Portal (gateway)

A portal is an interdimensional vortex of energy that is used to connect dimensions.

Transportation Use
A portal may be used for transport between two dimensions, but further research by the Resistance scientists at Black Mesa East (and workers at the Aperture Science Enrichment Center) revealed that portals could be used for transport within one dimension. This was a major discovery, as not even the Combine understood that portals could be used for instantaneous transport within one dimension and were forced to use much slower conventional means of transportation if they wanted to stay within a single dimension. Another notable fact is that through the use of the Handheld Portal Device, Chell could make objects exist in two dimensions simultaneously.

Consequences
Use of portals can lead to disastrous quantum events. A Resonance cascade was the consequence of the attempt to use a portal to teleport a pure sample of Xenian crystals, leading to the Black Mesa Incident.

After the resonance cascade, randomized portals opened often on Earth, sending in more Xenian life forms. This randomized opening of portals obviously causes chaos, and is known as a Portal Storm.

Researchers
Portals were extensively studied by Earth's most intelligent human beings, as well as the Combine (though Earth had a better understanding of portals). The installations that studied portals included Black Mesa, Black Mesa East, the Aperture Science Enrichment Center, and White Forest.