quantum mechanics: the branch of quantum physics that accounts for matter at the atomic level; an extension of statistical mechanics based on quantum theory (especially the Pauli exclusion principle)
natural science: the sciences involved in the study of the physical world and its phenomena
selective-serotonin reuptake inhibitor: an antidepressant drug that acts by blocking the reuptake of serotonin so that more serotonin is available to act on receptors in the brain