Conceptual illustration of the bipolarity principle having 2 poles or opposite extremes, of a nerve cell having 2 axions, one either side of the cell body. Bipolar disorder, also known as bipolar affective disorder, and originally called manic depressive illness, is a mental disorder characterized by periods of elevated mood and periods of depression. The elevated mood is significant and is known as mania or hypomania depending on the severity or whether there is psychosis. Supersymmetry (SUSY), is a particle physics theory that proposes a type of spacetime symmetry relating two basic classes of elementary particles: bosons, which have an integer-valued "spin", and fermions, which have a half-integer spin. If supersymmetry is a true symmetry of nature, it would explain many mysterious features of particle physics and would help solve paradoxes such as the cosmological constant problem.