CORRESPONDENCE 17 December 2024 In 1993, as part of Nature’s series of ‘Hypotheses’ articles, astronomer J. Richard Gott III proposed that, assuming the Copernican principle — no observer of the Universe is special — a random observer is likely to encounter an object during the mid-95% window of the object’s lifetime. The length of time for which something has been observable in the past is thus a rough measure of how long it is likely to be observable for in the future (R. J.