Is relativistic effect of length contraction physically "unreal"? One guru indicate that Length contraction has nothing to do with compression. It is more correct to view length contraction as a rotation in space time. If we rotate a box filled with gas or perfect fluid, clearly its density does not change. Suppose the box is accelerated to speed close to the speed of light. Its length will be shorten due to Lorentz contraction. My question is this: Will the density of the box increase with its speed?