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Equation 87 · Part 1 · The Atlas That Refuses to Close

Symbol psi

∣ψ⟩|\psi\rangle
ψ\psi

What this part means

psi is a part of this expression. Its role is fixed by the surrounding article and by the operations shown in the formula.

Its job in the formula

psi is a part of this expression. Its role is fixed by the surrounding article and by the operations shown in the formula.

The passage around this formula

There is a fifth kind of answer to “where,” and it is worth stating precisely how it differs from all four above before using it. Prepare a system in a state |ψ\psi⟩\rangle , couple it weakly to a pointer, and then postselect on a final state |f⟩\rangle measured after the coupling. The weak value of any observable A^\hat A , position among them, conditioned on that postselection is

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Learn the underlying idea

A variable is a named place for a value. Its letter is a local label: x can mean position in one formula and a data point in another.

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Sources cited in the article section

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