Polarized Light and Quantum Spin

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Discussion Overview

The discussion revolves around the nature of electromagnetic (EM) radiation, specifically focusing on the concept of spin in relation to polarized and unpolarized light. Participants explore whether EM radiation can exist with spin zero and the implications of photon spin in different polarization states.

Discussion Character

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

Main Points Raised

  • One participant questions whether EM radiation can have spin zero, distinguishing this from the sum of spins being zero.
  • Another participant proposes that a superposition of left- and right-handed photons with equal amplitude results in light with no net spin, describing this as linear polarization.
  • A participant seeks to understand the phase characteristics of ordinary incoherent light, contrasting it with polarized light where phase is defined.
  • It is suggested that unpolarized light consists of photons of all polarizations without a specific order.
  • A later reply asserts that while EM radiation can have net zero polarization, individual photons always possess spin values of +1 or -1 due to their massless nature.

Areas of Agreement / Disagreement

Participants express differing views on the nature of spin in EM radiation, with some agreeing on the concept of superposition leading to net zero spin, while others emphasize the inherent spin of individual photons. The discussion remains unresolved regarding the implications of these concepts.

Contextual Notes

There are limitations regarding the definitions of polarization and spin, as well as the assumptions about the nature of incoherent light versus polarized light. The discussion does not resolve the mathematical or conceptual nuances involved.

ImaLooser
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Can there be EM radiation with spin zero?

I don't mean that the sum of all spins is zero, as it usually is. My thinking is that all light spins and usually the left and right component is of equal intensity.

Am I correct in thinking that light reflecting off of a suitable horizontal surface, like water, is horizontally polarized because the left and right spinning components reinforce on the horizontal plane and cancel in the vertical plane?
 
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You can have a superposition of left- and right-handed photons with equal amplitude, this gives light without (net) spin, right. It has a linear polarization.
 
mfb said:
You can have a superposition of left- and right-handed photons with equal amplitude, this gives light without (net) spin, right. It has a linear polarization.

OK, so now I'm trying to understand ordinary incoherent light. With polarized light the phase is defined. Is the phase undefined or superposed in ordinary unpolarized light?
 
Unpolarized light just consists of photons of all polarizations without any specific order.
 

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