question for the Lorentz's space contraction I imagin this thought experiment: a train which travels with the speed of light is trying to enter a tunel which has absolutely the same form and dimmension like the train's shape, as if the the train goes slowly with his regular speed it will enter with no problem. If we put 3 observers one on the train, one staying on the top of the tunel waiting to see the train passing below him, and one staying near by watching the train's passage through the tunel? If the movement is relative and a fast traveling object (with c) contracts for a staying observer what phenomena will all the observers see? For the first one it's the tunel who comes, for the second it's the train as for the third who is hardly needed I am interested to know what will he see because I am picturing my self as him and I don't want to take the place of the others. With the time dilatation the things are more clear. As Brian Greene describes it : if two travellers in the open space are moving face to face with a fictional digital clock on their heads and if the are moving with the speed of ligft every one of them will consider the clock of the other ticking slower than the one they own. However it's explicable, my question does not argues with the theories, but there is this thing that I don't understand.