This Month in Physics History January 1965: Roger Penrose’s Seminal Proof of Blackholes The eminent physicist Roger Penrose won the 2020 Nobel Prize in Physics “for the discovery that black hole formation is a robust prediction of the general theory of relativity,” sharing the prize with Reinhard Genzel and Andrea Ghez, “for the discovery of a supermassive compact object at the center of our galaxy.” But the rough concept of a black hole dates back to the 18th century, before Albert Einstein had even formulated his general theory of relativity and before Penrose's discovery in 1965. British astronomer John Michell wrote a foundational paper in November 1783, later published in the Royal Society’s journal, that was the first to speculate on the existence of black hole-like objects. His intent was to discover a useful method to determine the mass of a star. He thought he could measure how much the speed of light was reduced by passing light from a star through a prism; it ought to be deflected differently because of the reduced energy. He could conceivably compare the refracted images of different stars to determine the difference in their surface gravity, and from that, calculate their respective masses.