Time Travel?

Originally Posted by B4-Hunter

They will want to travel in to the future and find any new weapons that they can use against others.

How absolutely dreadful! What kind of monster would ever try such a despicable thing?

Right, anyway. To say it's possible, even theoretically, is somewhat untrue. For example, take special relativity in its simplest form. The factor that governs time dilatation and space contraction is called the gamma factor and is defined as being the inverse of the square root of 1 minus the square of the speed of the object being observed relative to the observer divided by the square of the speed of light, that is gamma = 1/(1-v^2/c^2)^(1/2). Without going into details, the way it ties to time is with the following equation: t' = gamma*t, where both t' and t represent time in different frames of reference, that is, for different observers. Now, looking at the definition of gamma, we see that as the speed of an object nears the speed of light, gamma becomes larger and larger, that is, it tends towards infinity. Worst, when the speed is equal to the speed of light, you have a division by zero. That's the first half of the problem. To actually "go back in time" you'd need to have a negative gamma. The square root makes that impossible. If we were to assume that complex numbers somehow have an effect here, then we'd still need to go faster than the speed of light (that would still leave us the division by zero problem, of course).

The second, without going into details, is that while the kinetic energy of a moving object is usually given by Ek=1/2*mv^2, this is, like most classical mechanics, an approximation which doesn't hold well at velocities near the speed of light. In special relativity, the amount of kinetic energy contained in an object tends toward infinity as its speed tends toward the speed of light, so inversely, to get to the speed of light, you need infinite energy. What we know of cosmology essentially tells us that matter and energy are finite, making it impossible to reach the speed of light (for any particle with a rest mass larger than zero anyway). Of course even if it were to be possible, there'd still be the things I pointed out in my previous paragraph.

General relativity might give more precisions about this, but unfortunately, manifolds and their kin are still too complex mathematical objects for me to understand well.

Jam it back in, in the dark.