An antiproton is the antimatter counterpart of a proton. It is a baryon, or heavy particle, formed from two up and one down antiquarks. It is a hadron, meaning it is subject to the strong nuclear force, and it is a fermion, which means (among other things) that it has half-integral spin. Like baryonic matter, baryonic antimatter must be color neutral, according to the theory of quantum chromodynamics; this means the among the three quarks must be one yellow (anti-blue), one magenta (anti-green), and one cyan (anti-red).
Antiprotons form only at extremely high energy levels, such as those theorized to be present at the beginning of the universe. Upon contact with a proton, both particles are transformed mostly into energy. For this reason, they are extraordinarily rare in nature. As of the 20th century, scientists weren't sure exactly why the quantities of matter and anti-matter weren't equal in the universe, but they suspected that something in the early universe resulted in a breaking of this symmetry, causing the amount of matter to exceed the amount of anti-matter by a small proportion. When the mutual annihiliation ended, the excess matter formed what we know as the universe.
A beam of pure antiprotons is an incredibly destructive weapon. Such a weapon was used by the so-called "doomsday machine" to destroy planets. The Jem'Hadar also use antiprotons to reveal cloaked ships. (TOS: "The Doomsday Machine", DS9: "The Search, Part I")
External links
- Antiproton at Wikipedia