The universe’s greatest mystery, according to someone who has spent a fair amount of time exploring the great mysteries, is women.

Reuters reports that famous physicist Stephen Hawking, asked what he thinks about most, replied: "Women. They are a complete mystery."

It’s an answer that has been given before, by many a less accomplished thinker.

The author of “A Brief History of Time” will celebrate his 70th birthday Sunday by participating in a public symposium, "The State of the Universe," at the University of Cambridge’s Centre for Theoretical Cosmology.