In this blog, Professor Enrique Gaztanaga from the Institute of Cosmology and Gravitation at the University of Portsmouth, puts forward a new theory about how the Universe was created.
The Big Bang is often described as the explosive birth of the universe – a singular moment when space, time and matter sprang into existence. But what if this was not the beginning at all? What if our universe emerged from something else – something more familiar and radical at the same time?
In a new paper, published in Physical Review D, my colleagues and I propose a striking alternative. Our calculations suggest the Big Bang was not the start of everything, but rather the outcome of a gravitational crunch or collapse that formed a very massive black hole – followed by a bounce inside it.
This idea, which we call the black hole universe, offers a radically different view of cosmic origins, yet it is grounded entirely in known physics and observations.
Today’s standard cosmological model, based on the Big Bang and cosmic inflation (the idea that the early universe rapidly blew up in size), has been remarkably successful in explaining the structure and evolution of the universe. But it comes at a price: it leaves some of the most fundamental questions unanswered.
For one, the Big Bang model begins with a singularity – a point of infinite density where the laws of physics break down. This is not just a technical glitch; it’s a deep theoretical problem that suggests we don’t really understand the beginning at all.
To explain the universe’s large-scale structure, physicists introduced a brief phase of rapid expansion into the early universe called cosmic inflation, powered by an unknown field with strange properties. Later, to explain the accelerating expansion observed today, they added another “mysterious” component: dark energy.
In short, the standard model of cosmology works well – but only by introducing new ingredients we have never observed directly. Meanwhile, the most basic questions remain open: where did everything come from? Why did it begin this way? And why is the universe so flat, smooth, and large?
New model
Our new model tackles these questions from a different angle – by looking inward instead of outward. Instead of starting with an expanding universe and trying to trace back how it began, we consider what happens when an overly dense collection of matter collapses under gravity.
This is a familiar process: stars collapse into black holes, which are among the most well-understood objects in physics. But what happens inside a black hole, beyond the event horizon from which nothing can escape, remains a mystery.
In 1965, the British physicist Roger Penrose proved that under very general conditions, gravitational collapse must lead to a singularity. This result, extended by the late British physicist Stephen Hawking and others, underpins the idea that singularities – like the one at the Big Bang – are unavoidable.
The idea helped win Penrose a share of the 2020 Nobel prize in physics and inspired Hawking’s global bestseller A Brief History of Time: From the Big Bang to Black Holes. But there’s a caveat. These “singularity theorems” rely on “classical physics” which describes ordinary macroscopic objects. If we include the effects of quantum mechanics, which rules the tiny microcosmos of atoms and particles, as we must at extreme densities, the story may change.
In our new paper, 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. Our maths show that as we approach the potential singularity, the size of the universe changes as a (hyperbolic) function of cosmic time.
This simple mathematical solution describes how a collapsing cloud of matter can reach a high-density state and then bounce, rebounding outward into a new expanding phase.
But how come Penrose’s theorems forbid out such outcomes? It’s all down to a rule called the quantum exclusion principle, which states that no two identical particles known as fermions can occupy the same quantum state (such as angular momentum, or “spin”).
And we show that this rule prevents the particles in the collapsing matter from being squeezed indefinitely. As a result, the collapse halts and reverses. The bounce is not only possible – it’s inevitable under the right conditions.
Crucially, this bounce occurs entirely within the framework of general relativity, which applies on large scales such as stars and galaxies, combined with the basic principles of quantum mechanics – no exotic fields, extra dimensions or speculative physics required.
What emerges on the other side of the bounce is a universe remarkably like our own. Even more surprisingly, the rebound naturally produces the two separate phases of accelerated expansion – inflation and dark energy – driven not by a hypothetical fields but by the physics of the bounce itself.
Testable predictions
One of the strengths of this model is that it makes testable predictions. It predicts a small but non-zero amount of positive spatial curvature – meaning the universe is not exactly flat, but slightly curved, like the surface of the Earth.
This is simply a relic of the initial small over-density that triggered the collapse. If future observations, such as the ongoing Euclid mission, confirm a small positive curvature, it would be a strong hint that our universe did indeed emerge from such a bounce. It also makes predictions about the current universe’s rate of expansion, something that has already been verified.
