Knowra Rayleigh–Jeans law Rayleigh–Jeans law The Rayleigh–Jeans law gives classical blackbody spectral radiance as a function of frequency or wavelength and temperature. It matches long-wavelength measurements but diverges at short wavelengths, producing the ultraviolet catastrophe.
Blackbody radiation : Electromagnetic radiation emitted by an ideal absorber in thermal equilibrium, with a spectrum determined by temperature. The law is a classical prediction for the spectrum of this thermal radiation.
John William Strutt, 3rd Baron Rayleigh : A British physicist whose work spanned acoustics, optics, and the theory of thermal radiation. Rayleigh published an early classical derivation of the radiation spectrum.
Radio astronomy : The study of astronomical objects through their emission and absorption of radio waves. At sufficiently low frequencies, the law approximates thermal source brightness in radio observations.
Wien approximation : The high-frequency approximation to Planck’s law, where spectral radiance falls exponentially with frequency. It describes the short-wavelength regime opposite the Rayleigh–Jeans law’s domain of accuracy.
Equipartition theorem : A classical statistical-mechanics principle assigning equal average energy to each quadratic degree of freedom in thermal equilibrium. Applying equipartition to cavity modes gives each mode an average energy of kT.
James Jeans : A British physicist and astronomer who developed theories of stellar structure, radiation, and the origin of the solar system. Jeans refined the classical derivation and extended it to the full mode count.
Cosmic microwave background : Relic thermal radiation from the early universe, now observed primarily as microwave radiation. Its low-frequency spectrum approaches the Rayleigh–Jeans form.
Classical physics : Physical theories developed before quantum mechanics and relativity, including Newtonian mechanics and classical electromagnetism. The law’s equipartition-based derivation embodies classical physics’s failure at high frequencies.
Electromagnetic cavity : A bounded region in which electromagnetic waves form discrete standing-wave modes. The law counts the cavity’s electromagnetic modes to derive its frequency dependence.
Gustav Kirchhoff : A German physicist who established foundational principles of blackbody radiation and spectroscopy. His work on universal blackbody spectra framed the problem the law sought to solve.
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