History Projection Operators
The key observation of the HPO formalism is to represent history propositions by projection operators on a history Hilbert space. This is where the name "History Projection Operator" (HPO) comes from.
For a homogeneous history we can use the tensor product to define a projector
where is the projection operator on that represents the proposition at time .
This is a projection operator on the tensor product "history Hilbert space"
Not all projection operators on can be written as the sum of tensor products of the form . These other projection operators are used to represent inhomogeneous histories by applying lattice operations to homogeneous histories.
Read more about this topic: HPO Formalism
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