By Kirk Miller What was Stephen Hawking thinking? A new exhibit at the Science Museum of London hopes to answer that question by looking at one of his old blackboards. Hawking, the revered theoretical physicist, cosmologist and author who passed away in 2018, kept a blackboard “smothered with cartoons, doodles and equations” from a conference on superspace and supergravity he arranged in 1980, according to The Guardian. Are there lost secrets and amazing discoveries amongst these doodles and in-jokes? The best bet to decipher the blackboard might be if any of the attendees from that long-ago e…