Discussion Overview
The discussion revolves around the concept of degrees of freedom for photons, specifically questioning why energy and momentum are not considered degrees of freedom, while helicity states are. Participants explore the implications of these definitions and relate them to mechanics and constraints on motion.
Discussion Character
- Conceptual clarification
- Debate/contested
Main Points Raised
- One participant questions why energy and momentum are not considered degrees of freedom for photons, despite being Lorentz invariant.
- Another participant states that for each value of the propagation vector, there are two degrees of freedom.
- A participant reflects on their initial question, comparing it to mechanics where momentum is not a degree of freedom, but the directions of movement are.
- A subsequent post suggests that constraints on movement directions could imply constraints on momentum, using the example of an ice skate to illustrate this point.
- One participant expresses uncertainty about the distinction between phase space coordinates and degrees of freedom, inviting further discussion on the topic.
Areas of Agreement / Disagreement
Participants do not reach a consensus on the definitions and implications of degrees of freedom for photons, with multiple competing views and uncertainties remaining in the discussion.
Contextual Notes
There is a lack of clarity regarding the definitions of degrees of freedom and phase space coordinates, as well as the implications of constraints on movement and momentum.