Dark energy is the name given to the universal "fifth force" identified by astronomers during Earth's late 20th century. Like gravity, dark energy influences all matter in the galaxy, and its effects can be seen on both cosmological and subatomic scales. The repulsive effects of dark energy are the primary reason the expansion of the universe is gradually accelerating.
Dark energy is manipulated using the extremely rare material element zero. When subjected to powerful electrical currents, element zero releases dark energy that can be harnessed to create mass effect fields, effectively raising or lowering the relative mass of all objects within the field. With the eezo nodules and natural electrical impulses in their nervous systems, biotics can generate and wield dark energy biologically, but the effort is physically demanding.
Dark energy and mass effect fields have practical uses across a wide range of manufacturing and technology fields. Most significant is the enabling of FTL travel, which has opened up the vast distances of space to exploration and colonization.
Mass Effect 2 Edit
In the years following the Battle of the Citadel, a further interest in dark energy itself has begun to emerge. Quarian studies upon the planet Haestrom reveal that its sun, Dholen, is aging prematurely as a result of the influence of dark energy. In addition, Gianna Parasini of Noveria Internal Affairs mentions that her superiors are worried about the potential issues of their clients' increased dark energy interests.
The manipulation of dark energy also figures into the events of Arrival. The mysterious Object Rho found in the Bahak system's asteroid field utilizes vast amounts of dark energy to maintain itself and the barriers protecting it so that it can continue broadcasting its enigmatic signals. The nearby Alpha Relay, the oldest known mass relay in the galaxy, can also make use of hidden dark energy reserves. When Alpha's control switches are adjusted, the relay taps into an unprecedented amount of dark energy, dramatically extending its range to sixteen other mass relays and even the Citadel.