The Jelly Universe: Why Black Holes Got Heavier ✛ ✎ ✦
Right after the Big Bang, the cosmos resembled jelly — hot, super-dense, and viscous. Tiny density fluctuations, blown up by inflation, could have collapsed under their own gravity into black holes. Previously, the medium was thought to be ideal, free of friction. New computer simulations factoring in viscosity revealed: the thicker the “jelly,” the denser a clump must be for collapse — even weak viscosity demands 7% more density. The irony is that viscosity usually hinders flow, but here it creates a barrier that gravity must overcome.
This reshapes tests of the hypothesis that dark matter, the invisible scaffolding of galaxies, is made of primordial black holes. With viscosity, holes are born rarer and more massive, which aligns better with light bending from distant stars. This approach helps refine how the expansion of the Universe unfolded.
The viscosity paradox: it usually slows things down, but in the early Universe it became a barrier that gravity had to overcome with greater force, like squeezing jelly into a point.