How long is a second? It's a question most of us have never even really considered, but one that has captivated physicists for centuries, not least because the most accurate answer to that question promises to reveal the deepest truths about the makeup of our universe. 

Jun Ye is a Chinese-American physicist and clockmaker extraordinaire at the University of Colorado, in the U.S. 

He has built an optical lattice clock, a cloud of 100,000 strontium atoms, which is inching closer to redefining the second. 

Ye's clock is so precise that it neither gains nor loses one second in some 15 billion years, roughly the age of the universe. 

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