CPT symmetry analogue of free electron laser?

[jarekd]

Quantum unitary evolution is time symmetric, what leads to retrocausality phenomenas like delayed choice quantum erasure or Wheeler's experiment.
However we understand why they don't allow to send information back in time - I would like to ask for help with understanding why another experiment also does not allow for that:

As physics we use in all scales is time or CPT symmetric Lagrangian mechanics like QFT, let us imagine CPT analogue of laser (lasar: stimulating absorption instead of excitation), like the conceptually simplest free electron laser (FEL):

https://dl.dropboxusercontent.com/u/12405967/freeelectron.jpg

In standard FEL we use magnetic field to enforce electrons to travel in sinus-like pattern, what stimulates photon emission due to synchrotron radiation. These photons are later absorbed by the target, exciting it.
Let us now imagine CPT analogue of this situation: excited target deexcitates - producing photons finally absorbed by positron moving in opposite direction ... but the situation is stimulated by the sinus-like trajectory - we get stimulated absorption setting instead of standard stimulated emission.

So imagine we constantly excite the target (e.g. a sodium lamp), surround it with detectors - we should observe energy conservation.
Now if there is a small hole in detectors to the FEL in stimulated absorption setting (oppositely directed) and set to the same frequency as the excitement (it is rather not fulfilled in standard settings) - shouldn't turning it on change the lamp-detectors energy balance?

 

[eljose79]

First of all, it's important to note that the concept of retrocausality is still a topic of debate and is not widely accepted in the scientific community. While there have been some experiments that suggest the possibility of retrocausality, the results are not conclusive and require further investigation.

Now, regarding your question about the CPT analogue of a free electron laser, it is important to understand that the CPT symmetry is a fundamental principle in quantum field theory and it ensures that physical laws remain unchanged under a combination of charge conjugation (C), parity transformation (P), and time reversal (T). This symmetry is essential for the consistency and predictability of physical phenomena.

In the case of a CPT analogue of a free electron laser, the scenario you describe is not possible because it violates the fundamental principles of quantum mechanics. In quantum mechanics, the state of a system is described by a wave function, and the evolution of this wave function is governed by the time-dependent Schrödinger equation. This equation is time symmetric, meaning that the evolution of the wave function is independent of the direction of time. Therefore, it is not possible for a process to be stimulated by a future event.

Additionally, the concept of stimulated absorption in this scenario is not physically meaningful. In a standard free electron laser, the emission of photons is stimulated by the presence of a magnetic field, not by the trajectory of the electrons. In the CPT analogue, the presence of a positron traveling in the opposite direction would not stimulate the absorption of photons in the target.

In conclusion, the CPT analogue of a free electron laser does not allow for retrocausal effects, as it violates fundamental principles of quantum mechanics and is not physically meaningful. The concept of retrocausality is still a topic of ongoing research and debate in the scientific community, and further experiments and investigations are needed to fully understand its implications.