Physics: from the quantum to the cosmos

Physics is the attempt to find the fewest rules that explain the most. When it works, a single equation covers falling apples and orbiting moons, or the glow of a hot coal and the colour of the sky. These pages trace how far that project has got, and are honest about where it has run into a wall.

One thread is gravity, space and time. Newton's law made gravity a force; relativity reimagined it as the bending of spacetime, with consequences that still feel outrageous: the twin paradox, black holes and their event horizons, wormholes, and the pull of ordinary gravity itself. Zoom out and the same theory describes the whole universe: the Big Bang, dark matter, the puzzle of the dark night sky (Olbers' paradox), the Fermi paradox, and the unruly three-body problem.

A second thread is the quantum world, where the rules that govern atoms defy every everyday instinct. The double-slit experiment is the whole strangeness in miniature; from there come the photoelectric effect, entanglement, Schrödinger's cat, the uncertainty principle, and the machines that exploit it all, quantum computers.

A third gathers matter, light and heat: the periodic table, entropy and the arrow of time, mass-energy equivalence, superconductivity, the Doppler effect, and the greenhouse effect. And a fourth reaches for the smallest pieces of all: the Standard Model, the Higgs boson, and the field that gives particles their mass.

Every explainer below is written at three depths on the same page. Level 1 is for a curious twelve-year-old, Level 2 for someone who has just finished school, and Level 3 for an undergraduate. Where a page has an interactive model, pull it apart: seeing the idea move is often worth a thousand words.

All physics topics