In the applied algebraic topology community, the persistent homology induced by the
Vietoris–Rips simplicial filtration is a standard method for capturing topological
information from metric spaces. We consider a different, more geometric way of
generating persistent homology of metric spaces which arises by first embedding a
given metric space into a larger space and then considering thickenings of the
original space inside this ambient metric space. In the course of doing this,
we construct an appropriate category for studying this notion of persistent
homology and show that, in a category-theoretic sense, the standard persistent
homology of the Vietoris–Rips filtration is isomorphic to our geometric persistent
homology provided that the ambient metric space satisfies a property called
injectivity.
As an application of this isomorphism result, we are able to precisely characterize
the type of intervals that appear in the persistence barcodes of the Vietoris–Rips
filtration of any compact metric space and also to give succinct proofs of the
characterization of the persistent homology of products and metric gluings of metric
spaces. Our results also permit proving several bounds on the length of intervals in
the Vietoris–Rips barcode by other metric invariants, for example the notion of
spread introduced by M Katz.
As another application, we connect this geometric persistent homology to the
notion of filling radius of manifolds introduced by Gromov and show some
consequences related to the homotopy type of the Vietoris–Rips complexes of spheres,
which follow from work of Katz, and characterization (rigidity) results for spheres in
terms of their Vietoris–Rips persistence barcodes, which follow from work of
F Wilhelm.
Finally, we establish a sharp version of Hausmann’s theorem for spheres which
may be of independent interest.