19/01/2012 10:03 GMT | Updated 20/03/2012 05:12 GMT

Leap Seconds Could Be Scrapped In Global Quest For Accurate Timekeeping

Greenwich Mean Time (GMT) could be effectively scrapped if a vote to redefine time is won in Geneva.

The 200 international members of the Switzerland-based International Telecommunications Union (ITU) will decide on Thursday whether to ditch the practice of adding a 'leap second' onto GMT to compensate for the slowing of the Earth's rotation.

Instead the world would definitively switch to UTC, or Coordinated Universal Time, which is based on more accurate atomic clocks.

Experts say that complex computer systems require the new, more predictable system - but some countries, including the UK, are opposing the change, on the grounds time has to stay in sync with human experience.

For most of human history time has been based on the rotation of the Earth and the position of the sun in the sky. GMT, or 'Universal Time' as it was declared in 1928, works in just this way.

Unfortunately for us, the rotation of the Earth is not constant. It can be altered by earthquakes, and over time it is gradually slowing down at the rate of about one second every 18 months.

As a result, an international decision was made in 1972 to switch to 'Coordinated Universal Time' or UTC, which syncronised the world's clocks with 400 atomic clocks, which are far more accurate.

These clocks tick out the seconds based on the vibration of atoms without being affected by fluctuations in the movement of the planet.

The result? The two methods of timekeeping fall out of sync - at a rate of about 10 seconds every 15 years.

Leap seconds have been added to GMT every 18 months since 1972 to compensate for this problem. Scientists determine when the clocks are 0.9 seconds out of sync and give the globe six months notice before the leap second is added.

Critics say that the inconvenience of this system is enormous, as it means that every computer system around the world has to make the change simultaneously.

Experts argue that this could even be dangerous - especially if complex and highly technical procedures, from space missions to financial transactions fall out of sync with each other.

Dr Felicitas Arias, who is the head of the time department at International Bureau of Weights and Measures in Paris, told New Scientist that it is vital for GPS and other international systems to have a reliable clock.

She said: "It is vital for global navigation satellite systems such as GPS to have a continuous time scale ... That means there is a 15-second difference between UTC and the time GPS uses. Someone who is unaware of this could make a tragic mistake when landing an aircraft, for instance. This could happen."

As a result the ITU will decide on whether or not to stop the practice of adding leap seconds, which could in effect snap the link between atomic time and solar time.

It is possible that the ITU's 200 member states will go to a vote over the decision, because countries on both sides of the debate feel so strongly about the change.

A 70% majority would be needed to abolish leap seconds, and the change would go into effect on 1 January 2018.

While the Huffington Post contacted the Royal Observatory at Greenwich, which describes itself as "the home of Greenwich Mean Time" on its website, they said they had no comment.

Others in the UK still feel strong historical links to GMT, however, including Science Minister David Willetts. He argues that time must keep its link to "everyday experience".

He told the BBC: "The UK position is that we should stick to the current system used throughout the world. Without leap seconds we will eventually lose the link between time and people's everyday experience of day and night."

In theory Willetts is right: over time clocks would not longer accurately indicate the position of the sun, and the atomic clocks would outrun solar time by up to 90 seconds a century.

In 600 years that would mean the sun would reach the highest point in the sky 30 minutes after noon.

Experts say the only way to bring clocks back into line with the sun at that point would be to change time zones.

Peter Whibberley, of the National Physical Laboratory, told Channel 4 News: "It is a concern, once you get rid of these seconds there's no longer any way to bring the atomic scale back into line with Greenwich Mean Time.

"The only option put forward so far that might be feasible is simply for countries to change their time zone."

Of course it is entirely possible that by that time there might be even more complicated issues with timekeeping - if it's 6pm on Earth, what time will it be on Mars?

Only time will tell.