# Tagged Questions

Fundamental characteristic property of particles which together with orbital angular momentum acts as the generator of rotations and which doesn't have a classical equivalent but is sometimes compared to and contrasted with classical intrinsic angular momentum.

569 views

### Do spin-spin interactions break time reversal symmetry?

I'm sure the answer is yes, but how is this shown? Normally for a single spin-1/2 you have a time reversal operator: $-i \sigma_y \hat{K}$ where $\sigma_y$ is the second Pauli matrix and $\hat{K}$ is ...
136 views

### What the quantum spin refers to? How we calculate the angular momentum $\omega$ from the spin quantum number?

How we calculate the angular momentum $\omega$ from the spin quantum number, to know how fast a particle rotating on its own axis?
120 views

### Is spin just due to uncertainty in angular momentum?

I can't seem to think of any way to envision electron spin. Can it be thought of as the uncertainty in angular momentum?
83 views

### Will macroscopic object change its angular velocity after absorbing electron?

Consider macroscopic object (a ball for instance) which has angular momentum equals 0. Now single electron hits the ball and is absorbed by it. Let's assume it hits in direction perpendicular to ...
1k views

### Why can't I just think the spin as rotating?

I'm going mad about the problem. I really don't understand why do electron have 1/2 spin number, why they are not actually spinning. I can accept that the electrons have their own magnetic field, ...
245 views

### Which way do black hole jets spin?

The centers of black holes and quasars often have jets coming out the two poles of an accretion disk, say north and south. Is it known if the two jets spin in the same direction or opposite ...
218 views

### Term symbol - how do we know the number of electrons $e^-$?

Lets say I have a term symbol $^4D_{5/2}$. From this I can simply read the total quantum numbers numbers $L=2$ and $J=5/2$. Now the superscripted number $4$ is called multiplicity if I am not ...
522 views

### Relation between the spin of a particle and the polarization of it's wave

Is there any intrinsic relation between the spin of a particle, and the degree of freedom of it's polarization? does it holds for any particle-wave couple? like EM-photon, ...
545 views

### How do you determine the elementary particle's spin number?

I know that electrons and protons have a spin of 1/2, whereas photons have a spin of 1,. However, I do not know how this is determined? How is it determined?
274 views

### What is the interpretation of the Chern-Simons electromagnetic spin density?

Hans de Vries (who happens to be a no-longer-active physics.SE user) has an online book (referenced below) in which ch. 6 is a presentation of an object he calls the Chern-Simons current, ...
294 views

246 views

### Chirality, helicity and their relationship for the massless case

Chirality can be interpreted as a property of Lorentz group - Lorentz transformation of field through representation $(s, 0)$ or representation $(0, s)$. For the massless particles one says, that ...
405 views

### Quantization of Electron Spin

Why is electron spin quantized? I've seen the derivation for the Hydrogen atom's energy levels, but my professor jumped to electrons having spin 1/2 or -1/2 as experimental. Why do electrons obey the ...
5k views

### How do we know photons have spin 1?

Electrons have spin 1/2, and as they are charged, they also have an associated magnetic moment, which can be measured by an electron beam splitting up in an inhomogeneous magnetic field or through the ...
149 views

393 views

### Can atoms have nonzero dipole moments?

Let's make the question easier by considering two-level atoms(with spin states, i.e. spin up $|\uparrow\rangle$ and spin down $|\downarrow\rangle$). An article I recently read claims that atoms do not ...
267 views

### How does spin appear in QFT?

In QFT, as I read, it appears naturally. It is connected with Poincare algebra, doesn't it? __ As explanation of the main part of the question. Operator of relativistic orbital angular momentum ...
940 views

### How does one show using QED that same/opposite electric charges repel/attract each other, respectively?

Why do same charges repel each other and opposite charges attract each other (please explain the phenomenon using real laws of nature (QED) not with the approximation model)?
52 views

### What physical value is described by following operator?

Let's have the system of point-like non-interacting particles and it's own angular momentum $$\mathbf L_{1} = \mathbf L - [\mathbf R_{E} \times \mathbf P],$$ where $\mathbf R_{E}$ - center of energy ...
523 views

### The connection between classical and quantum spins

I have two questions, which are connected with each other. The first question. In a classical relativistic (SRT) case for one particle can be defined (in a reason of "antisymmetric" nature of ...
352 views

### What is the meaning of spin two?

As the title suggests, what is the meaning of spin two? I kind of understand spin half for electrons. I can kind of understand spin one for other particles. However I'm not sure how something could ...
271 views

### Does the spin precession change sign when the angular momentum does?

Say you have a charged particle moving circularly in an electromagnetic field. Basic quantum mechanics tell us that its spin will precess with a certain frequency. If the same particle were traveling ...
398 views

### Charged pion decay and spin conservation

Charged pions $\pi^\pm$ decay via an intermediate $W$ to (e.g.) a lepton-neutrino pair. The pions being scalar (spin-0) particles and the intermediate $W$ having spin 1, how is spin conserved in ...
82 views

### Why do cosmic bodies revolve? [duplicate]

Why do cosmic bodies such as planets, stars, satellites revolve? What made them to revolve after the formation of universe?
263 views

### Anyons without fractional spin?

Is it possible to have particles obeying anyonic statistics but not having fractional spin? I am wondering, because while spin in quantum physics arises from the geometry/topology of spacetime, ...
465 views

### Lack of symmetry of the canonical stress-energy tensor

Why in the general case of classical field theory canonical stress-energy tensor doesn't have symmetry of the permutation of the indices? For explanation, let's have a "derivation" of an expression ...
3k views

### Writing wave functions with spin of a system of particles

Suppose I have 2 fermions in a potential $V(x)$. Both particles are moving in one dimension: the $x$ axis. Then, neglecting the interaction between the particles, the spatial wave function of the ...
83 views

### antiferromagnetic spin wave

I have a hamiltonian that is derived from a spin wave energy dispersion calculation for a nearest neighbor interacting cubic antiferromagnet. After a Holstein-Primakoff transformation and making a ...
54 views

434 views

### Can 3 photons be combined to give a spin-0 projection?

Motivation: The neutral pion decays to 2 photons ($\pi^0\to\gamma\gamma$) most of the time. For the decay of the neutral to 3 photons ($\pi^0\to 3\gamma$) we have an upper limit on the branching ...
Wigner classified particles in function of the eigenvalues of $P_\mu P^\mu$ and $W_\mu W^\mu$. Then, it can be proved that for massless particles spin values can be only $\pm s_{max}$. But for a ...