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Duda Jarek

Are all processes time/CPT-reversible, e.g. measurement, stimulated emission, state preparation, Big Bang?

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While CPT theorem suggests that all processes have time/CPT-symmetric analogues, there are popular doubts regarding some - starting with measurement:

1)   Example of wavefunction collapse is atom deexcitation, releasing energy - it is reversible, but it requires providing energy e.g. in form of photon to excite back an atom. Can measurement be seen this way - that there is always some accompanying process like energy release, which would need to be also reversed? For example in Stern-Gerlach experiment: spin tilting to parallel or anti-parallel alignment to avoid precession in strong magnetic field - does it have some accompanied process like energy release e.g. as photon? Can it be observed?

2)  Another somehow problematic example is stimulated emission used in laser - causing photon emission, which finally e.g. excites a target, later by light path. Does it have [urlhttps://physics.stackexchange.com/questions/308106/causality-in-cpt-symmetry-analogue-of-free-electron-laser-stimulated-absorbtion]time/CPT-symmetric analogue[/url]: some stimulated absorption - causing photon absorption, which e.g. deexcites a target, earlier by light path?

3)  Quantum algorithms usually start with state preparation: all 0/1 qubits are initially fixed to let say <0|. Could there be time/CPT analogue of state preparation: fixing values but at the end (as |0>)?

4)  One of cosmological examples is Big Bang: which hypothesis of the point of start of time seems in disagreement with CPT theorem - instead suggesting some symmetric twin of Big Bang before it, like in cyclic model of universe. Is hypothesis of the point of start of time in agreement with CPT theorem? Could these two possibilities be distinguished experimentally?

What other processes are seen as problematic from time/CPT symmetry perspective?
Which can be defended, and which essentially require some fundamental asymmetry?

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Neutrinos with neutrino oscillations and no identified right hand neutrinos..

Baryogenesis.

These two comes to mind.

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Regarding neutrinos, I haven't heard of suspicion that they might violate CPT?

 

Regarding baryogenesis as violation of baryon number conservation, it is a hypothetical process and could be avoided if assuming Big Bounce: maintaining fixed number of baryons before and after.

Assuming baron number can be violated, baryons should be also possible to destroy (as in proton decay) e.g. in Big Crunch, they are also hypothesized to be destroyed in Hawking radiation: effectively transforming matter into massless radiation.

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See the following for more detail.

https://www.google.com/url?sa=t&source=web&rct=j&url=https://www2.ph.ed.ac.uk/~vjm/Lectures/SHParticlePhysics2012_files/PPNotes4.pdf&ved=2ahUKEwjIv5PSqKbkAhVnJzQIHcsfASYQFjAJegQIARAB&usg=AOvVaw2LEaudxZszFP-YF1c7yrrW

It has a decent list with the CKM mixing angles.

The Sakharov condition relate to Leptogenesis and Baryogenesis.

Edited by Mordred

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Both these topics are very speculative,

- left-handed neutrino under CPT becomes left-handed antineutrino ... wouldn't it agree with hypothesis that it is a Majorana particle? I think we are very far from concluding something certain here,

- also for baryogenesis (against baryon number conservation law) - can we be certain that it wasn't just Big Bounce: a fixed baryon number collapsing and expanding again?

Accepting violation of baryon number conservation law e.g. in baryogenesis or Hawking radiation, means that proton decay is possible - this is a process we can now only speculate about.

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Very speculative isn't particularly accurate with current understanding being accurate to that paper. As far as I recall even if the neutrino is a Majarona particle it will still have a CPT violation but I will double check that later.

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7 hours ago, Mordred said:

Very speculative isn't particularly accurate with current understanding being accurate to that paper. As far as I recall even if the neutrino is a Majarona particle it will still have a CPT violation but I will double check that later.

I was convinced that its not conclusive whether fermions are Dirac fermions (not their own anti particle) or Majorana fermions (the particle is its own anti particle). Its a bit over my paygrade though. 

@Duda Jarek, Cóż za niefortunna korelacja nazwisk się Panu profesorowi trafiła :P 

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You are correct Koti it isn't conclusive. Also I confirmed that even in the Majorona you would still have assymmetry. The problem is with the mass eigenstate differences between the matter antimatter CKM mixing angles. This is recognized with Particle data group. PDG.

Edited by Mordred

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