Shortly before Stephen Hawking died in March, the legendary cosmologist was still thinking big.
The final paper he contributed to, titled “Black Hole Entropy and Soft Hair,” concerns what theoretical physicists call the information paradox — what happens when an object falls into a black hole?
Days before Hawking died, co-authors Malcolm J. Perry, Sasha Haco and Andrew Strominger were working on the paper. Perry called Hawking to give him an update, unaware of how ill he was. It may have been the last scientific exchange Hawking had. “It was very difficult for Stephen to communicate and I was put on a loudspeaker to explain where we had got to. When I explained it, he simply produced an enormous smile. I told him we’d got somewhere. He knew the final result,” Perry told The Guardian.
The physicists show in their paper that a black hole’s entropy may be recorded by photons that surround the black hole’s event horizon, the point at which light cannot escape the intense gravitational pull. They call this sheen of photons “soft hair.” You can see the paper for yourselfhere.
Hawking’s research played a key role in our current understanding of black holes. His book A Brief History of Time brought cosmology to a general audience in 1988 and became an international best-seller.
Hawking spoke with a computer-generated voice for decades after losing his voice due to Lou Gehrig’s disease, a neuromuscular disease also known as ALS. He was diagnosed as a 21-year-old graduate student in 1963, and doctors gave him less than three years to live. When he died at age 76, he was interred at Westminster Abbey in London between the remains of Isaac Newton and Charles Darwin.