Geometric topology (object)

Topological Object

For the mathematical subject area, see geometric topology.

In mathematics, the geometric topology is a topology one can put on the set H of hyperbolic 3-manifolds of finite volume.

## Use[edit]

Convergence in this topology is a crucial ingredient of hyperbolic Dehn surgery, a fundamental tool in the theory of hyperbolic 3-manifolds.

## Definition[edit]

The following is a definition due to Troels Jorgensen:

A sequence  { M i } {\displaystyle \\{M_{i}\\}} in H converges to M in H if there are

* a sequence of positive real numbers  ϵ i {\displaystyle \epsilon _{i}} converging to 0, and
* a sequence of  ( 1 + ϵ i ) {\displaystyle (1+\epsilon _{i})} -bi-Lipschitz diffeomorphisms ϕ i : M i , [ ϵ i , ∞ ) -> M [ ϵ i , ∞ ) , {\displaystyle \phi _{i}:M_{i,[\epsilon _{i},\infty )}\rightarrow M_{[\epsilon _{i},\infty )},}

where the domains and ranges of the maps are the  ϵ i {\displaystyle \epsilon _{i}} -thick parts of either the  M i {\displaystyle M_{i}} 's or M.

## Alternate definition[edit]

There is an alternate definition due to Mikhail Gromov. Gromov's topology utilizes the Gromov-Hausdorff metric and is defined on pointed hyperbolic 3-manifolds. One essentially considers better and better bi-Lipschitz homeomorphisms on larger and larger balls. This results in the same notion of convergence as above as the thick part is always connected; thus, a large ball will eventually encompass all of the thick part.

### On framed manifolds[edit]

As a further refinement, Gromov's metric can also be defined on framed hyperbolic 3-manifolds. This gives nothing new but this space can be explicitly identified with torsion-free Kleinian groups with the Chabauty topology.

## See also[edit]

* Algebraic topology (object)

## References[edit]

* William Thurston, The geometry and topology of 3-manifolds, Princeton lecture notes (1978-1981).
* Canary, R. D.; Epstein, D. B. A.; Green, P., Notes on notes of Thurston. Analytical and geometric aspects of hyperbolic space (Coventry/Durham, 1984), 3--92, London Math. Soc. Lecture Note Ser., 111, Cambridge Univ. Press, Cambridge, 1987.