501 lines
20 KiB
Text
501 lines
20 KiB
Text
/-
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Copyright (c) 2024 Joseph Tooby-Smith. All rights reserved.
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Released under Apache 2.0 license.
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Authors: Joseph Tooby-Smith
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-/
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import HepLean.SpaceTime.Metric
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import Mathlib.GroupTheory.SpecificGroups.KleinFour
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/-!
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# The Lorentz Group
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We define the Lorentz group.
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## TODO
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- Show that the Lorentz is a Lie group.
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- Prove that the restricted Lorentz group is equivalent to the connected component of the
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identity.
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- Define the continuous maps from `ℝ³` to `restrictedLorentzGroup` defining boosts.
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## References
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- http://home.ku.edu.tr/~amostafazadeh/phys517_518/phys517_2016f/Handouts/A_Jaffi_Lorentz_Group.pdf
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- A proof that the restricted Lorentz group is connected can be found at:
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https://diposit.ub.edu/dspace/bitstream/2445/68763/2/memoria.pdf
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The proof involves the introduction of boosts.
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-/
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noncomputable section
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namespace spaceTime
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open Manifold
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open Matrix
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open Complex
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open ComplexConjugate
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/-- The Lorentz group as a subgroup of the general linear group over the reals. -/
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def lorentzGroup : Subgroup (GeneralLinearGroup (Fin 4) ℝ) where
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carrier := {Λ | ∀ (x y : spaceTime), ηLin (Λ *ᵥ x) (Λ *ᵥ y) = ηLin x y}
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mul_mem' {a b} := by
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intros ha hb x y
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simp only [Units.val_mul, mulVec_mulVec]
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rw [← mulVec_mulVec, ← mulVec_mulVec, ha, hb]
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one_mem' := by
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intros x y
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simp
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inv_mem' {a} := by
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intros ha x y
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simp only [coe_units_inv, ← ha ((a.1⁻¹) *ᵥ x) ((a.1⁻¹) *ᵥ y), mulVec_mulVec]
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have hx : (a.1 * (a.1)⁻¹) = 1 := by
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simp only [@Units.mul_eq_one_iff_inv_eq, coe_units_inv]
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simp [hx]
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/-- The Lorentz group is a topological group with the subset topology. -/
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instance : TopologicalGroup lorentzGroup :=
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Subgroup.instTopologicalGroupSubtypeMem lorentzGroup
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lemma preserve_ηLin_iff' (Λ : Matrix (Fin 4) (Fin 4) ℝ) :
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(∀ (x y : spaceTime), ηLin (Λ *ᵥ x) (Λ *ᵥ y) = ηLin x y) ↔
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∀ (x y : spaceTime), ηLin (x) ((η * Λᵀ * η * Λ) *ᵥ y) = ηLin x y := by
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apply Iff.intro
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intro h
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intro x y
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have h1 := h x y
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rw [ηLin_mulVec_left, mulVec_mulVec] at h1
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exact h1
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intro h
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intro x y
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rw [ηLin_mulVec_left, mulVec_mulVec]
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exact h x y
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lemma preserve_ηLin_iff'' (Λ : Matrix (Fin 4) (Fin 4) ℝ) :
