What is Spin: Definition and 1000 Discussions

I'm a bit confused about quasars and neutron stars but is it the case that quasars are much much denser than our star and spin many times per second? I think the sun completes one rotation in about 25 days and it's spinning at about 4467mph. I'm pretty sure that density will effect the speed...

The below might need lots of corrections/modifications, since spin is a hard concept to grasp and I don't understand it much. We know that: The angular momentum (spin) of a photon does not have an analogy in classical mechanics. however let's use a loose/inaccurate analogy of something that...

Singularity Spin Mechanics Okay I within the last week too a look at a article about black hole spin and in this article it was said by a scientist that black hole's spin near the speed of light that are supermassive blazars I was thinking if a object is spinning wouldn't that make this...

In his book on GR, Wald writes "the notion of the mass and spin of a field requires the presence of a flat background metric...which one has in the linear approximation but not in the full theory..." Why do we need a flat background metric to define a field's mass and spin?

Say I have a particle in the rest frame with spin up in the z direction. If I boost the system in x direction, does the spin still point in the z direction? Why or why not? In Dirac Spinor, if I choose "spin up", namely setting \phi=\begin{bmatrix}1\\0\end{bmatrix} in the notation shown in...

Homework Statement For a homework problem, I have to work out ##\frac{d(\langle \hat{S}_x \rangle )}{dt}## for the four-by-four spin matrix ##\hat{S}_x##. I have a spin matrix ##\hat{S}_x## and I need to use the generalized Ehrenfest theorem. My problem is that I'm not sure whether my approach...

Permanent magnet can degenerate by many ways. But it really needed in compact generator to convert mechanical force into electric But are there any other way to generate electric from mechanical force without magnet? I want to design self exited magnet for dynamo. It need tobe an effect that...

Question. Is there a quantum reason why a lone electron in any of the three available (x,y,z) 2P orbital energy states must always be spin-up or spin-down ? Every figure I see always shows a single electron as spin-up for the three 2P energy states, but is there a quantum theory constraint...

The regular spin orbit Hamiltonian is H_{SO} = \frac{q\hbar}{4 m^2 c^2}\sigma\cdot(\textbf{E}\times \textbf{p}) If I consider a 2D system where E = E(x,y) and p is treated as an operator, i.e. \hat{p} = \hat{i}p_x + \hat{j}p_y then, clearly E and p do not commute, so this doesn't look like...

Why are the Pauli matrices multiplied by 1/2 ?? Why are they represented as σ1/2 σ2/2 and σ3/2 and not just σ1 σ2 σ3 ?

1 - How does an electron's spin generate its own magnetic field? 2 - Why are only the orientations of electrons taken into account in statements such as "permanent magnets are created when the orientations of the spin of the electrons are orientated in the same direction" when protons also have...

Hi, i have been trying to figure how to solve this problem, i just don't know how to proceed Homework Statement A particle with spin s=1 has due to rotational invariance all three states |s_z\rangle=1, |s_z\rangle=0 and |s_z\rangle=-1 degenated with energy E_0>0. Then its introduced an...

I have found what I think is the correct answer I just want to check an assumption. The magnetic field points in the +ve z-direction. We are given the initial state vector \left| A \right\rangle_{initial}=\frac{1}{5}\left[ \begin{array}{c}3\\4\end{array} \right] Am I right in thinking that...

Homework Statement Find expectation values ##\langle \hat{S}_x \rangle##, ##\langle \hat{S}_y \rangle##, ##\langle \hat{S}_z \rangle## in state ##|\psi \rangle =\frac{1}{\sqrt{2}}(|+\rangle +|- \rangle)## ##|+\rangle## and ##|-\rangle## are normalized eigen vectors of ##z## projection of...

Hey Everyone, I'm working on a question and can't quite get the answer out. QUESTION: Part (a) "\left|\alpha\right\rangle and \left|\beta\right\rangle are the eigenfunctions for neutrons polarized respectively along positive and negative z directions. If the neutron, initially in...

Homework Statement [S2 total, Sz ∅1] Homework Equations S2 total = S2∅1+ 1∅S2+2(Sx∅Sx+Sy∅Sy+ Sz∅Sz) The Attempt at a Solution I calculated it in steps: (1∅Sx 2 +Sx 2∅1) * Sz ∅1 =[S2x, Sz] ∅1 + Sz∅Sx 2 =-h_cut i (SxSy+SySx)∅1 + Sz∅Sx 2 Is it correct way of doing it? I...

