1. The problem statement, all variables and given/known data A train is passing a platform at 0.75c, and an observer, stationary and at the middle of the platform, sees two bolts of lightning simultaneously hit the front and back of the train when the train's middle was adjacent to the middle of the platform. A passenger on the train (and sitting in the middle) sees the two bolts of lightning at different times. Given that the two bolts of lightning were 50m apart(as viewed by observer on platform), calculate the time difference between the two bolts of lightning as viewed by the passenger on the train. 3. The attempt at a solution Before I delve into the computation, I just want to check something. From the platform observer's frame of reference, he sees the two bolts at the same time. If we define a coordinate system with x axis parallel to motion of train, then the two bolts strike the train at different spatial coordinates, but at the same time, relative to platform observer. Does this imply that the 50m is a proper length as viewed by the observer? Since the bolts are at either end of the train then does imply that the actual length of the train is 50m? If so, I don't see how this makes sense given that we know length contraction of the train occurs relative to the platform observer. On the other hand, I believe the def of proper length conforms with what I said above.