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(∀ (x y : spaceTime), ηLin (Λ *ᵥ x) (Λ *ᵥ y) = ηLin x y) ↔
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η * Λᵀ * η * Λ = 1 := by
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rw [preserve_ηLin_iff', ηLin_matrix_eq_identity_iff (η * Λᵀ * η * Λ)]
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apply Iff.intro
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· simp_all [ηLin, implies_true, iff_true, one_mulVec]
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· simp_all only [ηLin, LinearMap.coe_mk, AddHom.coe_mk, linearMapForSpaceTime_apply,
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mulVec_mulVec, implies_true]
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lemma preserve_ηLin_iff''' (Λ : Matrix (Fin 4) (Fin 4) ℝ) :
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(∀ (x y : spaceTime), ηLin (Λ *ᵥ x) (Λ *ᵥ y) = ηLin x y) ↔
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Λ * (η * Λᵀ * η) = 1 := by
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rw [preserve_ηLin_iff'']
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apply Iff.intro
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intro h
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exact mul_eq_one_comm.mp h
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intro h
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exact mul_eq_one_comm.mp h
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lemma preserve_ηLin_iff_transpose (Λ : Matrix (Fin 4) (Fin 4) ℝ) :
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(∀ (x y : spaceTime), ηLin (Λ *ᵥ x) (Λ *ᵥ y) = ηLin x y) ↔
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(∀ (x y : spaceTime), ηLin (Λᵀ *ᵥ x) (Λᵀ *ᵥ y) = ηLin x y) := by
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apply Iff.intro
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intro h
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have h1 := congrArg transpose ((preserve_ηLin_iff'' Λ).mp h)
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rw [transpose_mul, transpose_mul, transpose_mul, η_transpose,
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← mul_assoc, transpose_one] at h1
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rw [preserve_ηLin_iff''' Λ.transpose, ← h1]
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repeat rw [← mul_assoc]
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intro h
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have h1 := congrArg transpose ((preserve_ηLin_iff'' Λ.transpose).mp h)
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rw [transpose_mul, transpose_mul, transpose_mul, η_transpose,
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← mul_assoc, transpose_one, transpose_transpose] at h1
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rw [preserve_ηLin_iff''', ← h1]
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repeat rw [← mul_assoc]
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def preserveηLinGLnLift {Λ : Matrix (Fin 4) (Fin 4) ℝ}
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(h : ∀ (x y : spaceTime), ηLin (Λ *ᵥ x) (Λ *ᵥ y) = ηLin x y) : GL (Fin 4) ℝ :=
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⟨Λ, η * Λᵀ * η ,(preserve_ηLin_iff''' Λ).mp h , (preserve_ηLin_iff'' Λ).mp h⟩
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lemma mem_lorentzGroup_iff (Λ : GeneralLinearGroup (Fin 4) ℝ) :
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Λ ∈ lorentzGroup ↔ ∀ (x y : spaceTime), ηLin (Λ *ᵥ x) (Λ *ᵥ y) = ηLin x y := by
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rfl
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lemma mem_lorentzGroup_iff' (Λ : GeneralLinearGroup (Fin 4) ℝ) :
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Λ ∈ lorentzGroup ↔ ∀ (x y : spaceTime), ηLin (x) ((η * Λ.1ᵀ * η * Λ.1) *ᵥ y) = ηLin x y := by
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rw [mem_lorentzGroup_iff]
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exact preserve_ηLin_iff' Λ.1
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lemma mem_lorentzGroup_iff'' (Λ : GL (Fin 4) ℝ) :
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Λ ∈ lorentzGroup ↔ η * Λ.1ᵀ * η * Λ.1 = 1 := by
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rw [mem_lorentzGroup_iff]
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exact preserve_ηLin_iff'' Λ
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lemma mem_lorentzGroup_iff''' (Λ : GL (Fin 4) ℝ) :
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Λ ∈ lorentzGroup ↔ η * Λ.1ᵀ * η = Λ⁻¹ := by
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rw [mem_lorentzGroup_iff'']
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exact Units.mul_eq_one_iff_eq_inv
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def preserveηLinLorentzLift {Λ : Matrix (Fin 4) (Fin 4) ℝ}
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(h : ∀ (x y : spaceTime), ηLin (Λ *ᵥ x) (Λ *ᵥ y) = ηLin x y) : lorentzGroup :=
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⟨preserveηLinGLnLift h, (mem_lorentzGroup_iff (preserveηLinGLnLift h)).mpr h⟩
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-- TODO: Simplify using preserveηLinLorentzLift.
