And yet, if we imagine that all 3 ships emit a light towards the outside observer, whenever they send or receive the light from the other ships...? (They are moving perpendicular to the observer, so all lights take the same time to reach that observer)<br /><br />Then obviously, in the ships, nothing changes. The middle ship emits both lights at the same time and emits a light towards the observer, the end ships receive those lights 1 minute later and bounce them back, emitting lights towards the observer at the same time. The middle ship receives both lights back again after 2 minutes and emits another light towards the observer (if they happened to arrive at different times it would have emitted 2 lights, but that doesn't happen!)<br /><br />Now to the observer, they receive the first light from the middle ship as it emitted its lights fore and aft. Then, only 6 seconds later, it receives the light from the rear ship (when the aft light was bounced). 10 minutes later the observer sees the light from the front ship (emitted when the fore light was bounced). 6 seconds after that, it receives the final light from the middle ship when both bounced lights arrive back simultaneously.<br /><br />So when both lights return to the middle ship simultaneously, the symmetry of the process is intact, and the maths all works out. But can time-dilation on the ship explain what the observer sees?<br /><br />Let's back up a bit, to where the lights from the middle ship first reach the front and rear ships. To the observer the rear ship gets the light 6 seconds after emission, and the front ship gets the light after 10 minutes. Is <i>that</i> where we observe a difference in simultaneity which cannot be attributed to either time-dilation or light travel time? If the observer sees such a huge difference in the times that the front and rear ships bounce those lights back, how can the middle ship account for that difference with time-dilation? Surely time-dilation will affect that middle ship <div class="Discussion_UserSignature"> <p><font color="#ff0000">_______________________________________________<br /></font><font size="2"><em>SpeedFreek</em></font> </p> </div>