because they can be shown to be true physically (on on paper, geometry). Otherwise they are theorem.
Of course I can. It's been established for some time now. The Hoyle eternal steady state theory of the universe was rejected over 50 years ago. Science has established that the universe had a beginning. Whether one calls it the "big bang" or whater we know the Universe had a beginning and no modern theory of physics or cosmology can get around the singularity. Further we know that whatever begins to exist has a creator. The universe began to exist thus it had a creator. That creator is God. The Kalaam cosmological argument is irrufutable proof of the existance of God. Backed up by the best modern science has to offer.