# Are all processes CPT symmetric like measurement, stimulated emission?

• I
• Jarek 31
In summary: You have not provided a summary of the conversation, as requested in the original prompt, and have instead chosen to continue pushing your own perspective on the topic. This is not the purpose of this platform. Please refrain from using this forum to promote your own views and instead engage in productive discussions centered around the topic at hand. Thank you.
Jarek 31
TL;DR Summary
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)

When every other word is bolded this becomes very hard to read.

With six examples, it doesn't sound like you are asking questions so much as pushing a position. You might want to take a look at the PF Rules on this.

CPY symmetry is a statement that relates certain properties of particles and antiparticles (the C). It does not say that a broken vase must spontaneously reassemble or any of your six examples.

Demystifier
I have started with statement from Wikipedia saying that this symmetry holds for all phenomena, and wanted to discuss here some problematic cases.
Especially measurement - which is often seen as irreversible phenomenon - so does it invalidate the CPT theorem?

Wikipedia is not an acceptable reference here.

Wikipedia is kind of introductory reference, to get a glimpse without subjectively choosing references yourself, and it points to real references. If you disagree with this article, please improve it.
The original paper is Schwinger's https://journals.aps.org/pr/abstract/10.1103/PhysRev.82.914 - you can use it or some other references to support your view on the questions asked here.

Schwinger doesn't say any of that either.

Since it's clear that:
a. You misunderstand what CPT says, and
b. You are more interested in promoting your own flawed view than in gaining understanding yourself

vanhees71
Where I promote my view?
I am just asking if measurement invalidates CPT theorem?

Temporarily closed for moderation.

berkeman
Schwinger doesn't say any of that either.

Since it's clear that:
a. You misunderstand what CPT says, and
b. You are more interested in promoting your own flawed view than in gaining understanding yourself

After a Mentor discussion, this thread will remain closed.

## 1. Are all physical processes CPT symmetric?

No, not all physical processes are CPT symmetric. CPT symmetry is a fundamental principle in physics that states that the laws of physics are unchanged when the three operations of charge conjugation (C), parity transformation (P), and time reversal (T) are applied in sequence. However, there are some processes, such as weak interactions, that violate this symmetry.

## 2. What is CPT symmetry?

CPT symmetry is a fundamental principle in physics that states that the laws of physics are unchanged when the three operations of charge conjugation (C), parity transformation (P), and time reversal (T) are applied in sequence. This means that if you reverse the charges of all particles (C), reflect the system in a mirror (P), and reverse the direction of time (T), the system should behave in the same way.

## 3. How is CPT symmetry related to measurement and stimulated emission?

CPT symmetry is a fundamental principle in physics that applies to all physical processes, including measurement and stimulated emission. This means that these processes should also exhibit CPT symmetry, meaning that if you reverse the charges of all particles, reflect the system in a mirror, and reverse the direction of time, the outcome should be the same.

## 4. Are there any known violations of CPT symmetry?

Yes, there are some known violations of CPT symmetry, particularly in weak interactions. These violations are small and have only been observed in high-energy experiments. However, the overall principle of CPT symmetry remains a fundamental aspect of physics.

## 5. How is CPT symmetry tested and verified?

CPT symmetry is a fundamental principle in physics, and it is tested and verified through various experiments and observations. These include high-energy particle collisions, precision measurements of particle properties, and observations of the behavior of particles in different environments. So far, all experimental evidence supports the validity of CPT symmetry.

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