Physics
The laws that govern everything that moves.
From rest to change.
Mechanics begins with a single idea — that a force changes a body's motion in proportion to its mass. Given the forces acting on a system and its present state, the entire future is, in principle, determined. A thrown stone follows a parabola because gravity pulls it downward while it carries its initial velocity forward.
Interference and superposition.
When two waves meet, they do not collide — they add. The resulting pattern encodes both sources at once, and can cancel or reinforce in ways neither wave could alone. This single principle underlies sound, light, quantum amplitudes, and every measurement made in a laboratory.
Forces that fill space.
A charge does not reach out to another charge directly. It creates a field — a value at every point in space — and the other charge responds to what it finds there. Electric, magnetic, and gravitational fields turn empty space into an active medium of influence.
Geometry tells matter how to move.
In general relativity, mass and energy curve the fabric of spacetime, and objects follow the straightest possible paths through that curved geometry. Orbits are geodesics. Light bends around a sun not because a force pulls on it, but because the space it travels through is no longer flat.
The discrete and the continuous.
A particle confined to a region cannot hold arbitrary energy — only a discrete ladder of allowed values. Quantum mechanics replaces a pointlike trajectory with a wavefunction whose squared amplitude gives the probability of being found somewhere. Reality, at small enough scales, is granular.
Begin anywhere.
Pick a field and start reading. Derivations, problems, and references included.
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