Voyager Golden Record's Built-In Uranium Clock Will Mark Time for a Billion Years

In 1977, humanity launched two small vessels into the dark between stars, and on each one placed a golden record meant for eyes and ears unknown. To answer the question that no radio signal could — when did this come from? — scientists embedded a fragment of uranium in the cover, a radioactive clock patient enough to outlast civilizations, precise enough to mark a moment across a billion years. It is perhaps the most quietly profound act of communication our species has ever attempted: not just a message, but a timestamp written in the language of physics itself.