I think being 3 or 4 dimensional is our human perspective (limited by our understanding). Just like if we insist that the world is 2-dimensional, some things that we do now would be impossible.

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Added on June 15, 2009, 6:53 pm
Air-friction in the outer space is zero

Makes me think about mind travel, only in the form of frequency but when things are destroyed in the past, it does not exist anymore unless time or physical entity is recorded and can recall back like a video.

Imagine the food we ate, absorbed and passed out process in reverse! If human can do that, life becomes meaning less. Even if we are unable to interfere but can prevent something from happening like the movie "Minority report", it won't do us any good unless to prevent from near extinction trying to find clues from history.

I don't see why there is a need for time travel in the first place, life is such because we don't know, if you know when and how you will die, you will try to alter it so you can choose to die in bed peacefully.

4th dimension is in dream and 5th is teleport, I guess time travel would be 6D.

Actually no, space is full of space dust. At the speed of light, hitting a single sub atom is like the entire Jupiter slamming your body.

Outer space isn't actually void of nothing. If you travel beyond the border of universe, the empty 'space' is actually something. So it's sort of a perspective issue