Of the many substantial contributions to theoretical physics, Max Karl Ernst Ludwig Planck’s fame rests heavily on his role as the originator of quantum theory, which revolutionized human understanding (and Marvel movie subplots) of atomic and subatomic processes. The discovery of energy quanta won him the Nobel Prize in Physics in 1918.

To add a bit of color to Max Planck, the man… Max Born (a contemporary theoretical physicist) wrote about Planck: “He was, by nature, a conservative mind; he had nothing of the revolutionary and was thoroughly skeptical about speculations. Yet his belief in the compelling force of logical reasoning from facts was so strong that he did not flinch from announcing the most revolutionary idea which ever has shaken physics.”

In his quantum theory, Planck establishes that more than wave energy, light is also discrete energy packets, or quanta, that can be both emitted and absorbed. Taken as discrete units, Planck was able to calculate the energy of particles at given frequencies. Much later, these particles were named photons.

Why is this concept of light behaving as a particle so important to spectroscopy?

Each individual photon has a very specific amount of energy (no more, no less), which corresponds to its wavelength. Blue photons carry more energy than red photons. Ultraviolet photons carry more energy than infrared photons.

Important to us as geoscientists, the way in which light interacts with matter (i.e., absorbed, emitted, transmitted, reflected, or refracted) allows for the identification of everything from planets to minerals…

Is this mineral kaolinite or white mica? Actually, it’s pyrophyllite because of its absorption features at ~1392nm (OH), ~2075nm (AlOH), and 2165nm (AlOH).