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In one sense, the answer to the question "Is time travel possible?" is "Yes, of course, it's happening all the time". Everything is travelling in time; you, me, the Earth, the Sun, every atom, every proton, every electron, the whole Universe. This is, I suppose, a "trick" answer, time rolls forward and everything travels with it.

I suppose I'll have to deal with the real question: is it possible to move from one point in time to another without all that messy stuff (like getting older, or younger; or being born or dying) in between?

First, let's get the Einstein and Relativity angle sorted out.

The fundamental idea of relativity is that anything that is moving relative to your frame of reference displays changes in their space-time. If an object is moving relatively faster than you: it will shrink in the direction of motion; internal processes within the object will take longer; the mass of the object will increase. But all from your point of view. From the point of view of another observer, on the object itself, then: you will expand in the direction of motion; your internal processes will happen faster; your mass will decrease. But, as I say, all from the point of view of the observer on the object.

The size of these effects depends upon the relative velocity of the two frames of reference. For "normal" velocities, the sort that we experience (and most of the universe experiences) the size of these effects is very, very, very, very small. However, when the differences start approaching the speed of light, the effects become significant. No object with any mas at all (no matter how small) can ever travel at the speed of light relative to any other observer since its perceived mass would then be infinite.

As an object approaches the speed of light it begins to have the same velocity relative to all other frames of reference. As far as the object itself is concerned, however, it's the rest of the universe which has changed. If the object contained a clock, then, from the point of view of the rest of the universe, it has slowed down. From the point of view of the object itself, the clock keeps perfect time: the rest of the universe has slowed down. If the object could reach the speed of light, the rest of the universe would appear to have stopped, frozen in time.

Gravity comes into the scene in the following manner: the effects of gravity on an object are identical with the effects of acceleration on the object. If you were inside a spaceship without windows, there

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