In 2013, a masters student in physics named Paul Erker went combing through textbooks and papers looking for an explanation of what a clock is. “Time is what a clock measures,” Albert Einstein famously quipped; Erker hoped a deeper understanding of clocks might inspire new insights about the nature of time.

But he found that physicists hadn’t bothered much about the fundamentals of timekeeping. They tended to take time information for granted. “I was very unsatisfied by the way the literature so far dealt with clocks,” Erker said recently.

The budding physicist started thinking for himself about what a clock is — what it takes to tell time. He had some initial ideas. Then in 2015, he moved to Barcelona for his doctorate. There, a whole cadre of physicists took up Erker’s question, led by a professor named Marcus Huber. Huber, Erker and their colleagues specialized in quantum information theory and quantum thermodynamics, disciplines concerning the flow of information and energy. They realized that these theoretical frameworks, which undergird emerging technologies like quantum computers and quantum engines, also provided the right language for describing clocks.

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