Dark matter from eternal inflation express
The universe began with the Big Bang and subsequent inflation — a rapid expansion. Alan Guth suggested that in some regions this growth never stopped. They remained ‘underbaked’ pockets of eternal expansion forever. In our space, such regions manifested as primordial black holes — clumps of unimaginable density. Their collective mass is dark matter — the invisible scaffolding holding galaxies together.
The process resembled dough rising: while most of it smoothed into a uniform loaf, separate bubbles stayed inside, never merging with the crumb. These inclusions are the black holes. Some are smaller than an atom yet weigh as much as a mountain. Their birth shook the very fabric of reality, generating a faint but pervasive hum — gravitational waves. This echo of the Big Bang can still be caught by sensitive detectors of the future.
Original abstract
as written by the authors arXiv:2602.08338
We propose that the totality of dark matter in the universe might ascribe its origin to one of the key properties of cosmological inflation, that it may be eternal: regions that at the end of the primordial accelerated expansion of the universe never reheated, but keep eternally inflating, manifest themselves as primordial black holes in our observable universe. This mechanism can provide a primordial black hole abundance which is larger than the standard one due to the gravitational collapse of sizeable overdensities in the radiation phase. It also predicts a broad spectrum for the curvature perturbation and a flat stochastic gravitational wave background at a level of $$\Omega_\text{GW} h^2 \simeq 10^{-10}$$ up to the mHz.
A single primordial black hole can be smaller than an atom but weigh as much as a mountain.