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ncarron

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That physical laws are invariant under the observer’s displacement in position leads to conservation of momentum.

Invariance under rotation leads to conservation of angular momentum, and under displacement in time leads to conservation of energy.

However, there is one more symmetry: That physical laws are invariant when the entire system is moving at a constant velocity relative to a first system (Galilean or Lorentz invariance; Lorentz "boost"). What is the associated conserved quantity under that symmetry?