Spin angular momentum of electron

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Discussion Overview

The discussion revolves around the nature of spin angular momentum in electrons, exploring whether electrons can be considered to rotate or vibrate, and the implications of their motion in relation to radiation and quantum mechanics.

Discussion Character

  • Exploratory
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Some participants question whether an electron rotates or vibrates to possess spin angular momentum, referencing classical dynamics.
  • One participant argues that spin is a quantum mechanical phenomenon without a classical analogue, suggesting that treating the electron as rotating leads to absurd conclusions.
  • Another participant raises the Heisenberg Uncertainty Principle, proposing that it implies the electron is always in motion.
  • There is a suggestion that if an electron were to move in a vacuum, it might radiate, but this is challenged by the application of classical electromagnetism to quantum particles.
  • Some participants express confusion over classical versus quantum interpretations, indicating a need for deeper understanding of quantum mechanics.

Areas of Agreement / Disagreement

Participants express differing views on the nature of electron motion and radiation, with no consensus reached on whether electrons can be considered at rest or if they radiate when moving in a vacuum.

Contextual Notes

Participants highlight limitations in applying classical physics to quantum phenomena, indicating a need for clarity on the distinctions between these frameworks.

dev70
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hi pf, i got following questions in my mind while reading about the spin angular momentum of an electron.
1. From rotational dynamics we know that to have angular momentum a body must necessarily rotation or motion? so does an electron rotates as it has spin angular momentum or does it vibrates?

2. And if it does, won't it radiate ?
 
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dev70 said:
hi pf, i got following questions in my mind while reading about the spin angular momentum of an electron.
1. From rotational dynamics we know that to have angular momentum a body must necessarily rotation or motion? so does an electron rotates as it has spin angular momentum or does it vibrates?

2. And if it does, won't it radiate ?

Spin is a quantum mechanical phenomenon. It doesn't have a classical analogue, so you can't treat the electron as if it's rotating. In fact, if we naively treated the angular momentum classically, we'd find that the electron (if it were spherical) would have a tangential velocity many times the speed of light -- obviously absurd!

The name "spin" itself is therefore misleading. Spin is simply an intrinsic degree of freedom that we can't intuitively understand.
 
ok.i got it. so does that mean an electron is a rest always with no motion. if we have a look at Hisenberg's Uncertainty Principle then i think we can say that the electron is always in a motion?? could we?
 
dev70 said:
ok.i got it. so does that mean an electron is a rest always with no motion.

No, it doesn't imply that.

dev70 said:
if we have a look at Hisenberg's Uncertainty Principle then i think we can say that the electron is always in a motion?? could we?

Precisely. For the electron to be at rest, it would necessarily have a well-defined position (x=x_rest). But it must also necessarily have a well-defined momentum since it is at rest (v=0), and this violates the uncertainty relation.
 
Then a electron is always in a kind of motion. If we just take up a thought experiment where an electron is moving just in an empty space i.e., vacuum should it radiate?
 
dev70 said:
Then a electron is always in a kind of motion. If we just take up a thought experiment where an electron is moving just in an empty space i.e., vacuum should it radiate?

The problem is that you're applying classical electromagnetism to a particle that doesn't behave classically. Hopefully someone who knows QED will step in at this point and maybe elaborate a little, but I can't really give a deeper reason than that at the moment.
 
Yaa. You are right. With Classical physics i am getting confused. I need quantum mechanism. I did a brief search and i think i have got it.
 

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