When space-reflection and time-reversal symmetries are broken, the Thomas precession formulas derived by Thomas' method and from the BMT equation differ from each other. This apparent contradiction is resolved by pointing out that the breakdown of discrete symmetries may lead to a change in the operational meaning of the Lorentz-group elements.

I propose to consider photon tunneling as a space-time correlation phenomenon between the emission and absorption of a photon on the two sides of a barrier. Standard technics based on an appropriate counting rate formula may then be applied to derive the tunneling time distribution without any ad hoc definition of this quantity. General formulae are worked out for a potential model using Wigner–Weisskopf method. For a homogeneous square barrier in the limit of zero tunneling probability a vanishing tunneling time (...) is obtained. (shrink)