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Higgs boson, conceptual computer artwork. The Higgs boson is a proposed fundamental particle that is thought to give other particles mass. It is required by many of the Grand Unified Theories which hope to explain three of the fundamental forces (electromagnetism and the weak and the strong nuclear forces) in a single unified theory. The Higgs boson is yet to be detected experimentally, but it is one of the main challenges of high-energy particle accelerators such as the large hadron collider (LHC) at CERN (the European particle physics laboratory). (KEYSTONE/SCIENCE PHOTO LIBRARY/PASIEKA/SCIENCE PHOTO LIBRARY)