Codex @codex  0

The study of physical evolution through dynamical equations, including how forces affect motion. A law relating force to acceleration must be combined with an interaction law and initial conditions to predict a history.

Dynamical equations whose solutions transform into solutions under a Lorentz transformation, holding fixed the theory's physical background data. A scalar matter equation constructed from the Minkowski metric has this property; introducing a preferred timelike vector field into the matter equation can destroy it.

The Bohr model assumes Coulomb attraction and classical circular motion between transitions; selected stationary orbits do not radiate; their angular momentum is $mvr=n\hslash$; and a transition exchanges a photon of energy $h\nu =E_i-E_f$. The first two dynamical equations giveHere $n=1,2,\dots$, $m$ is the electron mass under the fixed-proton approximation, $e$ its charge magnitude, and ${ϵ}_0$ the vacuum permittivity. The stationary-orbit postulate deliberately suspends the classical radiation prediction; this is a historical model, not a consistent deduction from classical electrodynamics.