This model does more than fix technical problems with standard cosmology. It could also shed new light on other deep mysteries in our understanding of the early universe – such as the origin of supermassive black holes, the nature of dark matter, or the hierarchical formation and evolution of galaxies.
These questions will be explored by future space missions such as Arrakhis, which will study diffuse features such as stellar halos (a spherical structure of stars and globular clusters surrounding galaxies) and satellite galaxies (smaller galaxies that orbit larger ones) that are difficult to detect with traditional telescopes from Earth and will help us understand dark matter and galaxy evolution.
These phenomena might also be linked to relic compact objects – such as black holes – that formed during the collapsing phase and survived the bounce.
The black hole universe also offers a new perspective on our place in the cosmos. In this framework, our entire observable universe lies inside the interior of a black hole formed in some larger “parent” universe.
We are not special, no more than Earth was in the geocentric worldview that led Galileo (the astronomer who suggested the Earth revolves around the Sun in the 16th and 17th centuries) to be placed under house arrest.
We are not witnessing the birth of everything from nothing, but rather the continuation of a cosmic cycle – one shaped by gravity, quantum mechanics, and the deep interconnections between them.
Read the original article
Comments
By carbocation 2025-06-1120:184 reply I think it's neat that this summary is written by an author of the scientific manuscript. Oversimplification is a risk, but this approach eliminates the possibility that the writer did not understand the underlying science.
Yea, and it was a great read too. I wish more researchers would publish blog posts alongside their technical whitepapers, although I acknowledge that not everyone involved in science has or wishes to acquire the skills needed to write blog-form content.
(I'd also be worried about a world where researchers are evaluated based on the virality of their blog posts, vs. how impactful their work was.)
Communication skills are often missing in engineering too, but I think I'd argue they should be required - all work is fundamentally collaborative.
Being able to effectively communicate to different people on your team, outside your team, managers, business people, etc is not optional and more than once I've seen things get stalled or turn into a mess because communication didn't happen.
STEM is often a haven for neurodivergence but I think communication skills are something that is largely learned and not something that comes naturally for everyone. People who are good at communicating spend a fair amount of effort rewriting, trying different wordings, different introductions, getting feedback from people, etc.
FWIW I see things like being able to sell a proposal, managing expenses, planning, etc as optional - these are good to have, but someone else can do them if you can communicate well, but in the end the only person who can communicate what you're thinking is you.
By jasonm23 2025-06-133:30 "Required" is a bit of a gatekeeper, while I agree good communication skills are valuable.
Blog form content in particular, _requires_ proofing, re-editing, and so on and there's a whole skill set which contributes to makes such content sticky and engaging.
You also seem to be confounding your own point. Indeed all work is collaborative, someone who lacks communication skills, will generally team up with other collaborators who can bring those skills to bear.
I think the benefits greatly outweigh any dangers. I far prefer to read something like this than something written up by a journalist.
> I acknowledge that not everyone involved in science has or wishes to acquire the skills needed to write blog-form content.
They should. If your research is publicly funded you should make it as available to be public as possible. Academics should be able to communicate, and I very much doubt they are unable to acquire the skills
> I'd also be worried about a world where researchers are evaluated based on the virality of their blog posts, vs. how impactful their work was
Given how bad the measures of impact and the distorted incentives this produces I am not even sure this would even be a bad thing.
If nothing else it improves transparency about what they are doing, again with public money.
By quantum_magpie 2025-06-129:514 reply >They should. If your research is publicly funded you should make it as available to be public as possible. Academics should be able to communicate, and I very much doubt they are unable to acquire the skills
So in addition to being:
-professional researchers
-professional teachers
-professional project managers
-professional budget specialists
-professional scientific writers
-a failed idea away from losing it all
They should also become:
-professional PR managers
-professional popular writers
While still being paid (poorly) for a single job of all of these.
By ericmay 2025-06-1214:23 We have similar demands for folks in other professions. I know software engineers who are still coding day to day who also have to manage team budgets and track hours/projects, write patents, write blog posts to make the company look good, mentor juniors, sometimes teach internally or even to external audiences, present at conferences, etc.
By graemep 2025-06-1210:12 They should not being doing a lot your first list, and should have specialist help available for some of the rest.
I am not suggesting they become PR managers, and the writing skills I am suggesting they acquire is simply that required to do things like blogging. I am not suggesting they achieve the standards a professional writer would have, just the ability to write clearly and make the effort to do so.
