ON TIME AND THE QUANTUM-TO-CLASSICAL TRANSITION IN JORDAN-BRANS-DICKEQUANTUM-GRAVITY

Any quantum theory of gravity which treats the gravitational constant as a dynamical variable has to address the issue of superpositions of states corresponding to different eigenvalues. We show how the unobser vability of such superpositions can be explained through the interacti on with other gravitational degrees of freedom (de-coherence). The for mal framework is canonically quantized Jordan-Brans-Dicke theory. We d iscuss the concepts of intrinsic time and semi-classical time as well as the possibility of tunnelling into regions corresponding to a negat ive gravitational constant. We calculate the reduced density matrix of the Jordan-Brans-Dicke field and show that the off-diagonal elements can be sufficiently suppressed to be consistent with experiments. The possible relevance of this mechanism for structure formation in extend ed inflation is briefly discussed.