Spin and Direction: A Complex Relationship in Particle Physics

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Discussion Overview

The discussion revolves around the relationship between spin and the direction of motion of particles, particularly in the context of particle physics. Participants explore how changes in motion, influenced by magnetic fields, might affect the spin of both massless and massive particles.

Discussion Character

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

Main Points Raised

  • One participant questions the relationship between spin and direction of motion, specifically how spin behaves when the direction of motion changes due to a magnetic field.
  • Another participant asserts that the statement about spin being parallel to the direction of motion applies to massless particles but not to massive ones.
  • A further inquiry is made regarding the reasoning behind the behavior of spin in massless particles, seeking an explanation for this distinction.
  • One participant mentions the complexity of the explanation, referencing advanced theoretical concepts related to massless representations of the Poincaré group and suggesting a specific section in Weinberg's work for further reading.

Areas of Agreement / Disagreement

Participants exhibit disagreement regarding the applicability of the spin-direction relationship to massless versus massive particles, with no consensus reached on the underlying reasons for these differences.

Contextual Notes

The discussion touches on advanced theoretical concepts that may require specific background knowledge in quantum field theory and particle physics, which could limit accessibility for some participants.

Who May Find This Useful

This discussion may be of interest to those studying particle physics, particularly in understanding the nuances of spin and motion in different types of particles.

maxverywell
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How this two are related? I read somewhere that the spin is always parallel to the direction of motion of particle. If the direction of motion changes by some magnetic field (Lorentz force) what happens to tha spin? Will its axis direction change too?
 
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maxverywell said:
I read somewhere that the spin is always parallel to the direction of motion of particle.
That's true for massless particles, but not for massive particles.
 
Why it's true for massless particles? Is there any explanation to this?
Btw thnx for your answer!
 
There is, but it's very complicated. It's a part of the mathematical theory of massless representations of the Poincaré group. If you're a bit of a masochist, check out section 2.5 in Weinberg's "The quantum theory of fields" (vol. 1).
 

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