Garay Elizondo, Luis JavierGarcía Bellido, Juan2023-06-202023-06-201993-07-120550-321310.1016/0550-3213(93)90411-Hhttps://hdl.handle.net/20.500.14352/59560© Elsevier. We would like to thank Pedro González–Díaz, Guillermo Mena Marugán and Mariano Quirós for a careful reading of the manuscript and valuable discussions. We also thank Andrei Linde for clarifying our conclusions on extended inflation.We consider the quantum gravity and cosmology of a Jordan-Brans-Dicke theory, predicted by string effective actions. We study its canonical formalism and find that the constraint algebra is that of general relativity, as a consequence of the general covariance of scalar-tensor theories. We also analyze the problem of boundary conditions and propose that they must be imposed in the Jordan frame, in which particles satisfy the strong equivalence principle. Specifically, we discuss both Hartle-Hawking and wormhole boundary conditions in the context of quantum cosmology. We find quantum wormhole solutions for Jordan-Brans-Dicke gravity even in the absence of matter. Wormholes may affect the constants of nature and, in particular, the Brans-Dicke parameter. Following Coleman's mechanism, we find a probability distribution which is strongly peaked at zero cosmological constant and infinite Brans-Dicke parameter. That is, we recover general relativity as the effective low energy theory of gravity.engjournal articlehttp://dx.doi.org/10.1016/0550-3213(93)90411-Hhttp://www.sciencedirect.comhttp://arxiv.org/pdf/gr-qc/9209015v2.pdfopen access51-73Extended inflationBaby universesSpacetime diffeomorphismsCosmological constantString theoryGravityFieldRepresentationsFlatnessHorizonFísica-Modelos matemáticosFísica matemática