What is Spin: Definition and 1000 Discussions

I am still learning about all the Groups related to the Dirac Equation for spin 1/2 particles. Apparently, the reason that the Hilbert Space for spin 1/2 particles is 2-dimensional is because when you try to map SU(2) to SO(3), the mapping is 2-to-1, i.e. SU(2) is a double cover for SO(3)...

i have the following questions: Bell inequalities use spin 1/2 matrices and experiments use photons. Is then the electric field horizontal or vertical after the measurement with a polarizer in other words can we assimilate the orientation of the field with a vector in the hilbert space ? How...

After coming across an article by Schwinger where he tries to deduce the spin of a neutron, I started to wonder when the same thing was done for the photon... Specifically, I've been trying to locate "the" article where the spin of the electromagnetic field was theoretically determined to be 1...

This is an exercise from an old examination that I am trying to understand by following the given solution to this problem. The exercise is about to calculate the four spin average <SiSjSkSl> and the indices i,j,k and l, given a Hamiltonian H. Solution: The problem is that i can't follow the...

Homework Statement Consider two spin 1/2 particles interacting through a dipole-dipole potential \hat{V} = A\frac{(\hat{\sigma_1} \cdot \hat{\sigma_2})r^2 - (\sigma_1 \cdot \vec{r})(\sigma_2 \cdot \vec{r})}{r^5} If both spins are fixed at a distance d between each other, and at t = 0 one of...

hello, i am new in this forum , :) i want to ask if anyone know how to calculate the nuclear spin of an atom in general, i searched in google i didnt find any method of calculation :/ can anyone help me please, thanks

Does an electron really spin about its own axis? If not, what does spin magnetic moment imply? My physics teacher said "Besides the orbital moment, an electron has an intrinsic magnetic moment, it is called the spin magnetic moment, But I hasten to add that it is not as though the electron is...

Hi, Does the solar system spin around an axis as it travels through space, much like a planet rotates as it orbits the sun and if it does where is the axis point. I know the solar system is orbiting the centre of the galaxy, I was just wondering if it behaved like a planet because things tend...

Do the corrections after renormalization to the gyromagnetic ratio of the electrón, more precisely its g-factor, that slightly deviate from the relativistic Dirac equation prediction of g=2 as corresponds to a spin 1/2 fermion, mean that the fermions spin symmetry is only aproximate? i.e. that...

For a spin 1 field described by a 4-vector, the condition m \partial_\mu A^\mu=0 can be derived from the equations of motion. This condition reduces the degrees of freedom from 4 to 3 for a massive particle (when m is not equal to zero). However, for the photon, \partial_\mu A^\mu=0 has to be...

Hello everyone, I have a problem with deriving following equality: \begin{equation} u^{s}(p) \bar{u}^{s}(p) = 1/2 ((\slashed{p} + m)(1+\gamma^5 \slashed{s})) \end{equation} where s is spin 4-vector. I know how to calculate this tensor product when there is spin sum in front of it, but without...

For a massive particle, say, an electron, we can use a spin vector ##\vec{S}## to denote its spin state, and the corresponding covariant four vector ##S^\mu##. And we have ##P \cdot S = 0## in the particle rest frame, so it holds in any frame for it is an Lorentz scalor. But, what if the...

Wieland gave his ILQGS talk yesterday, 16 September. Audio and slides are on line. Title: Covariant loop quantum gravity: Its classical action, phase space and gauge symmetries http://relativity.phys.lsu.edu/ilqgs/wieland091614.pdf http://relativity.phys.lsu.edu/ilqgs/wieland091614.wav The...

What exactly entangled-spin pairs do in Stern–Gerlach experiment that ordinary particles pairs with opposite magnetic dipole moments do not? http://upload.wikimedia.org/wikipedia/en/thumb/e/e2/Bell.svg/600px-Bell.svg.png What equation represents the blue line and what equation if for the...

