Abbey Malone and Jess Stribling, of Christ the King School, asks :-

Hillary Riddle, of Mokoia Intermediate School, asked:- Giles Reid, of Ilam Primary School, asked:-

What happens if you travel at the speed of light? Why can't you go faster than light?

Noel Doughty, a physicist at the University of Canterbury, responded.

No energy, matter or information can travel faster than the speed of light. In addition, very few effects can travel exactly at the speed of light. Everything that has mass, like you and me, is excluded.

Electric, magnetic and gravitational forces all travel at the same speed as light which is three hundred thousand kilometres every second or, put another way, 300 metres every millionth part of a second. That is very fast but it still takes 8 minutes for light from the sun to reach the earth.

People can travel almost at the speed of light. The more energy an astronaut can use to accelerate a spaceship the faster she goes. However, the energy required to accelerate a 10 tonne craft to near the speed of light exceeds by a very large factor all the known sources of energy on earth. Installing the necessary power station on the spaceship raises the power required even further.

This is a pity because relativity tells us that if she undergoes a space journey at speeds approaching the speed of light she will return a lot younger than the friends she left behind.

This idea, which is called the 'Twin Effect', has been tested by scientists who flew a very accurate atomic clock around the world by aeroplane. They measured a time difference of about one millionth of a second, as theory predicted, between the travelling clock and the one they left behind.