OBSERVER DEPENDENCE IN QUANTUM COSMOLOGY

The main thesis of this paper is that minisuperspace quantum cosmology reproduces the observer dependence of the vacuum found in quantum fie ld theory in curved spacetime. We show that the vacua picked up by the Hartle-Hawking ''no boundary'' proposal in two different minisuperspa ces sharing the same classical limit (k = 0 and k = 1 de Sitter minisu perspaces) are nonequivalent. A closer inspection suggests that the ob server dependence is introduced through the choice of the Wick rotatio n. This hypothesis is supported by the analysis of the static de Sitte r minisuperspace, where two different Euclidean sections are available , and where again two inequivalent vacua are obtained. These examples are not conclusive, but point to the possibility of a similar ambiguit y even in full quantum cosmology.