On a Question of Hamkins and Löwe on the modal logic of collapse forcing

Abstract

Hamkins and Löwe asked whether there can be a model $N$ of set theory with the property that $N\equiv N[g]$ whenever $g$ is a generic collapse of a cardinal of $N$ onto $\omega$. We give equiconsistency results for two weaker versions of this property. We also include a proof of Woodin's result that the consistency of the full Hamkins-Löwe property follows from that of a Woodin cardinal with an inaccessible above.

Revised and expanded