Seconds out for battle over time

BRITAIN has objected to plans that could see Greenwich Mean Time sidelined in favour of a time standard overseen by the International Bureau of Weights and Measures (BIPM) in Paris.

Proposals by the International Telecommunications Union in Geneva have been attacked by British Science Minister David Willetts who spoke of “undercurrents of nationalism” concerning the changes.

Proposals to move away from GMT and the equivalent Coordinated Universal Time (UTC) come because the way these standards are worked out means that UTC has to be adjusted about every 18 months with a “leap second” to stay in tune with GMT. This causes problems with the precise time synchronisation needed for systems such as satellites and mobile phones.

UTC is calculated from an average of atomic clocks around the world and the ITU study group wants to use this information for a new “atomic time” standard or Temps Atomique International (TAI). It will drop the “leap second” and the link with GMT.

However, Mr Willetts, in an attack in the Sunday Times, said we should stick to “real time as experienced by humans”, that is based on the world’s rotation, not energy variations in atoms of the chemical caesium as TAI is calculated. A decision is due to be made in January but Britain has objected to the atomic time proposals.

GMT is traditionally based on the rotation of the Earth. It is midday GMT when the sun is at its highest over zero longitude on the Prime Meridian at the Royal Observatory, Greenwich. This was accepted as the world standard at a conference in Washington in 1884.

This causes problems because the Earth’s rotation is slowing and UTC, the standard since 1972, needs the “leap second” to match changes in GMT.

Britain still refers to “GMT” because the standards are so closely linked.

The history of timekeeping has seen several tussles between France and the UK with France continuing to use Paris Mean Time until 1911. There was even disagreement on the names of the 1972 standard. Officials could not agree on an English acronym (UCT) or a French one (TUC), so went for UTC.

As recently as 1999 France planned to mark the Millennium with a project for a line of trees down the country’s meridian line.

BIPM spokeswoman Felicitas Arias said: “France was compelled to adopt this reference and it’s a little bit as if we are coming back to that dispute today. France did not want to accept that the standard references were in England, now it seems to be the contrary.”

Greenwich Observatory spokeswoman Sheryl Twigg said: “There’s always been this debate about atomic time and GMT, or as it is now, UTC, which is basically the same. If this is adopted time will move away from the way we naturally experience the day.”

Ms Arias said the UK objections were because losing the leap second meant the difference between official time and GMT would increase but, she said:

“This is not really true. It will be about a minute a century and no one will care.” However, it is true “GMT will become less accurate and less relevant”.

Under TAI, she said occasional large adjustments would be needed. But an hour adjustment would be needed only every 6,000 years – and people were used to clocks going forwards or back.

Ms Arias said the BIPM did not want the change for nationalistic reasons – as it was an international body – but because leap seconds caused problems.

“We only keep the system linked to the Earth’s rotation because we are used to it; there are many applications with a big impact on everyday life that want to get rid of this nuisance. Yes, we should consider the social and cultural impact of such decisions, but what’s more important, progress in technology or national pride?”