Academics should be highly skilled people.
In fact a lot of the problem is not they cannot do it, but of distribution. A lot of universities to have academic blogs and subsites about departments and individuals research. Its not anything like as visible as the journalists write ups about it
By StableAlkyne 2025-06-1215:37 Yes, in a perfect world there would be professionals doing this instead of putting it all on the academic.
However, we live in an imperfect world. When people say "should" in these contexts, they're not describing some ideal way the world works. They're prescribing actions that are realistic based on the current system we live in.
The world sucks. It's more useful to work with the small amount of control one has, than to do nothing because the action doesn't solve a wider systemic problem.
By Elextric 2025-06-1211:46 yes
By michaelmrose 2025-06-138:11 > They should. If your research is publicly funded you should make it as available to be public as possible.
The public can access it by becoming subject matter experts. If the government or the public to which it is responsible requires a popsci treatment they can pay other people with this skill set.
I don't doubt having this skill set is useful I merely disclaim any sort of obligation on the part of the scientific staff to possess or exercise such a skill.
By gms7777 2025-06-1220:05 A few years ago, at least in my field, there was definitely a trend of people at least doing twitter threads explaining the key findings of their papers. It's obviously less in-depth than a blog post would be, but it was still usually a far more accessible version of the key ideas. Unfortunately, this community has basically dissolved in the last few years due to the changes in twitter and to my knowledge hasn't really converged on a new home.
By bdbenton 2025-06-126:31 It's a controversial observation, but it is very true. I work with AI models and have to read recently published research to work with the latest developments in the field.
Do a quick keyword search on papers related to the subject. So much of it is completely useless. It is clearly written to keep people busy, earn credentials, boost credibility. Papers on the most superfluous and tangential subjects just to have a paper to publish.
Very little of it is actually working with the meat of the matter: The core logic and mathematics. It is trend following and busywork. Your sentiment is controversial because people are religiously loyal to the intellectual authorities of these credentialed systems, but a lot of published research does not push any boundaries or discover anything new. This paper seems to be an exception.
I would argue that a lot of the research published in the social sciences also falls under this category. It is there so that someone has a job. I'm not discrediting social sciences in general, am just pointing out that there is a lot of ways to creatively take advantage of academia to secure a paycheck and this is certainly exploited. The kneejerk reaction to reasonable criticism just proves this point even further.
By tracerbulletx 2025-06-122:022 reply This is a good thing. This is where the economy surplus went. Not to 5 days of leisure for everyone. But to jobs that keep us occupied, engaged, and motivated but aren't strictly required. The alternative is just either starving everyone to death, except for a few elite and their slaves, or everyone being bored out of their minds and wondering what the point of life is.
If the solution is ever more manuscripts that solve no interesting problems and that nobody will ever read, let's find another solution.
By hyperhello 2025-06-124:162 reply Why would you assume someone would write the paper at all, if the problem was uninteresting?
That's literally the basis of employment. People write papers, they get paid. Science does not get done.
By melagonster 2025-06-1317:21 The funding for scientific projects comes from applying for grants from the government. Researchers must write proposals to demonstrate the value of their projects. After the project is completed, they are also required to submit a final report to verify that the project was indeed carried out as approved by the supervising authority.
By inimino 2025-06-1222:53 For one thing, because I watch the AI and ML categories on arxiv.org.
By superb_dev 2025-06-125:48 Is this a joke or so wildly out of touch? Both of your alternatives sounds very much like the world today, but we’re all still working anyways
Sabine Hossenfelder has a few comments on this topic in her YT channel.
By lynx97 2025-06-128:54 Hossenfelder feels like a fraud. She likely is.
By refulgentis 2025-06-120:521 reply Sabine Hossenfelder cast herself out from academia and took a recent turn to monetizing laundering peoples vague understanding string theory is a waste of time (cannot be proven empirically) into academia is doing fake work and if they'd apologize and own up to it, maybe we would trust them again.
Most famously, through a bizarrely written letter from an anonymous whistleblower pleading that she not topple the academy, as it would ruin the lives of thousands of academics making up things to get grant money to survive.
I can't parse either of your sentences. Maybe you could introduce some intermediate variables, or use parentheses to give them structure?
