Global symmetry

In physics, a global symmetry is a symmetry that holds at all points in the spacetime under consideration, as opposed to a local symmetry which varies from point to point. In physics, a global symmetry is a symmetry that holds at all points in the spacetime under consideration, as opposed to a local symmetry which varies from point to point. Global symmetries require conservation laws, but not forces, in physics. An example of a global symmetry is the action of the U ( 1 ) = e i θ {displaystyle U(1)=e^{i heta }} (for θ {displaystyle heta } a constant - making it a global transformation) group on the Dirac Lagrangian: Under this transformation the fermionic field changes as ψ → e i θ ψ {displaystyle psi ightarrow e^{i heta }psi } and ψ ¯ → e − i θ ψ ¯ {displaystyle {ar {psi }} ightarrow e^{-i heta }{ar {psi }}} and so: