Q. Why is Stephen Hawking so good at air guitar?
A. Because he has excellent string theory.
Stephen Hawking's Air Guitar Skills
Explanation
This is a play on words. 'String theory' is a physics concept, but it sounds like 'string' which is what's on a guitar. Stephen Hawking was a famous theoretical physicist, so the answer ties his field of expertise with the action of playing the air guitar.
Big Al
Thumbs up from the scientists and engineers who got it.