What is Spin: Definition and 1000 Discussions

When constructing the Lie algebra of the Lorentz Transformation, the references usually start with an infinitesimal proper-orthochronous transformation, and then find the infinitesimal generators. Let's call the set of these generators L. after finding L, the references usually compute the...

I should Use the fact that in general the eigenvalues of the square of the angular momentum operator is J(J + 1)h and show the spin of the electron. I have J= L+S and J2 = L2+ S2 Homework Statement But how could i find the spin of the electron

In Perkins's Introduction to High Energy Physics, the author obtained the spin of neutral pions from the decay \pi^0 → 2\gamma He argued that the z-component of the total photon spin in the above decay can have the value S_z=0 or 2. If s_\pi=1, then only S_z=0 is possible, and the two-photon...

It seems as though many of the threads on this site deal with issue of what the concept of "spin" actually means. I think it may be useful to devote a thread designed to solicit out of the community just what this property of fundamental particles is. Intrinsic angular momentum as opposed to...

Quote from wikipedia about the electron's spin But in optics and other fields we learned that speeds exceeding c are possible, if they do not propagate information. So is the concept of a classical electron with definite radius still physically correct in the sense that it's surface is...

If spin particles are in \vec{B} = 0, then is it impossible to determine their magnetic moment at a given time given any investigative method?

A friend of mine was reading Penrose's new book on CCC; I do not want to discuss this story here but a rather interesting detail which could be relevant w/o the whole CCC stuff. SR and GR rely on (global and local) Lorentz invariance. From these symmetries one can derive invariant mass M² and...

Hi there. I have to solve this problem. The statement says as follows: A particle beam with l=1, without spin and with momentum p is incident on the plane x= 0. In the region x<0 the particles move freely and for x>0 are under the action of a constant magnetic field H in the z direction V(x) =...

Not sure if the question makes sense, nevertheless it can help clarify some concepts, I guess. What is the amount of energy required to change the spin (intrinsic angular momentum) of a photon?

When we speak about wave function of an electron, we write it as ψ_{n,σ} (x,ζ) so that we specify here the orbital quantum number by n and spin quantum number by σ. σ can take two values according to spin up or down. x is space position and ζ has two discrete values related to spin up and down...

Dear Forum, I would like to understand what the origin of spin 1/2 is. I read in Feynman's lectures that the origin is related to quantum field theory. I know nothing about quantum field theory. Is there an easy explanation? Thanks Cabrera

In relativistic limit the spin and the angular momentum are not of conservation because of spin-orbit interaction.Then the symmetry SU(2) is broken because vector spin does not commute with the interaction Hamintonian.The SO(3) symmetry is also broken for the same reason.So I do not understand...

I'm currently taking a first course in quantum mechanics and we just recently introduced generalized angular momentum. Now, take the special case of a spin-1/2 particle. If i understood this correctly there are two possibilities spin up: ms = 1/2 , and spin down ms = -1/2 , this comes from...

I know that the generators of the Poncaire group that are associated with *orbital* angular momentum belong to an infinite dimensional representation, i.e. \begin{equation} L = \frac{\partial}{\partial \theta} \end{equation} Also the spin generators are associated with some finite...

Homework Statement A light string can support a stationary hanging load of 27.0 kg before breaking. An object of mass m = 2.81 kg attached to the string rotates on a frictionless, horizontal table in a circle of radius r = 0.809 m, and the other end of the string is held fixed as in the...

Positronium annihilation opportunities are strongly restricted by the requirement to conserve spin. The spin of a photon is 1; and for some reasons two photons are completely unable to have spins in different directions. They can only have parallel spins (total 2) or antiparallel spins (total 0)...

Homework Statement The z-component of the spin of an electron is measure and the value h-bar/2 is found. Immediately afterwards, the spin along a direction making an angle θ with the z-axis is measured. What are the possible outcomes of this second measurement and with which probabilities do...

So in my quantum class we learned that if you measure spin in one direction and get h/2 and then in another direction that it will be (plus or minus)h/2 as well. I was wondering how you would know the probability of it being the positive value vs the negative value. It's a function of the...

Does the cooper pairs spins (up and down) cancelling out have anything to do with anything? Is the current spin polarized in a superconductor?

I’m a layman who has reviewed some popular literature on QM. Apologies in advance for my naivety. I’m of the impression that the quantum spin (±½) of an electron can be determined as it travels through a Stern-Gerlach apparatus (SGA) for the single direction in which the SGA is aligned (say...

What does the spin of an electron mean? Is it the z component of the spin angular momentum or the spin quantum number?

In experiments with polarized beams of particles, I suppose one knows the spin orientation probabilities of those particles, is that the case? When physicists make experiments with polarized beams of unstable particles, how do they treat spin in a decay of such a polarized particle? If the...

As I understand it, the spin of anything is with respect to the background spacetime. So I have to wonder if the spin of elementary particles depends on the background metric, on the number of dimensions of the background, or the expansion rate, or the curvature, etc. Or is spin independent of...

Does photon has spin induced magnetic moment? I think the answer is no. But why? You know, electron has. Does this have something to do with the fact that electron is massive while photon massless?:confused:

Homework Statement A tennis player slices the ball to spin and deviate from its normal parabolic path. What is an explanation for this phenomenon? I am having trouble visualizing the phenomena that is occurring with the slice and as well as the explanation give by the book. How is the...

