Motivations for the C*-algebra of observables?

In summary, the Hilbert space formalism in quantum mechanics can be derived using functional analysis and representation theory. This requires that observables form a C*-algebra and the possible states of a system map to actual measurement results. Real numbers are commonly used to represent these results due to their convenience and predictive power. The mathematical models for observables also need to form a C*-algebra, but this approach is considered rare and mathematically demanding. There are no known weaknesses in this formulation, but it is not as popular as other approaches in quantum mechanics. Further reading on the subject is recommended.
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TangledMind
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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.
 
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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.
 
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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?
 
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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
 
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1. What is the C*-algebra of observables?

The C*-algebra of observables is a mathematical structure used in quantum mechanics to describe the set of all possible observables of a physical system. It is a type of mathematical object known as a "*-algebra", which is a linear algebra over the complex numbers with additional operations of multiplication and an involution operation. In quantum mechanics, the C*-algebra of observables is used to represent the set of all possible measurements that can be made on a quantum system.

2. How are motivations for the C*-algebra of observables determined?

The motivations for the C*-algebra of observables are determined by the fundamental principles and mathematical framework of quantum mechanics. These include the uncertainty principle, the superposition principle, and the probabilistic nature of quantum measurements. Additionally, the C*-algebra of observables is motivated by the desire to have a mathematical structure that can accurately represent and predict the behavior of quantum systems.

3. What are the key properties of the C*-algebra of observables?

The C*-algebra of observables has several key properties that make it a useful tool in quantum mechanics. These include the fact that it is a complete normed algebra, which means that it contains all possible limits of sequences of observables and has a well-defined notion of distance between elements. It also has an involution operation, which is used to represent the adjoint of an observable. Additionally, the C*-algebra of observables is a non-commutative algebra, reflecting the non-commutative nature of quantum measurements.

4. How does the C*-algebra of observables relate to other mathematical structures in quantum mechanics?

The C*-algebra of observables is closely related to other mathematical structures used in quantum mechanics, such as Hilbert spaces and operators. In fact, the C*-algebra of observables can be represented as a subalgebra of the algebra of all bounded linear operators on a Hilbert space. This allows for a convenient way to represent and manipulate observables in quantum mechanics.

5. What are some applications of the C*-algebra of observables?

The C*-algebra of observables has many practical applications in quantum mechanics, including the ability to accurately describe and predict the behavior of quantum systems. It is also used in the development of new quantum algorithms and in the study of quantum information theory. Additionally, the C*-algebra of observables is used in the development of quantum field theory and in the study of quantum gravity.

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