this kind of things train you up for GP.
Firstly about the professor story. this kind of things have no end. the professor could be like real hardcore and say : "I could go for an operation to open up my skull to show you my brain, it does exist, unless u do not trust ur sense of sight"
Well, thats the ideal thought, just to prove the point, that no operation, none, can ever prove to people that God exists.
That was from a scientist's point of view.
Now from the Christians'.
One of our five senses is touch, meaning feel. And we can feel God. So God exists.

my point of view is the top one, and the bottom one comes from my friend. didnt wanna post but tagboard's not working >.<