By refulgentis 2025-06-1218:261 reply I can't parse what you're asking for :|
Ran my comment + your reply through AI and asked it to respond to you, as I do want to help. Let me know if there's other instructions I can give it, it may have taken your variable ask too literally? :(
Here's its output:
Sabine Hossenfelder, after distancing herself from academia, has recently pivoted to monetizing a specific narrative: Let’s define Premise A as “String theory is a waste of time because it cannot be empirically proven.”
She generalizes from Premise A to a broader Claim B: “Academia, more broadly, is producing fake work.”
Her argument seems to imply that:
If academia were to publicly acknowledge this, or apologize for promoting unverifiable theories, then the public might begin to trust it again.
This general thrust reached a kind of crescendo in one of her more notorious moments: — An oddly written letter, allegedly from a whistleblower within academia, essentially begging her not to “bring down the system.” The letter’s rationale? That dismantling the status quo would destroy the livelihoods of thousands of academics who, according to the letter, are fabricating just enough plausible-sounding work to secure grants and stay afloat.
By nwienert 2025-06-1220:58 Pretty valuable to have people who see A to be true, have presumably seen some of B to be true too (trivial to see with the many replication crises) - and then to do their best to disseminate that to the general public so change can be made. I see no problem there, and I'd hate for the case where people were afraid to make content covering it because they were waiting for years for huge studies (which could also be poorly done) to 'prove' it.
By 4ndrewl 2025-06-1420:21 Yeah, you see that's 100% not a citation, and shows why we need academia...
Sabine is an asshole. Doesn't mean she is wrong, and I appreciate when she reads some paper that has made a bunch of headlines to figure out if they're full of crap or not (spoiler alert: the answer is usually yes), but while she can identify the problem she's not part of the solution. Her divorce from academia means she has little power to affect change for the better given how the incentives are currently aligned. She can make a lot of noise, but the people actually pulling the levers have rigged the system in their favor enough to not care.
By NL807 2025-06-1220:36 So she is an arsehole for exposing bullshit? I don't see the problem. I think people take issue with her because of her confrontational persona.
>while she can identify the problem she's not part of the solution
Does she have to be, in principle?
> Her divorce from academia means she has little power to affect change for the better given how the incentives are currently aligned.
Wouldn't be so sure about that. She is getting more public exposure than most academic would in their lifetime. More importantly, exposure to audience _outside_ of academia. Voters. Her effort in creating public awareness has certainly stirred the nest in some academic circles.
There have been countless academics who have discussed this topic, occasionally not behind closed doors. Regardless, it’s certainly my observation as well.
By fc417fc802 2025-06-121:10 Countless academics have leveled targeted criticisms at various practices and gone on to back those up. They are targeted, actionable objections; not vague blanket dismissals.
By johnisgood 2025-06-1121:593 reply Most jobs are really not important either, they just keep people busy. Do you need sources for this claim, too?
Yes. Who are these people paying for jobs that don't do anything, and why are they more concerned about "keeping people busy" than their own profits?
I’m not the one you were referring to, but I have similar experiences. I’m living in Germany, and most bigger companies here have such issues. I also worked for companies in Netherlands and Island, so I assume it’s an European, if not global problem. No one is concerned about keeping people busy. It’s a systemic problem. And there are multiple reasons for it. One reason is that the bigger a company grows, the more hierarchy is necessary. But increasing hierarchy will lead to people doing the work are not the people that are most responsible for it. So we have people that should do the work but they aren’t too motivated because they are not responsible enough - they are too low in hierarchy level. And we have people that are responsible but don’t do the work. They delegate. If something goes wrong or takes too long, they will have enough time and skill to find an excuse. Another issue is that you need more people to get specific things done. At some point in time these things have been done, and you actually don’t need the amount of people anymore. But you can’t quit them because of worker’s laws. You maybe even don’t want to quit them because you think you still need them. People, of course, tend to find reasons why their own work is important. And they will communicate that. And the chance is good you’ll believe that and don’t question it enough. There are more reasons for that. But it’s a fact that in many, many companies the economical results of a lot of employees is almost zero. If you don’t believe this, just google the biggest companies in Germany, pick one, apply for an office job and start to work there. It won’t take a month until you’ll find out. Btw. I don’t want to criticize the situation too much. Probably it’s good that people are employed, even if they don’t work efficiently. Otherwise the unemployment rate would be much higher. Then again, Germany‘s economy is flatlining and a crash is not unlikely.
