Is SPIN a calculated or physically measureable characteristic?

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Discussion Overview

The discussion centers around the concept of "spin" in quantum mechanics, exploring whether it is a calculated or physically measurable characteristic. Participants examine the definitions, implications, and measurement methods related to spin, including its representation in particles like electrons and photons.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants describe spin as a measure of rotational motion and angular momentum, questioning whether its values (e.g., 1 for photons, 1/2 for electrons) are derived from calculations or physical measurements.
  • Others argue that spin is both calculated and observed, noting that the concept of spin was necessary for accurately describing electron behavior in atoms.
  • It is suggested that spin is defined within theoretical frameworks, with its meaning tied to how particle descriptions change under rotation.
  • Some participants propose that spin values are determined through calculations based on measurable effects, indicating that spin cannot be directly measured.
  • There is discussion about the relationship between spin values and the behavior of wave functions under rotation, particularly the distinction between spin 1 and spin 1/2 particles.
  • One participant recalls a notion that the photon’s spin was originally considered to be 2, raising questions about the labeling of spin values and their implications for rotation.
  • Another participant provides a reference to an article discussing experimental measurements of spin without destruction, highlighting advancements in quantum computing related to spin states.

Areas of Agreement / Disagreement

Participants express a range of views on the nature of spin, with no consensus reached on whether it is primarily a calculated or measured property. Multiple competing interpretations of spin's significance and measurement persist throughout the discussion.

Contextual Notes

Some claims about the definitions and implications of spin rely on specific theoretical frameworks, and there are unresolved questions regarding the historical context of spin value assignments and their physical interpretations.

  • #31


Tahnk you so much ... :approve:
 
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  • #32


hmmm ... that second one goes a bit further than I had in mind. I wanted you to see the Stern-Gerlach experiment done for electrons: let's you see why the property is called "spin".
 
  • #33
MY question is this ...
for example an electron behaves like a wave and a particle ...
how can we define electrons spin when it behaves like a wave ? ?
 
  • #34
radioactive8 said:
MY question is this ...
for example an electron behaves like a wave and a particle ...
how can we define electrons spin when it behaves like a wave ? ?
We can't and we don't.

Electrons have been observed to give results in some experiments that are normally associated with classical waves and classical particles. However, it is neither of these things. It is a fundamental or quantum-mechanical particle. Called "particle" for short.

Particles can have spin.

Particles have a fundamentally statistical nature which looks a lot like the results of classical wave equations - but it isn't: it has an entirely different origin. The QM "wave", though, is a wave function that can include the spin, where appropriate, as a parameter.

The phenomenon of electron spin is one of the things which highlights the distinction between quantum and classical behavior - look up "Stern-Gerlach experiment".
 
  • #35
what is spin and its associated things like momentum..?

hi

what does it mean by spin of +1/2 -1/2 ,0,1,2. and what is spin angular momentum and spin dipole momentum and what is the difference between orbital angular momentum and spin angular momentum and in same way what is the difference between orbital dipole momentum and spin dipole momentum.i know that they are intrinsic properties of an electron like mass and charge ,but I'm unable to visualize it and understand it as i did mass and charge..!
 
  • #36


It's impossible to visualize spin. Just think of it as a property. Some people think of it as a particle spinning about an axis, and while spin is technically angular momentum, this can be very misleading under some circumstances..
 
  • #37


then what does "orbital angular momentum " and "orbital dipole momentum" refers to..?.orbit is region of space where there is a probability of finding an electron.does a space aslo have angular momentum and dipole momentum as spin...?
 
  • #38


I suspect this may be misleading, but I have a feeling it isn't.

A way to visualize orbital angular momentum would be this. Take an object, put it on the end of a massless rope, swing it around. (A bit unrealistic, but the point still holds.) The orbital angular momentum will refer to the angular momentum from the spinning of the ball. In this case, orbital angular momentum would probably refer to the angular momentum of an electron from orbiting an atom's nucleus. Orbital dipole momentum I'm probably not the one to ask about.
 
  • #39
One more question ...
I know that the magnetic forces come from the electrons spin ... i want to know how can this happen ... Why are magnetic forces cauzed by the electrons spin ... ?
 
  • #40
radioactive8: It's more that we deduce the existence of the electron's spin by its reaction to a magnetic field. It is part of the QM properties of the electron - the wavefunction has a magnetic moment component.

Whovian: Electrons do not "orbit" their nuclei and electrons outside an atom still have spin.

ajayguhan: the terms are a historical leftover from the Bohr model of the atom. Quantum Mechanics has to have equivalent terms in order to replace Bohr theory.

We have to be careful making classical analogies of quantum behavior ... QM is a superset of classical mechanics so there will be some quantum phenomena that just cannot be modeled classically. That's why we have it. At some stage you just have to accept that quantum mechanics is weird - but accurate.
 
Last edited:
  • #41
radioactive8 said:
One more question ...
I know that the magnetic forces come from the electrons spin ... i want to know how can this happen ... Why are magnetic forces cauzed by the electrons spin ... ?
Classically, magnetic fields are caused by currents. An electron with orbital angular momentum is moving and thus causes a current and a magnetic field.

In QM, we have a new type of angular momentum, which is a intrinsic property of particles independent of motion. This is the spin. So simplistically, we can say that in QM magnetic fields are not only caused by currents, but by any form of angular momentum.
 

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