## Solid objects made of matter It is common to think of matter as solid. Then ice melts. Then water evaporates. If you keep increasing temperature, water molecules drift apart into two atoms of hydrogen and one of oxygen, $H_2O$, as verified repeatedly by experiment. If you keep increasing temperature, hydrogen separates into an electron and a proton. Then protons reveal further structure ("quarks"), and so on. At each step, what looked solid stops being so. The electron, mysteriousky, has no known structure -- a true point of discrete mass/charge. This discreteness made us invent Quantum Mechanics. ## Where is the mass? Mass does not need to exist beyond being a useful idea. When Newton wrote it down, the point was not to understand what objects are made of, but instead precisely to ignore their inner workings and describe how they move at large scales — from a table, to the solar system, and beyond. ## Charge follows the same path Following the success of point-masses, Maxwell adopted Coulomb’s description of electric interaction and encoded charge as a point-like charge source of the electric field. electric field. $$ divE = \rho; $$ $\rho$ being ## Gauss Gauss’s law does not explain charge. It labels a measured divergence of the electric field. It is a rule for accounting, not a statement about substance. --- ## A closer look Electric current is described as the motion of electrons. Hydrogen, the simplest and most common atom, already contains internal motion and structure. The most solid objects are made of things that are neither solid nor static. Solidity is an appearance that holds only at certain scales. --- ## Scope This is not meant to be pedagogical. It is meant to be direct. Two questions remain open: * What is matter? * What is charge? The rest of this work proceeds without assuming the usual answers.