What is Spin: Definition and 1000 Discussions

1. What are the possible eigenvalues of the spin operator \vec{S} for a spin 1/2 particle? Homework Equations I think these are correct: \vec{S} = \frac{\hbar}{2} ( \sigma_x + \sigma_y + \sigma_z ) \sigma_x = \left(\begin{array}{cc}0 & 1\\1 & 0\end{array}\right),\quad...

Homework Statement What is the expectation value of \hat{S}_{x} with respect to the state \chi = \begin{pmatrix} 1\\ 0 \end{pmatrix}? \hat{S}_{x} = \frac{\bar{h}}{2}\begin{pmatrix} 0&1\\ 1&0 \end{pmatrix}Homework Equations <\hat{S}_{x}> = ∫^{\infty}_{-\infty}(\chi^{T})^{*}\hat{S}_{x}\chi...

Homework Statement The evolution of a particular spin-half particle is given by the Hamiltonian \hat{H} = \omega\hat{S}_{z}, where \hat{S}_{z} is the spin projection operator. a) Show that \upsilon = \frac{1}{\sqrt{2}}\begin{pmatrix} e^{-i\frac{\omega}{2}t}\\ e^{i\frac{\omega}{2}t}...

I wondered about them sometime; I came across many theories, such as it might be because the of the black hole at its centre, but another question rises! Why black holes spin? I thought it might be because at first when the black hole was a star just like our sun, before supernovae happening...

If you see a statement like "Spin analysis of H(22S) atom can be achieved through the use of Stern Gerlach interferometry" are they talking about the spin of protons or electrons? Are they perhaps always correlated ie. the same? What about H(22P)?

Dear PhysicsForum, We have just treated the Dirac equation and its lagrangian during our QFT course, but we have only gone in depth in 3+1 dimensions. My question is about what happens to spin in 2+1 dimensions. In 3+1 dimensions we have to use 4 by 4 gamma matrices, but in 2+1 dimensions we...

I understand that the degrees of freedom must match. A Weyl spinor has 2 d.o.f (spin up and spin down), thus the superpartner must also have 2 d.o.f Is there a reason why it is a complex scalar and not of spin-1?

I'm no physicist, so please enlighten me. Is an electron's spin related to the spin of a proton? Do they spin at the same frequency? I read that electrons have a higher magnetic moment and stuff.

I have read about the Stern-Gerlach experiment in Wikipedia, this experiment proved that electron spin could only take two discrete values. The experiment consist in sending neutral charged atoms through a inhomogeneous magnetic field so it would change the particle’s direction a quantity...

Say an electron tunnels from one state, through a tunneling barrier, to another state. Is the spin of that electron preserved (the same before and after)? If an electron is traveling through a bulk phase conductive metal (a wire), is its spin stable in one state? What will happen to its spin...

The detection of spin in Hadrons and Leptons is done through magnetism, a spin 1/2 particle has two states in a magnetic field, an up particle goes up, a down particle goes down. A spin 1 particle has three states, an up/up goes up, a up/down stays straight and a down/down goes down. A spin 3/2...

If we consider a spin 1/2 particle, then, the rotation of the spinor for each direction is given by a rotation matrix of half the angle let say theta Rspin=\left(\begin{array}{cc} cos(\theta/2) & -sin(\theta/2)\\sin(\theta/2) & cos(\theta/2)\end{array}\right) and the new component of the spin...

Homework Statement A beam of spin-1/2 particles is prepared in the state \left|\psi\right\rangle=\frac{2}{\sqrt{13}}\left|+\right\rangle_x+i \frac{2}{\sqrt{13}}\left|-\right\rangle_x a) What are the possible results of a measurement of the spin component Sz, and with what probabilities...

Homework Statement An ultra-centrifuge has a cylindrical disk mounted on an axle that is almost frictionless. The disk spins about an axis through its centre as shown. If the disk is spinning with an angular speed of 4.50 x 10^5 rad/s and the driving force is turned off, its spinning slows...

