In the early Universe, primordial black holes emerged — objects no larger than an atom but with the mass of a mountain. They gradually evaporate and, before disappearing, should produce gravitational waves — ripples in spacetime. If they were all identical, they would pop simultaneously, like popcorn kernels: the roar would be deafening.

But physics dislikes uniformity. According to Stephen Hawking, even twin black holes inevitably have a tiny mass spread. A difference of less than a percent changes everything: the holes evaporate not in chorus, but one by one. The gravitational 'concert' turns into a barely audible crackle. This faint signal is almost lost against the backdrop of other cosmic noises, and it is precisely this discovery that rehabilitates primordial black holes as candidates for dark matter. Remarkably, out of the entire gravitational spectrum, only the portion linked to the birth of the holes has a chance of being detected — but even this whisper can betray the presence of invisible mass.