Coherence is a collective property that is present in BoseEinstein condensates (BEC), an example of which when charged is superconductivity (SC). Coherence is also believed to be present to a degree in highly efficient energy transfer in certain biological systems. Attributes of coherent systems are examined in BEC, superfluidity and Bardeen, Cooper, and Schrieffer SC and a laser in part 1. Part 2 consists of examination of various proposals for coherence including ' 'emergent coherent systems' ' where there may be coherence but no phase transition. We discuss ' 'cold' ' atomic gases, the Casimir effect, an extended version of F€ orster's resonance energy transfer, Fr€ ohlich's model, exciton-coupled quantum wells, and conceptually ' 'old' ' polaritons rejuvenated by new developments. A discussion about highly efficient energy transfer in photosynthesis along with our proposal for a possible new model for this system is the last of the examples. We finish with a discussion about emergent coherent systems and attempt to classify the examples of parts 1 and 2.
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