Classically, the unimodular theory of gravity with a constrained determinant ${\mathit{g}}_{\mathrm{\mu }\nu }$ is equivalent to general relativity augmented by an arbitrary cosmological constant Λ, which arises as an integration constant. At the quantum level we argue that an integration over Λ should be included in the Euclidean path integral for the vacuum functional. The fully renormalized Λ=0 overwhelmingly dominates all other contributions yielding a zero observed cosmological constant. While the technical part of our argument is similar to that of the ‘‘wormhole’’ argument, the two approaches are logically different.

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