Because the exchange of two identical particles is mathematically equivalent to the rotation of each particle by 180 degrees (and so to the rotation of one particle’s frame by 360 degrees), the symmetric nature of the wave function depends on the particle’s spin after the rotation operator is applied to it. Integer spin particles do not change the sign of their wave function upon a 360 degree rotation — therefore the sign of the wave function of the entire system does not change. Semi-integer spin particles change the sign of their wave function upon a 360 degree rotation (see more in spin-statistics theorem).

— Wikipedia on Exchange symmetry

2013.02.27 Wednesday ACHK