# 2018 seminar talk: Virtual large cardinal principles

Talk held by Victoria Gitman (Graduate Center, City University of New York (CUNY), USA) at the KGRC seminar on 2018-04-12.

### Abstract

Given a set-theoretic property $\mathcal P$ characterized by the existence of
elementary embeddings between some first-order structures, we say that $\mathcal P$
holds *virtually* if the embeddings between structures from $V$ characterizing $\mathcal
P$ exist somewhere in the generic multiverse. We showed with Schindler that virtual
versions of supercompact, $C^{(n)}$-extendible, $n$-huge and rank-into-rank cardinals
form a large cardinal hierarchy consistent with $V=L$. Sitting atop the hierarchy are
virtual versions of inconsistent large cardinal principles such as the existence of an
elementary embedding $j:V_\lambda\to V_\lambda$ for $\lambda$ much larger than the
supremum of the critical sequence. The Silver indiscernibles, under $0^\sharp$, which
have a number of large cardinal properties in $L$, are also natural examples of virtual
large cardinals. With Bagaria, Hamkins and Schindler, we investigated properties of the
virtual version of Vopěnka's Principle, which is consistent with $V=L$, and
established some surprising differences from Vopěnka's Principle, stemming from the
failure of Kunen's Inconsistency in the virtual setting. A recent new direction in the
study of virtual large cardinal principles involves asking that the required embeddings
exist in forcing extensions preserving a large segment of the cardinals. In the talk, I
will discuss a mixture of results about the virtual large cardinal hierarchy and virtual
Vopěnka's Principle. Time permitting, I will give an overview of Woodin's new
results on virtual large cardinals in cardinal preserving extensions.