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lemma mem_lorentzGroup_iff_transpose (Λ : GL (Fin 4) ℝ) :
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Λ ∈ lorentzGroup ↔ ⟨transpose Λ, (transpose Λ)⁻¹, by
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rw [← transpose_nonsing_inv, ← transpose_mul, (coe_units_inv Λ).symm]
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rw [show ((Λ)⁻¹).1 * Λ.1 = (1 : Matrix (Fin 4) (Fin 4) ℝ) by rw [@Units.inv_mul_eq_one]]
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rw [@transpose_eq_one], by
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rw [← transpose_nonsing_inv, ← transpose_mul, (coe_units_inv Λ).symm]
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rw [show Λ.1 * ((Λ)⁻¹).1 = (1 : Matrix (Fin 4) (Fin 4) ℝ) by rw [@Units.mul_inv_eq_one]]
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rw [@transpose_eq_one]⟩ ∈ lorentzGroup := by
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rw [mem_lorentzGroup_iff''', mem_lorentzGroup_iff''']
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simp only [coe_units_inv, transpose_transpose, Units.inv_mk]
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apply Iff.intro
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intro h
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have h1 := congrArg transpose h
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rw [transpose_mul, transpose_mul, transpose_transpose, η_transpose, ← mul_assoc] at h1
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rw [h1]
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exact transpose_nonsing_inv _
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intro h
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have h1 := congrArg transpose h
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rw [transpose_mul, transpose_mul, η_transpose, ← mul_assoc] at h1
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rw [h1, transpose_nonsing_inv, transpose_transpose]
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/-- The transpose of an matrix in the Lorentz group is an element of the Lorentz group. -/
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def lorentzGroupTranspose (Λ : lorentzGroup) : lorentzGroup :=
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⟨⟨transpose Λ.1, (transpose Λ.1)⁻¹, by
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rw [← transpose_nonsing_inv, ← transpose_mul, (coe_units_inv Λ.1).symm]
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rw [show ((Λ.1)⁻¹).1 * Λ.1 = (1 : Matrix (Fin 4) (Fin 4) ℝ) by rw [@Units.inv_mul_eq_one]]
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rw [@transpose_eq_one], by
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rw [← transpose_nonsing_inv, ← transpose_mul, (coe_units_inv Λ.1).symm]
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rw [show Λ.1.1 * ((Λ.1)⁻¹).1 = (1 : Matrix (Fin 4) (Fin 4) ℝ) by rw [@Units.mul_inv_eq_one]]
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rw [@transpose_eq_one]⟩,
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(mem_lorentzGroup_iff_transpose Λ.1).mp Λ.2 ⟩
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/-- A continous map from `GL (Fin 4) ℝ` to `Matrix (Fin 4) (Fin 4) ℝ` for which the Lorentz
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group is the kernal. -/
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def lorentzMap (Λ : GL (Fin 4) ℝ) : Matrix (Fin 4) (Fin 4) ℝ := η * Λ.1ᵀ * η * Λ.1
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lemma lorentzMap_continuous : Continuous lorentzMap := by
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apply Continuous.mul _ Units.continuous_val
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apply Continuous.mul _ continuous_const
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exact Continuous.mul continuous_const (Continuous.matrix_transpose (Units.continuous_val))
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lemma lorentzGroup_kernal : lorentzGroup = lorentzMap ⁻¹' {1} := by
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ext Λ
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erw [mem_lorentzGroup_iff'' Λ]
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rfl
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/-- The Lorentz Group is a closed subset of `GL (Fin 4) ℝ`. -/
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theorem lorentzGroup_isClosed : IsClosed (lorentzGroup : Set (GL (Fin 4) ℝ)) := by
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rw [lorentzGroup_kernal]
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exact continuous_iff_isClosed.mp lorentzMap_continuous {1} isClosed_singleton
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namespace lorentzGroup
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lemma det_eq_one_or_neg_one (Λ : lorentzGroup) : Λ.1.1.det = 1 ∨ Λ.1.1.det = -1 := by
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simpa [← sq, det_one, det_mul, det_mul, det_mul, det_transpose, det_η] using
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(congrArg det ((mem_lorentzGroup_iff'' Λ.1).mp Λ.2))
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local notation "ℤ₂" => Multiplicative (ZMod 2)
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instance : TopologicalSpace ℤ₂ := instTopologicalSpaceFin
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/-- A group homomorphism from `lorentzGroup` to `ℤ₂` taking a matrix to
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0 if it's determinant is 1 and 1 if its determinant is -1.-/
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@[simps!]
