Jarek 31
- 157
- 31
- TL;DR
- While CPT theorem says that CPT symmetry holds for all physical phenomena, for some processes such reversibility seems highly nonintuitive - starting with measurement ...
https://en.wikipedia.org/wiki/CPT_symmetry says "CPT theorem says that CPT symmetry holds for all physical phenomena" - e.g. we could imagine decomposition of given phenomena into Feynman diagrams and apply CPT symmetry to all of them.
However, for some o processes such reversibility seems highly nonintuitive - let us try to discuss them.
1) It is good to start with deexcitation as it seems there is no problem with it (?):
excited atom <-> deexcited atom + photon
2) Let us look at measurement, e.g. in Stern-Gerlach idealization, for example of spin - which seems changed during measurement, and corresponds to angular momentum - so shouldn't there be something more e.g. photon carrying this difference of angular momentum?
unmeasured spin <-> measured spin + something carrying difference of angular momentum (e.g. EM wave like photon)
Including such hypothetical artifact carrying difference of angular momentum, momentum, energy etc. allows to see measurement as CPT symmetric reversible process - explain asymmetry by difficulty of preparing the right hand side situation ...
But can we do it - does measurement always have such artifact? Could it be confirmed or disproved?
3) Synchrotron radiation in which electrons usually in strong external magetic field produce photons:
electron before synchrotron radiation <-> electron after + photon
It seems to require some internal change in this electron (?) - could it be rotation of its spin accordingly to magnetic field used to bend the trajectory (V = -mu B like in Zeeman effect)?
4) Stimulated emission in laser: causing absorption of such photon by target later.
So is there stimulated absorption e.g. in CPT analogue of laser: causing emission of such photon by target earlier?
5) State preparation of e.g. <0| qubit out of {<0|, <1|} requiring nonunitarity - can it have CPT symmetric analogue: enforcing e.g. |0> at the end of quantum algorithm? (it is done in postselection but it is cheating).
6) Big Bang - does the hypothetical initial point satisfy CPT symmetry? Doesn't this symmetry suggest Big Bounce instead?
So are all of them CPT symmetric, reversible?
Any other problematic phenomena? (... beside entropy growth)
However, for some o processes such reversibility seems highly nonintuitive - let us try to discuss them.
1) It is good to start with deexcitation as it seems there is no problem with it (?):
excited atom <-> deexcited atom + photon
2) Let us look at measurement, e.g. in Stern-Gerlach idealization, for example of spin - which seems changed during measurement, and corresponds to angular momentum - so shouldn't there be something more e.g. photon carrying this difference of angular momentum?
unmeasured spin <-> measured spin + something carrying difference of angular momentum (e.g. EM wave like photon)
Including such hypothetical artifact carrying difference of angular momentum, momentum, energy etc. allows to see measurement as CPT symmetric reversible process - explain asymmetry by difficulty of preparing the right hand side situation ...
But can we do it - does measurement always have such artifact? Could it be confirmed or disproved?
3) Synchrotron radiation in which electrons usually in strong external magetic field produce photons:
electron before synchrotron radiation <-> electron after + photon
It seems to require some internal change in this electron (?) - could it be rotation of its spin accordingly to magnetic field used to bend the trajectory (V = -mu B like in Zeeman effect)?
4) Stimulated emission in laser: causing absorption of such photon by target later.
So is there stimulated absorption e.g. in CPT analogue of laser: causing emission of such photon by target earlier?
5) State preparation of e.g. <0| qubit out of {<0|, <1|} requiring nonunitarity - can it have CPT symmetric analogue: enforcing e.g. |0> at the end of quantum algorithm? (it is done in postselection but it is cheating).
6) Big Bang - does the hypothetical initial point satisfy CPT symmetry? Doesn't this symmetry suggest Big Bounce instead?
So are all of them CPT symmetric, reversible?
Any other problematic phenomena? (... beside entropy growth)