Man-Made Universality of Blackbody Radiation

Pierre-Marie Robitaille is one of few physicists still concerned with the physics of blackbody radiation supposed to be the first expression of modern physics as presented by Max Planck in 1900, as expressed in this article and this article and  this talk.

Robitaille points to the fact that a blackbody is a cavity/box $B$ with interior walls covered with carbon sooth or graphite. Experiments show that the spectrum of the radiation $B_r$ from a little hole of such a cavity only depends on frequency $\nu$ and temperature $T$ according to Planck's Law:

• $B_r=\gamma T\nu^2$   if $\nu <\frac{T}{h}$  and $B_r=0$ else,       (P)     

where $\gamma$ and $h$ are universal constants, and we refer to $\nu <\frac{T}{h}$ as high-frequency cut-off. 

Experiments show that putting any material body $\bar B$  inside the cavity will not change (P), which is seen as evidence that the spectrum of $\bar B$ is the same as that of $B$  independent of the nature of $\bar B$ as an expression of universality. 

This is questioned by Robitaille, but not by main-stream physicists. Robitaille insists that the spectrum depends on the nature of the body. 

Let us see what we can say from our analysis in Computational Blackbody Radiation. We there identify a perfect blackbody to have a spectrum given by (P) with $\gamma$ maximal and $h$ minimal, thus by maximal radiation and maximal cut-off. By experiment we determine that graphite is a good example of a perfect blackbody. By maximality a blackbody spectrum dominates all greybody spectra.

Let then a greybody $\bar B$ be characterised by different constants $\bar\gamma (\nu)=\epsilon (\nu)\gamma$ with $0<\epsilon (\nu) <1$ a coefficient of emissivity = absorptivity possibly depending on $\nu$, and $\bar h >h$. The radiation spectrum of $\bar B$ is given by 

• $\bar B_r=\epsilon (\nu)\gamma T\nu^2$  if $\nu <\frac{T}{\bar h}$ and $\bar B_r=0$ else.

This is not universality since $\epsilon (\nu)$ and $\bar h$ depend on the nature of $\bar B$. 

But let us now put $\bar B$ at temperature $\bar T$ inside the cavity $B$ with graphite walls acting as a blackbody and let $B$ take on the the same temperature (assuming $\bar B$ has much bigger heat capacity than $B$) with thus

• $\bar B_r=\epsilon (\nu)B_r$ for $\nu<\frac{\bar T}{\bar h}$ and $\bar B_r=0$ else.

We then measure the spectrum of the radiation from the hole, which is the blackbody spectrum of $B_r$:

• $B_r=\gamma\nu^2$ for $\nu<\frac{\bar T}{h}$ and $B_r=0$ else.

If we then insist  that this is the spectrum of $\bar B$, which it is not, we get a false impression of universality of radiation. By maximality with $h<\bar h$ the cavity spectrum $B_r$ dominates $\bar B_r$.

 

We conclude that the universality of blackbody radiation is a fiction reflecting a dream of physicists to capture existential essence in universal terms. It comes from using the cavity as a transformer of radiation from a greybody to a blackbody pretending that the strange procedure of putting objects into cavity with graphite walls to measure their spectrum, is not strange at all. 

We may compare with US claiming that the dollar $D$ represents a universal currency backing that by imposing an exchange rates $\epsilon <1$ for all other currencies $\bar D$, thus imposing the dollar as the universal currency for the the whole World forgetting that all currencies have different characteristics. This gives the FED a man-made maximal universally dominating role, which is now challenged... 

PS1 To meet criticism that painting the walls of the cavity with graphite may be seen as a rigging of the measurement of radiation through the hole, physicists recall that removing the graphite and letting the walls be covered with perfect reflectors, will give the same result, if only a piece of graphite is left inside the cavity. This shows to be true, but the piece of graphite is necessary and its effect can be understood from the maximality of blackbody radiation independent of object size. 

PS2 Recall radiation spectra of solid state is continuous while gasses have discrete spectra. Also recall that measuring spectra typically is done with instruments like bolometer or pyrgeometer, which effectively measure temperature from which radiation is computed according to some Planck law which may but usually does not represent  reality. Atmospheric radiation spectra play an important role in climate modelling, and it is important to take them with a grain of salt, since what is de facto measured is temperature with radiation being computed according to some convenient formula serving man-made climate alarmism.  

PS3 The Sun has a continuous spectrum and so probably consists of liquid metallic hydrogen. Main-stream physics tells that it has a gaseous plasma state.