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def detRep : lorentzGroup →* ℤ₂ where
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toFun Λ := if Λ.1.1.det = 1 then (Additive.toMul 0) else Additive.toMul (1 : ZMod 2)
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map_one' := by
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simp
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map_mul' := by
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intro Λ1 Λ2
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simp only [Submonoid.coe_mul, Subgroup.coe_toSubmonoid, Units.val_mul, det_mul, toMul_zero,
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mul_ite, mul_one, ite_mul, one_mul]
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cases' (det_eq_one_or_neg_one Λ1) with h1 h1
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<;> cases' (det_eq_one_or_neg_one Λ2) with h2 h2
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<;> simp [h1, h2]
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rfl
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/-- A Lorentz Matrix is proper if its determinant is 1. -/
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def IsProper (Λ : lorentzGroup) : Prop := Λ.1.1.det = 1
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instance : DecidablePred IsProper := by
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intro Λ
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apply Real.decidableEq
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lemma IsProper_iff (Λ : lorentzGroup) :
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IsProper Λ ↔ detRep Λ = Additive.toMul 0 := by
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apply Iff.intro
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intro h
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erw [detRep_apply, if_pos h]
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simp only [toMul_zero]
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intro h
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by_cases h1 : IsProper Λ
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exact h1
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erw [detRep_apply, if_neg h1] at h
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contradiction
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section Orthochronous
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/-- The space-like part of the first row of of a Lorentz matrix. -/
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@[simp]
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def fstRowToEuclid (Λ : lorentzGroup) : EuclideanSpace ℝ (Fin 3) := fun i => Λ.1 0 i.succ
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/-- The space-like part of the first column of of a Lorentz matrix. -/
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@[simp]
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def fstColToEuclid (Λ : lorentzGroup) : EuclideanSpace ℝ (Fin 3) := fun i => Λ.1 i.succ 0
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lemma fst_col_normalized (Λ : lorentzGroup) :
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(Λ.1 0 0) ^ 2 - (Λ.1 1 0) ^ 2 - (Λ.1 2 0) ^ 2 - (Λ.1 3 0) ^ 2 = 1 := by
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have h00 := congrFun (congrFun ((mem_lorentzGroup_iff'' Λ).mp Λ.2) 0) 0
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simp only [Fin.isValue, mul_apply, transpose_apply, Fin.sum_univ_four, ne_eq, zero_ne_one,
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not_false_eq_true, η_off_diagonal, zero_mul, add_zero, Fin.reduceEq, one_ne_zero, mul_zero,
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zero_add, one_apply_eq] at h00
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simp only [η, Fin.isValue, of_apply, cons_val', cons_val_zero, empty_val', cons_val_fin_one,
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vecCons_const, one_mul, mul_one, cons_val_one, head_cons, mul_neg, neg_mul, cons_val_two,
