格林尼治时间或被原子时取代

格林尼治时间以英国首都伦敦市郊格林尼治天文台命名，作为全球通用的时间参考标准已使用120多年。如今，这一以地球自转为依据的“世界时”可能由以原子振荡周期为依据的“原子时”彻底取代。上世纪70年代一项国际协议确定世界时和原子时两种时间计量系统。世界时受地球自转速度减缓影响，有一定误差；原子时用原子能级跃迁振动频率计时，1000万年误差1秒，相对精准。一些研究人员呼吁废除时间计量系统的“双轨制”，以原子时作为单一计时标准。50多名研究人员11月3日至4日在伦敦市郊开会，讨论相关议题。国际电信联盟定于明年1月在瑞士日内瓦表决是否以原子时替代世界时。不过，这一提议无疑会伤害英国人的“国家自豪感”。英国有官员表示，我们应该以地球自转为依据，依照人们所感知的真实时间来计时。

For more than 120 years, Greenwich Mean Time (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, despite protests from Britain.

The two-day meeting of about 50 experts at a country house north-west of London, under the aegis of the prestigious Royal Society, on Thursday and Friday will look at some of the issues involved.

Predictably the question has hurt Britain's national pride - particularly when the British believe their old rivals France are leading the push to change from GMT to the new time standard.

"We understand that in Britain they have a sense of loss for GMT," said Elisa Felicitas Arias, director of the time department at the France-based International Bureau of Weights and Measures (BIPM), which pushed for the change.

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 had 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.

Tiny variations

But the 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," Dr Arias said.

"We are starting to have parallel definitions of time. Imagine a world where there were two or three definitions of a kilogram."

The meeting in London will look 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, and there would need to be "leap minutes" a couple of times a century to bring the two in line.

The proposal would then formally be voted on in Geneva.

Damaged pride

The potential loss of GMT has prompted soul searching in the British press, particularly at a time when the country is itself considering switching to British Summer Time, one hour ahead of GMT, on a permanent basis.

The Sunday Times said GMT had "symbolised Britain's role as a Victorian superpower" but that "just as that role has inexorably diminished, so GMT itself could in effect disappear".

British science minister David Willetts has opposed the plan, saying it has become more than just a scientific row.

"This is primarily a finely balanced scientific argument but I do detect undercurrents of nationalism," he said.

"Britain's position is that we should stick to real time as experienced by humans, which is based on the Earth's rotation, not atomic clocks.

"Without leap seconds we will lose contact with the reality of Earth's rotation. Eventually our midnight would happen at noon."

China meanwhile is said to oppose the change on the grounds that its astronomers want to retain Earth-rotation-based time.