The Voyager Golden Record carries a small sample of uranium on its cover, placed there so that whoever finds it can measure the decay and work out how long it has been drifting — a built-in clock for a message engineered to last around a billion years.

Voyager’s Golden Record cover carries a tiny uranium-238 reference whose decay can reveal elapsed time, independently checking its pulsar-map date. The post The Voyager Golden Record carries a small sample of uranium on its cover, placed there so that whoever finds it can measure the decay and work out how long it has been drifting — a built-in clock for a message engineered to last around a…