By wizzwizz4 2025-06-1122:38 Sounds like you're describing the principal-agent problem. https://en.wikipedia.org/wiki/Principal–agent_problem
By HeyLaughingBoy 2025-06-121:57 > But you can’t quit them because of worker’s laws
This is generally not a problem in the US.
By chucksmash 2025-06-120:301 reply It's like saying "if you know half of your advertising dollars are wasted, why don't you just cut your ad buy in half?"
I still remember the joke from my first job:
Q: How many people work at this office?
A: About half.
By fc417fc802 2025-06-121:04 An apt analogy. Circling back to scientific research, I'm sure an investigator would be more than happy not to spend the time, effort, and grant money on a project that wasn't going to produce worthwhile results. If only we could know in advance without doing the work.
That does not, of course, mean that "most research being produced isn't really research, just people keeping busy" or whatever other nonsense an uninformed outsider feels like spewing.
By leereeves 2025-06-1123:03 Most people involved like hiring more people.
Workers generally like jobs where the workload is low. Managers gain status by having bigger teams, whether they need the extra people or not. Even investors often prefer hiring (a sign of growth) to layoffs, and executives are mostly concerned with pleasing investors.
Even well run tech companies with money to burn hired more people than they needed.
By itsoktocry 2025-06-1211:091 reply Companies can lay off thousands of employees and not have it affect growth, profits or, really, the workload of remaining employees. How could that be possible if everyone's work is so crucial?
By johnisgood 2025-06-1413:23 Everyone (eh, most) believes their work is crucial.
There are cognitive biases like the self-serving bias, or the IKEA effect, which leads individuals to overvalue their own contributions, as well as subjective importance derived from their immediate impact and daily responsibilities. And of course limited visibility into the broader organizational priorities often obscures how different roles contribute to overall growth and success.
By LPisGood 2025-06-1122:55 The people doing the hiring are typically not the people concerned about profits at medium and large sized companies. Sure someone has to approve the headcount numbers, but realistically this is an extremely flawed process.
By sieabahlpark 2025-06-1122:55 [dead]
By amanaplanacanal 2025-06-1122:551 reply I would think that profits are important to investors, since that's why they invest in the first place. Maybe not though.
By wizzwizz4 2025-06-1212:15 The original claim was "Most jobs are really not important either, they just keep people busy." Causing numbers to change on a balance sheet is not important, unless that corresponds to actual worthwhile work – in which case, the worthwhile work is what matters, and the balance sheet is just an artefact of accounting for it.
Ever since I first read this theory, I have always been wondering how credible is this. Where have you heard it from ?
By johnisgood 2025-06-1413:27 I am not sure, but probably related: https://evonomics.com/why-capitalism-creates-pointless-jobs-....
The Bullshit Jobs jobs theory has been widely discredited by researchers, but you probably won't believe them. Consider that most business is B2B so it makes sense that the casual observer would not know what it's for. Additionally, the Bullshit Jobs book relies on a magazine survey, actual studies shows that the percent of people who consider their jobs meaningless is very low and also decreasing over time
By johnisgood 2025-06-128:021 reply > the percent of people who consider their jobs meaningless
Worth to point out that there is a huge difference between people considering their jobs meaningless AND their job being meaningless, though.
By rcxdude 2025-06-1219:25 No, but it's a core part of the Bullshit Jobs theory, that the jobs are obviously bullshit to everyone involved. I would suggest that most jobs that aren't particularly valuable are probably not locally recognised as such (i.e. by the person or by their manager).
(In general I think while plenty of people are familiar with varying levels of pointless effort in their jobs, it's rare that a whole job consists of that, at least as far as the person doing it and the person hiring for it are concerned)
I think you're right, but it's not how I remember it for some reason.
I didn't read the book "Bullshit Jobs" [1] as an attempt to quantify how many jobs were bullshit. The author was an anthropologist with no interest in quantifying the economic impact. It's lots of amusing anecdotes from frustrated workers and a nudge for people to question the efficiency of capitalism.
At least that's how I read it. But reading the wikipedia page it sounds like a lot of people fixated on the idea that society could double its efficiency. Hard to know if there's a correct interpretation of the book's claims, and unfortunately we can't ask: the author David Graeber died in 2020.
