6 Nov 2011

GMT timekeeping may be no more

6:33 am on 6 November 2011

Scientists have met in Britain to consider a proposal that could eventually see Greenwich Mean Time relegated to a footnote in history.

For more than 120 years GMT has been the international standard for timekeeping, but it is now under threat from a new definition of time itself, based not on the rotation of the Earth, but on atomic clocks.

In January the International Telecommunication Union will meet in Geneva to vote on whether to adopt the new measure.

GMT is based on the passage of the Sun over the zero meridian line at the Greenwich Observatory in southeast London, and became the world standard for time at a conference in Washington in 1884.

France lobbied for Paris Mean Time at the same conference.

In 1972 it was replaced in name by Universal Coordinated Time (UTC) but that essentially remained the same as GMT.

UTC is based on about 400 atomic clocks at laboratories around the world but then corrected with "leap seconds" to align itself with the Earth's rotational speed, which fluctuates.

But the BBC reports that tiny variations between Earth speed and atomic speed have become a problem for GPS, the global positioning systems and mobile phone networks on which the modern world relies. These networks need to be synchronised to the millisecond.

The meeting in London under the aegis of the Royal Society looked at the implications of abolishing the leap seconds and moving fully to atomic time.

That would see atomic time slowly diverge from GMT, by about one minute every 60 to 90 years, or by an hour every 600 years. "Leap minutes" would be needed a couple of times a century to bring the two in line.

The proposal will formally be voted on in Geneva next year.