So we are doing problems involving potential energy of electrons, wave functions, and all that jazz, but I am utterly lost on how to do this problem... The professor threw it at us, and I am completely lost on how to even begin. Please help me In a different universe from ours the spin...

How come normal current has a magnetic moment if 50% of electrons have spin up and 50% have spin down. Is it because they have to be in pairs? Would a wire of current with electrons all polarized up attract a wire next to it with electrons all polarized down? Extra question How come...

Homework Statement |\psi >=a|z>+b|-z> find <S_x > The Attempt at a Solution So I just need to find <S_x>=({|<x|\psi >|}^2-{|<-x|\psi>|}^2)\frac{\hbar}{2} right

Help please! Where can I start if I want to learn Quantum Spin Hall Effect? I have learned the some fundamental ideas of integer quantum hall effect by myself. Under this background, what more should I read? cause I really can't find any notes or videos that are teaching about QSHE. I am now in...

Spin is the art of presenting facts in such a way as to make yourself look good. The best spin, IMO, utilizes accurate facts (to avoid being shown a liar), but utilizes cherry-picking and carefully worded descriptions to paint a picture much more favorable than another view might present. In...

I can't seem to reconcile a part of the vector model of spin and some of its operators. to quote wiki just above the "Bohr model" section: http://en.wikipedia.org/wiki/Vector_model_of_the_atom#Mathematical_background_of_angular_momenta "2.The magnitude of the vectors must be...

I'm currently reading Sakurai's 'Modern Quantum Mechanics' (Revised Edition) and at page 76 he introduces a spin half hamiltonian H = - (\frac{e}{mc}) \vec S \cdot \vec B. But what is c doing in this hamiltonian? Clasically the energy of a magnetic moment in a magnetic field is E = -...

My understanding is that spin angular momentum is just as real as bulk angular momentum. So, if we get the spin of some electrons in an object to flip, then the object should start spinning in the opposite direction to conserve angular momentum. Right? If we mount a permanent magnet in an...

'Ello, I have a question regarding the results in this paper (and another which I will mention later) http://arxiv.org/abs/hep-ph/0212199 Now, I'm not so concerned about the 'braney' bit, but more their definition of the cross section in Eqn. (46). They have included the usual (2j+1)...

Regarding the term "Spin"... I've see a number of different descriptions. In the book I'm currently reading it says it is "loosely" the measure of the strength of rotational motion, and "technically" the measure of the quantity called angular momentum. It also states we consider the spin...

this is from Omnes' book Understanding QM Has this problem been resolved or is it still outstanding?

what do we mean by spin of a particle when we say it a point particle?how do we measure spin experimentally and give it values like +1,+2 etc. what does it mean by a spin 0 particle?

Hi there, I was wondering what is the spin of a magnetic monopole. To be specific, I mean the 't Hooft-Polyakov monopole in the Georgi-Glashow model. Sure, it is a purely classical object and as far as I know, there is no known way how to fully quantize it. So, strictly speaking, the notion...

I don't understand this very well...

Hi ! I am working on the modelling of the Table Tennis game. Can I calculate the Spin of the Ball after hitting without using any camera and any vision system. I know the velocity of the ball before and after the hitting in all directions (x,y,z) and velocity of the racket as well. Is...

Hi all, I was just pondering why spin is odd under time reversal. I am trying to get my head around CPT invariance and am failing to find good material online. Thanks

Can there be EM radiation with spin zero? I don't mean that the sum of all spins is zero, as it usually is. My thinking is that all light spins and usually the left and right component is of equal intensity. Am I correct in thinking that light reflecting off of a suitable horizontal...

The "spin family" art works have a model of something with spin 2 1/2. I can't find any particle with this property. The max seems to be the graviton with spin 2. ?

I'm wondering how the spin of a particle, whether a particle is a fermion or a boson... how does this relate to the symmetry of a particle, U(1) or SU(2) or SU(3)? I'm trying to understand SUSY in relation to the other internal symmetries? Is there spin 1/2 and spin 1 particles associated with...

I can't visualize spin... I know that its not just a particle rotating about its axis... Then how do I think of it?

Can we measure the spin of a particle by measuring the force on a Magnet? I wish to consider a modified stern gerlach like apparatus where a Magnet of mass M is attached to a spring. Can we measure Spin of the particle by studying the deflection of the magnet? Even if it is possible, I can...

From what I've learned atoms with unpaired electrons are paramagnetic and those without are diamagnetic. Strontium has electron configuration of [Kr] 5s^2 so why is it paramagnetic?

As a preface to a different question, it is valid to think of the property of spin of elementary and related particles as basically just tiny magnets, right?

I have a problem understanding the Lorentz transformation of the spin. The spin 4-vector is defined in the rest frame of the particle as s^{\mu} = (0, \vec{s}) and then boosted in any other frame according to s'^{\mu} = (\gamma \vec{\beta} \cdot \vec{s}, \vec{s} +...

Spin 1/2--Raising and Lowering operators question Hi, Quick question regarding raising and lowering operators. Sakurai (on pg 23 of Modern QM), gives the spin 1/2 raising and lowering operators S_{+}=\hbar \left|+\right\rangle \left\langle-\right| and S_{-}=\hbar \left|-\right\rangle...