Comment by JulianPGough

Yes, this is a very common, and understandable, question; I get asked it a lot. But in fact new (child) universes aren't constrained in size by the initial energy/mass entering the parent black hole. Actually, that's one of the most attractive aspects of the theory. Universes have a huge reproductive advantage over, say, animals.

We know that in our own universe, the (positive) mass energy of matter and its (negative) gravitational energy net out to zero. But that means the amount of energy required to build a universe like ours is essentially… well, none. (See Laurence Krauss’s book, A Universe from Nothing; or Stephen Hawking and James Hartle’s 1983 paper, The Wave Function of the Universe, and Hawking’s later book with Leonard Mlodinow, The Grand Design, etc.)

Child universes are therefore effectively free to produce. Thus, over time, evolution will favor making more (and smaller) black holes from the same amount of matter. Yes, the black holes will get smaller – but the universes they give birth to, through Big Bangs, will still be full sized.

And universes aren’t constrained by a shared environment with limited resources – newborn universes aren’t all competing in a valley with a limited amount of grass. Indeed, each new universe is entirely self-contained and self-sufficient, being both organism and environment – it supplies its own energy for its own development, efficiently and frugally, through stellar fusion, gravitational collapse, et cetera.

This means evolution should ultimately favour runaway black hole production. (And that checks out: in the most recent estimate, in 2022, by a team from the International School of Advanced Studies in Trieste, our universe was estimated to have already generated up to a trillion supermassive black holes – and 40 quintillion stellar-collapse black holes.)

It's actually not taking a lot of speculative ideas at all. It's taking one hypothesis (universal reproduction) and noticing that if it has one interesting feature (slight variation in parameters), you automatically and essentially unavoidably get Darwinian evolution which could very cleanly and succinctly explain a lot of the weird fine-tuning that seems to be present in our universe.

I think this cuts through that Gordian knot. "Nothingness" is just an idea in our heads: we have never encountered "nothing". There's no such thing, it's an idea. There is always something; there was always something. And sure enough, in this model, there was always something, some original universe. (Back when it was actually "uni"!) Some unbelievably primitive always-existent universe, made of the original ur-matter, long before the modern periodic table evolved, long before even electrons, protons, and neutrons. All you need is that always-existent universe, time, and change.

How primitive can it be and still reproduce? Because to kick-start an evolutionary process, the only thing that it needs to do is reproduce.

How does a universe reproduce, in this model? VERY VERY SIMPLY. Mass-energy collapses to a point, bounces to form a new universe. All it has to do is collapse. So you have some primitive matter that collapses. It doesn’t have to collapse millions of times and produce millions of offspring (like our universe). Not yet. It just has to do it once. Flip/flop, a collapse and an expansion. A black hole/big bang cycle. And then eventually (and it has infinite time in which for this to happen!), it has to do it twice.

It produces two new universes. There’s two direct collapses that bounce to form new big bangs, new universes, right? And there’s no structure. There’s no complexity. But that’s a direct collapse, forming supermassive black holes. (Which is how, I argue, the supermassive black holes we find today in our universe must still form; evolution conserves successful reproductive strategies, she isn't going to invent a far more complicated way to do it, when a simple way is already available.)

That has to be how the earliest universes reproduced, without complex structures. All they have to do is just be a cloud of totally unstructured ultra-primitive matter, just collapsing. A directly collapsing cloud. No fancy nuclear fusion or stellar masses. And all that more complex stuff – stars, stellar collapse black holes, life, technology, technologically manufactured small black holes – comes later. They are later evolutionary breakthroughs. But they build on that earlier foundation, of direct collapse supermassive black holes.

Why does there need to be an original?

Which one?