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Nat.succ_eq_add_one, Nat.reduceAdd, tail_cons, cons_val_three, head_fin_const] at h00
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rw [← h00]
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ring
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lemma fst_row_normalized (Λ : lorentzGroup) :
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(Λ.1 0 0) ^ 2 - (Λ.1 0 1) ^ 2 - (Λ.1 0 2) ^ 2 - (Λ.1 0 3) ^ 2 = 1 := by
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simpa using fst_col_normalized (lorentzGroupTranspose Λ)
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lemma zero_zero_sq_col (Λ : lorentzGroup) :
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(Λ.1 0 0) ^ 2 = 1 + (Λ.1 1 0) ^ 2 + (Λ.1 2 0) ^ 2 + (Λ.1 3 0) ^ 2 := by
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rw [← fst_col_normalized Λ]
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ring
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lemma zero_zero_sq_row (Λ : lorentzGroup) :
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(Λ.1 0 0) ^ 2 = 1 + (Λ.1 0 1) ^ 2 + (Λ.1 0 2) ^ 2 + (Λ.1 0 3) ^ 2 := by
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rw [← fst_row_normalized Λ]
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ring
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lemma zero_zero_sq_col' (Λ : lorentzGroup) :
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(Λ.1 0 0) ^ 2 = 1 + ‖fstColToEuclid Λ‖ ^ 2 := by
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rw [zero_zero_sq_col, ← @real_inner_self_eq_norm_sq, @PiLp.inner_apply, Fin.sum_univ_three]
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simp only [Fin.isValue, fstColToEuclid, Fin.succ_zero_eq_one, RCLike.inner_apply, conj_trivial,
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Fin.succ_one_eq_two]
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rw [show (Fin.succ 2) = 3 by rfl]
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ring_nf
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lemma zero_zero_sq_row' (Λ : lorentzGroup) :
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(Λ.1 0 0) ^ 2 = 1 + ‖fstRowToEuclid Λ‖ ^ 2 := by
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rw [zero_zero_sq_row, ← @real_inner_self_eq_norm_sq, @PiLp.inner_apply, Fin.sum_univ_three]
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simp only [Fin.isValue, fstRowToEuclid, Fin.succ_zero_eq_one, RCLike.inner_apply, conj_trivial,
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Fin.succ_one_eq_two]
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rw [show (Fin.succ 2) = 3 by rfl]
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ring_nf
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lemma norm_col_leq_abs_zero_zero (Λ : lorentzGroup) : ‖fstColToEuclid Λ‖ ≤ |Λ.1 0 0| := by
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rw [(abs_norm (fstColToEuclid Λ)).symm, ← @sq_le_sq, zero_zero_sq_col']
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simp only [le_add_iff_nonneg_left, zero_le_one]
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lemma norm_row_leq_abs_zero_zero (Λ : lorentzGroup) : ‖fstRowToEuclid Λ‖ ≤ |Λ.1 0 0| := by
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rw [(abs_norm (fstRowToEuclid Λ)).symm, ← @sq_le_sq, zero_zero_sq_row']
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simp only [le_add_iff_nonneg_left, zero_le_one]
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lemma zero_zero_sq_ge_one (Λ : lorentzGroup) : 1 ≤ (Λ.1 0 0) ^ 2 := by
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rw [zero_zero_sq_col Λ]
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refine le_add_of_le_of_nonneg ?_ (sq_nonneg _)
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refine le_add_of_le_of_nonneg ?_ (sq_nonneg _)
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refine le_add_of_le_of_nonneg (le_refl 1) (sq_nonneg _)
