Gravitational singularity, quantum mechanics, the many-worlds interpretations. These were the things he might have mentioned had his wife asked him "what are you thinking about?"

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The answer most probably never was 'nothing'.

Stephen William Hawking of Oxford, Oxfordshire, England has passed away, or were he able to explain to us now, he's just slipped into another facet of spacetime and likely one where his Lou Gehrig's disease doesn't exist and he's free to run, jump, and yell for joy.

If you knew how to do the math, you could probably see him waving to you from there.

Hawking first came to prominent notice as a world-class physicist in 1993 when he co-edited a book on Euclidian Quantum Gravity, subsequently publishing several articles about black holes and the big bang. He was widely known and respected prior to thatby those in the higher reaches of physics academia, going back to the '70s in his undergraduate and graduate study years.

Wherever you are, Stephen Hawking, rest in peace.