New Universes Can Form Inside Dying Stars, Physicists Show

Sabine Hossenfelder

AI-assisted summary of New Universes Can Form Inside Dying Stars, Physicists Show — original source. Check the original for full context.

Source published: 2026-08-19

Key ideas

A newly publicized solution to Einstein's equations models a collapsing star whose interior expands outward like a Big Bang, preventing an event horizon or black hole from ever forming. (1:56)
Contrary to the stereotype of ultradense black holes, average mass density decreases as a black hole's radius grows, meaning a sufficiently massive black hole can be less dense than our observable universe. (0:00)
Because general relativity allows physicists to mathematically cut and patch disparate spacetime geometries together, theorists can replace the unphysical infinite-curvature singularity of a dying star with almost any arbitrary structure. (2:48)
Despite being mathematically valid, the new collapsing-star universe paper receives a 9 out of 10 on the "bullshit meter" because its geometry was reverse-engineered to achieve a desired outcome without observational evidence or physical plausibility. (2:48)

Detailed notes

## Background Published on YouTube by Sabine Hossenfelder on August 19, 2026, this video examines sensational headlines claiming that our universe could have originated inside a collapsing star. According to the video description, the segment analyzes a recently published paper featuring a novel solution to Einstein's equations where a dying star expands internally rather than forming a conventional black hole.

## TL;DR Recent headlines suggested that baby universes can form inside collapsing stars, leading to speculation that our own cosmos originated inside a black hole. However, the featured theoretical paper actually presents a solution to Einstein's equations where the collapsing matter begins to expand internally like a Big Bang, preventing an event horizon from ever forming. While mathematically valid, general relativity permits theorists to patch virtually any arbitrary geometry into a collapsed interior, leading the host to assign the study a 9 out of 10 on her 'bullshit meter.' Ultimately, while baby universe creation remains theoretically conceivable, this particular model is an engineered mathematical artifact completely lacking observational support.

## Atmosphere & style The presentation carries Sabine Hossenfelder's trademark blend of dry wit, sharp skepticism, and clear-eyed theoretical physics deconstruction. It feels like an insider pulling back the curtain on sensationalized academic press releases, moving briskly from foundational astrophysics to a caustic critique of mathematical cherry-picking. The tone shifts playfully between intellectual respect for general relativity's flexibility and exasperation at theorists who engineer solutions simply to achieve a desired outcome.

## Bulletin - [01:56](https://www.youtube.com/watch?v=_vJD0gdkKHo&t=116s) A newly publicized solution to Einstein's equations models a collapsing star whose interior expands outward like a Big Bang, preventing an event horizon or black hole from ever forming. - [00:00](https://www.youtube.com/watch?v=_vJD0gdkKHo&t=0s) Contrary to the stereotype of ultradense black holes, average mass density decreases as a black hole's radius grows, meaning a sufficiently massive black hole can be less dense than our observable universe. - [02:48](https://www.youtube.com/watch?v=_vJD0gdkKHo&t=168s) Because general relativity allows physicists to mathematically cut and patch disparate spacetime geometries together, theorists can replace the unphysical infinite-curvature singularity of a dying star with almost any arbitrary structure. - [02:48](https://www.youtube.com/watch?v=_vJD0gdkKHo&t=168s) Despite being mathematically valid, the new collapsing-star universe paper receives a 9 out of 10 on the "bullshit meter" because its geometry was reverse-engineered to achieve a desired outcome without observational evidence or physical plausibility.

