Understanding Spinors: Rank-1/2 Tensors & Square Roots of Vectors

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Discussion Overview

The discussion revolves around the nature of spinors, specifically whether they can be considered as rank-1/2 tensors or as square roots of vectors. Participants explore the transformation properties of scalars, vectors, tensors, and spinors under rotations, particularly in a four-dimensional context.

Discussion Character

  • Conceptual clarification
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant suggests that a spinor can be loosely described as a rank-1/2 tensor or the square root of a vector, noting the transformation behavior of scalars, vectors, and tensors under rotations.
  • Another participant points out that a spinor has two complex components, which equate to four real components.
  • A participant explains that a rank-2 tensor transforms by multiplying the coordinate transformations two times, referencing the definition of a tensor in physics.
  • There is a question raised about whether a rank-2 tensor remains unchanged after a rotation by pi.

Areas of Agreement / Disagreement

Participants express differing views on the characterization of spinors and the implications of tensor transformations, indicating that the discussion remains unresolved.

Contextual Notes

Participants have not fully clarified the assumptions behind their definitions and statements regarding the transformation properties of tensors and spinors, leaving some aspects open to interpretation.

scope
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hi,

can se say loosely that a spinor is a rank-1/2 tensor or the square root of a vector, since a scalar does not change under rotations, a vector changes one time, a rank 2-tensor two times, a rank 3 tensor 3 times, and a spinor 1/2 time.
also a scalar in 4d has 1 component, a vector 4 components, a rank-2 tensor 16 components, and a spin 2 components.

does that make sense?
 
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scope said:
and a spin 2 components.

Two complex components = four real components.

rank 2-tensor two times...

?
 
arkajad said:
Two complex components = four real components.



?

yes a rank-2 tensor when we change coordinates, is transformed by multiplying it 2 times by the coordinate transformations, that is the definition of a tensor in physics.

for example if this transformation is a 2pi rotation, the graviton as a tensorial particle is rotated 2 times by 2pi.
 
Do you want to say that after rotation by pi any rank2 tensor does not change?
 

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