From The Sunday Times
February 8, 2009
Laser clocks stay spot on for 2bn years
SCIENTISTS have developed a new generation of clocks that can keep time without missing a beat in almost 2 billion years.
They are so precise that they will allow satellites to track moving objects to within less than a metre. This could eventually lead to automated cars and an autopilot accurate enough to land a plane without human intervention.
Laboratories in the US, Britain, Germany, France and Japan are now competing to make a clock capable of measuring time so accurately that it would not have lost a second since the Big Bang 13.7 billion years ago. Scientists believe it will be built within a decade.
The new devices are known as optical clocks because lasers “look at” and measure the frequency with which electrons in atoms vibrate. This enables them to divide time into ever tinier increments.
The most advanced clock, created by researchers at the National Institute of Standards and Technology (NIST) in Boulder, Colorado, measures the vibrations of electrons in mercury ions and can go 1.7 billion years without missing a beat. Previously, the most accurate devices were atomic clocks which can measure to an accuracy of one second over 80m years. A normal wristwatch, by contrast, will lose about 15 seconds a month.
The international committee for weights and measures, which is based in Sèvres, in Paris, and sets universal time, is planning to replace its atomic clocks with optical ones by 2020.
Dr Elise Arias, executive secretary of the committee for time and frequency, said: “Optical clocks are the future. They are a very exciting development and we will come to a conclusion on them by 2015.”
The most exciting developments are likely to come in the field of global positioning systems \, which track planes, ships and cars.
GPS devices receive microwave signals sent by satellites and, by measuring the time these take to arrive, can pinpoint the location of an object on Earth to within 10 metres.
Scientists believe that by installing optical clocks on satellites they will be able to refine the level of accuracy to within less than a metre. Such precision could lead to automated motorway driving or landing aircraft on autopilot.
The technology could also enable satellites to map ice caps and mountains more accurately and monitor areas near earthquake faultlines for signs of movement.
The European Space Agency is considering fitting an optical clock to a satellite as part of its cosmic vision programme, which will explore ways of using space for scientific advancement from 2015 to 2025.
Dr Helen Margolis, principal researcher at the National Physical Laboratory, and her colleagues in Teddington, in southwest London, are pioneers of the new technology.
She said: “It is mind- boggling when you think about the accuracy we are getting today. “If you could put these clocks in space that would be useful for measuring the thickness of the ice caps in the Arctic and Antarctic. We probably haven’t even thought of some of the applications these clocks will have yet.”
Scientists have an even more ambitious use for optical clocks. They hope they will enable them to test the most basic laws of physics.
Till Rosenband, a physicist at NIST said: “It would be testing the basic properties of the cosmos. We should be getting to an accuracy where perhaps you could start seeing changes in the basic physics. It’s a strange thing to wrap your mind around. We haven’t seen anything like this yet but it’s exciting to look for.”
The optical clocks will eventually replace atomic clocks, which have provided the standard measure of time since 1967. Atomic clocks, first created by Louis Essen, a British physicist, in 1955, measure microwave radiation emitted by vibrating caesium atoms.
In 1989 Steve Chu, energy secretary in the Obama administration, improved the technology while at Stanford University using caesium atoms to create an “atomic fountain”, which still forms the basis of the most accurate atomic clocks today.
In 2001, NIST developed the first optical clock using lasers instead of microwaves.
It was further improved by British scientists at the National Physical Laboratory in 2004, and last year scientists at NIST developed a clock 21 times more accurate than the best atomic equivalent.