科学家建成更加精确的原子钟

MELISSA BLOCK, HOST: This is ALL THINGS CONSIDERED from NPR News. I'm Melissa Block. A team of scientists claims they've created the most advanced clock ever. They say this clock is so precise it would neither lose nor gain one second in about five billion years of continuous operation. NPR's Nell Greenfieldboyce reports on why anyone would want a timekeeping device this powerful.

NELL GREENFIELDBOYCE, BYLINE: At the most basic level, to make a clock you just need something that repeats itself over and over in a way that lets you count off equal increments of time. Like, say, the sun rising and moving across the sky or the phases of the moon.

ADAM FRANK: Those were literally the first clocks for people.

GREENFIELDBOYCE: Adam Frank is an astrophysicist at the University of Rochester who wrote a book called "About Time." He says for ages telling time by the sun was good enough.

FRANK: If you asked somebody a thousand years ago what time is it, the best they'd be able to do is say lunch maybe?

GREENFIELDBOYCE: But when societies got more complicated, mechanical clocks took off. They were in bell towers, then in homes. Clock technology advanced from merely ticking off the hours to keeping track of every minute. It was a huge change for humanity that today we take utterly for granted.

FRANK: When you're waiting for the bus and the bus is late, you feel those five minutes. The bus was supposed to be here at 9:55. It's 10 - oh my God, what's wrong this system, right? You feel those minutes as boredom, as anger, but that's only because you have a device that allows you to count off those minutes.

GREENFIELDBOYCE: These days, though, we can do way better than count off minutes or even seconds. Since the 1960s, official timekeeping has been based on the natural oscillations of atoms. And so-called atomic clocks just continue to improve. A few years ago, a team unveiled a clock that would neither gain nor lose one second in about 3.7 billion years. You'd think that would be good enough, but physicist Jun Ye says no, it's not. He works at the National Institute of Standards and Technology. This week, he and his colleagues published a report in Nature that describes an even more precise clock - one that would neither gain nor lose a second in five billion years.

JUN YE: Many people would say, well, one second in five billion years - how is that going to impact our life? It's not. It's going to be irrelevant to what we are doing in daily life or in the society. Well, that's actually not true.

GREENFIELDBOYCE: He says all kinds of technology we depend on - computer networks, GPS systems - is only possible because of the precision timekeeping of atomic clocks, even though the first atomic clock makers could not have predicted where their inventions would lead.

YE: Nobody would have imagined everybody can have a cell phone and know exactly where you are.

GREENFIELDBOYCE: His team's new clock is the most precise and stable in the world. It uses laser light to trap a few thousand atoms of a metallic element called strontium. Scientists can detect the oscillations or ticks of these atoms - 430 trillion per second. The team already has upgrades in mind to improve the clock's performance. Ye says maybe they'll be able to build a clock that is accurate to one second in 50 billion years or even way better than that.

YE: Where does it end? Does nature place a fundamental limit of how good you can keep up, you know, you can keep the time? And as far I can tell at the moment, I don't see the limit.

GREENFIELDBOYCE: He says future super clocks could help scientists explore the bizarre quantum world or probe the space-time fabric of the universe. He says imagine a network of immensely powerful clocks distributed around the Earth. If a black hole explodes in a distant galaxy...

YE: ...there will space-time ripples - they'll call it gravitational waves - will propagate. And we can actually just listen to the clock and they would know the heartbeat of the universe.

GREENFIELDBOYCE: That's the kind of thrill that keeps clockmakers ticking. Nell Greenfieldboyce, NPR News.