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Strontium atoms floating in the center of this photo are the heart of the world's most precise clock. The clock is so exact that it can detect tiny shifts in the flow of time itself. Courtesy of the Ye group and Brad Baxley/JILA hide caption

Strontium atoms floating in the center of this photo are the heart of the world's most precise clock. The clock is so exact that it can detect tiny shifts in the flow of time itself.

"My own personal opinion is that time is a human construct, " says Tom O'Brian. O'Brian has thought a lot about this over the years. He is America's official timekeeper at the National Institute of Standards and Technology in Boulder, Colorado.

To him, days, hours, minutes and seconds are a way for humanity to "put some order in this very fascinating and complex universe around us."

We bring that order using clocks, and O'Brian oversees America's master clock. It's one of the most accurate clocks on the planet: an atomic clock that uses oscillations in the element cesium to count out 0.000001 second at a time. If the clock had been started 300 million years ago, before the age of dinosaurs began, it would still be keeping time — down to the second. But the crazy thing is, despite knowing the time better than almost anyone on Earth, O'Brian can't explain time.

"We can measure time much better than the weight of something or an electrical current, " he says, "but what time really is, is a question that I can't answer for you."

Maybe its because we don't understand time, that we keep trying to measure it more accurately. But that desire to pin down the elusive ticking of the clock may soon be the undoing of time as we know it: The next generation of clocks will not tell time in a way that most people understand.

The New Clock

In fact, this knot of wires and lasers actually is the clock. It's spread out on a giant table, parts of it wrapped in what appears to be tinfoil. Tinfoil?

"That's research grade tinfoil, " says Travis Nicholson, a graduate student here at the JILA, a joint institute between NIST and CU-Boulder. Nicholson and his fellow graduate students run the clock day to day. Most of their time is spent fixing misbehaving lasers and dealing with the rats' nest of wires. ("I think half of them go nowhere, " says graduate student Sara Campbell.)

At the heart of this new clock is the element strontium. Inside a small chamber, the strontium atoms are suspended in a lattice of crisscrossing laser beams. Researchers then give them a little ping, like ringing a bell. The strontium vibrates at an incredibly fast frequency. It's a natural atomic metronome ticking out teeny, teeny fractions of a second.