Hi guys, this is my first post/thread, so I'd like to start with an easy one I've searched the web and I wasn't able to find a satisfying proof of the fact that Lorentz contraction is NOT applied to the dimensions, that are not parallel to the direction of motion (e.g. perpendicularly). It's a bit annoying, because in most of the textbooks it is stated that this proof would be easy. Nevertheless it's NEVER provided!!! I don't need another first postulate reductio ad absurdum but rather a mathematically consistent counter-argument (if one exists...). Thanks a lot!