History of variational principles in physics involves integrals over an interval of time and (for fields) extended region of space. Moreover, in the usual formulation of classical action principles, the initial and final states of the system are fixed, e.g., In particular, the fixing of the "final" state appears to give the action principle a teleological character which has been controversial historically. This apparent teleology is eliminated in the quantum mechanical version of the action principle. History of variational principles in physics A variational principle in physics is an alternative method for determining the state or dynamics of a physical system, by identifying it as an
Non-physical entity a ghost that makes it a specifically non-physical, rather than a physical entity. Were the existence of ghosts ever demonstrated beyond doubt, it has been claimed that would actually place them in the category of "physical" entities. Purported non-mental non-physical entities include things such as gods, angels, demons, and ghosts. Lacking demonstrations of their existence, their existences and natures are widely debated, independently of the philosophy of mind. Non-physical entity In ontology and the philosophy of mind, a non-physical entity is a spirit or being that exists outside physical reality. Their existence divides the philosophical school of physicalism from the