- #1

Jarek 31

- 158

- 31

- TL;DR Summary
- Spin corresponds to angular momentum - isn't it modified in measurement of spin?

If so, what happens with this difference of angular momentum?

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 change of energy, which requires carrier for this energy e.g. photon - getting reversible:

The question is if

e.g.: unpolarized spin <-> measured spin + e.g. photon carrying angular momentum difference

Spin corresponds to angular momentum, so doesn't its measurement mean change of angular momentum?

In other words, while angular momentum of measured spin is clear, can it be the same before the measurement?

In magnetic field e.g. Stern-Gerlach there is also involved energy change: like in Zeeman V=-mu\cdot B.

If so, what is happening with this difference of angular momentum, energy?

One of examples of (allegedly?) going out of QM unitary evolution is atom deexcitation - we can save its reversibility by remembering about change of energy, which requires carrier for this energy e.g. photon - getting reversible:

**excited atom <-> deexcited atom + photon**The question is if

**can we save reversibility of measurement in analogous way?**e.g.: unpolarized spin <-> measured spin + e.g. photon carrying angular momentum difference

Spin corresponds to angular momentum, so doesn't its measurement mean change of angular momentum?

In other words, while angular momentum of measured spin is clear, can it be the same before the measurement?

In magnetic field e.g. Stern-Gerlach there is also involved energy change: like in Zeeman V=-mu\cdot B.

If so, what is happening with this difference of angular momentum, energy?

Last edited: