What is Spin: Definition and 1000 Discussions

Homework Statement Prove, for the matrix ##S = exp \bigg(-\frac{i}{\hbar}\mathbf{\hat{n}}\cdot \mathbf{\hat{S}}\bigg)## (spin-rotation matrix), and for an arbitary vector ##\mathbf{a}## that: $$ S^{-1} \mathbf{a} \cdot \mathbf{\hat{x}} S = a(-\theta) \cdot \mathbf{x} = a \cdot...

Hi, I'm currently investigating magnetic fields/their cause. This has inevitably led me to learn all about electrons. Here I want to post my understanding on electron 'spin' so people can correct me if I'm wrong/help others get a better understanding. So I watched this YouTube video for...

So I have been studying the case of spin 1/2 and I have understood how the formulations work through to find the spin matrices. However I do not get an intuitive understanding of what they mean and why they are formulated the way they are. I follow Griffith's book and in it as he begins to solve...

My question is conceptual but specific. I'm self-studying Townsend's text 'A Modern Approach to Quantum Mechanics.' In Sec. 2.2 pg 33 (in case you have the book handy), he introduces rotation operators, in the context of spin states for spin-1/2 particles. He states that the rotation operator...

Homework Statement S=1/2 I1=I2=1/2 (nuclear spin) I=I1+I2 J=S+I Homework Equations H= a S . I1 + a S.I2 The Attempt at a Solution A) Find the values of I, the eigenvalues of I2, their degree of degeneracy and show that [H,I2]=0Using momentum addition I get I = 0 or 1 I2 has for...

Homework Statement Finding eigenvalues of an hamiltonian Homework EquationsH = a S²z + b Sz (hbar = 1) what are the eigenvalues of H in |S,M> = |1,1>,|1,0>,|1,-1> The Attempt at a SolutionH|1,1> = (a + b) |1,1> H|1,0> = 0 H |1,-1> = (a-b) |1,-1> which gives directly the energy : a+b , 0 ...

If we define Si=(1/2)× (reduced Planck's const)×sigma Then what will be (sigma dot vect{A})multiplied by (Sigma dot vect{B}) Here (sigma)i is Pauli matrix. Next one is, what will we get from simplifying <Alpha|vect{S}|Alpha> where vect{S} is spin vector & |Apha>is equal to " exp[{i×(vect{S} dot...

I have a question concerning the nature of Ms. Wu's experiment confirming parity violation. I'm very familiar with this experiment and its outcomes, but the setup of the experiment itself, alludes me. Wu found that the electron's emitted from the Cobalt-60 atom always went in the direction...

If we put a toy gyroscope in space, like the ones we all played with as kids with the wheel on the inside of a wire frame, and had nothing to reference it to. (stars, planets, dust, exc.) How could you tell if the inside was spinning or the wire frame??

Hi folks. (I have no way of knowing if the prefix is at the right level) I've been working on a very low scale, totally elastic 2D physics engine for a while, this is only for learning, it will serve no important purpose when it's complete, I'm just building it for fun really, to keep the...

Homework Statement Consider a spin ##\frac{1}{2}## particle at rest in a B-field ##\vec B = B_0\vec e_z##. (a) Find the Heisenberg equations for ##\hat S_x## and ##\hat S_y##. (b) Obtain from the Heisenberg equations two decoupled second-order differential equations for ##\langle \hat S_x...

I try to understand where the intrinsic spin symmetry of spacetime (ISSS) is established. I read articles but still do not understand how to put together all the information to make a clear picture of where ISSS comes from. Minkowski space - Lorentz group O(1,3) - Covering SO(1,3) with SL(2)c -...

Imagine we take a vertical, infinite wire and we let electric current pass through. The charges create magnetic field all around the wire. Now if we introduce an electron in the magnetic field, it will have a circular motion around the wire. The Lorentz force is not conservative, this means...

I’ve been reading on the physics of how a Magnetic Resonance Imaging (MRI) works from this link regarding the T1 and T2 relaxation time of protons. So far I understand the concept except what they’re trying to explain in the last 2 paragraphs about spin echo. This is what I got from these last...

Hi, I'm trying to rotate 2 different plotted circles in matlab, which have the Jet colourmap. Colormap has the Spinmap function, but when I use it, it only spins the Jet colormap in 1 circle, leaving out the other. I would like to spin the Jet colormap in2 different circles in opposite...

If you have a free neutron viewed from a known frame of reference which is known to be spin up and it decays, is there anything in theory or experiment which indicates whether the remaining proton will be spin up or down? Thanks Jerry

Homework Statement Consider an electron described initially by ##\psi = \frac{1}{\sqrt{10}} \begin{pmatrix} 1\\ 3 \end{pmatrix}##. A measurement of the spin component along a certain axis, described by an operator ##\hat{A}##, has the eigenvalues ##\pm \frac{\hbar}{2}## as possible outcomes (as...

The following picture shows a rogue planet (in purple) approaching Earth (in blue). It is spinning prograde like Earth. We're talking about a close approach. For example a planet the size of the moon approaching within 12,000km of Earth. That would be just outside the roche limit. I presume the...

I'm having trouble finding the correct names for the 4 standard labels: n, l, m, s. Where might I find, free online: their correct names (ie, no colloquialisms or short cuts) and the accepted formula for each (to be sure I use them correctly)? Thanks.

When we rotate a disk, can this process be fully explained by looking worldlines of the particles the rotating disk is composed of, hence their x,y,z,t position "as time passes", or do particles have some kind of "facing direction", hence also spin(not the quantum mechanical notion of spin)...

I'm interested in understanding the key physical differences between classical and quantum dynamics. I understand that spin (intrinsic angular momentum) is one major physical difference.* So I wonder whether all else flows from this? Or are there other major (unrelated) physical differences...

Homework Statement Considering a neutral particle with spin +½ and a dipolar momentum μ placed on an uniform magnetic field. Find the variation of the expected value of the 3 cartesian components of the angular momentum spin operator for the following situations: a) the angular momentum of...

Hello I'm wondering, what is difference in trajectory or period or...something if I try to compare solution of Kepler problem for point bodies and "rigid" bodies with spins. More precisely is some easy way how to include a spin of bodies to this problem? Or this procedure for describing of such...

Hey, I am studying Spin 1/2 system, the case of 2 electrons in a magnetic field, since we have 2 electrons, we expect that the matrix will be of the size 4x4, which is what I have got. As I know that I could use the density matrix to calculate the expectation values of any physical quantity...

We all know we see only one part of moon means part which is facing towards earth But moon rotates also so we should able to see its other part(dark part) but we cant. I know rotational period of moon is equal to revolutionary period of moon but if moon is having rotational motion So we should...

Hi everyone, As the title says, I was wondering if the third quantum number affects spin since they are both linked by magnetism. If not, will an excited particle have a different spin than a non-excited one ? Thanks for your answer and sorry for the possible mistakes, I'm just a young french...

There is a video from the Space Station here: At around the 1 minute mark, you see the stability of the CD player when the CD inside is spinning. Don Pettit goes on to tape additional CD players together at 90 degrees to the original to make it stable in 2 directions, but my questions is are a...

I have some trouble understanding the concept of spin precession in an external field from a quantum mechanics viewpoint. Hopefully someone will be willing to enlighten me. Consider a single spin ½ particle. In the absence of an external field, the projection of the spin angular momentum on...

Hello everybody, I'm playing with a ne -ne laser And i conducted an interesting experiment I did colliding beams the type of interferometer Fabry Pero between the mirrors I put the cuvette with different substances I tried to detect changes of polarization of the laser beam with the help of a...

I need websites or books that has quantum mechanical exercises in particular that finds the total angular momentum eigenvalues (for example two spin 1/2 systems). Do you know where I can train?

Hi All, I'm hoping you all can help me with what I think should be some relatively simple calculations. I'm looking to determine how large (diameter / weight) of a flywheel a particular AC motor can spin from a stop to full RPM given the torque / HP of the motor. For instance, if I have a 1/3...

According to this article an electron can be split into 3 quasiparticles: ‘holon’ carrying the electron’s charge ‘spinon’ carrying its spin ‘orbiton’ carrying its orbital location The article links to an experiment that was made in 2012, where physicists were able detect the spinion and the...