## Key takeaways - [00:00](https://www.youtube.com/watch?v=_vJD0gdkKHo&t=0s) When a massive star collapses under its own gravity, conventional astrophysics predicts the formation of a black hole defined by an inescapable event horizon. - [00:00](https://www.youtube.com/watch?v=_vJD0gdkKHo&t=0s) A black hole's average density scales inversely with its radius, allowing a sufficiently large black hole to have an average density lower than that of our observed universe. - [00:00](https://www.youtube.com/watch?v=_vJD0gdkKHo&t=0s) Because an observer on the inside cannot see the enclosing horizon, it is mathematically plausible that we already live inside an enormous black hole. - [00:00](https://www.youtube.com/watch?v=_vJD0gdkKHo&t=0s) Since the 1970s, physicists have explored how black hole interiors might trigger Big Bang-style expansions, addressing both how our universe began and what happens behind an event horizon. - [01:56](https://www.youtube.com/watch?v=_vJD0gdkKHo&t=116s) The new paper behind recent headlines presents a solution to Einstein's equations in which the interior matter of a collapsing star expands outward rather than collapsing into a trapped surface. - [01:56](https://www.youtube.com/watch?v=_vJD0gdkKHo&t=116s) Because this internal expansion counteracts the inward gravitational pull, an event horizon never materializes, creating "a black hole origin story without the black hole." - [01:56](https://www.youtube.com/watch?v=_vJD0gdkKHo&t=116s) Science headlines mischaracterized the study by conflating a collapsing star setup with an actual black hole, missing the paper's core twist that no black hole ever forms. - [02:48](https://www.youtube.com/watch?v=_vJD0gdkKHo&t=168s) Consensus on stellar collapse remains elusive because general relativity allows theorists to mathematically cut and patch different spacetime geometries together across boundaries. - [02:48](https://www.youtube.com/watch?v=_vJD0gdkKHo&t=168s) Through spacetime patching, researchers can excise a collapsing star's interior and graft on almost anything, including a baby universe, a wormhole to the Andromeda Galaxy, or an ad-hoc geometry. - [02:48](https://www.youtube.com/watch?v=_vJD0gdkKHo&t=168s) The simplest, unpatched solution to stellar collapse produces a gravitational singularity where spacetime curvature becomes infinite, a result virtually no physicist believes is physically real. - [02:48](https://www.youtube.com/watch?v=_vJD0gdkKHo&t=168s) The new paper earns a 9 out of 10 on the "bullshit meter" because its mathematical geometry was artificially pieced together to achieve a desired outcome rather than a physically plausible scenario. - [02:48](https://www.youtube.com/watch?v=_vJD0gdkKHo&t=168s) While collapsing matter or black holes could theoretically seed new universes, there is zero observational evidence to single out this model from countless other mathematically valid configurations.

## Detailed walkthrough ### [00:00](https://www.youtube.com/watch?v=_vJD0gdkKHo&t=0s) The Allure of Living Inside a Black Hole

A flurry of recent science headlines declared that entire universes could be born inside collapsing stars, prompting widespread curiosity about whether our own cosmos might have originated through such a mechanism. When a massive star dies and collapses under its own gravity, conventional astrophysics predicts the formation of a black hole defined by an event horizon—a boundary beyond which nothing, not even light, can escape. While popular depictions typically portray black holes as ultradense knots where vast mass is compressed into a tiny space, this stereotype misses a crucial geometric reality: the larger a black hole’s radius, the lower its average density. In fact, a sufficiently massive black hole can have an average density at horizon formation that is actually lower than the average density of our observed universe.

Because an observer situated entirely on the inside would be unable to see the enclosing horizon, it is mathematically entirely plausible that we are already living inside an enormous black hole without realizing it. Theoretical physicists have explored this possibility since the 1970s, producing multiple mathematical frameworks showing how the interior of a black hole might give rise to a baby universe undergoing a cosmic expansion analogous to the Big Bang. This hypothesis has endured because it elegantly tackles two fundamental cosmological headaches at once: it provides an origin story for our own universe while simultaneously answering what actually transpires behind a black hole's horizon.

- The defining feature of a black hole is its event horizon, an inescapable threshold from which light cannot break free. - Contrary to common belief, average mass density scales inversely with black hole radius; large black holes can have densities lower than the average density of the observable universe. - Theoretical models proposing that black hole interiors trigger a Big Bang-style expansion have circulated in the literature since the 1970s.

[01:56](https://www.youtube.com/watch?v=_vJD0gdkKHo&t=116s) The New Paper: A Black Hole Origin Story Without the Black Hole

The study driving the latest round of breathless reporting introduces a novel solution to Einstein’s field equations of general relativity, but the actual mathematics diverges significantly from the popular narrative. In a standard gravitational collapse, falling matter is drawn inward toward a central point until a trapped surface forms. In this newly proposed solution, however, the interior matter begins to expand outward just like a universe in the wake of the Big Bang. Because this internal outward swelling counteracts the inward pull, an event horizon never actually manages to materialize.

