Imagine a 2.3 Ly long box. At the middle of the box there's a half silvered mirror (S) which splits laser beam into two and reflects to the both end of the box which is also mirrors that are facing each other (mirror A & B). Another observer (O) is placed 1.15 Ly away from mirror A in a series position. O A S & B are in series. Total distance between O and B is 3.45 Ly O sends a laser pulse S (takes 2.3 years), it splits and reflects both beam towards A & B and reaches there simultaneously (in 3.45 years) After that O starts his instantaneous acceleration towards the box and reaches at 90%c in his 1hr. Now from his point of view, the beam that reflected from A moves towards the laser earlier than the laser that reflected from B. So the laser A hits the Centre of box earlier than laser B. Isn't that a paradox?