I chanced upon an article http://homepage.mac.com/ardeshir/TrainDisprovesRelativity.html which sought to show through a thought experiment that SR is inherently contradictory. Now I am not a pro in Relativity but from whatever understanding I have built up, here is the response that I sent across to the author. Guys, can you comment whether I make a point here or make a fool of myself? I would like to point out that the fallacy you are making is the same one as in the commonly discussed 'Twin Paradox'. You basic gist is that at the end of the thought experiment, it is possible to determine in an absolute sense whether it was the track/ platform that were moving or whether it was the train that was moving. You conclude on this basis that SR is contradictory since it refutes the concept of absolute motion. Let me now explain why your argument is incorrect. You believe that the whole thought experiment is symmetrical from the point of view of the platform and from the point of view of the lady riding in the train. Therefore you say that if SR is correct, either of them should not be able to conclude that one of them was moving in an absolute sense. However, you are mistaken in your belief that the situation was symmetrical. In fact, for the lady and the man both to be able to take the two sets of measurements (distance between the marks on the tracks and distance between the ends of the train in the frame of the platform), the train would need to stop and then the two of them would take the measurements. However, here is where the symmetry ends. The train has undergone an 'acceleration' in order to stop to a halt. 'Acceleration' is absolute even according to Relativity. So there is a clear mismatch in the experiences of the lady and the man. The lady in the train felt the train decelerate whereas the man felt nothing of the sort. Hence, since the two observers have not gone through the same experiences, there is nothing contradictory about them concluding that one of them did accelerate. Infact, the observations of the marks would indeed permit them to conclude that one of them accelerated and this would be consistent with what they would have experienced. And as for Relativity, it has no objection to absolute acceleration being detected. Hence your thought experiment does not disprove special relativity. A similar confusion is responsible for the Twin 'paradox'. People think both the twins are in a symmetrical position and therefore it is paradoxical for one to be younger when they meet. However, a similar reasoning as above reveals that for the twins to meet again, one of them has to accelerate and this causes the dis-symmetery in experiences. And then, its not paradoxical any longer to see them age differently on return. It all boils down to the fact that Relativity does believe in the concept of absolute acceleration even though it does not believe inthe concept of absolute velocity. Please let me know your comments.