A Brief Discussion on Particle and EM Field Interaction Action

In classical mechanics, to fully describe a particle, one only needs to write down its Lagrangian: S=โˆซabLdt=โˆซabTโˆ’Udt =โˆซabTdt+โˆซabโˆ’Udt=SP+SPF Here, the kinetic term T can be regarded as the Action SP of a free particle, and the potential term U is the Action SPF of the interaction between the particle and the field. In electromagnetism, we learn that the field also carries momentum and energy, so the complete description of electromagnetic motion includes the Action SF of the field: S=SP+SPF+SF

Originally written in Chinese by the author, these articles are translated into English to invite cross-language resonance.