[00:06.37]The United States has a new official clock.
[00:10.95]The clock began operating late last year in the American city of Boulder,Colorado.
[00:18.39]Experts say the new clock is so exact that it will neither gain nor lose so much as one second in the next 20,000,000 years.
[00:30.82]Scientists with the National Institute of Standards and Technology developed the new atomic clock.
[00:39.47]The agency is part of the United States Department of Commerce.
[00:44.72]The new clock was built and tested in less than four years.
[00:49.92]It is now being used to measure the official world time, known as Coordinated Universal Time.
[00:58.28]The clock measures time by counting the movements of atoms of the element cesium.
[01:05.72]The natural rate of movement of cesium atoms has been used to measure time since 1967.
[01:13.67]Researchers have found that cesium atoms move back and forth at a rate of almost 9,200,000,000 times in one second.
[01:26.02]The new clock is less than two meters tall.
[01:30.98]This is how it works.
[01:33.31]First, a gas of cesium atoms is released in an empty container.
[01:39.55]All other matter has been removed from this vacuum chamber.
[01:45.06]Six beams of laser light are directed at the center of the chamber.
[01:50.86]The lasers slow the movement of the cesium atoms.
[01:55.83]The lasers force the atoms into a cloud of gas shaped like a ball.
[02:02.36]Two lasers push the ball of gas upward through a passage filled with microwave energy.
[02:10.17]Then,all of the lasers are turned off.
[02:13.69]Gravity pulls the ball of cesium atoms back down through the passage.
[02:20.23]The microwaves change some of the atoms.
[02:24.46]The microwaves cause some of the atoms to move quickly back and forth.
[02:30.62]Another laser causes the cesium atoms to produce light.
[02:35.48]The light is measured by special observation equipment.
[02:40.76]This process is repeated many times while different levels of mierowave energy are used.
[02:49.25]The researchers find a level of ehergy that makes the cesium atoms produce the most light.
[02:57.24]This is the rate of movement used to define one second.
[03:02.36]The new device replaces another atomic clock that has served as the official clock of the United States since 1993.
[03:12.21]The new clock is said to be three times more exact than the atomic clock it replaced |