Comment author:Ronak
10 April 2013 03:29:46PM
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PEP is not a force, in the sense that it's not 'dynamical:' it can't actually affect the Hamiltonian/Lagrangian of the world. And it's not a symmetry either, it's a consequence of the behaviour of 'fields' under rotations: see spin-statistics theorem.
(Explanation of the field business: modern physics postulates that at every point in space and time there are a certain number of degrees of freedom, and we call them fields and 'quantising' gives us particles - and particles are just spatially localised excitations when you don't look closely at them.)

The rest of the forces, however, do come from symmetries called local gauge symmetries; roughly, since the wavefn is a complex no, change the phase by some amount which depends on the point and then requiring that physics be invariant under this. (Even gravity, though only in classical field theory as of now: it can be found by a Lorentz transformation by a different amount at every point.)

This explanation is horrible, so sorry; but on the bright side, the math is simple enough that you may actually understand wikipedia on these things.

## Comments (44)

BestPEP is not a force, in the sense that it's not 'dynamical:' it can't actually affect the Hamiltonian/Lagrangian of the world. And it's not a symmetry either, it's a consequence of the behaviour of 'fields' under rotations: see spin-statistics theorem. (Explanation of the field business: modern physics postulates that at every point in space and time there are a certain number of degrees of freedom, and we call them fields and 'quantising' gives us particles - and particles are just spatially localised excitations when you don't look closely at them.)

The rest of the forces, however, do come from symmetries called local gauge symmetries; roughly, since the wavefn is a complex no, change the phase by some amount which depends on the point and then requiring that physics be invariant under this. (Even gravity, though only in classical field theory as of now: it can be found by a Lorentz transformation by a different amount at every point.)

This explanation is horrible, so sorry; but on the bright side, the math is simple enough that you may actually understand wikipedia on these things.