# What is Cpt symmetry: Definition and 15 Discussions

Charge, parity, and time reversal symmetry is a fundamental symmetry of physical laws under the simultaneous transformations of charge conjugation (C), parity transformation (P), and time reversal (T). CPT is the only combination of C, P, and T that is observed to be an exact symmetry of nature at the fundamental level. The CPT theorem says that CPT symmetry holds for all physical phenomena, or more precisely, that any Lorentz invariant local quantum field theory with a Hermitian Hamiltonian must have CPT symmetry.

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1. ### A CPT symmetry in a copy world?

Say we have a copy of our world, but with the "parity" and "time" reversed. (For example, the mirror world from the novel "Alice Through the Looking Glass".) If the "charge" is also reversed, then due to the CPT symmetry, the same physics law would apply to the mirror world, right? If we...
2. ### A Possibility of Discrete Symmetries in GR: Exploring CPT Symmetry

Our current model (FLRW) is clear that the universe has a continuous temporal asymmetry. This is seen as the expansion factor grows with time, and thermodynamically with entropy. A continuous transformation in the current model ##t \rightarrow t + dt## is not the same as ##t \rightarrow t - dt...
3. ### I Do measurements modify angular momentum and energy?

While physics is generally believed to be CPT symmetric, there are processes for which such symmetry is being questioned - especially the measurement. One of examples of (allegedly?) going out of QM unitary evolution is atom deexcitation - we can save its reversibility by remembering about...
4. ### B Symmetry of parity: Mistake in the experiment?

Recently I saw this YouTube video from Veritassium about CPT -Symmetry: In this video an experiment of Prof. Chien-Shiung Wu is presented, which has proven that parity is not symmetric, by observing the emmition of electrons from Co60 atoms with synchronised spin. After thinking about this...
5. ### I Are all processes CPT symmetric like measurement, stimulated emission?

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...
6. ### Is there a conflict between CPT symmetry and the 2nd law of thermodynamics?

Naively there is a conflict between CPT symmetry being at heart of fundamental physics models like QFT, and 2nd law of thermodynamics: saying that entropy grows toward future. Is there really a conflict here - so is physics symmetric or not? How to understand it? Personally I disagree with that...
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### A What does a CPT transformation do to particle properties?

If I have a particle with: Momentum: p Spin: s Energy: E Position: x Time coordinate: t Charge: q And I preform a CPT transformation on said particle, what will these variables become? Can you show me mathematically? Also, could you show me how this effects the wavefunction/quantum state of...
8. ### B CPT Symmetry: Proving the Theorem & Lorentz Transformation

Some books prove CPT theorem basing on scalars,vectors, tensors building from 4-spinor of fermion and gamma matrices.Why can they do that?Because a general Lagrangian can contain bose scalar,bose vector,bose tensor fields and spinor fields. The CPT theorem says CPT symmetry is a strictly...
9. ### A CPT symmetry and antimatter gravity in general relativity

CPT symmetry and antimatter gravity in general relativity M. Villata Published 28 March 2011 • Europhysics Letters Association EPL (Europhysics Letters), Volume 94, Number 2 Abstract The gravitational behavior of antimatter is still unknown. While we may be confident that antimatter is...
10. ### B Violations of CPT symmetry?

Consider a photon undergoing pair production and turn into a particle-antiparticle pair. Now play this in reverse, you got a particle and an antiparticle colliding to create a single photon. But in annihilation, the result is two or more photons. Violation of T symmetry? There also seems to be...
11. ### I Beta decay and CPT symmetry

I read that CP-symmetry violation occurs (or can occur) in beta decay. Does that mean that, since CPT-symmetry must hold, there is no T-symmetry?
12. ### CPT symmetry analogue of free electron laser?

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...
13. ### P, CP and CPT symmetry in neutrino oscillation? (quick question)

Just a quick question about notation really here. In neutrino oscillation we can calculate a probability of an oscillation occurring between two flavour eigenstates - invariably denoted P(\nu_{\alpha} \rightarrow \nu_{\beta}) . I've got some confusion about what happens to this when we apply...
14. ### Why should there be CPT symmetry?

A few of the books and magazines I have read talk about maintaining CPT symmetry, but I can't see why it should be the case. What is the evidence, theoretical or experimental, of CPT symmetry?
15. ### Weak Interaction Invariance Under CPT Symmetry

Is weak interaction invaraint under CPT Symmetry? Why?