What causes the change in the axial tilt of the earth? Why does it change?

Why are particle with half integer spins anti-symmetric while integer spin particles are symmetric? Or in other words, how does spin relate to the symmetry of indentical particles?

Homework Statement Consider one rod of length L which is spun at its center perpendicular to its length; it will have a certain moment of inertia. Now, if the same rod is folded in the middle creating a certain angle and still spun at its center, what happens to its moment of inertia? Homework...

As I understand it, a relativistic reversal can occur in a Lorentz boost. A particle's forward angular momentum can become backward angular momentum, if the observer accelerates sufficiently. But the particle and its angular momentum are unchanged. The only change is in the observer’s frame...

Hello! I am reading (from Griffiths' book) about Casimir's trick in calculating the amplitude of an interaction. At a point it says that we need to average over all initial spin configurations and sum over all final spin configurations. Why is it a sum for the final states and not an average...

Maybe this is more quantum, but I'm not sure. I was watching Susskinds first String lecture on youtube, and he was talking about how, within each particle family, you get a straight line called a regge trajectory if you plot spin vs. mass^2. He also mentioned that there was some slight insight...

Homework Statement Let's consider conduction electrons (at T=0K) that are put in a magnetic field. The electrons can have spin that is parallel or antiparallel to the magnetic field. Below is the density of occupied states for such a system (horizontally) as a function of energy (vertically)...

Homework Statement Write down a spinor that represents the spin state of the particle at any time t > 0. Use the expression to find the expectation values of ##S_x## and ##S_y## Homework Equations The particle is a spin-##\frac 1 2## particle, the gyromagnetic ratio is ##\gamma_s \lt 0##, and...

Homework Statement Earlier my teacher put this equation on the board, π_0 --> γ+γ It appears to work until you consider spin. Homework Equations a quick google search reveals that the spin of a photon is +1 and the spin of a pi meson is 0 The Attempt at a Solution This appears to work for...

I've got to explain how spin art works to some 5th graders tomorrow. Basic setup: Paper is attached to center of a horizontal disk. Paint droplets are placed at different places on the paper. Disk is spun which causes paint to produce a pattern flowing away from the center of the disk/paper...

How can we be so sure? I know it's fast ..but, what if it swaps by the speed of light instead? I know there are some experiments that try to rule this out, however, I don't think they take into consideration that the signal to swap may be initiated by the action that observes one of the...

This is not part of my coursework but a question from a past paper (that we don't have solutions to). 1. Homework Statement Construct the matrix ##\sigma_{-} = \sigma_{x} - i\sigma_{y}## and show that the states resulting from ##\sigma_{-}## acting on the eigenstates of ##\sigma_{z} ## are...

If a space station has artificial gravity created by spinning, how can it best be spun up to speed? Little attitude rockets could do it, but they would use up fuel, and limit your ability to change the spin rate in future. What if you had an external wheel that you spin up very fast in the...

What is the basic concept which decides the spin of a particle. Like, electron has a spin of +- 1/2... What do this 1/2 signifies. Other spins are also there like 1 and 2. What do they signify? Is there any possibility of any particle with spin other than 1/2, 1 or 2?

So, we can break down the Dirac equation into 4 "component" equations for the wave function. I was going to post a question here a few days ago asking if a fermion (electron) could possesses a "spin" even if it were at rest, I.e., p=0. I did an internet scan, though, and found out that...

I have previously read that the spin of a particle is comparable to angular momentum of a system or object on the macroscopic level. However, the quantum world is much different and all I can imagine is a minuscule ball rotating on it's axis.

I am having difficulty thinking through how a ferromagnetic substance is permanently magnetized. I think I understand that when for example a sample of iron is heated above it curie temperature and then exposed to an external magnetic field , the sample will become permanently magnetized. The...

Hi guys! I'm struggling with the following problem: Consider two distinguishable (not interacting) particles in a quadratic 2 dimensional potential well. So ## V(x,y)=\left\{\begin{matrix} 0,\quad\quad-\frac { L }{ 2 } \le \quad x\quad \le \quad \frac { L }{ 2 } \quad and\quad -\frac { L }{...