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T-symmetry

In theoretical physics, T-symmetry is the theoretical symmetry of physical laws under a time reversal transformation:


T : t ↦  − t.
Although in restricted contexts one may find this symmetry, the observable universe itself does not show symmetry under time reversal, primarily due to the second law of thermodynamics. Hence time is said to be non-symmetric, or asymmetric, except for equilibrium states when the second law of thermodynamics predicts the time symmetry to hold. However, quantum noninvasive measurements are predicted to violate time symmetry even in equilibrium, contrary to their classical counterparts, although it has not yet been experimentally confirmed.

Time asymmetries are generally distinguished as between those intrinsic to the dynamic physical laws, those due to the initial conditions of our universe, and due to measurements

  1. The T-asymmetry of the weak force is of the first kind,
  2. The T-asymmetry of the second law of thermodynamics is of the second kind, while
  3. The T-asymmetry of the noninvasive measurements is of the third kind.