Indexing the archive…
Your Universe of Digital Possibilities
A spacetime diagram in units where c = 1, so light runs the 45° diagonals and the light cone is the one thing no observer can tilt. Drag the boost β: the rest-frame axes scissor toward the cone, the lattice shears, and now rotates — yet the cone holds, because the speed of light is the same in every frame. Read it three ways: Boost (γ and the invariant interval), Simultaneity (two events trade order), and Twin (the traveller comes home younger).
The map between frames moving at relative speed β (units of c). It mixes space into time and time into space — which is why a boost shears the diagram instead of just sliding it.
The Lorentz factor. At β = 0 it is 1; as β → c it runs to infinity — moving clocks slow and moving rulers shrink without bound. The ember dot on the inset rides this curve.
The one number every observer measures the same. It is the metric of flat spacetime, and the reason the 45° cone is absolute while the axes are not.
Two events at the same time in one frame are not at the same time in another. "Now" is a frame-dependent slice — the root of every relativity paradox, drawn live in the Simultaneity scene.
The time a carried clock actually reads. The straight (inertial) path between two events racks up the most proper time, so the twin who turns around comes home younger — by exactly 1/γ.
Inside the cone (timelike, s² < 0) cause precedes effect for everyone — the order is absolute. Outside it (spacelike, s² > 0) no signal connects the events and their order is up for grabs.
This is the flat-spacetime floor under the whole gravity wing. Where The Well (INST·07) curves space with a mass and bends starlight, and The Orbit(INST·17) runs Newton’s gravity as the β → 0 limit, The Cone shows the spacetime they all live in — the causal scaffold that general relativity only later allowed to curve. It is also the rack’s second answer to the Time question: where The Arrow (INST·18) finds time’s direction in statistics, The Cone finds time’s structure in geometry — a per-event past and future, fixed by light, that no amount of speed can tilt. Two faces of the same clock the engine runs on.