Megan Vernel, of Riccarton High School, asks :-

Is time travel possible?

Amanda Peet, a New Zealand graduate who is now at Princeton University in America working on advanced theory concerned with black holes and the big bang, responded.

No, time travel isn't possible. Before I try to describe why not, I'll start by saying something about travelling in general.

The fastest anything in the universe can travel is the speed of light. That's really fast: light travels approximately three hundred thousand kilometres in one second! However we measure its speed in space it always goes at exactly the same speed. It's the same for radio waves, for ultraviolet light, for infrared, for X-rays, and microwaves - they're cousins of light.

Material things, like you or me or a spaceship, can speed up, or slow down, or stop. But even if you could attach incredibly powerful rockets onto your feet, you wouldn't be able to accelerate to light-speed. As you sped up, it would get harder and harder to go faster and faster. You could get very close to the light-speed barrier, but you would never quite get there.

Now, about time travel. Time travel is theoretically when something would go faster than light: if it can go faster than light, then it can go backwards in time. However, there is a big problem with going backwards in time. You could do things like going back to before you were born and murder your mother. Then you couldn't possibly have been born! And that's a contradiction, because you were alive to start with.

So overall, time travel, or faster-than-light travel, is impossible, because it doesn't make sense, and because it would take an impossible amount of energy to do it.