Supersymmetry, often referred to as SUSY in the scientific community, is a theory in particle physics that attempts to account for missing matter or dark matter in the universe, and unify gravity with the other three fundamental forces of nature, which are electromagnetism and the weak and strong nuclear forces. The concept behind supersymmetry is an aspect of string theory that can be tested with current nuclear accelerator technology to some degree, and states that all subatomic particles that carry a force are matched by subatomic particles that have mass. An example of this is the boson, which is believed to be a supersymmetric force carrier for that of the matter particle known as the fermion.
While the theory of supersymmetry solves many fundamental problems discovered in how elementary particles behave, there has been no direct evidence to support it as of 2011. The Large Hadron Collider (LHC), which, as of 2011, is the biggest particle accelerator to be built on Earth and consists of 17 miles (27 kilometers) of tunnel below the French-Swiss border, conducted a direct experiment in August 2011 to detect supersymmetry effects and failed to find any evidence to support the theory. This is in contrast to earlier promising indications from the Tevatron particle accelerator that suggested supersymmetry might be observed in the decay of B-meson subatomic particles. The Tevatron is a 3.9 mile (6.28 kilometer) accelerator located at Fermilab outside Chicago, Illinois, in the US.
The concept of partner particles in a grand supersymmetry theory has been evolving in particle physics for 20 years. Researchers are now questioning the foundation of the theory, as supporting experiments at the LHC, which should have also provided some evidence to support the theory, have not done. The theory has been attractive to physicists for some time, as it allows for a basic testing of aspects of string theory that are otherwise far beyond the capabilities of human technology for the foreseeable future.
The theory also could explain the great mystery of what dark matter is, which makes up an estimated 25% of the universe, with another roughly 70% attributed to dark energy. All normal matter and energy that are observable by conventional science make up less than 5% of the total mass and energy of the universe. Supersymmetry theory would also explain the presence of the concept of the Higgs boson. Bosons are hypothetical particles that have been worked into calculations to resolve issues with the Standard Model in particle physics, but they are the only subatomic or elementary particle that has not been observed in physics experiments as of 2011.
Though simple versions of supersymmetry may now be ruled out as likely, other complex approaches to it are also being considered. The most fundamental of elementary particles, the quark, would also have a supersymmetric partner known as the squark, which would be matched individually to each of the six quark flavors, which are up, down, strange, charm, bottom, and top. Other supersymmetric partners, if they are ever discovered, would be the gravitino matched to the graviton, the photino matched to the photon, the gluino matched to the gluon, and several others. Even well-known subatomic particles would have supersymmetry partners, such as the electron, which would have a selectron as its superpartner.