How does the spin of a pair of particles work if both particles are known to be chiral? generically if I sum the spins of two different (EDIT: spin 1/2, indeed ;-) particles I expect to get a triplet with S=1 \uparrow\uparrow, \uparrow\downarrow+\downarrow\uparrow, \downarrow\downarrow and...

I am interested in the topic of the thread https://www.physicsforums.com/showthread.php?t=768539 ,especially for those unpair 1p1n case. As I know, for the simplest case deuteron, the Jπ (groundstate here and later) is 1+ but 0+. This is very different to the atomic physics case. For He...

Is there a theoretical basis for the spin of the nucleus of an arbitrary atom? I'm looking at this website: http://hyperphysics.phy-astr.gsu.edu/hbase/nuclear/nspin.html

I have only ever seen the wavefunction for a spin 1/2 particle written in the basis set |α> |β>. I was interested in how a wavefunction |ψ> = a|α> + b|β> might be rewritten in a continuous basis and hence would need to know what the actual functions of |α> & |β> were. Thanks

Everywhere I read about the angular momentum / spin of electrons and how a 1/2 spin particle has a unique characteristic that you need to turn it 720 degrees in order to get it turned back to where it was before you started turning it. How exactly do people "turn" an electron in this fashion...

Homework Statement The photograph shows a device called a radiometer. The four regular panels are black on one side and shiny like a mirror on the other side. In bright light, the panel arrangement spins around in a direction from the black side of a panel toward the shiny side. Do photon...

How to prove when electron spin is perpendicular to linear momentum, orbital angular momentum can't be 0. And when they are paralleled, orbital angular momentum is 0. Thanks.

I'm trying to design mechanism similar to this video https://www.youtube.com/watch?v=t1JNWnTpmkA where i have concentric rings that spin within them selves around x, y and z axis. I intend to use track roller cam follower bearings to support each ring, with a bearing width of 10mm and a...

Hello, I read in an article that in GR it is possible to use a connection with torsion to model ponctual particle with spin. The connection can be decomposed in a curvatue part and a torsion part. In an other part, we know that the invariance under pointcarré group imply conservation of spin of...

Does Magnetic Field (=/need) electron spin + movement of charge? A proton can create a magnetic field too, but does it have spins as well? Hmm super confused. What is a spin?

Homework Statement The spin 1/2 electrons are placed in a one-dimensional harmonic oscillator potential of angular frequency ω. If a measurement of $$S_z$$ of the system returns $$\hbar$$. What is the smallest possible energy of the system? Homework Equations...

Mass-less particles travel at the speed of light. If such a particle has an intrinsic spin, the DIRECTION of the spin angular momentum vector must be in the same direction as the linear motion of the particle. Why exactly is that? Thanks in advance.

The spin of an arbitrarily oriented electron precesses in the presence of a magnetic field (see Feyman lectures 10-7). The energy states also split due to magnetic fields (see Feynman lectures 12-4). I am trying to understand how to think about spin precession, spin flipping, and spin...

The uuu hadron doesn't violate Pauli's exclusion principle presumably because there is color. But even without color, can't the uuu exist if spatial wavefunctions are different? Suppose one u quark is located at r1, another at r2, and another at r3, and say that all three u quarks have spin up...

OK so we have a dipolar bond between two elements. This bond makes the other electrons redistribute in order to rest in peace. Everything's OK up until now. What happens, however, when two of these other electrons have the same spin an yet they end up together because of this redistribution? I...

Are there any experiments or theories about the relation between magnetic dipole moment orientation and velocity vector of free electrons?

Homework Statement Find the matrix representation of S_z in the S_x basis for spin 1/2. Homework Equations I have the Pauli matrices, and I also have the respective kets derived in each basis. There aren't really any relevant equations, other than the eigenvalue equations for the...

Consider a composite particle. Its spin is determined by the spins of its constituent particles. But the constituent particles are in a superposition of different spin states and so don't have a definite spin. So it seems it shouldn't be possible to ascribe a definite spin to the composite...