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lemma abs_zero_zero_ge_one (Λ : lorentzGroup) : 1 ≤ |Λ.1 0 0| :=
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(one_le_sq_iff_one_le_abs _).mp (zero_zero_sq_ge_one Λ)
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lemma zero_zero_le_minus_one_or_ge_one (Λ : lorentzGroup) : (Λ.1 0 0) ≤ - 1 ∨ 1 ≤ (Λ.1 0 0) :=
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le_abs'.mp (abs_zero_zero_ge_one Λ)
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lemma zero_zero_nonpos_iff (Λ : lorentzGroup) : (Λ.1 0 0) ≤ 0 ↔ (Λ.1 0 0) ≤ - 1 := by
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apply Iff.intro
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· intro h
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cases' zero_zero_le_minus_one_or_ge_one Λ with h1 h1
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exact h1
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linarith
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· intro h
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linarith
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lemma zero_zero_nonneg_iff (Λ : lorentzGroup) : 0 ≤ (Λ.1 0 0) ↔ 1 ≤ (Λ.1 0 0) := by
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apply Iff.intro
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· intro h
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cases' zero_zero_le_minus_one_or_ge_one Λ with h1 h1
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linarith
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exact h1
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· intro h
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linarith
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/-- An element of the lorentz group is orthochronous if its time-time element is non-negative. -/
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@[simp]
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def IsOrthochronous (Λ : lorentzGroup) : Prop := 0 ≤ Λ.1 0 0
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instance : Decidable (IsOrthochronous Λ) :=
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Real.decidableLE 0 (Λ.1 0 0)
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lemma not_IsOrthochronous_iff (Λ : lorentzGroup) : ¬ IsOrthochronous Λ ↔ Λ.1 0 0 ≤ 0 := by
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rw [IsOrthochronous, not_le]
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apply Iff.intro
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intro h
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exact le_of_lt h
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intro h
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have h1 := (zero_zero_nonpos_iff Λ).mp h
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linarith
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lemma IsOrthochronous_abs_zero_zero {Λ : lorentzGroup} (h : IsOrthochronous Λ) :
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|Λ.1 0 0| = Λ.1 0 0 :=
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abs_eq_self.mpr h
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lemma not_IsOrthochronous_abs_zero_zero {Λ : lorentzGroup} (h : ¬ IsOrthochronous Λ) :
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Λ.1 0 0 = - |Λ.1 0 0| := by
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refine neg_eq_iff_eq_neg.mp (abs_eq_neg_self.mpr ?_).symm
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simp only [IsOrthochronous, Fin.isValue, not_le] at h
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exact le_of_lt h
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lemma schwartz_identity_fst_row_col (Λ Λ' : lorentzGroup) :
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‖⟪fstRowToEuclid Λ, fstColToEuclid Λ'⟫_ℝ‖ ≤ ‖fstRowToEuclid Λ‖ * ‖fstColToEuclid Λ'‖ :=
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||
norm_inner_le_norm (fstRowToEuclid Λ) (fstColToEuclid Λ')
|
||
|
||
