Overview
Exotic Matter is matter that possesses characteristics beyond the bounds of normal physics or are composed of non-baryon matter. Depending on the type of exotic matter it can have negative mass or imaginary mass. Negative mass matter causes strange effects to the space-time field. Imaginary mass matter cannot travel below the speed of light and can travel instantly to any point in the universe(s).
Discovery
In the year 2638 large naturally occurring deposits of exotic matter composed of "strings" or string energy arcs were discovered in the vicinity of the neutron star "Schwarzschild's Star". It was found that when subjected to certain electromagnetic currents the string matter gained negative mass and would warp space-time in its vicinity.
Collection and Processing
Exotic matter occasionally occurs in nature, this natural exotic matter is often found in space-time anomalies left over from the big bang. It is almost entirely composed of what is called "Exotic Hydrogen" a particle similar in size and mass to a proton. Rarely, one would be able to find a small amount of "Exotic Helium" an alpha-particle made up of two Exotic Hydrogen atoms and two exotic neutrons. The rarest conceivable form is "Exotic Lithium" a form of exotic matter so rare that only several dozen particles were discovered.
Civilizations first developing warp drives need to synthesize the exotic matter at great expense, making only governments capable of creating and using the substance. To synthesize exotic matter, one needs to synthesize matter within an inverted Higgs Field. Put another way, one would need to create a certain amount of matter with large amounts of energy, according to the famous e=mc^2. This takes large amounts of energy only available to a Kardashev II civilization. This matter is almost entirely composed of protons when normally created. To make the matter exotic, one would need to invert the Higgs Field, which requires creating exotic Higgs Bosons. In other words, one would need to create force-carrier particles with negative mass to create matter with negative (or sometimes complex) mass. This substance can be used to create warp drives and all other manner of space-bending technologies.
This process is incredibly expensive. Once civilizations create exotic matter, they invariably set out to find the nearest deposit, usually with their nearly created warp drives but sometimes with slower-than-light technology if they begin earlier.
Once economical warp drives are created, civilizations gain the ability to travel through their galaxy efficiently. Warp drives, however, leave behind a "snail trail," so to speak, of material as they traverse the galaxy. This material can interfere with the warp drives of ships behind them en masse, centuries of build up can cause ships travelling in oft-traveled areas to be damaged. The solution to this issue is cleaner ships designed to easily and cheaply gather this remaining exotic matter. This ships have to move at sub-light speeds to avoid leaving any exotic matter behind themselves.
Application
Due to the lack of space-field sensors and proper extraction technology string matter was very rare until 3013 with the advances of high radiation shielding and space-field sensor technology. Exotic matter was first used in 2660 to develop Military warp drives capable of traveling at 2000C. These Military drives were twenty times faster than any other civilian class warp drive and were reserved solely for military vessels until the year 3014 when Exotic Matter became much more abundant. In 9952, when star-harvesting technology was demonstrated for the first time Exotic String Matter was used to create the first stable wormhole.
Imaginary Exotic Matter, or Tachyons were first discovered in the year 2684. They were used to instantly send and receive data over thousands of lightyears. Use of tachyons in information and computing technology was strictly regulated by the UFSS until the year 3000 with the birth of the Confederacy. While it hasn't been invented yet, scientists hypothesize that creation of an "imaginary drive" is possible. The drive would convert a spaceship's mass into imaginary mass and would be able to instantly send the ship anywhere in the Borealis Cluster, or perhaps other galactic clusters.