In simple terms, an Aperture Science portal is a small, stable black hole, generated by a Quantum Tunneling Device, or “Portal Gun”.   The placing of two portals in separate, appropriate locations via the same Quantum Tunneling Device creates a tear in time and space that temporarily intersects the two locations, allowing for instantaneous transition between them.  As opposed to traditional black holes, the black holes generated by an Aperture Science Quantum Tunneling Device are semi-contained, meaning that they do not bend matter or light into themselves and are able to remain stable in a desired window.  When two windows are created with a single device, a link is established.  This process, appropriated named “Quantum Tunneling”, is possible due to the integration of Aperture Science’s Event Horizon Estimation Wheel, paired with a Lower and Upper Singularity Ring, into the Quantum Tunneling Device.