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Comment by jarend | Hacker News Reader

The article is based on a physics paper (arXiv:2505.23877), not management theory or institutional metaphors.

What the paper actually proposes is that the Big Bang may have been a gravitational bounce inside a black hole formed in a higher-dimensional parent universe. Quantum degeneracy pressure stops the collapse before a singularity forms. From the outside, it looks like a black hole. From the inside, it evolves as a 13.8 billion year expansion. That is general relativity applied across frames.

Simply put this is a relativistic collapse model with quantum corrections that avoids singularities and produces testable predictions, including small negative curvature and a natural inflation-like phase.

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>in a higher-dimensional parent universe

That's incorrect: The parent universe is not higher-dimensional, it's the same good old 3+1 as our universe.

What they propose is: Let's take our good old GR, and start with a (large, dilute) compactly supported spherically collapsing collapsing cloud of matter. During that, you get an event horizon; afterwards, this looks like a normal black hole outside, and you never see the internal evolution again ("frozen star", it's an event horizon). Inside, you have the matter cloud, then a large shell of vacuum, then the event horizon.

Quantum mechanics suggests that degeneracy pressure gives you an equation of state that looks like "dilute = dust" first, and at some point "oh no, incompressible".

They figure out that under various assumptions (and I think approximations), they get a solution where the inside bounces due to the degeneracy pressure. Viewed from inside, they identify that there should be an apparent cosmological constant, with the cosmological horizon somehow (?) corresponding to the BH horizon as viewed from the outside.

All along the article, they plug in various rough numbers, and they claim that our observed universe (with its scale, mass, age, apparent cosmological constant, etc) is compatible with this mechanism, even hand-waving at pertubations and CMB an-isotropies.

This would be super cool if it worked!

But I'm not convinced that the model truly works (internally) yet, too much hand-waving. And the matching to our real observed universe is also not yet convincing (to me). That being said, I'm out of the cosmology game for some years, and I'm a mathematician, not a physicist, so take my view with a generous helping of salt.

(I'm commenting from "reading" the arxiv preprint, but from not following all computations and references)

PS. I think that they also don't comment on stability near the bounce. But I think that regime is known to have BKL-style anisotropic instability. Now it may be that with the right parameters, the bounce occurs before these can rear their heads, and it might even be that I missed that they or one of their references argue that this is the case if you plug in numbers matched to our observed universe.

But the model would still be amazing if it all worked out, even if it was unstable.

> with the cosmological horizon somehow (?) corresponding to the BH horizon as viewed from the outside.

That’s not mentioned in the summary. After inflation the event horizon would not exist.

I have not really looked at the summary, opted to go straight to the source.

This identification happens in equations 31-34 on page 7f subsection "Cosmic Acceleration" in https://arxiv.org/abs/2505.23877

The justification looks super sketchy and hand-wavy to me, though, which I summarized as "somehow (?)".

"After inflation the event horizon would not exist."

Apparent cosmological constant viewed from the bouncing inside induces a cosmological horizon, which they identify with the black hole horizon viewed from the outside. Super elegant idea, but I don't buy that this is supposed to be true.

Why does this black hole bounce whilst others from the limited info we possess appear to be stable regardless of lack of singularity

The bounce is invisible from the outside -- an event horizon means causal decoupling. From outside, the formation of the black hole looks like the good old "frozen star" picture.

There will never be observational evidence on what happens on the other side of any event horizon, you'd have to cross over to the other side to see it for yourself (but you won't be able to report back your findings). There's a fun greg egan short story about that ;)

What's the story?

"The Planck dive", freely available on Greg Egan's website https://www.gregegan.net/PLANCK/Complete/Planck.html

> What the paper actually proposes [...]

(Emphasis mine)

I haven't read the paper yet, but this sounds like a (good) summary of exactly what the article is saying. It makes me wonder what, if anything, you feel is different from the way you put it and the way it is explained in the article? As a layman they seem the same to me.

The article was written by the main author of the paper, so yes, it's a good summary :)

I meant that the parent comment to mine was a good summary of the article.

However, the comment was worded as if it meant to highlight some difference between how the article summarized the paper and what the paper is actually saying. Since I couldn't see a difference between the above poster's summary and that in the article, I was curious what I was missing.

Looking at the paper, I don't see any higher dimensions of the parent universe, it is still using the same 4D General relativity framework for the parent.

So, could the same interaction create planar universes inside our own black holes? Linear universes inside those as well?

It's incredible how big a 4-D universe would have to be to contain our own, even crazier if there are more levels; but our own universe could contain easily uncountable planar universes.

Isn't it more a matter of how space is folded in higher dimensions rather than an increase in volume that accounts for containment? There is plenty of space in the corners:

[0]: https://observablehq.com/@tophtucker/theres-plenty-of-room-i...

Sigh: https://arxiv.org/abs/2505.23877

They have basically disproved Penrose-Hawking's theories of singularity? Isn't that like a pretty big deal? To people working in this field, what is the reaction to this paper?

They predict a non flat curvature, so no (not with existing data and measures, which may improve in the future).

Could you elaborate for a layman? Is there more to the following statements than it seems?

> Penrose proved that under very general conditions, gravitational collapse must lead to a singularity..... we show that gravitational collapse does not have to end in a singularity. We find an exact analytical solution – a mathematical result with no approximations

seems like this is just giving up on quantum gravity and saying the pauli exclusion principle will hold regardless of the gravitational force.

You mean small positive curvature.

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