Entanglement, Observers and Cosmology: a view from von Neumann Algebras

Understand

Infinite entanglement fluctuations appear when a quantum field theory on a causally complete domain of space-time is a type $III$ factor.

• In the weak gravity limit $G_N=0$ this factor can be transformed into a crossed product type $II$ factor with finite entanglement fluctuations by adding a physical reference frame system (observer).
• The use of a physical reference frame to define a regularization of divergent entanglement is formally identical to the quantum information approach to superselection charges.
• In that case the added reference frame allows quantum superpositions between different superselection sectors.