Dark matter fraction
How much of the universe's mass is invisible. Galaxies are held together by matter that light cannot see.
Lukasz Szramuk ·
About 26 percent of the universe's energy budget is dark matter; ordinary matter is 5 percent. The invisible outweighs the visible five to one. Dark matter is the scaffolding: it falls first, digs the gravitational wells, and ordinary matter falls in after it. Without it, baryons alone could not have built galaxies in time — the afterglow of the Big Bang is too smooth for visible matter to have done the job alone.
In the toy, χ scales how much of the gravitational budget is dark. Ours sits at 0.84 in tuner units. Like Λ, it is not pinned to any one phase — it shifts everything gravity touches.
Why life cares about dark matter
Life needs stars; stars need galaxies; galaxies need deep potential wells that formed early. Dark matter provides them, because it has a property ordinary matter lacks: it does not collide and it does not glow. It cannot radiate away its energy, so it cools only by falling — and falling is exactly what structure needs. Ordinary matter, tangled up with light, stayed puffed up and smooth for hundreds of thousands of years longer. The galaxies you live in were drafted by an invisible hand.
Both ways to die
• Too little: no wells, no galaxies. Baryons stay a diffuse, cooling fog. No stars, no planets, no observers.
• Too much: structure forms too efficiently. The early universe collapses into black holes before chemistry can begin, and whatever stars do form live in violent, crowded neighborhoods.
In the toy
Raise χ and everything gravitational arrives sooner and heavier: dust gathers faster, stars light denser, the end phase swells. Lower it and the late universe starves — the fires and hatching are unchanged, because they happen before gravity takes over, but the dust has nothing deep enough to fall into.
What you will see when you break it
χ drops from 0.84 to 0.1. Fires still burn. Hatching still completes. But the dust phase arrives thin and late — the wells are too shallow, so less dust gathers, stars come up sparse and small, and the end barely registers. You are watching a universe try to build galaxies out of baryons alone: it manages a mist where there should be a spiral.