English: This shows how Planck's model predicts that oscillators with "photon" constrained-energies ε ≡ hν = hc/λ greater than kT get significantly frozen out of the black body mix, thus solving the ultraviolet catastrophe to which the Rayleigh-Jeans model gave birth. This freeze-out may be explained if (for whatever reason) "quantum oscillators" exist only in packets with energy/frequency & momentum/spatial-frequency linked by the constant h = E/ν = p/g = 2πL.
The dot-dashed lines show the (additive) fractional-contribution of one, two, three, and four photon excitations to the average energy per oscillator at frequency ν. As you can see, when hν>>kT the single-photon fraction dominates as the average energy-per-oscillator drops to zero i.e. finding one of them in the mix is unlikely and finding more than one is much much less likely. This compensates for the fact that with increasing frequency (also decreasing wavelength) the number of oscillators per unit frequency (or wavelength) interval is going through the roof.
The probability of an oscillator having photons is given by
The energy contribution of an oscillator with photons is given by
The average black body energy is the sum of contributions from all oscillators.
#! /usr/bin/env gnuplot# This work is in the public domain.## It was completed by Arun I in 2016.## Though you are not legally obliged to do so, I would appreciate it# if you credit me for this work by not removing this notice, and# hopefully linking to my blog post at# https://systemreboot.net/post/black-body-energy-as-a-sum-of-photon-oscillator-energies# Base filename for output filesfilename='blackbody-energies'# Set terminal and output filesettermepslatexcolorcolortextstandalonesetoutputsprintf('%s.tex',filename)# Axes' properties, title and keysetxrange[-0.01:5]setyrange[0:1.05]setmxtics5setytics0.2setmytics4setxlabel'$ h\nu/kT $'setylabel'Average oscillator energy (in units of $ kT $)'settitle"Planck's solution as a freeze-out of\nphoton oscillator-energies as $ h\\nu/kT \\to \\infty $"unsetkey# Line stylessetstyleline1lc'blue'dt4setstyleline2lc'red'dt4setstyleline3lc'dark-yellow'dt4setstyleline4lc'forest-green'dt4# Labelssetarrowfromgraph0,first1tograph1,first1noheadlc'black'dt6setlabel'$ E_{\textrm{\tiny avg}}^{\textrm{\tiny Rayleigh}} = kT $'atgraph1,first1rightoffsetgraph-0.05,-0.05setlabel'\footnotesize $ h\nu $'at1.4,0.15tcls1setlabel'\footnotesize $ 2h\nu $'at1,0.33tcls2setlabel'\footnotesize $ 3h\nu $'at0.8,0.45tcls3setlabel'\footnotesize $ 4h\nu $'at0.65,0.53tcls4setlabel'$ E_{\textrm{\tiny avg}}^{\textrm{\tiny Planck}} $'at0.6,0.8# Expressions to plotEn(x,n)=n*x*exp(-n*x)*(1-exp(-x))yN(x,N)=sum[n=1:N]En(x,n)plotx/(exp(x)-1)withlineslc'black',\
for[N=1:4]yN(x,N)withlineslsN# Convert tex -> pdf -> svgsetoutputsystem(sprintf('pdflatex %s.tex && pdf2svg %s.pdf %s.svg',filename,filename,filename))
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