Perturbations of C*-algebraic invariants

Kadison and Kastler introduced a metric on the set of all C$^*$-algebras on a fixed Hilbert space. In this paper structural properties of C$^*$-algebras which are close in this metric are examined. Our main result is that the property of having a positive answer to Kadison's similarity problem transfers to close C$^*$-algebras. In establishing this result we answer questions about closeness of commutants and tensor products when one algebra satisfies the similarity property. We also examine $K$-theory and traces of close C$^*$-algebras, showing that sufficiently close algebras have isomorphic Elliott invariants when one algebra has the similarity property.