Superluminal interstellar travel (S.I.T.), often called faster-than-light travel or simply F.T.L. travel, refers to any method of travel that permits the user to exceed to speed of light in the reference frame of "normal space".
In the expanse universe the only way to achieve S.I.T. is to build and sustain an Einstein-Rosen bridge, also known as an wormhole. A sustainable wormhole is able to link two solar systems, allowing space travel between the them almost "instantaneously".
The only known species to have developed S.I.T. is the protomolecule's parent race. Humanity uses the wormhole provided by the protomolecules parent species without fully understanding the underlying physics.
Physics Trivia Edit
In the context of special relativity as well as quantum mechanics a wormhole create various causality paradoxes. The concept of "faster then light" travel of physical objects or information are not trivially reconcilable. In other words, while a wormhole is theoretically possible within the framework of general relativity, it violates basic assumptions of quantum mechanics (causality) by introducing time like loops (what looks like time travel).