text: Classical variables that do not change upon time reversal include:
  :, position of a particle in three-space
  :, acceleration of the particle
  :, force on the particle
  :, energy of the particle
  :, electric potential (voltage)
  :, electric field
  :, electric displacement
  :, density of electric charge
  :, electric polarization
  :Energy density of the electromagnetic field
  :, Maxwell stress tensor
  :All masses, charges, coupling constants, and other physical constants, except those associated with the weak force.