Charge and parity inversions are linked to this symmetry by the CPT theorem.
At vanishing Reynolds number, the Navier-Stokes equations become linear and gain this property, leading to Purcell's scallop theorem that zero Reynolds number swimmers must have more than one degree of freedom in order to avoid reciprocal motions. The invariance of electric fields under this operator leads to Kramers' degeneracy theorem. A lack of this property is one requirement for the existence of permanent electric dipole moments of fundamental particles. The apparent conflict between this property of microscopic dynamics (*) and the second law of thermodynamics is the subject of Loschmidt's paradox. Charge and parity inversions are linked to this symmetry by the CPT theorem. For 10 points, name this fundamental symmetry that flips the order in which events appear to happen.
At vanishing Reynolds number, the Navier-Stokes equations become linear and gain this property, leading to Purcell's scallop theorem that zero Reynolds number swimmers must have more than one degree of freedom in order to avoid reciprocal motions.
time reversal [accept T before "CPT", prompt after]