Who are Einstein and Picasso?

Einstein dies and goes to heaven. Saint Peter says, "You look like Einstein, but you have no idea the lengths some people will go to, to sneak in. Can you prove who you really are?" Einstein ponders for a few seconds and asks, "Could I have a blackboard and some chalk?"
Saint Peter snaps his fingers and a blackboard and chalk instantly appear. Einstein proceeds to describe with arcane mathematics and symbols his theory of relativity. Saint Peter is suitably impressed. "You really are Einstein! Welcome to Heaven!"

The next to arrive is Picasso. Once again Saint Peter asks for his credentials. Picasso asks, "Mind if I use that blackboard and chalk?" Saint Peter says, "Go ahead." Picasso erases Einstein's equations and sketches a truly stunning mural with just a few strokes of chalk. Saint Peter claps. "Surely you are the great artist you claim to be! Come on in!"

Then Saint Peter looks up and sees George W. Bush. Saint Peter scratches his head and says, "Einstein and Picasso both managed to prove their identity. How can you prove yours?" George W looks bewildered and says, "Who are Einstein and Picasso?" Saint Peter sighs, "Come on in, George."