So, you wanna travel through time. Sure!
All you need is the location of every single particle in the universe at the moment you want to re-enter space-time. Uh oh, you don't have that?
You see, every particle in the universe is in motion. Every single one. The earth is spinning, and revolving around the sun. The sun is also
revolving, in fact the whole galaxy is. When you look up at night and see stars, they're not just sitting there. They're in motion, but relative to
us, so it might appear like they haven't moved. But they have.
So, let's say you "leave" spacetime, using whatever made-up scientific gadget or metaphysical process you wanna come up with. Fine. Let's say you
wanna go back to, oh, the Stone Age and study those people. Cool beans.
But where was the Earth then? Where was the Milky Way in relation to all the other celestial bodies out there? In order to find out where the earth
was, you'd have to know where all the bodies in the Milky Way were. But they're in motion with other bodies too, so you'd have to know where those
were at the time.
Then you have "cosmic drift" or "expansion" or whatever else you wanna call it. It appears
as though the visible universe is expanding in some
way. So you have to account for that in your equations. You'd have to know the rate of expansion, precisely, and of course that would require
knowledge of all the bodies in the visible universe.
So, ya. You'd need to know where all the particles in the universe were to calculate where your destination will be before you get there. Or you run
the risk of ending up in a vacuum. Or a rock.
edit on 17-3-2011 by PrincessAura because: Code Fix