Link: The “missing link” in the greenhouse effect
The link above is a broad treatise to help understand the essay below.
Photons and Photonic Confusion
Tom Shula
November 25, 2024
At the end of his 1920 Nobel lecture (Planck Nobel Lecture 1920), Max Planck stated:
There is in particular one problem whose exhaustive solution could provide considerable elucidation. What becomes of the energy of a photon after complete emission? Does it spread out in all directions with further propagation in the sense of Huygens’ wave theory, so constantly taking up more space, in boundless progressive attenuation? Or does it fly out like a projectile in one direction in the sense of Newton’s emanation theory? In the first case, the quantum would no longer be in the position to concentrate energy upon a single point in space in such a way as to release an electron from its atomic bond, and in the second case, the main triumph of the Maxwell theory- the continuity between the static and the dynamic fields and, with it, the complete understanding we have enjoyed, until now, of the fully investigated interference phenomena- would have to be sacrificed, both being very unhappy consequences for today’s theoreticians.
Be that as it may, in any case no doubt can arise that science will master the dilemma, serious as it is, and that which appears today so unsatisfactory will in fact eventually, seen from a higher vantage point, be distinguished by its special harmony and simplicity. Until this aim is achieved, the problem of the quantum of action will not cease to inspire
research and fructify it, and the greater the difficulties which oppose its solution, the more significant it finally will show itself to be for the broadening and deepening of our whole knowledge in physics.”
Some in climate science who use radiative transfer theory to quantify the so-called “Greenhouse Effect, cite Planck as “discovering quantum theory.” Planck was skeptical of photons as particles, and I believe he was expressing that skepticism in his speech as quoted. He did not coin the term “photon”, and in his development of the Planck radiation equation he spoke of the quantization of emission and absorption, but not of the radiation field itself.
In his paper Anti-photon, W.E. Lamb, Jr. expresses his disdain for the use of the “photon” concept backed up by extensive mathematics. The summary of his paper is:
“It is high time to give up the use of the word "photon", and of a bad concept which will shortly be a century old. Radiation does not consist of particles, and the classical, i.e., non-quantum, limit of QTR is described by Maxwell's equations for the electromagnetic fields, which do not involve particles. Talking about radiation in terms of particles is like using such ubiquitous phrases as "You know" or "I mean" which are very much to be heard in some cultures. For a friend of Charlie Brown, it might serve as a kind of security blanket.”
Michael Mischenko in Directional radiometry and radiative transfer_ The convoluted path from centuries-old phenomenology to physical optics also extensively discusses the problems with the photon concept. His discussion begins on page 13 where are also illustrated various configurations associated with directional radiometry pertinent to his work.
You may be asking why this is important. In the RTT as applied in contemporary climate science, the one-dimensional RTE uses spectral radiance as the energy source that interacts with the IR active gases in the atmosphere. In many treatments this is “translated” to a gas of photons,
“particles” of electromagnetic energy that fly around at random in space being emitted and absorbed by IR active gas molecules. My favorite descriptor, from van Wijngaarden and Happer GreenhousePrimerArxiv.pdf is “quasi-diffusional transport of thermal radiation in opaque spectral regions.” This leads to the concept of “trapping” or “slowing the progress” of photons, aka the “Greenhouse Effect.” We have all seen the animations of photons “bouncing back” to the surface.
As Mischenko has shown, it is not spectral radiance or “packets of light energy” that interact with particles, it is the electric and magnetic fields that interact with the particles. A “photon” is defined not by what it is, but what it does. It is convenient as a concept for the exchange of electromagnetic energy, but it does not share many physical attributes of matter particles.
We know now from Mischenko’s work that while the scalar RTE as applied in atmospheric climate science coincidentally provides the spectral intensity as detected by a well collimated radiometer (the spectra we see in climate papers, for example), this is just an intermediate result of the complete energy field represented by the Poynting-Stokes tensor and cannot by itself be used infer the energy transport in all directions. Paraphrasing Mischenko, it is a case of “getting the right answer for the wrong reasons.”
While the use of the concept “photon” is convenient in many circumstances, it is important to keep in mind that electromagnetic radiation can exhibit “particle like characteristics”, it is not composed of physical particles. There exists no wave function for the position of a “photon.” In my next comments I will discuss Planck’s perspective on spectral radiance.