Hello, i am new here. I have been studying SR en GR for a while on a hobby level, and i keep pondering on the following : Consider the following situation : A train with a person on it leaves the station. SR says that while moving with constant velocity, the trainguy cannot tell the difference between him riding out of the station or the station leaving him, relatively to each other. ok. It is also understood that no experiment can be used to distinguish between these two possibilities. By extention, no current technology can make the distiction. ok. >> What about this 'experiment' ? I am trainguy (and i also drive the train), and i have to figure it out : I know that i had to startup the train from 0 km/h to start leaving the station. For this i had to accellarate for a while first, and then gradually lower the power again to approach a constant speed, until indeed i have reached a constant speed. then maintaining the same level of power. How can i now distinguish between the station leaving me and the train, or me and the train leaving the station ? ('Now' = while going at constant speed, after the accellaration has terminated.) > I simply consult my memory , and if i don't suffer any rare medical condition such as instant Altzheimer from the moment on where accellaration turned into constant speed, then i can safely conclude that : -It was definately me starting up the train and performing the necessary handlings to get to a constant speed. -It was definately not the station that was 'started up' in any way. -And so it was definately me and the train moving away from the station, the station that was set in motion in any way. I don't experience it, i know it. >>>> So me and the train are moving away from the station, not vice versa. I know this by consulting my memory , although i may not experience the difference, or detect the difference with a device. So i simply know the situation is not symmetric, i doesn't matter anymore wether or not i can distinguish between the two by experience, observation, or device detection. Is this a valid thought experiment ?