concepts.how
Big ideas you can take apart and play with. Each page explains one concept, shows where it came from and lets you try it yourself.
Metric units
64 metric units grouped by quantity: what each name means, how it was first defined, how it’s defined today, and its imperial equivalent, plus a live converter.
Voting methods
Twelve ways to count votes, with their benefits and limitations, where they’re used, and an election simulator showing how the same voters can elect different winners.
Time paradoxes
The twin paradox, Zeno’s race, the arrow of time and the grandfather paradox, with spacetime diagrams and demos you can run.
Blockchain & consensus
Edit a live SHA-256 hash chain, race a 51% attacker, and watch Byzantine generals vote, plus a field guide to proof of work, proof of stake and BFT.
Quantum mechanics
Build a double-slit pattern one particle at a time, rotate a qubit, run a Bell test and speed up a search with Grover’s algorithm.