theorem
proved
time_invariance_implies_conservation
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IndisputableMonolith.QFT.NoetherTheorem on GitHub at line 137.
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134
135/-- **THEOREM**: Any time-translation-invariant function is conserved.
136 (Energy is time-translation invariant ⟹ Energy is conserved) -/
137theorem time_invariance_implies_conservation {E : ℝ → ℝ}
138 (hinv : ∀ t, IsSymmetryOf (TimeTranslation.flow t) E) :
139 IsConservedAlong E TimeTranslation.flow :=
140 noether_core hinv
141
142/-! ## Space Translation and Momentum -/
143
144/-- Space translation by dx. -/
145def SpaceTranslation : OneParamGroup ℝ where
146 flow dx x := x + dx
147 flow_zero x := by ring
148 flow_add s t x := by ring
149
150/-- **THEOREM**: Any space-translation-invariant function is conserved.
151 (Lagrangian invariant under space translation ⟹ Momentum conserved) -/
152theorem space_invariance_implies_conservation {P : ℝ → ℝ}
153 (hinv : ∀ dx, IsSymmetryOf (SpaceTranslation.flow dx) P) :
154 IsConservedAlong P SpaceTranslation.flow :=
155 noether_core hinv
156
157/-! ## Phase Rotation and Charge -/
158
159/-- Phase rotation on ℂ. -/
160noncomputable def PhaseRotation : OneParamGroup ℂ where
161 flow θ z := Complex.exp (θ * Complex.I) * z
162 flow_zero z := by simp [Complex.exp_zero]
163 flow_add s t z := by
164 rw [← mul_assoc, ← Complex.exp_add]
165 congr 1
166 push_cast
167 ring