Homework Statement A qubit is in the state |ψ(0)>=|0> . A magnetic field is applied in the x^ direction at t=0. This corresponds to the Hamiltonian H=BX, where B is a constant and X is the usual bit flip gate. What are the coordinates (θ,ϕ) of this qubit on the Bloch sphere at time t, as a...

Homework Statement A number of spin 1/2 particles are run through a Stern-Gerlach apparatus and when the emerge they all have the same spin wave function (ψ1, ψ2)τ and 9/25 are in the +z direction and 16/25 are in the -z direction with the normal basis column vectors for +z and -z...

This is how I understand it: Bohr argued that universe was inherently unpredictable as was the spin of the particle, and it was only based on probabilities. Einstein argued that the spin of the particle was actually always the same, just that our physics is not capable of determining it. But...

Let's say we have 200 electrons. The first batch of 100 of those electrons are prepared in a way that 50% are UP in the x-axis while 50% are DOWN in the x direction. The order is unknown. The second batch of 100 electrons are prepared in the same manner but in the y axis. Bob picks one...

So consider a 2D system with a circular potential and a spin-orbit interaction: V(r) = V_0 \theta(r_0 - r) + c r_0 V_0 L_z S_z \delta(r-r_0) where θ is step function. So the operators Lz and Sz commute with the Hamiltonian are are therefore conserved quantities. For the same reasons...

The S_{z} operator for a spin-1 particle is S_{z}=\frac{h}{2\pi}[1 0 0//0 0 0//0 0 -1] I'm given the particle state |\phi>=[1 // i // -2] What are the probabilities of getting each one of the possible results? Now... we can say the possible measure results will be 1,0,-1 and the...

According to QM, given two entangled electrons A and B, if you measure the y-axis spin on A to be up, then you know electron B's y-axis spin is down. Also according to QM, if i understood it properly, you cannot then go on to measure the x-axis spin on B, because then you would know both y...

σx|x>=+|x> σx|-x>=-|-x> These equations also follows for σy and σz corresponds states |y> and |z>. if we measure along axis X then X state vector let it go which means up spin and opposite not go through which means down spin. and also same for y and z axis. But, σx|u>=|d> σx|d>=|u>...

Hi, The transmission of nano devices are generally done without cosidering the spin polarization. However, as I saw in some papers, the effect of spin is sometimes included. How can I decide to use spin or not when simulationg transmission of nanoscale devices? Thanks in advance...

Mellow, all Physics Forum member, Please help me to have the answer of question, Why electron spin is +-1/2. What is the reason of integral spin of subatomic particle?

Hi folks, In his seminal work of 1937, Wigner showed that the rest mass and (absolute) spin of a particle are the same for all observers related by Lorentz transformation. Does anyone know whether these quantities are also preserved under transformations to relatively accelerated observers...

Hi, If you have a even-even nuclei which is deformed, you get a rotational spectrum of 0+,2+,4+,... I don't understand why the parities are positive for even I and why all members of a rotational band must have the same parity. I read about this in Krane's book: an introduction to nuclear...

The wavefunction for a spin 1/2 particle is a spinor field of the form \psi(\mathbf{x},t)=\left( \begin{array}{cc} \psi_{+}(\mathbf{x},t)\\ \psi_{-}(\mathbf{x},t) \end{array} \right). \psi_{+}(\mathbf{x},t) is the amplitude that the particle is both spin up and located at position x at time...

Let me apologize in advance for not reading the entire rotating disk thread. I think that the following question is closely related, but if it was answered in that thread, I didn't spot it. Let us consider the following timelike congruences, which maps congruence parameters t,r,theta and z...

hi guys, i have a question about the orbit-spin relationship of the celestial objects. for example in our solar system i understand the orbital period becomes lengthy for the planets more distant than the sun, it's logical, but what happens with their spinning motion..? i don't understand why...

Spin superposition--am I understanding things right? Hi, I am going to sound ridiculous, but I was watching an online lecture on QM and the professor mentioned spins can be in superposition (as in a particle's spin can be in a superposition between different spins--if I heard right). I'm...

