Consider the path of a proton at 7 TeV Ke at LHC. Wikipedia says: Length contraction is the phenomenon of a decrease in length of an object as measured by an observer which is traveling at any non-zero velocity relative to the object. This contraction (more formally called Lorentz contraction or Lorentz–FitzGerald contraction after Hendrik Lorentz and George FitzGerald) is usually only noticeable at a substantial fraction of the speed of light. Length contraction is only in the direction parallel to the direction in which the observed body is travelling But I read everywhere that the path of a moving body is shortened by gamma factor, which is right? Can it be both? How long is one circle in the proton's frame?