We have to face up to the fact that there is no such thing as time travel: it is not possible now, nor can it ever become possible in the future. We can prove that to ourselves simply by answering the question: 'where are they all, the time travellers?' If time travel were ever to become possible in the remote future, we would all, right now, be crowded out by people milling around in silver catsuits trying to mess about with the space-time continuum.
But it does happen all the time in books. It's an enticing fantasy - to be able to actually go back and live among people from past times to see what it was really like, and with the benefit of hindsight, to perhaps change a few things for the better. No matter what the fantasy, though, writers must create for us a world which stands up to a certain amount of scrutiny.
The major issue is to decide whether your characters can change the past. Obviously some small changes occur simply by travelling back in time. In 'An Angel for May' for instance Tam steals some clothes from a washing line in wartime England because his own clothes call too much attention to himself. Nothing significant stems from this so it is allowed to pass, although we only know with hindsight that this act of theft is insignificant. However, when Tam realises that his friends are in danger he tries to travel back in time for the sole purpose of warning them about the fire. The implications of allowing someone to live who might otherwise have died are too great though and Melvin Burgess backs away, so Tam doesn't work out how to pass through the portal until it is too late. Of course, if he had more control over the portal, with time travel there is no such thing as arriving too late. But I do like the way Melvin Burgess uses the time travel experience to change the present and future. When Tam finally returns to the present he understands why things are how they are and sets about changing them.
What you can permit your characters to do while they are time travellers obviously has a huge impact on the way you tell your story. In 'The Sterkarm Handshake' Susan Price wants to create a major interference with the path of history and achieves this simply by asking us not to worry about the implications:
Of course, she was a dimension removed from her own world, so this wasn't the 16th century of her own time-line - if she'd understood the scientific explanations at all correctly. But, she'd been assured, the two dimensions were so close, there was no essential difference.
So, once she's told us that anything is possible in this dimension, we go on to see settlers from the 21st century going to live 16th side, major 21st century surgery saving the lives of 16th siders and plenty of other dramatic events. It doesn't really matter what the rules are as long as they work for the book.
If time travel is in fact possible, it seems to me the only way it could work is for the traveller to find himself transported to a place where he can neither be seen by, nor interact in any way with the locals. He is merely a watcher. A witness to the facts. That may explain where all those silver catsuited people are - they're peering invisibly over your shoulder while you read these notes...
mitchell, boy, age 16, from wollongong, Australia, on 13th April 2006.
If it was possible to travel through time it only be forwared because even the smallest change in the past like an bug being killed could change everything, but most likely wont. I doubt that matter going the speed of light would have a eough energy to travel time though even though i do beleive that matter can go way faster the speed of light becaues back before planes could not go the speed of sound, people thought it was impossible but it wasn't. Time travel may destroy the univers and I doubt that there are others. Time travel could very well be possible in the future but coujld be band becaues in thorey it cold destroy everthing, remember that time is only a force and most forces can be broken or weakoned or nutraliszed by other forces acting apon it.
Perkie, girl, age 12, from Guildford, United Kingdom, on 27th November 2005.
Whilst Lou's point may be correct, I think that time-travelling is impossible as there is only one Earth in Universe and that cannot be changed. If you want to travel backwards in time, you can't, because those people are already dead, and if you do that, 21st century wouldn't exist. If you travel forwards, the people who WOULD be living there wouldn't be alive yet... again, 21st century wouldn't exist. Therefore, however possible it is in books, in real life, it is simply impossible.
Xelnaga, boy, age 15, from North East, United Kingdom, on 20th July 2005.
In response to "Lou"'s point made abotu time dilation and the theory of relativity, if you go far enoguh into quantum mechanics then yes there are particales which can thoretically travel faster than light. I say theoretically because of the speed they move they are beyond measurment. The Particles in question are tachyons. They in theory can move approximately 0.00006m/s faster than the speed of light. Yes nothing can beging at a sub-light speed and then accelerate to the speed of light, but if something with a 0 mass were created at light speed it could accelerate to beyong light speed. The closer you come to the speed of light not only the slower you move, but infact the heavier you become, an object will, relativley, slow down, and it will increase in mass. Because of this only something with a 0 mass can exceed the speed of light. also there are several exceptions to the theory of relativity, matter can be created and destroyed, in very rare circumstances, the only "normal" one is at the tip of the event horizon of a black hole, when due to the unique forces acting with each other new particles will be created, but at the same time, their anti-particles will also be created, and with in about 0.000000000000352 seconds they will cancel each other out, so over all nothing changes, but just as an example, there are exceptions to every rule. If time travel were possible, the quantum string theory means that if a time traveler from the future were to go back in time, and alter anything, it would not alter anything in his future, as the events there have allready happened, the theory means that a split of parralel reality would be created and the events there would be different through out history, but for what would affect us, time travel cannot do anything as the events are allready set in motion.