Editing Wormhole (section)

=== Modern definitions ===
Wormholes have been defined both [[Geometry|''geometrically'']] and [[Topology|''topologically'']]. {{explain|are these definitions equivalent?|date=March 2017}} From a topological point of view, an intra-universe wormhole (a wormhole between two points in the same universe) is a [[Compact space|compact]] region of spacetime whose boundary is topologically trivial, but whose interior is not [[simply connected]]. Formalizing this idea leads to definitions such as the following, taken from Matt Visser's ''Lorentzian Wormholes'' (1996).<ref name="Visser1996" />{{page needed|date=January 2018}}

{{blockquote|If a [[Minkowski space]]time contains a compact region Ω, and if the topology of Ω is of the form Ω ~ S × Σ, where Σ is a three-manifold of the nontrivial topology, whose boundary has the topology of the form ∂Σ ~ S<sup>2</sup>, and if, furthermore, the [[hypersurface]]s Σ are all spacelike, then the region Ω contains a quasi-permanent intrauniverse wormhole.}}

Geometrically, wormholes can be described as regions of spacetime that constrain the incremental deformation of closed surfaces. For example, in Enrico Rodrigo's ''The Physics of Stargates, ''a wormhole is defined informally as: {{blockquote|a region of spacetime containing a "[[world tube]]" (the time evolution of a closed surface) that cannot be [[homotopy|continuously deformed]] (shrunk) to a [[world line]] (the time evolution of a point or observer).}}