This question has probably been asked millions of times and me coming back here will be nagging, but the threads I read on here did not seem satisfactory and I hope someone can offer me a quick but personal explanation. My problem is rather classic and asks why one of the twin paradox' twins ages and one doesn't. While I came across this problem reading Brian Greene's Elegant Universe, I have previous experience with Special Relativity with some (very minor) maths background in the calculations concerned. As proven per thought experiment (and later, of course, per real-life experiment), if one inertial reference frame moves against another, the reference frame "standing still" (I know this frame doesn't exist but for the sake of explaining, bear with me) will experience the other reference frame having a slower "time" (as light's speed is constant but needs more time to move distances in the frame). Thus, if a friend sprinted away from me and then came back, we could say he was a very tiny fraction of a millisecond younger than me. Furthermore, if one twin makes a spaceship journey through the cosmos, the twin will come back to see its other half much older. What I don't get is how this observation/thought experiment combines with the theory that all reference frames are equal. Thus, one would not be entirely wrong in saying I float away from my sprinting friend, or the planet flies away from the twin's rocket. Other threads argue that in both reference frames, the other ages slower. As per the physics of SR, I would agree with this. What I don't understand, is how a twin coming back to its other half, or my friend sprinting back towards me could still be decisively younger than me. Doesn't this imply that there is an absolute state of lower velocity?