Big Bang Nucleosynthesis — First 20 Minutes (2D)

This 2D companion runs the exact same Big Bang Nucleosynthesis equations as the 3D version — the radiation-era temperature curve T(t) ≈ 1.3·t^-1/2 MeV, the neutron/proton freeze-out at T ≈ 0.8 MeV followed by free-neutron decay with an 880-second lifetime, and the density-dependent logistic synthesis curve that fixes the final helium-4, deuterium, helium-3 and lithium-7 yields — but renders them on a plain HTML5 canvas instead of a WebGL scene: a particle field on the left recolors ~140 dots proton-red, neutron-grey or nucleus-colored in proportion to the live abundances, while a log-log chart on the right traces all six curves against time with a scrubbable marker, so the same physics reads clearly without a 3D renderer.