Causal retarded potentials
The source-generated vacuum Lorenz potentials are φ(r,t)=(1/(4πε₀))∫ρ(r′,t−R/c)d³r′/R and A(r,t)=(μ₀/(4π))∫J(r′,t−R/c)d³r′/R, where R=|r−r′|.
Key knowledge
The source-generated vacuum Lorenz potentials are φ(r,t)=(1/(4πε₀))∫ρ(r′,t−R/c)d³r′/R and A(r,t)=(μ₀/(4π))∫J(r′,t−R/c)d³r′/R, where R=|r−r′|. The propagation delay selects past source values; independent incoming or initial free waves require an additional homogeneous solution.
Values and equations
φ(r,t)=1/(4πε₀)∫[ρ(r′,t−R/c)/R]d³r′; A(r,t)=μ₀/(4π)∫[J(r′,t−R/c)/R]d³r′
- φ
- Retarded scalar potential V
- A
- Retarded vector potential T m
- r,r′,R
- Observation/source positions and separation m
- ρ
- Charge density C m⁻³
- J
- Current density A m⁻²
- t
- Time s
- c
- Vacuum light speed m s⁻¹
- ε₀
- Vacuum permittivity F m⁻¹
- μ₀
- Vacuum permeability H m⁻¹
Conditions and scope
- Conserved localized sufficiently regular sources in all-space vacuum, retarded/outgoing Green function, convergent integrals and no independent incoming field in the displayed source-only expression.
- Retarded boundary/initial conditions select causality; the local wave equation or a falloff statement alone does not uniquely eliminate all free waves. Boundaries/materials require their appropriate Green functions.
Sources · 2
References
Sources retain their recorded scope. A source link alone does not establish verification of every statement.
Evidence and review
Classical Electromagnetism (2014): Retarded potentials: Equations 71–76: source wave equations and retarded 1/R integrals. Keep the time delay and vacuum factors; qualify the source's uniqueness discussion with explicit retarded and homogeneous-field data. Maxwell equations: causal Green function and free-field data (2018): Printed pages 12–14, equations 69–70 and the paragraphs around 73–75: causal delta Green function and incoming/free-field versus source-only distinction. Does not copy the extra 4π denominator printed inside its equations 71–74; the normalized integrals use the separately inspected Fitzpatrick equations 73–76.
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Entry details
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