Hi all, I've recently been reading a paper by Richard Muller and Shaun Maguire (which is not the exact topic of this post). In that work, the authors mention: "We note that in quantum field theory, very small, localized and rapid events contain amplitudes that can be interpreted as taking place in reversed time. Such reversed time is not, however, directly observable. " I'm somewhat confused by this - specifically, what interpretation the authors are referring to? Although the event may contain some amplitudes taking place in reversed time, the overall result is fully causal, correct? Also, what defines such as event as 'rapid'?