Imaginary numbers are inherently unobservable

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Discussion Overview

The discussion revolves around the nature of imaginary numbers in relation to observables in physics, particularly focusing on why variables with imaginary values are considered inherently unobservable compared to real-numbered variables that correspond to measurable quantities like position and momentum. The scope includes philosophical implications, mathematical definitions, and quantum mechanics concepts.

Discussion Character

  • Debate/contested
  • Conceptual clarification
  • Technical explanation

Main Points Raised

  • One participant questions the inherent unobservability of imaginary numbers compared to real numbers, suggesting there is no a priori reason for this distinction.
  • Another participant references a previous discussion on measuring complex quantities and the appropriateness of labeling numbers as "real" or "imaginary."
  • A participant seeks clarification on why Hermitian operators in quantum mechanics, which have real eigenvalues, correspond to observables, questioning the significance of real numbers over complex numbers in this context.
  • One participant argues that all measurements ultimately relate to position, citing historical perspectives on the realization of irrational numbers in nature and asserting that complex numbers do not model displacements in space, thus giving real numbers a different status.
  • The same participant reiterates their point about the realization of real numbers in nature, emphasizing that they are the quantities that correspond to observable phenomena.

Areas of Agreement / Disagreement

Participants express differing views on the nature of imaginary numbers and their relation to observables. There is no consensus on the reasons behind the distinction between real and imaginary numbers, and the discussion remains unresolved.

Contextual Notes

The discussion touches on philosophical and mathematical assumptions regarding the definitions of real and imaginary numbers, as well as the implications of these definitions in physical measurements. Some claims rely on historical perspectives that may not be universally accepted.

madness
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Maybe this should be in the philosophy of science/math forum, but i thought it fitted here. Why is it that variables taking imaginary values are inherently unobservable, whereas real numbered variables correspond to observables like position/momentum? As far as I can see there is no a priori reason why this should be the case.
 
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Thanks that's an interesting thread. Here is a more specific question to explain what i mean. Why is it that Hermitian operators in quantum mechanics (ones with real eigenvalues) correspond to observables. What is it about real numbers over complex ones that make them observable? I don't think this question was directly covered in that thread.
 
Well, ultimately everything boils down to measurements of position: whether it's where the pointer is pointing to, or which LEDs are lit etc. The Ancient Greeks discovered (much to their dismay) that irrational numbers are realized in nature (e.g. the right-angled triangle with the two smaller unit sides has a hypotenuse of irrational length).

And so it was known, that the set of real numbers were realized in nature. There is no displacement in our space that is modeled by a complex number: this is why they have a slightly different status.
 
Last edited:
masudr said:
Well, ultimately everything boils down to measurements of position: whether it's where the pointer is pointing to, or which LEDs are lit etc. The Ancient Greeks discovered (much to their dismay) that irrational numbers are realized in nature (e.g. the right-angled triangle with the two smaller unit sides has a hypotenuse of irrational length).

And so it was known, that the set of real numbers were realized in nature. There is no displacement in our space that is modeled by a complex number: this is why they have a slightly different status.

thank you for saying here about what it was that i was trying to say in the other thread (that got so contentious). i would say it as "the set of numbers are realized quantities in nature are called "real numbers".
 

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