tisdag 25 oktober 2011
Radiative Heat Transfer: Phlogistons and Photons
I will now argue that phlogiston theory has similarities with photon theory of light in the case of infrared radiation of global climate.
Phlogiston theory says that all combustible resources contain particles named phlogistons without colour, odor, taste or mass, which are liberated in burning.
Photon theory says that light consists of particles named photons without mass and charge carrying energy along straight lines at a constant speed of light. Photons have different frequencies and and energy proportional to frequency.
Photon theory describes radiative heat transfer between two bodies as a two-way stream of photons emitted/absorbed by the bodies, with the hotter body emitting photons of higher frequency and in higher numbers as compared to the colder body, which results in a net transfer of heat energy from hot to cold.
Photon theory is a particle theory of light going back to Newton's corpuscular theory of light,
and is to be compared with the wave theory of light as electromagnetic waves described by Maxwell's equations. The wave theory of light describes almost all observed phenomena of light.
The wave theory of light replaced the particle theory in the late 19th century, but was revived in the early 20th century by Planck to describe blackbody radiation and by Einstein to describe the photoelectric effect.
Phlogiston theory is no longer taught, but the photon theory of light is still used to explain certain phenomena believed to be difficult to explain by a wave model, typically related to the
phenomena of emission and absorption involving interaction between matter and electromagnetic waves. In photon theory emission is seen as ejection of photon particles and
absorption as the opposite.
For visible light, emission of photons as finite quanta of energy can be associated with discrete changes of atomic electronic structure. For infrared radiation with much larger wave lengths than atomic dimensions, the interaction between matter and waves must involve collective motion of many atoms and the photon theory does not seem to be applicable.
This mean that photon theory cannot be used to describe blackbody radiation at the modest temperatures of global climate. In this case the photon theory is similar to the phlogiston theory as a very simplistic theory with little predictive capability, and a wave theory based on Maxwell's equations can be preferable, as shown in Mathematical Physics of Blackbody Radiation.
The fact that photon theory can be useful for certain applications at high-energy short wave-lenghts, does not mean that it is also uselful for completely different applications at low-energy long wave-lengths.
Nevertheless, the photon theory serves as support of the propaganda of CO2 alarm based on
the idea that streams of photons from the atmosphere contribute to global warming as DLR/backradiation, which rather represents phlogiston theory than real physics.