lemma zero_zero_mul (Λ Λ' : lorentzGroup) :
|
||
(Λ * Λ').1 0 0 = (Λ.1 0 0) * (Λ'.1 0 0) + ⟪fstRowToEuclid Λ, fstColToEuclid Λ'⟫_ℝ := by
|
||
rw [@Subgroup.coe_mul, @GeneralLinearGroup.coe_mul, mul_apply, Fin.sum_univ_four]
|
||
rw [@PiLp.inner_apply, Fin.sum_univ_three]
|
||
simp
|
||
rw [show (Fin.succ 2) = 3 by rfl]
|
||
ring_nf
|
||
example (a b c : ℝ ) (h : a - b ≤ a + c) : - b ≤ c := by
|
||
exact (add_le_add_iff_left a).mp h
|
||
|
||
lemma zero_zero_mul_sub_row_col (Λ Λ' : lorentzGroup) :
|
||
0 ≤ |Λ.1 0 0| * |Λ'.1 0 0| - ‖fstRowToEuclid Λ‖ * ‖fstColToEuclid Λ'‖ :=
|
||
sub_nonneg.mpr (mul_le_mul (norm_row_leq_abs_zero_zero Λ) (norm_col_leq_abs_zero_zero Λ')
|
||
(norm_nonneg (fstColToEuclid Λ')) (abs_nonneg (Λ.1 0 0)))
|
||
|
||
lemma orthchro_mul_orthchro {Λ Λ' : lorentzGroup} (h : IsOrthochronous Λ)
|
||
(h' : IsOrthochronous Λ') : IsOrthochronous (Λ * Λ') := by
|
||
apply le_trans (zero_zero_mul_sub_row_col Λ Λ')
|
||
have h1 := zero_zero_mul Λ Λ'
|
||
rw [← IsOrthochronous_abs_zero_zero h, ← IsOrthochronous_abs_zero_zero h'] at h1
|
||
refine le_trans
|
||
(?_ : _ ≤ |Λ.1 0 0| * |Λ'.1 0 0| + (- |⟪fstRowToEuclid Λ, fstColToEuclid Λ'⟫_ℝ|)) ?_
|
||
· erw [add_le_add_iff_left]
|
||
simp only [neg_mul, neg_neg, neg_le]
|
||
exact schwartz_identity_fst_row_col Λ Λ'
|
||
· rw [h1, add_le_add_iff_left]
|
||
exact neg_abs_le ⟪fstRowToEuclid Λ, fstColToEuclid Λ'⟫_ℝ
|
||
|
||
lemma not_orthchro_mul_not_orthchro {Λ Λ' : lorentzGroup} (h : ¬ IsOrthochronous Λ)
|
||
(h' : ¬ IsOrthochronous Λ') : IsOrthochronous (Λ * Λ') := by
|
||
apply le_trans (zero_zero_mul_sub_row_col Λ Λ')
|
||
refine le_trans
|
||
(?_ : _ ≤ |Λ.1 0 0| * |Λ'.1 0 0| + (- |⟪fstRowToEuclid Λ, fstColToEuclid Λ'⟫_ℝ|)) ?_
|
||
· erw [add_le_add_iff_left]
|
||
simp only [neg_mul, neg_neg, neg_le]
|
||
exact schwartz_identity_fst_row_col Λ Λ'
|
||
· rw [zero_zero_mul Λ Λ', not_IsOrthochronous_abs_zero_zero h,
|
||
not_IsOrthochronous_abs_zero_zero h']
|
||
simp only [Fin.isValue, abs_neg, _root_.abs_abs, conj_trivial, mul_neg, neg_mul, neg_neg,
|
||
add_le_add_iff_left]
|
||
exact neg_abs_le ⟪fstRowToEuclid Λ, fstColToEuclid Λ'⟫_ℝ
|
||
|
||
lemma orthchro_mul_not_orthchro {Λ Λ' : lorentzGroup} (h : IsOrthochronous Λ)
|
||
(h' : ¬ IsOrthochronous Λ') : ¬ IsOrthochronous (Λ * Λ') := by
|
||
rw [not_IsOrthochronous_iff]
|
||
refine le_trans
|
||
(?_ : _ ≤ - (|Λ.1 0 0| * |Λ'.1 0 0| + (- |⟪fstRowToEuclid Λ, fstColToEuclid Λ'⟫_ℝ|))) ?_
|
||
· rw [zero_zero_mul Λ Λ', ← IsOrthochronous_abs_zero_zero h,
|
||
not_IsOrthochronous_abs_zero_zero h']
|
||
simp only [Fin.isValue, mul_neg, _root_.abs_abs, abs_neg, neg_add_rev, neg_neg,
|
||
le_add_neg_iff_add_le, neg_add_cancel_comm]
|
||
exact le_abs_self ⟪fstRowToEuclid Λ, fstColToEuclid Λ'⟫_ℝ
|
||
· apply le_trans ?_ (neg_nonpos_of_nonneg (zero_zero_mul_sub_row_col Λ Λ'))
|
||
simp only [Fin.isValue, neg_add_rev, neg_neg, neg_sub, add_neg_le_iff_le_add, sub_add_cancel]
|
||
exact schwartz_identity_fst_row_col _ _
|
||
|
||
lemma not_orthchro_mul_orthchro {Λ Λ' : lorentzGroup} (h : ¬ IsOrthochronous Λ)
|
||
(h' : IsOrthochronous Λ') : ¬ IsOrthochronous (Λ * Λ') := by
|
||
rw [not_IsOrthochronous_iff]
|
||
refine le_trans
|
||
(?_ : _ ≤ - (|Λ.1 0 0| * |Λ'.1 0 0| + (- |⟪fstRowToEuclid Λ, fstColToEuclid Λ'⟫_ℝ|))) ?_
|
||
· rw [zero_zero_mul Λ Λ', ← IsOrthochronous_abs_zero_zero h',
|
||
not_IsOrthochronous_abs_zero_zero h]
|
||
simp only [Fin.isValue, neg_mul, PiLp.inner_apply, fstRowToEuclid, fstColToEuclid,
|
||
RCLike.inner_apply, conj_trivial, abs_neg, _root_.abs_abs, neg_add_rev, neg_neg,
|
||
le_add_neg_iff_add_le, neg_add_cancel_comm]
|
||
exact le_abs_self ⟪fstRowToEuclid Λ, fstColToEuclid Λ'⟫_ℝ
|
||
· apply le_trans ?_ (neg_nonpos_of_nonneg (zero_zero_mul_sub_row_col Λ Λ'))
|
||
simp only [Fin.isValue, neg_add_rev, neg_neg, neg_sub, add_neg_le_iff_le_add, sub_add_cancel]
|
||
exact schwartz_identity_fst_row_col _ _
|
||
|
||
/-- The homomorphism from `lorentzGroup` to `ℤ₂` whose kernal consists of precisely the
|
||
orthochronous elements. -/
|
||
@[simps!]
