Marie Curie’s work on radioactive substances led her to engage with concepts of inertia and momentum, particularly in the context of J.J. Thomson’s research on charged particles. She described how experiments on radium rays showed that the mass of a particle increases with velocity, a discovery that hinted at a deeper connection between motion, charge, and inertia.
In her writings, she referenced J.J. Thomson and Townsend’s assumption that the moving particles in radium rays carried a charge equal to that of a hydrogen ion in electrolysis. This led to the idea that a particle’s inertia arises from its charge in motion, meaning that modifying the velocity of an electric charge requires energy. She explained this phenomenon as follows:
“These theoretical considerations lead to the idea that the inertia of the particle is due to its state of charge during motion, the velocity of an electric charge in motion being incapable of modification without expenditure of energy. To state it otherwise, the inertia of the particle is of electromagnetic origin, and the mass of the particle is—in part at least—a virtual mass or an electromagnetic mass.”
This insight foreshadowed later developments in relativistic physics, where mass and momentum are understood as functions of velocity. The idea that inertia could be tied to an object’s interaction with electromagnetic fields marked a shift from classical mechanics, where mass was considered an inherent property.
Curie’s work contributed to the growing recognition that momentum, charge, and inertia are interconnected at the atomic scale. In a sense, she extended Newton’s concept of momentum into a realm where matter and energy were no longer separate, but interwoven through electromagnetism. Her research ultimately set the stage for 20th-century discoveries that showed how inertia is not simply an intrinsic resistance to motion but can also emerge from interactions between charged particles and their surrounding fields.