I'm not sure if travel to the past will ever be possible, but you could theoretically build a machine to travel into the future as follows:
As was mentioned previously in this thread, the closer an object is travelling to the speed of light, the slower time passes for that object. This is best explained by the well-known
Twin Paradox:
Quote:
|
In physics, the twin paradox refers to a thought experiment in Special Relativity, in which a person who makes a journey into space in a high-speed rocket will return home to find he or she has aged less than an identical twin who stayed on Earth.
|
Imagine that it was possible to build a centrifuge here on Earth that could move at the speed of light. Obviously the energy requirements would be extremely prohibitive and the g-forces of such a centrifuge would crush anyone inside, but for the sake of this discussion we'll pretend that future technology is able to overcome those and any other practical limitations.
So a man enters the centrifuge and it spins up to light speed. Say he spends a year (by his reckoning) spinning around like this. When he emerges, the world outside the centrifuge will have seen many more years pass. If he had a twin brother (as in the aforementioned paradox), his brother might now be an old man while he still appears to be young.