Isn't the universe so simple!
I can explain this to you in a more... accurate way
.
In the universe ALL IS RELATIVE, NOTHING IS ABSOLUTE (even time and space). This means that if you are "flying" into the space you can consider the spaceship motionless
in relation to its pilot, or moving many kilometers per second
in relation to Earth; again, when you are in the car, you can still say that it is the world that is moving under you, and not your car over it (when you launch a ball in the air in the car, you don't need to calculate his parabole
in relation to the Earth, to catch it again). We find easier to consider Earth orbiting the Sun because the other planets, with this reference system, will follow simplier orbits. However it isn't wrong to consider the Earth at the centre of the Universe! Simply all the other planets, moons, stars, galaxies, ecc. will follow EXTREMELY complicated paths (this is way they took so many time to explain the planets' orbits. Someone, a day, discovered that putting the Sun at the centre everything resultes clear).
Assuming that all is relative, we can't find a "centre of the Universe", as all the points of it can be considered "centres".
(I hope it is clear
).
This is a very important point of the Einstain's "Relativity" (...what a strange name...). With this principle he descovered some very important rules. (e.g. the space-time dilatation)
About the Interstellar travel: (i have the vice of going off topic quite often...)
Most of the sci-fi "engines" have been explained teoretically AFTER their invention (e.g. The Star-Trek warp and the hyperspace) but every time, they need A LOT of energy to work. The warp, for example, needs the energy that the Sun produce in its whole live to work a few hours (don't remeber where i heard this, probably on Discovery channel... probably wrong...).
We will reach stars firstly with robots (as we are doing with Mars now) and then when (and "IF"!) the time to reach them will be short enough (less than some months, maybe 2 years). Otherwise we can freeze ourselves and de-freeze at the end, but in this period (could be a century for relatively distant stars) the technology on Earth will have done enormous progresses...). It would be a problem even communication! If we don't find a way to win the light speed we will need 4 years receve news from Earth, and 8 for a reply (imagine to post something here and receive the reply 8 years later... quite daunting...)