|
||
def orthochronousRep : lorentzGroup →* ℤ₂ where
|
||
toFun Λ := if IsOrthochronous Λ then (Additive.toMul 0) else Additive.toMul (1 : ZMod 2)
|
||
map_one' := by
|
||
simp
|
||
map_mul' := by
|
||
intro Λ1 Λ2
|
||
simp only [toMul_zero, mul_ite, mul_one, ite_mul, one_mul]
|
||
cases' (em (IsOrthochronous Λ1)) with h h
|
||
<;> cases' (em (IsOrthochronous Λ2)) with h' h'
|
||
rw [if_pos (orthchro_mul_orthchro h h'), if_pos h, if_pos h']
|
||
rw [if_neg (orthchro_mul_not_orthchro h h'), if_neg h', if_pos h]
|
||
rw [if_neg (not_orthchro_mul_orthchro h h'), if_pos h', if_neg h]
|
||
rw [if_pos (not_orthchro_mul_not_orthchro h h'), if_neg h', if_neg h]
|
||
rfl
|
||
|
||
lemma IsOrthochronous_iff (Λ : lorentzGroup) :
|
||
IsOrthochronous Λ ↔ orthochronousRep Λ = Additive.toMul 0 := by
|
||
apply Iff.intro
|
||
intro h
|
||
erw [orthochronousRep_apply, if_pos h]
|
||
simp only [toMul_zero]
|
||
intro h
|
||
by_cases h1 : IsOrthochronous Λ
|
||
exact h1
|
||
erw [orthochronousRep_apply, if_neg h1] at h
|
||
contradiction
|
||
|
||
|
||
|
||
end Orthochronous
|
||
|
||
end lorentzGroup
|
||
|
||
open lorentzGroup in
|
||
/-- The restricted lorentz group consists of those elements of the `lorentzGroup` which are
|
||
proper and orthochronous. -/
|
||
def restrictedLorentzGroup : Subgroup (lorentzGroup) where
|
||
carrier := {Λ | IsProper Λ ∧ IsOrthochronous Λ}
|
||
mul_mem' {Λa Λb} := by
|
||
intro ha hb
|
||
apply And.intro
|
||
rw [IsProper_iff, detRep.map_mul, (IsProper_iff Λa).mp ha.1, (IsProper_iff Λb).mp hb.1]
|
||
simp only [toMul_zero, mul_one]
|
||
rw [IsOrthochronous_iff, orthochronousRep.map_mul, (IsOrthochronous_iff Λa).mp ha.2,
|
||
(IsOrthochronous_iff Λb).mp hb.2]
|
||
simp
|
||
one_mem' := by
|
||
simp only [IsOrthochronous, Fin.isValue, Set.mem_setOf_eq, OneMemClass.coe_one, Units.val_one,
|
||
one_apply_eq, zero_le_one, and_true]
|
||
rw [IsProper_iff, detRep.map_one]
|
||
simp
|
||
inv_mem' {Λ} := by
|
||
intro h
|
||
apply And.intro
|
||
rw [IsProper_iff, detRep.map_inv, (IsProper_iff Λ).mp h.1]
|
||
simp only [toMul_zero, inv_one]
|
||
rw [IsOrthochronous_iff, orthochronousRep.map_inv, (IsOrthochronous_iff Λ).mp h.2]
|
||
simp
|
||
|
||
/-- The restricted lorentz group is a topological group. -/
|
||
instance : TopologicalGroup restrictedLorentzGroup :=
|
||
Subgroup.instTopologicalGroupSubtypeMem restrictedLorentzGroup
|
||
|
||
end spaceTime
|
||
|
||
end
|