Well, you have to remember, the time measured "on board" seems no different. They measure a second as a second.<br /><br />However, the outside frame can be said to be "moving" in special relativity. As such the outside frame experiences time dilation (it's clocks move slow relative to the ship), which is the foundation of the classic twin "paradox".<br /><br />The outside frame <i>also</i> experiences length contraction in the direction of travel, thus the ship actually measures a shorter distance to the destination.<br /><br />It makes some sense if you think about how things must work out in the end. Earth knows the ship is moving (as the ship accelerates and decelerates, breaking "reciprocity") as earth doesn't feel any change in motion, but the ship does.<br /><br />So the earth, and the ship, when they compare clocks after the trip will both agree that the ships clocks are those that are slow.<br /><br />So, a trip at .866c to alpha centauri takes 4.6 years. The ships clock (and earth's reading of the ships clock) says it took 2.3. So, how'd the ship go 4 light years in a percieved time of 2.3 years? Thats faster than light!<br /><br />If you factor in the length contraction, the ship actually observes the distance to alpha centauri to be only 2 light years.<br /><br />The ship, before stopping, measured as shorter distance, and expects to arrive in 2.3 years (the time dilated duration). Earth sees it as 4 ly, and expects a 4.6 ly trip, but knows the ships clock is going to run slow.<br /><br />The only reason this comes out to an "absolute" answer of who was slower, etc. is because one of the groups accelerated.<br /><br />And as for becoming a teacher...I intend to. I've been a tutor/teachers assistant during my undergraduate career, and I'm now taking on the role as a graduate student. <div class="Discussion_UserSignature"> <p align="center"><font color="#c0c0c0"><br /></font></p><p align="center"><font color="#999999"><em><font size="1">--------</font></em></font><font color="#999999"><em><font size="1">--------</font></em></font><font color="#999999"><em><font size="1">----</font></em></font><font color="#666699">SaiphMOD@gmail.com </font><font color="#999999"><em><font size="1">-------------------</font></em></font></p><p><font color="#999999"><em><font size="1">"This is my Timey Wimey Detector. Goes "bing" when there's stuff. It also fries eggs at 30 paces, wether you want it to or not actually. I've learned to stay away from hens: It's not pretty when they blow" -- </font></em></font><font size="1" color="#999999">The Tenth Doctor, "Blink"</font></p> </div>