Homework Statement Find the eigenvalues and eigenstates of the spin operator S of an electron in the direction of a unit vector n; assume that n lies in the xz plane. Homework Equations S|m>= h m|m> The Attempt at a Solution This question is from Zettili QM and they have...

Homework Statement "A spin 1/2 electron in a hydrogen atom is placed in a time-independent magnetic field B=B0(k) The electron's spin starts in the |z+> state at t=0. Calculate probability o ffinding the electron in the |y-> state as a function of time for t>0. Homework Equations...

Given two spin-1/2 particles, the overall spin of the pair decomposes into a spin singlet and a spin triplet. Using the Clebsch-Gordon series and referring to the z-axis, we find the spin singlet is: ##|\Psi^- \rangle = \frac{1}{\sqrt{2}}(|\uparrow_z \downarrow_z \rangle - |\downarrow_z...

Homework Statement Show that the state d^{\dagger}_{\alpha}(0)\mid 0\rangle describes a postrion at rest by showing that it is an eigenstate of the operators P^{\mu}, Q, J^z . Homework Equations The Fourier expansion of \psi, \psi^{\dagger}: \psi = \int \frac{d^3k}{(2\pi)^3} \frac{m}{k_0}...

Homework Statement Hi All, this problem is related to spin-1/2 in an arbitrary direction, in particular building off of, but going beyond, Griffiths QM 4.30. I am given an unnormalized general spin state, \chi in the z basis, and then asked "in what direction is the spin state pointing?"...

Show that all hermitian 2x2 matrices with trace 0 are elements of three dimensional vector space in \mathbb{R}, which basis vectors are Pauli spin matrices. Any clues on how to begin? :/

What makes the world spin?

Suppose we have a Stern-Gerlach apparatus through which we send spin-1/2 particles and subsequently measure their position. If a passing particle "collapses" to the spin up state about X, it moves "up" and is registered by detector U, otherwise it "collapses" to the spin down state about X and...

Homework Statement Homework Equations The Attempt at a Solution To be honest I'm clueless. I've missed a large amount of the course and just struggling to find any sources that explain this. I don't want the answer to the question, I want to figure that out for myself. What I really need is...

I read somewhere that a magnetic field is caused by the spin of a charge particle, in most cases the electron. So, I take it then that the electrons in the eddy currents in a bar magnet are all spinning in the same direction? Also, do those eddy currents induce currents in the virtual electrons...

I'm studying electron spin/magnetic field and I was taught electrons can have only 2 spin orientations, as seen in the Stern and Gerlach experiment. But this orientations are given in relation to what? Do all electrons in the universe have the only 2 same orientations, or only the electron in...

I'm learning about NMR and it's been stated that deuteron has a spin 1 nucleus and so should exhibit different behavior. Why? I've heard of electrons having spin, and now protons, but I don't see why the spin of a neutron should matter since it's uncharged. I'm thinking a spin of 1 means...

I was just reading in "Spin physics in semiconductors" by Dyaknonov section 1.2.4, page 4 in the footnote, how the Earth's spin is expected to precess around its orbital angular momentum. Does anyone know if this has been considered as a possible cause for Geomagnetic reversal...

Homework Statement Consider the so-called Spin Hamiltonian H=AS2Z+B(S2X-S2Y) for a system of spin 1. Show that the Hamiltonian in the SZ basis is the 3x3 matrix: \hbar2*[(A,0,B; 0,0,0; B,0,A)].Find the eigenvalues using degenerate pertubation theory. Homework Equations Spin Pauli MatricesThe...

I think I understand this only up to a point. 1. Photon spin is quantized to be +1 or -1 and these represent left- and right-hand circular polarization. 2. A photon can have a superposition of 2 spin states in any proportion. 3. Having probability amplitude of 0.5 of spin 1 and 0.5 of spin -1...

I've been trying to wrap my head around spinors, and I think I'm beginning to understand the mathematical formalism, but one thing in particular continues to confuse me. Whenever I read anything mathematically rigorous on spinors, the authors refer to spinors being associated with isotropic...

I am trying to understand the measurement of spin, in order to understand Bell's paper on the Einstein-Podolsky-Rosen paradox. When we measure the spin of a fermion in the direction of unit vector a, will the result be: 1. a value of either +0.5 or -0.5, and upon measurement, the fermion...

