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The Hamiltonian is arbitrary upto a constant anyway. Why don't we just subtract off the vacuum energy? The Hamiltonian was always observable only upto a constant.

Instead, we do normal-ordering, in which we suddenly assume that creation and annihilation operators commute, just for this one step! This procedure is indefensible.

Qmechanic
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Ryder Rude
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1 Answers1

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A normal ordered operatpr has finite matrix elements between any pair of states. Subtracting a constant only gurantees you a finite number for the diagonal matrix element between one specific state and itself.

mike stone
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