Motivations for the C*-algebra of observables?

Click For Summary

Discussion Overview

The discussion revolves around the motivations for using C*-algebras to model observables in quantum mechanics, exploring the theoretical foundations and implications of this mathematical framework. Participants seek clarification on the relationship between observables, measurement results, and the structure of C*-algebras, as well as the validity and popularity of this formulation compared to others in quantum mechanics.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant suggests that the Hilbert space formalism can be derived from the requirement that observables form a C*-algebra, questioning the implications of this relationship for measurement results.
  • Another participant points out the rarity of the Segal formulation of quantum mechanics and references literature that discusses the algebraic formulation of quantum field theory.
  • A participant recommends a book as a resource that may address questions about the mathematical modeling of observables in C*-algebras.
  • There is a query regarding potential weaknesses in the axioms of the C*-algebra formulation and its scientific validity compared to other formulations.
  • Another participant asserts that the C*-algebra approach is considered non-trivial and mathematically demanding, suggesting that this complexity may contribute to its unpopularity.

Areas of Agreement / Disagreement

The discussion reflects a lack of consensus regarding the popularity and perceived weaknesses of the C*-algebra formulation. While some participants express concerns about its complexity, others defend its validity without reaching a definitive conclusion.

Contextual Notes

Participants express uncertainty about the foundational aspects of the C*-algebra formulation and its implications for observable measurement, indicating a need for further exploration of its axioms and their acceptance in the scientific community.

TangledMind
Messages
5
Reaction score
1
As far as I understand, the Hilbert space formalism can be derived using functional analysis and representation theory (not familiar with those) from the requirement that observables (their mathematical models) form a C*-algebra and the possible states of a system map the members of the algebra to the actual measurement results (that would be R). This needs clarification. Hence, questions:

1) At some point the result of a measurement must be translated (from a state of a probe) into a symbol that we can write down on paper - a number perhaps. Real numbers seem to be intuitively optimal: they have ordering, some familiar metric can be used, and they can also describe diagonals and circumferences. In pairs, they can even describe complex numbers. Very convenient. An ordered set which is a metric space allows some predictive power for models built (getting results that could not be ordered at all would be...restrictive). In reality, we always get a result in Q, right? This is not familiar ground at all. Am I missing something here?

2) For each observable (the set of possible numerical(?) results above) a mathematical model/entity is needed (e.g. a matrix). What experimental results or intuitive motivations do we have that require the mathematical objects modeling observables to form a C*-algebra? (=Abelian additive group, a ring with multiplication, the required existence of an adjoint element A* (and A*A - does this relate to positivity?), and so on)

Any pointers to the right direction appreciated.
 
Last edited:
  • Like
Likes   Reactions: dextercioby
Physics news on Phys.org
You're questioning about the (paradoxically) rarest formulation of QM: the Segal one. Except for the defining article http://www.jstor.org/discover/10.2307/1969387?sid=21106089071023&uid=2134&uid=70&uid=2&uid=4, I couldn't find any reference in the literature, even if the algebraic formulation of QFT which originated in the 1950s in the work of R. Haag has thousands of articles/books.
 
  • Like
Likes   Reactions: bhobba and TangledMind
These answers were very helpfull. Thank you.

Are there some hidden weaknesses in the axioms of the C*-algebra formulation that have made it unpopular, or is it still considered scientifically as valid as the other formulations?
 
Last edited:
TangledMind said:
Are there some hidden weaknesses in the axioms of the C*-algebra formulation that have made it unpopular, or is it still considered scientifically as valid as the other formulations?

No.

Its just what mathematicians call non-trivial - meaning its hard. Other approaches are (on the surface anyway - dig deeper and issues arise) less mathematically demanding.

If that type of approach interests you I recommend:
https://www.amazon.com/dp/0387493859/?tag=pfamazon01-20

Thanks
Bill
 
Last edited by a moderator:
  • Like
Likes   Reactions: dextercioby

Similar threads

  • · Replies 2 ·
Replies
2
Views
1K
  • · Replies 5 ·
Replies
5
Views
1K
  • · Replies 3 ·
Replies
3
Views
2K
Replies
4
Views
2K
  • · Replies 7 ·
Replies
7
Views
3K
  • · Replies 29 ·
Replies
29
Views
4K
  • · Replies 1 ·
Replies
1
Views
2K
  • · Replies 1 ·
Replies
1
Views
2K
  • · Replies 4 ·
Replies
4
Views
2K
  • · Replies 1 ·
Replies
1
Views
1K