Evidence of primordial black holes may be hiding in planets, or even everyday objects here on Earth

A theoretical study suggests that small black holes born in the early universe may have left behind hollow planetoids and microscopic tunnels, and that we should start looking within rocks and old buildings for them. The research proposes thinking both big and small to confirm the existence of primordial black holes, suggesting that their signatures could range from very large — hollow planetoids in space — to minute — microscopic tunnels in everyday materials found on Earth, like rocks, metal and glass.