Etherington reciprocity theorem

Target entity: Etherington reciprocity theorem
Context triple: [Tolman surface brightness test, relatedTo, Etherington reciprocity theorem]

• A. Poynting theorem
  The Poynting theorem is a fundamental principle in electromagnetism that expresses the conservation of electromagnetic energy by relating the flow of energy, energy density, and work done on charges.
• B. Kirchhoff diffraction theory
  Kirchhoff diffraction theory is a classical wave optics framework that models light propagation and diffraction by treating wavefronts as superpositions of secondary spherical waves emitted from an aperture.
• C. Huygens–Fresnel principle
  The Huygens–Fresnel principle is a fundamental concept in wave optics that explains how every point on a wavefront acts as a source of secondary wavelets whose interference determines the wave’s subsequent propagation and diffraction.
• D. Poynting vector
  The Poynting vector is a fundamental quantity in electromagnetism that represents the directional energy flux (power per unit area) carried by an electromagnetic field.
• E. The Fourier Integral and Certain of Its Applications
  The Fourier Integral and Certain of Its Applications is a foundational mathematical work by Norbert Wiener that develops and applies Fourier analysis to problems in harmonic analysis and related areas.
• F. None of above. chosen
• G. Unsure - the case is ambiguous/there is not enough information to decide.

Target entity: Etherington reciprocity theorem
Target entity description: The Etherington reciprocity theorem is a fundamental result in relativistic cosmology that links luminosity distance and angular diameter distance, underpinning observational tests of the expanding universe.

• A. Poynting theorem
  The Poynting theorem is a fundamental principle in electromagnetism that expresses the conservation of electromagnetic energy by relating the flow of energy, energy density, and work done on charges.
• B. Kirchhoff diffraction theory
  Kirchhoff diffraction theory is a classical wave optics framework that models light propagation and diffraction by treating wavefronts as superpositions of secondary spherical waves emitted from an aperture.
• C. Huygens–Fresnel principle
  The Huygens–Fresnel principle is a fundamental concept in wave optics that explains how every point on a wavefront acts as a source of secondary wavelets whose interference determines the wave’s subsequent propagation and diffraction.
• D. Poynting vector
  The Poynting vector is a fundamental quantity in electromagnetism that represents the directional energy flux (power per unit area) carried by an electromagnetic field.
• E. The Fourier Integral and Certain of Its Applications
  The Fourier Integral and Certain of Its Applications is a foundational mathematical work by Norbert Wiener that develops and applies Fourier analysis to problems in harmonic analysis and related areas.
• F. None of above. chosen