von Neumann double commutant theorem
The von Neumann double commutant theorem is a remarkable result in the theory of self-adjoint algebras of operators on Hilbert spaces, as it expresses purely topological aspects of these algebras in terms of purely algebraic properties.
Theorem - von Neumann - Let be a Hilbert space (http://planetmath.org/HilbertSpace) and its algebra of bounded operators. Let be a *-subalgebra of that contains the identity operator. The following statements are equivalent:
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1.
, i.e. equals its double commutant.
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2.
is closed in the weak operator topology.
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3.
is closed in the strong operator topology.
Thus, a purely topological property of a , as being closed for some operator topology, is equivalent to a purely algebraic property, such as being equal to its double commutant.
This result is also known as the bicommutant theorem or the von Neumann density theorem.
Title | von Neumann double commutant theorem |
Canonical name | VonNeumannDoubleCommutantTheorem |
Date of creation | 2013-03-22 18:40:27 |
Last modified on | 2013-03-22 18:40:27 |
Owner | asteroid (17536) |
Last modified by | asteroid (17536) |
Numerical id | 4 |
Author | asteroid (17536) |
Entry type | Theorem |
Classification | msc 46H35 |
Classification | msc 46K05 |
Classification | msc 46L10 |
Synonym | double commutant theorem |
Synonym | bicommutant theorem |
Synonym | von Neumann bicommutant theorem |
Synonym | von Neumann density theorem |