Ok guys, I know this must be pretty basic for but I am new to this section of physics. Anyway, my question is a two-part one, I guess: 1) Why does the spin number get only half integer values in fermions and integer values in bosons, mesons, etc.? 2) How do we conclude that the spin number is...

Hi. According to Griffiths the conmutation relations for the angular momentum and spin operators conmutation relations can be deduced from the rotational invariance, as in Ballentine 3.3. For the angular momentum seems logical that it is so, but how is it that rotational invariance leads to...

Hello. I was going through the problems in the angular momentum chapter of the text "Problem Book in Relativity and Gravitation"-Lightman et al in preparation for a project and I came upon part (c) of problem 11.10. It basically starts with a family of observers with 4-velocity ##u^{\mu} =...

What gives an atom its atomic spin?

So I want to design a propeller that will slow down a motor and I want to know what formulas or equations I would use to calculate that torque. Also, if I decided I wanted to run it in a fluid, what it just be a matter of density change? I have attached a picture of what I want to do. Thanks

I believe I understand the mathematical derivation of the Dirac equation. I understand how the four 4X4 matrices, and their relation to the 2X2 Pauli Matrices, arise from that derivation. I understand that the 3 spin observables for Fermions are ALSO represented by the 3 Pauli Matrices...

Hi, Assume I’m solving a 2-particle (fermions) problem in a potential well. If I set the wavefunction as anti-symmetric, then by default I’m assuming that the two particles has the same spin and hence exchange interaction has to be accommodated for. But what if the 2 fermions have different...

The spin 4-vector is defined in the rest frame of the particle as s^{\mu}= (0, \vec{s}). Why is the zeroth component of the same zero in this frame?

As we know photon's helicity are \pm1. Helicity is the projection of the spin S onto the direction of momentum, p, which is considered as Sz. What about Sx and Sy? They are both ZERO?

"Locally, the spin density S is an intrinsic (i.e. origin-independent) quantity, which is associated with the local ellipticity of the polarization of light. In turn, the orbital AM density L=r x P0 is a manifestly extrinsic (origin-dependent) and is produced by the corresponding canonical...

If a fast moving and heavy object strikes earth,can it change its spin or rotation or both?

i mean, people are creating LHC to split the atoms, but why don't we just spin it? spin in in high speed and see if a quark/photon/electron would break can we not do that? is it mathematically impossible to have a mass in the center of rotation?

I'm trying to get my head around this spin idea, the idea that particles behave like tiny dipole magnets when passing through a magnet field, either spin up or spin down. Because unlike magnets they don't produce a spread on at the end, they are either top or bottom. So the problem I have...

So I've just been reading about the Stern-Gerlach apparatus/experiment and had some questions about the half spin probabilities... First let's say a collection of spin-half particles are sent through a S-G apparatus (which I know measures the z component of particles spin angular momentum)...

To define spinors in QM, we consider the projective representations of SO(n) that lift to linear representations of the double cover Spin(n). Why don't we consider projective representations of Spin?

Trying to get my head around this one. Given that you can have a proton and an electron in a hydrogen atom for example, and they can create a singlet or triplet configuration, with spin 1 and spin 0 respectively. The total spin operator can be derived as: S^2 = (Se + Sp)^2 = Se^2 + Sp^2 +...

Homework Statement The interaction between the spins of the two particles in a hydrogenic atom can be described by the interaction Hamiltonian $$\hat{H_I} = A \hat{S_1} \cdot \hat{S_2}.$$ Compute the splitting of the ground state due to ##\hat{H_I}##. Both particles have spin 1/2. Homework...

Number of Spin "s" States Homework Statement For a system of two identical particles with spin s, determine the number of symmetric and anti-symmetric spin states. 2. The attempt at a solution This does not seem like a problem that is that difficult, but I am having some trouble...