Hi, I'm sorry to have to ask this, but I can't seem to reason this one out by myself at the moment. Given the metric is the Minkowski spacetime, is the group of diffeomorphisms the poincare group, or are there diffeomorphisms for flat-space that are not metric preserving? I would really appreciate your help. Thanks, EDIT: Nevermind, sorry for making a new thread for this... I had some tea and thought it out.