7.5. Probabilistic interpretation of the cosmological constant

It is also possible to produce more complex scenarios which could justify the small or zero value of cosmological constant. One such idea, which enjoyed popularity for a few years [272, 273, 274, 275], is based on the conjecture that quantum wormholes can change the effective value of the observed constants of nature. The wave function of the universe, obtained by a path integral over all possible spacetime metrics with wormholes, will receive dominant contributions from those configurations for which the effective values of the physical constants extremize the action. Under some assumptions related to Euclidean quantum gravity, one could argue that the configurations with zero cosmological constant will occur at late times. It is, however, unlikely that the assumptions of Euclidean quantum gravity has any real validity and hence this idea must be considered as lacking in concrete justification.