Magnetohydrodynamics. Two dimensions. Zero shortcuts.
A 128×128 ideal-MHD solver, running continuously. Orszag-Tang initial conditions on a 2π periodic domain. It drives the public entropy beacon: every pulse names the frame it hashed and the seed that frame replays from, so the physics behind a pulse can be recomputed by anyone with the solver.
Lax-Friedrichs · Δm/m and ΔE/E read from the frame header the solver writes
Ideal MHD in conservation form. 6 field components per cell (ρ, vx, vy, p, Bx, By). Lax-Friedrichs fluxes on a 128² periodic grid. First-order in space — diffusive at shocks, exact where it counts.
The canonical 2D MHD test. Smooth initial conditions evolve into turbulent small-scale structure with sharp shock fronts. Mass and energy drift are measured against their step-zero anchors every 40 steps and written into each frame's header; the readouts on the viewport are parsed from those bytes in your browser, never typed by us.
Density (ρ) sampled from /entropy/frame/current: the solver grid, served
straight from the beacon origin, min-max normalized and color-mapped in your GPU. A new
frame lands about once a second, and the display cross-dissolves between frames: a video
fade, not fabricated physics. What is signed: the Pi witness signs the SHA-256 of the
solver's full 589,904-byte state file at /entropy/frame/latest.attestation.json,
about twice a minute. Those bytes are not published, so the ⌁ buttons check the
signature over that digest, not the picture. The frame you see is the first 393,264 bytes
of the same file, and every beacon pulse commits to its six planes.
Plasma is chaotic. Small perturbations blow up fast. That makes it a good random-source — the output of a correctly-running MHD step is hard to predict without running the solver. It is not unpredictable to us: the solver is deterministic, and any frame replays bit for bit from its seed. The beacon's unpredictability comes from 32 fresh random bytes per pulse, committed one pulse ahead. And it's beautiful to look at.
There's a serious version of this argument involving fusion reactor control, but we'll let the beacon make the case.