Q.M., Q.M.+Spin, Q.M.+Relativity; C^1, C^2, C^4, why ?

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Discussion Overview

The discussion revolves around the representation of quantum mechanics, particularly how the number of complex numbers relates to the inclusion of spin and relativity. Participants explore theoretical frameworks and interpretations, examining the implications of these representations in the context of quantum mechanics, spin, and relativistic effects.

Discussion Character

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

Main Points Raised

  • Some participants propose that one complex number suffices for quantum mechanics, while two are needed when spin is introduced, and four when relativity is considered.
  • Another viewpoint suggests that spin distinguishes between up and down states, leading to the necessity of two complex numbers, while relativity introduces additional complexity with electron and positron states.
  • One participant offers an interpretation involving phase relationships, stating that one complex number represents phase in relation to a frame of reference, while two complex numbers represent phase between two objects.
  • Further, it is suggested that three complex numbers can describe phase relationships in three dimensions, but do not uniquely define relationships due to non-commuting properties of rotations.
  • Four complex numbers are proposed to represent phase in three dimensions plus time, again noting the limitations due to non-commuting properties.
  • A later reply questions the initial framing, arguing that it may be more accurate to refer to a complex function rather than a complex number for quantum mechanics, emphasizing the role of wave function phase.
  • Another participant mentions that a real function may suffice for certain equations in quantum mechanics, suggesting a potential alternative perspective.

Areas of Agreement / Disagreement

Participants express differing interpretations of the number of complex numbers needed for various aspects of quantum mechanics, spin, and relativity. There is no consensus on a singular representation or deeper understanding that resolves these complexities.

Contextual Notes

Some statements rely on specific interpretations of quantum mechanics and may depend on definitions of terms like "complex number" versus "complex function." The discussion includes unresolved mathematical implications and assumptions regarding the nature of phase relationships.

Spinnor
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One complex number for quantum mechanics, two complex numbers when we add spin to quantum mechanics, and four complex numbers when we add relativity theory to quantum mechanics.

Can you give me some deeper representation of Nature such that the above is obvious and natural?

Thanks for any help!

U(1) , SU(2) , SU(2) X SU(2)
 
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Spinnor said:
One complex number for quantum mechanics, two complex numbers when we add spin to quantum mechanics, and four complex numbers when we add relativity theory to quantum mechanics.

Spin distinguishes between up and down --> 2 numbers.
Relativity also between electron and positron --> 2x2 numbers.
Including heavier leptons, we get 3 families --> 2x2x3 numbers.
 
Another possible interpretation:

One complex number represents all possible phase relationships of one object in relation to a given frame of reference (where 2 dimensions are involved).

Two complex numbers represent all possible phase relationships of one object in relation to another object rather than a fixed frame of reference (where 2 dimensions are involved).

Three complex numbers (embedded in a quaternion) represent all possible phase relationships of one object in relation to a given frame of reference (where 3 dimensions are involved). However, those do not uniquely describe the relationship because of the non-commuting properties of rotations in 3 dimensions.

Four complex numbers (embedded in a quaternion) represent all possible phase relationships of one object in relation to a given frame of reference (where 3 dimensions plus time are involved). However, those do not uniquely describe the relationship because of the non-commuting properties of rotations in 3 dimensions.

If multiple complex numbers are used to represent phase in more than 2 dimensions and are not used within a quaternion then they need to obey quaternion algebra (or an equivalent algebra). The Pauli spin matrices are inherently quaternionic.
 
Last edited:
Spinnor said:
One complex number for quantum mechanics, two complex numbers when we add spin to quantum mechanics, and four complex numbers when we add relativity theory to quantum mechanics.

Can you give me some deeper representation of Nature such that the above is obvious and natural?

I don't know about "natural", but I am not sure any "deeper representation" can make the above "obvious".

First of all, maybe I am splitting hairs, but I would say it's not "One complex number for quantum mechanics", but "One complex function for quantum mechanics", as one complex number cannot describe much, maybe just probability density in one point, but then how is it any better than the probability density itself, which is a real number? A wave function phase in one point does not make much sense.

Second, strictly speaking, one real function may be enough both for the Klein-Gordon equation and for the Dirac equation (with some caveats). See details at https://www.physicsforums.com/showpost.php?p=3008318&postcount=11
 

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