[AnimalMuppet]

I think the claim is like this: You have the primordial universe, shortly after the big bang, with fluctuations in density. But the whole density is very high. A fluctuation over a large region could put the region over the threshold to become a black hole, because the density required for that to happen is lower than for a small region.

Mind you, I don't know if this actually works. What was the density of the early universe, compared to the density required to form a black hole? How large were the fluctuations? Is this scenario plausible at all?

I suppose that if you go back close enough to the big bang, then you can get a density high enough. But then, if you go back not much farther, shouldn't the whole universe have formed a black hole? And if it didn't, can we trust the logic that says that the situation should have led to the formation of giant black holes?