Hello all! I'm trying to wrap my head around this quantum entanglement thingy. As far as I have understood, if you have two entangled particles, say two electrones, it is impossible to predict their spins since they are thought to be in superposition of both up and down. But if you measure...

Spin and "intrinsic angular momentum" After searching this forum for what exactly spin is my inference is that it is a misnomer for an electrons "intrinsic angular momentum"...so some doubts; may be I am being too blunt; What is the difference between +1/2 and -1/2 spin? Is the electron...

Homework Statement Hi there, thanks in advance for any help! I have a first order DE: \frac{\partial \vec{m}}{\partial t} = -\vec{m} \times \vec{h}_{eff} + \alpha \vec{m} \times \frac{\partial \vec{m}}{\partial t} (a scaled Landau-Lifshitz-Gilbert equation) where m is a magnetism...

Homework Statement A cubical box whose sides are length L contains eight electrons. As a multiple of $$\frac{h^2}{2mL^2}$$ what is the energy of the ground state of the eight electrons? Assume the electrons do not interact with each other but do not neglect spin. Homework Equations...

Homework Statement The problem is stated on page 10 and it is number 9. http://panda.unm.edu/pandaweb/graduate/prelims/QM_F11.pdfHomework Equations I know how to write Sy in the z basis for either spin up or down and I have all the spinors.The Attempt at a Solution I tried solving for |ψ(t)> by...

Two questions 1) The total orbital spin angular momentum is given as L2=l(l+1). What is the source of or meaning of the (l+1). 2) Similarly for the electron the total spin angular momentum is given as S2-1/2(1/2+1) hbar2. Is the total angular momentum precessing to give sz 1/2 hbar object?

Hello, I need to understand the following: Considering an element Sulfur - S which has 16 electrons. How do we calculate the valency electron of S? Please correct me if I am wrong:2+2+6+2+4=16. So, the valency electron = 4+2=6 Is it that always valency electron is the addition of...

Is there a connection between the Dirac four spinor and "spin up", i.e one of the four spinor states is spin up or are these two separate unconected things.

Ok, so for some reason this section of the GRE book makes 0 sense to me ... maybe because i haven't taken the class yet, maybe I'm missing something ... It says "If you have a spin-1 particle with m = +1 and a spin-1/2 particle with m = +1/2, then m_tot = +3/2 (this part makes sense, you just...

Homework Statement Consider a system consists of two subsystem A and A' in which A contains 3 spins and A' contains 2 spins. Suppose that, when the systems A and A' are initially separated from each other, measurements show the total magnetic moment of A to be - 3{\mu _0} and the total...

I have a pair of non interacting, identical 1/2 spin fermions in a one dimensional infinite square well with walls at x=0 and x=L. One particle is in ground state, the other in first excited state. This two-particle system has total spin quantum number S=0 I have normalized energy...

In general I could understand the meaning of spin.But in quantum level it is getting more complicated that I couldn't understand what is integral spin and all.can anyone explain it in a macroscopic level?

Schrodinger's equation is what is used to determine the probability of finding a particle somewhere, but where are charge and spin? How do you know if the probability wave you solved for is for a proton or electron or some other particle? I see m in the equation for plugging in mass, but nothing...

There is something I'm struggling with and I can't seem to find the problem. We have the Z spinbase with: z = (1/sqrt(2))² <BRA|*(|s_z,+> + |s_z,->) which gives following z matrix: 1 0 0 1 and we have for X: |s_x, +> = 1/sqrt(2) |s_z,+> + |s_z,->) |s_x, -> = 1/sqrt(2)...

Forgive me in advance if this appears to be a dumb question but, as I was reviewing a few basic chemistry topics, namely orbital hybridization, I came across a question. From what I gather, according to Hund's Rule, an electron must be put into all open orbitals before the remaining orbitals can...

When entangled photons are generated from a cascade of a Calciums' 6s level this inequality : n[y+z-] + n[x-y+] ≥ n[x-z-] is derived for what is equivalent to spin in photons. When the detectors at A and B are parallel the perfect anti correlations are due to conservation laws of angular...

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?