Spin Explained for the "Wikipedia Physicist" - No QM Needed!

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    Spin
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Discussion Overview

The discussion centers around the concept of electron spin, particularly for participants who may not have a background in quantum mechanics (QM). Questions raised include the nature of spin, its units, and its implications in physics, as well as its representation and measurement.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Some participants describe spin as a fundamental attribute of quantum systems, linking it to mass and energy, and suggest it relates to the symmetry of space-time.
  • Others inquire about the units of spin, comparing it to mass and energy, and note that measurements of spin are expressed in units of angular momentum.
  • One participant emphasizes that without a background in QM, understanding spin may be challenging, suggesting that it is a property required by the principles of QM and rotational invariance.
  • Several participants clarify that spin should not be thought of as literal spinning, citing issues such as the electron's size and the implications of its angular momentum exceeding the speed of light if interpreted literally.
  • Some participants propose that spin is synonymous with a magnetic moment, which can be experimentally measured, and discuss historical phenomena like the anomalous Zeeman effect as relevant to understanding spin.
  • There are claims that the term "spin" is misleading, with one participant arguing that it is synonymous with charge, while others challenge this view and discuss the conventions around positive and negative values of spin.
  • Participants discuss the concept of "up" and "down" spins as degrees of freedom for electrons, linked to the direction of the spin along a defined axis.
  • One participant mentions the eigenstates associated with spin-1/2 systems, indicating the mathematical representation of spin states.

Areas of Agreement / Disagreement

Participants express a range of views on the nature and interpretation of spin, with no consensus reached on its implications or the appropriateness of the term itself. Disagreements exist regarding the relationship between spin and charge, as well as the interpretation of spin as a physical property versus a mathematical construct.

Contextual Notes

Some limitations in the discussion include the lack of a shared understanding of quantum mechanics among participants, which affects the depth of explanation. There are also unresolved questions about the definitions and implications of spin in various contexts.

  • #91
what is chirality of spin state?
 
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  • #92
Well, chirality usually refers to "handedness" of something, or perhaps a better term, nonsymmetry. So it probably has the same sort of meaning here.
 
  • #93
what exactly is Earth spin?
is there a quantum effect on the Earth spin?what is exactly causes the Earth spin?
Matterwave said:
You can think of spin as the intrinsic angular momentum of a particle (rather than say, orbital angular momentum).

E.g. If the Earth is moving around the sun, and rotating, the orbit is the regular angular momentum, while the rotation is the "spin" angular momentum.

This is JUST a tool to help you make the concept a bit more concrete. DON'T take it literally. Particles, as far as we know are point particles and therefore can't really spin like the Earth does. Also, if you take an upper limit for the size of the electron, and try to find out how fast it must "spin" then a "point" at the electron's equator would need to be moving faster than the speed of light. This is no good! So don't think of this analogy in the literal sense.
 
Last edited:
  • #94
es.no said:
what exactly is Earth spin?
is there a quantum effect on the Earth spin?what is exactly causes the Earth spin?

Welcome to PhysicsForums, es.no!

Earth does not spin because of quantum effects. It is considered to spin due to classical effects. When free matter in space coalesces to form a celestial object such as a star or planet, total momentum is conserved. Therefore the object takes on the net momentum of its constituents. Usually, there is a net spin component in addition to other components. That is what we observe.
 
  • #95
hello

my question isn't correlate with Earth spin'''''

can you explain to me:
1- In spectroscopy of atoms, such sodium, is specified that in absence of magnetic field,
Apiece of energy levels split to two component except S level.

Why S level isn’t split?
 
  • #96
sah-sah said:
hello

my question isn't correlate with Earth spin'''''

can you explain to me:
1- In spectroscopy of atoms, such sodium, is specified that in absence of magnetic field,
Apiece of energy levels split to two component except S level.

Why S level isn’t split?

A better question is why are the other energy levels split? Recall that the S-term correlates with L=0, whereas the other terms have non-zero L. Do you remember the formula for the degeneracy of a particular l-level? Do you know what the particular form of the interaction of the magnetic field with the atomic states is? If you can answer those last two questions, then you should be able to understand why the S-state is unsplit.
 
  • #97
thank you.
you are right

actually,i don't know what the particular form of the interaction of the magnetic field with the atomic states is.

can you tell me?



SpectraCat said:
A better question is why are the other energy levels split? Recall that the S-term correlates with L=0, whereas the other terms have non-zero L. Do you remember the formula for the degeneracy of a particular l-level? Do you know what the particular form of the interaction of the magnetic field with the atomic states is? If you can answer those last two questions, then you should be able to understand why the S-state is unsplit.
 

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