About time

13.7 billion years ago: Time begins. Or maybe it didn't. Anyway, the universe starts and with it, perhaps, came time. But what we before it? Was there no time at all? And does time always have to run forward?

3000 BC:Newgrange is built, and it acts as an annual 'timepiece' so accurate that each year it still works when sunlight streams into its chamber for four and a half minutes of the Winter Solstice (December 21st).

2000 BC:The ancient Egyptians split the day into 12-hour periods, something we're still doing now. They used the shadow of a large obelisk as a timepiece — something we're not doing anymore (and not just because it's got no alarm on it).

400 BC: But the philosopher Plato did invent an alarm clock, adapting a water clock so that vessels filled with liquid until a whistle was sounded.

1335: The first known mechanical clock was built in Milan. Almost 200 years later the first pocketwatch is made.

1773: The first writer to use the idea of travelling backwards in time is often said to be Irish clergyman Samuel Madden, whose book Memoirs of the Twentieth Centuryfeatured an angel travelling back from 1998.

1868: The first wristwatch is made. In 1880 2,000 are made for German naval officers. But men don't buy into the fashion with women being the earliest users of them. They finally became popular after the first World War, when soldiers needed to keep their hands free for fighting.

1949: Harold Lyons develops an atomic clock based on the quantum mechanical vibrations of the ammonia molecule. If you have an ammonia molecule handy, you can make one of your own* *Not really.

1972: Two extra "leap" seconds are added to the world's clocks because the earth's rotation around the sun is slowing down. Several more seconds have been added since, including one in 2008.

1994: The first digital sundial is made, which notes the position of the Sun and uses its energy to display the time.

2000: Some pacific islands move time back so that they can become the first to welcome in the new Millenium. The Republic of Kiribati was first, but only by moving its dateline a full 2,000 miles east, which would be like Ireland stretching its dateline to Greece.

2010: UK begins early steps to changing clock, which would mean that Dundalk and Derry would be an hour apart. More importantly, X-Factorwould start in Ireland at 7pm instead of 8pm.

** What year is it? Silly question, right? Well, it depends on where you live. In Thailand, which uses a Buddhist calendar, it’s 2553. In Ethiopia, which has its own calendar, it’s 2003 (its new year began on September 11 of our 2010). So, the year you’re living in is a very human notion based on the culture you come from. Ireland uses the Gregorian calendar introduced in the 16th century.

Bonus fact: the stardates in Star Trekdidn't really mean anything. The writers just used them to avoid having to mention the year each time.

** Time travel of sorts is possible if a person was to get on a spaceship and travel very fast away from the Earth. If an identical twin was travel at even half the speed of light for a few years, they would return to find that they were younger than the twin who had stayed behind. Albert Einstein explained this in his theory of relativity.

400 million yearsTime it takes some atomic clocks to lose just a second

70.22 km a secondSpeed of the fastest spacecraft yet built

2021The next year that will be identical to 2010

299792.458 km a secondThe speed of light

86,400Number of seconds in a day