Rather than describing a nested universe nestled safely within an established black hole, the authors have constructed what amounts to "a black hole origin story without the black hole." The collapse of the dying star triggers a temporary cosmic expansion on the inside instead of producing a traditional event horizon. The headlines conflated the initial setup of a collapsing star with the creation of a literal black hole interior, missing the paper's central twist: you get an expanding, universe-like region, but no black hole ever forms.

```mermaid flowchart TD accTitle: Standard Collapse vs New Expansion Model accDescr: A comparison showing how stellar collapse either forms a horizon or transitions into an expanding interior.

subgraph Standard["Standard Gravitational Collapse"] A1["Collapsing Stellar Matter"] --> A2["Inward Gravitational Pull"] A2 --> A3["Event Horizon Forms"] A3 --> A4["Black Hole Interior & Singularity"] end

subgraph NewModel["New Mathematical Solution"] B1["Collapsing Stellar Matter"] --> B2["Internal Space Expands"] B2 --> B3["Event Horizon Never Forms"] B3 --> B4["Temporarily Expanding Universe Region"] end ```

[02:48](https://www.youtube.com/watch?v=_vJD0gdkKHo&t=168s) Spacetime Patching and the Bullshit Meter Rating

The inability of physicists to reach a consensus on what happens when a star dies is not simply a matter of researchers being bad at math—though, as a dry aside, "some of them are." The root cause is a fundamental mathematical ambiguity built directly into general relativity. Einstein's field equations govern the local curvature and behavior of spacetime, but they permit theorists to cut and patch disparate spacetime geometries together across boundaries. In practice, a theorist can mathematically excise the troublesome interior of a collapsing star or black hole and graft on virtually any geometric alternative: a freshly expanding universe, a wormhole leading directly to the Andromeda Galaxy, or even a literal bookshelf.

``` ┌──> Expanding Universe │ [Collapsing Star Interior Excised] ───┼──> Wormhole to Andromeda │ └──> Bookshelf / Ad-hoc Geometry ```

Faced with this mathematical freedom, physicists ordinarily default to the simplest possible configuration with the fewest ad-hoc assumptions. However, applying that standard default to stellar collapse inevitably produces a gravitational singularity—a point where spacetime curvature skyrockets to infinity, which virtually no one believes represents true physical reality. This impasse drives the endless production of speculative alternative solutions.

While the new paper's derivation is mathematically valid, it earns a "9 out of 10 on the bullshit meter" because the geometry is clearly "fumbled together to give a result that they wanted to have, not a result that's remotely physically plausible." While such hand-crafted constructions are entirely legal in theoretical physics, they require regular bullshit meter maintenance. Although it remains entirely possible that collapsing matter or black holes could seed baby universes—or even that our own cosmos originated this way—there is currently zero observational evidence to single out this model from the countless other mathematically permissible configurations. Borrowing a riff on Shakespeare: "there are more things in mathematics, Horatio, than are dreamt of in your philosophy."

- General relativity allows theorists to "patch together" different spacetime manifolds, replacing collapsed interiors with exotic geometries. - The standard, unpatched solution yields a physical singularity with infinite curvature, which physicists broadly reject as unphysical. - The paper receives a 9/10 bullshit meter rating because the solution is mathematically engineered to reach a desired outcome rather than rooted in realistic physics.

## Notable quotes > [01:56](https://www.youtube.com/watch?v=_vJD0gdkKHo&t=116s) a black hole origin story without the black hole — Sabine Hossenfelder

> [02:48](https://www.youtube.com/watch?v=_vJD0gdkKHo&t=168s) some of them are — Sabine Hossenfelder

> [02:48](https://www.youtube.com/watch?v=_vJD0gdkKHo&t=168s) 9 out of 10 on the bullshit meter — Sabine Hossenfelder

> [02:48](https://www.youtube.com/watch?v=_vJD0gdkKHo&t=168s) fumbled together to give a result that they wanted to have, not a result that's remotely physically plausible — Sabine Hossenfelder

> [02:48](https://www.youtube.com/watch?v=_vJD0gdkKHo&t=168s) there are more things in mathematics, Horatio, than are dreamt of in your philosophy — Sabine Hossenfelder

## Mentioned OpenStar Technologies, Sabine Hossenfelder, Albert Einstein, Andromeda Galaxy, William Shakespeare

## Video description This video was sponsored by nuclear fusion startup OpenStar Technologies https://www.openstar.tech/ Thank you, OpenStar, for supporting Science News!

