Tiny ancient black holes may live in a five-dimensional world

Primordial black holes (PBHs) don't exist as far as we know. But if they did, these hypothetical objects would have formed in the early universe rather than from dying stars, and they may even make up dark matter. That's not the end of the weirdness. Their formation could have been even stranger if it occurred in a universe with a dark dimension, which is another theoretical construct. It posits that our space includes a hidden extra spatial dimension.