By johnisgood 2025-06-128:04 > while he claims that 50% of jobs are useless, less than 20% of workers feel that way, and those who feel their jobs are useless do not correlate with whether their job is useless. (Garbage collectors, janitors, and other essential workers more often felt like their jobs were useless than people in jobs classified by Graeber as useless.)
Well, again, there is a huge difference between one's own perception of their job being useful or not. I believe garbage collectors, janitors, and nurses, are not examples of useless jobs. Useless jobs are mainly in the office, called "paper pushers". I mean come on, have you not been to any jobs (nor heard of any) where you had to pretend you were busy just to get paid? I saw plenty of cases.
By itsoktocry 2025-06-1211:29 >The Bullshit Jobs jobs theory has been widely discredited by researchers, but you probably won't believe them. Consider that most business is B2B so it makes sense that the casual observer would not know what it's for.
I'm not sure how it's possible that anyone over the age of 30 can say something like this with a straight face. Have you ever worked anywhere? I'd love to know how the "researchers" have discredited this. I'd also love to see their other papers (likely, also, bullshit).
By torial 2025-06-1217:47 There used to be a common practice of scientists writing summaries of their research for lay people. I think they viewed it as their civic duty. I had a collection called the World of Physics which included essays written by various scientists. I originally had it in the 90s and found it again after many decades. Would highly recommend.
https://www.amazon.com/World-Physics-Library-Literature-Anti...
By beloch 2025-06-1121:11 It's far preferable to having university PR people write some hype piece. Where they'd spend the whole time gushing about it being a world first, paradigm shifting, blah blah blah, the author focuses on things that actually matter. e.g. Is it testable? Yes, here's what to look for.
Yeah, wow. That was great. His solution seems so simple and clears all the previous model's problems. I guess every black hole could contain its own universe.
Too bad the author didn’t explain more the concept of the “parent” universe and how our own (contracting & expanding) universe got created. Nice things to read/consider/ponder late at night :-)
By alkyon 2025-06-1123:03 I would be surprised if the size doesn't matter in this case. On the one hand, tiny black holes tend to be rather short-lived. On the other, I suppose some threshold mass/energy is needed to generate a child universe that doesn't collapse immediately.
By raxxorraxor 2025-06-128:281 reply Ironically that was basically the first thought many had when it was clear we cannot explain what happens in the edge case of a singularity. It was always "perhaps another unsiverse or a way into a parallel one".
It still leaves a lot of questions though, especially if you try to marry quantum mechanics to these makroscopic models. Where did the initial black hole come from and should a corresponsing anti matter black hole exist?
Well that's an indsight bias if I've seen one. This is the first time I ever read that the "bottom" of a black hole could be a entirely new universe. If there ever "always was" a common hypothesis, it was the wormhole.
By raxxorraxor 2025-06-136:30 There wasn't much substance to it back then, but the idea certainly had been circulated in context of singularities where physics break down. So hypothesis is probably an exaggeration.
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.
>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.
By leiroigh 2025-06-1310:33 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.
By michaelmrose 2025-06-138:261 reply 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 ;)
By IggleSniggle 2025-06-1311:421 reply What's the story?
By leiroigh 2025-06-1319:22 "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 :)
By Agentlien 2025-06-129:18 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.
By empiricus 2025-06-126:58 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.
By ASalazarMX 2025-06-121:361 reply 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.
By dleeftink 2025-06-121:58 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...
By thechao 2025-06-124:01 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?
By mensetmanusman 2025-06-1416:041 reply They predict a non flat curvature, so no (not with existing data and measures, which may improve in the future).
By potamic 2025-06-156:12 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
By eggn00dles 2025-06-124:50 seems like this is just giving up on quantum gravity and saying the pauli exclusion principle will hold regardless of the gravitational force.
By cbolton 2025-06-1211:40 You mean small positive curvature.
By molticrystal 2025-06-1120:551 reply If the crux of the article is the fermion bounce, and you compare that to how much matter and energy we are aware of, that is quite the black hole, which leads one to start wondering what environment it existed in to become that size. Even if it is now stuck due to a positive curvature of just bouncing back and forth.
I would like the article to acknowledge a bit more though that blackhole universe theories and speculation are quite old now, not radical and a striking alternative, as it is natural to think about it once you learn of the concept of event horizons. What differentiates this though is the analytical solution.
