Universal time could clock out by 2022

June 11, 2004

Experts are planning to break the age-old link between measuring the passage of time and the motion of the Earth and Sun.

Increasing conflict between the need for precision in the modern age and the unreliability of the natural clock of the solar system is pushing the existing international convention towards breaking point.

The practical measurement of the passage of time has always linked the rotation of our planet and its progress around the Sun to the count of years, days and seconds.

But Dennis McCarthy, director of the US Naval Observatory in Washington, which is responsible for keeping time in the US, told the Transits of Venus conference at the University of Central Lancashire that this could end in 2022.

He said a new system that would provide the level of constancy and accuracy demanded by today's global communication, navigation and computer networks would be discussed by the government-level agency that co-ordinates global time in September.

"The Earth is not a very good timekeeper," he said.

Coordinated universal time, which is kept to worldwide, uses atomic clocks to measure out each second but has to be corrected increasingly frequently to keep it in tune with the solar system.

Leap seconds are added to many years to compensate for the unpredictability of the Earth's rotation, which is the result of a host of factors, including poorly understood processes in its interior, continuing changes in its shape in wake of the last ice age and the drag of the moon.

The planet has been gradually rotating more slowly - though since 1998 it has marginally speeded up - prompting an increase in the number of leap seconds required to keep clocks and nature in synch.

The International Telecommunications Union is to consider a proposal from a special rapporteur group that would get rid of leap seconds in 2022 and provide a continuous time scale to meet the needs of modern society.

The price would be to put our clocks at odds with the unpredictably of the earth.

Dr McCarthy said: "If you drop the leap second, you lose the connection between clock time and the rotation of the earth and that means given a long enough period of time - thousands of years - your clock would say noon when it looks like the middle of the night."

steve.farrar@thes.co.uk

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