On the Border Between Light and Matter: Continuity and Discontinuity in the Development of Optical Dispersion

By Marta Jordi Taltavull

Max-Planck-Institut für Wissenschaftsgeschichte


The talk is about conceptual continuities and discontinuities in the history of optical dispersion from late 19th century to the beginning of the 20th century. Optical dispersion is the phenomenon observed in rainbows and in the spectra produced by prisms. From the 1870s onwards, all theories on optical dispersion made use of the same dynamical model: the covibrations. According to it, dispersion stems from the interaction between light waves and particles of matter vibrating at specific frequencies. Due to its basic simplicity, the covibrations quickly became the common structural basis of any account for the light-matter interaction.

The model led to a satisfactory analytical formula agreeing with experimental results on optical dispersion both in classical and in quantum theories. However, this model was embedded over time into different conceptual frameworks and ontologies. From the 1870s to the 1920s the constitutive elements of the model (waves of light and matter oscillators) changed repeatedly their interpretation. Light was first understood as mechanical ether waves and later as electromagnetic waves. The structure of matter underwent substantial transformations as well: from an undetermined bunch of vibrating particles to an orderly structure of valence electrons following Bohr’s quantum rules.

In the talk I will analyze the dynamics between the structural continuities and the discontinuities regarding the concrete nature of physical entities involved, namely how the model and its exemplifications were entangled and what tensions the new quantum insights originated.