Not that the clocks are wrong. Atomic clocks, which measure the frequency of vibrations in caesium atoms, are accurate to one second in 1,400,000 years. It is the rotation of the earth that is not quite keeping up.
"The length of a second was defined according to measurements of the earth's rotation taken in the 18th and 19th centuries - but the earth is slowing down, mainly because of friction caused by the tides," explains Peter Whibberley, senior time scientist at the National Physics Laboratory. He will be responsible for programming the extra second into the UK's clock, based in a laboratory in Teddington, south-west London, which has careful controls on its temperature, humidity and levels of vibration. Because atomic clocks are so accurate, they are now a full second ahead of the rotation of the earth. If this were allowed to go on for thousands of years, our clocks would eventually read midnight with the sun high in the sky. "Obviously we can't correct the earth's rotation," adds Mr Whibberley, "so we need to add a second to the clocks."
This will not be the first time that we have gained a second. The first atomic clocks were built in 1955, but scientists didn't start correcting them like this until 1972. Between then and 1997, 22 seconds were added. This year's second will be the 23rd. If the earth were to speed up, the scientists would have to start taking them away again.
After Mr Whibberley has programmed in the extra second, a number of things will happen. On 31 December, the atomic clock will switch from 23:59:59 to 23:59:60, before flipping to 00:00:00. Radio listeners will hear an extra "pip" at the top of the hour. Global positioning systems will momentarily find themselves 300,000km from where they think they are, but then correct themselves. Big Ben will chime as usual: the Palace of Westminster clock is constantly regulated by the addition and removal of old pennies piled on its pendulum.
Mr Whibberley will take it all in his stride. "I'll probably use the extra second to take an extra sip of champagne."
So what can you do in one extra second?
Fall in love at first sight. Romeo and Juliet did, but scientists say this is rarer than we think. Which may be just as well ...
Change your life by proposing marriage. And get turned down: "Marry me?" "No."
Yodel. Very quickly. The fastest ever yodel included 22 tones (15 of them falsetto) in one second, and was performed on 9 February 1992 by Thomas Scholl of Munich, Germany.
Take eight award-winning photographs (with a Canon EOS 1D Mark-II camera, for example). Printing them takes a little longer.
Watch grass grow 0.000579mm.
Commit a crime. There are 87,000 every day in England and Wales, according to new figures. They cost the victim on average £1,350.
Read these four words. Or these different ones.
Put your fingers in your ears to listen to your favourite fragment of John Cage's 4' 33".
Look up "extra second" on Google, three times if you type quickly.
Start a rumour that the extra second will bring about millennium bug-style computer chaos, causing systems to shut down and planes to drop out of the sky.
Open 2.8 bottles of beer, if you are the champion beer bottle opening team of the Unertl Brewery, Munich.
Stop 34.2 yards sooner on a motorway (at 70mph), thereby avoiding a potentially fatal accident.
Get 300,000km off-course. The global positioning system (GPS) in satellite navigation devices uses atomic clocks to set its course. If your GPS were out by a second, you would be 300,000km out of your way.
Lose a basketball match. The previously unbeatable American team did just that at the 1972 Olympics, losing to the Russians after a basket was scored in the very last second. The silver medals still lie in a Munich bank after the uppity Americans refused to accept them.
Try to say, "Two smart fellows they felt smart" without getting it amusingly wrong.
Watch time go by. "It's quite possible I might do a very geeky thing and watch how my computer behaves [when the extra second is added]," says Marcus Kuhn of Cambridge University's computer laboratory.
Spare a thought for all the seconds you have wasted.
Shout: "Not yet!" at the host of your New Year's Eve party as she primes a champagne bottle. (But remember to shout, "Now!")
Run a marathon, sing Aida and meet the Queen: in a dream.
Say goodbye. This only takes a second, according to the song by U2 called, er, "Seconds". So, goodbye.
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