Okay, so I was looking at some ideas of storage based on making electrons spin "up" or "down" to store binary data, and I began wondering two things: 1) How does one change the spin "orientation" (for lack of a better word) of a particle? 2) How does one detect the spin "orientation" of a...

(1,a^2,a^2,a^2)) from the action; \mathcal{S}_{D}[\phi,\psi,e^{\alpha}_{\mu}] = \int d^4 x \det(e^{\alpha}_{\mu}) \left[ \mathcal{L}_{KG} + i\bar{\psi}\bar{\gamma}^{\mu}D_{\mu}\psi - (m_{\psi} + g\phi)\bar{\psi}\psi \right] I can show that, i\bar{\gamma}^{\mu}D_{\mu}\psi -...

In trying to derive the Dirac equation in space-time (1,-a^{2},-a^{2},-a^{2}), I have read that the Dirac equation is (i\bar{\gamma}^{\mu}(\partial_{\mu}+\Gamma_{\mu})-m)\psi=0 where, \Gamma_{\mu}=\frac{1}{2}\sum ^{\alpha \beta}e_{\alpha}^{\mbox{ }\nu}(\frac{\partial}{\partial...

Paulis exclusion principle say that two electrons around a nucleus can't have the same quantum number. Does that mean that, say, two hydrogen atoms with electrons with the same spin can't make hydrogen gas? Or does one of the electrons change its spin?

This may be a basic question, but it's something I'm having a hard time understanding. The Wikipedia article I am reading about spin http://en.wikipedia.org/wiki/Particle_spin seems to be saying that spin isn't really what we think of on the macroscopic scale (ie: spinning on an axis like a...

I have a basic understanding of what particle spin is, but I'm not clear on how how integer spins are different than fractional spin values. I also need help understanding how fractional spins are different from each other (difference between spin 1/2 and spin 3/2) and how integer spins are...

Homework Statement Spin-system: A spin-system has N = 30 localized particles with spin quantum number s = ½ and magnetic moment µ0. m = M/µ0 is the magnetic moment M in vertical direction (ms = +½) in units of µ0. Calculate the probability PN(m) for the total magnetic moment M to achieve...

As we know, spin is an internal symmetry. but it seems a bit different from other internal symmetry, e.g. electrical charge, color, flavor... because it can be coupled with orbital angular momentum and in some aspects be linked to space-time. further more, we can classify all the particles into...

Is spin the only physical parameter that can be entangled? If not, what else? If so, it seems there is something special about spin?

This is a bit embarrassing, but by convention does |0> = (1,0)^T and |1>=(0,1)^T, where we are in the basis of the eigenvectors of \sigma_{z}?

I don't know if you are familiar with it, but in pertubationt theory for hydrogen it is handy to look for eigenstates of J = L + S since this commutes with the hamiltonian (L and S are not separately conserved). My book then says that the good quantum numbers are: n,l, j, mj I must admit I'm...

I have been reading up on spin networks and spin foams... but most of the publications seem to come from 1999 or 2000. Does anyone know what happened to this idea? Is it still valid, or was it a dead end? Is it still an active area of research, or did the idea perhaps evolve into something with...

Homework Statement I put this in the math forum because although it's for my EM waves class, it's a math question. Show that the spin force can be written as: F_{spin}=\frac{-1}{2}Im(\alpha)Im(E\cdot\nabla E^{*})=\nabla\times L_s Find L_s. Where \alpha is complex. I'm using E^{*} to denote...

Homework Statement Consider an electron, described initially by psi = 1/sqrt(10) with column vector (1 3). A measurement of the spin component is made along a certain axis, described by operator A, it has the eigenvalues +h/2 and - h/2 as possible outcomes, and the corresponding eigen states...

I have a question about how my book derives a formula. It starts with: We have an electron free too move on a cylinder and from the cylinder there is an electric field pointing radially outwards. Now for an electron moving in an electric field it sees local magnetic field given by: B =...

If two quarks are in a S=1 state, are they in either ##|\uparrow \uparrow \rangle ## or ## |\downarrow \downarrow \rangle ## ?

I seem remember hearing that spin-1 was ruled out but since reading this paper I am unable to find any info on spin-1 Higgs. Has there been any further developments on this? Honestly, I am not a particle guy so I'm not sure on the details... can someone explain why Higgs' particle has to have...