Could our universe have been born inside a collapsing star? That idea recently made headlines, and I got a lot of questions about it. The paper behind them describes a new solution to Einstein's equations in which a collapsing star expands on the inside and never forms a black hole. Let's take a look.

Paper: DOI: https://doi.org/10.1103/c6lw-nx7k

#science #sciencenews #physics #space #blackhole #universe

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[Source](https://www.youtube.com/watch?v=_vJD0gdkKHo)

中文简报

物理学家表明：垂死恒星内部可形成新宇宙近期有新闻头条称，坍缩恒星内部可以形成婴儿宇宙，这引发了关于我们所在的宇宙也起源于黑洞内部的猜测。然而，相关理论论文实际上提出的是爱因斯坦方程的一个解：其中坍缩物质开始在内部像大爆炸一样膨胀，从而使事件视界根本无法形成。尽管这在数学上成立，但广义相对论本就允许理论学家将几乎任何任意的几何结构拼接到坍缩的内部区域，这促使主持人在她的“胡扯指数”上给这项研究打出了9分（满分10分）。归根结底，虽然婴儿宇宙的产生在理论上是可以设想的，但这一特定模型只是一个人为构造的数学产物，完全缺乏观测支持。一项最新公布的爱因斯坦方程解模拟了一颗坍缩恒星，其内部像大爆炸一样向外膨胀，从而使事件视界或黑洞根本无法形成。 (1:56) 与黑洞具有超高密度的刻板印象相反，黑洞的平均质量密度会随着其半径的增大而降低，这意味着一个质量足够大的黑洞，其密度可能低于我们的可观测宇宙。 (0:00) 由于广义相对论允许物理学家在数学上将截然不同的时空几何结构剪切并拼接在一起，理论学家可以用几乎任何任意的结构来替代垂死恒星中那不符合物理实际的无限曲率奇点。 (2:48) 尽管在数学上成立，这篇关于坍缩恒星演化出宇宙的新论文还是在“胡扯指数”上拿到了9分（满分10分），因为其几何结构是为了达到预期结果而逆向推导出来的，既无观测证据，也缺乏物理合理性。 (2:48)

Reading summary

Sabine Hossenfelder critiques recent science headlines claiming dying stars form universes inside black holes, explaining that the featured study actually models an expanding interior that prevents an event horizon from forming at all. While general relativity mathematically allows theorists to splice together such scenarios, Hossenfelder argues the model is an engineered mathematical exercise lacking physical plausibility and observational support. The Precedent for Living Inside Black Holes (0:00) Theoretical physicists have examined the possibility that black hole interiors could seed baby universes since the 1970s. The concept is theoretically attractive because it addresses two major cosmological problems at once: providing an origin mechanism for a Big Bang-style expansion while offering a physical description of what transpires past an event horizon. Geometrically, a black hole's average density scales inversely with its radius. For a sufficiently massive black hole, the average density at horizon formation can be lower than the average density of the observable universe. Because an observer situated entirely inside would not see the surrounding event horizon, it remains mathematically plausible that our own cosmos exists within a massive black hole. A Stellar Collapse Without a Black Hole (1:56) The study behind the recent media coverage introduces a new solution to Einstein’s field equations, but its actual mechanics diverge from popular reports. Standard gravitational collapse pulls stellar matter inward until a trapped surface forms an inescapable event horizon. In the authors' proposed model, the interior matter begins expanding outward like an early universe, counteracting the inward gravitational pull. Hossenfelder characterizes the result as "a black hole origin story without the black hole." Because the internal outward expansion prevents an event horizon from ever materializing, the dying star produces a temporary, expanding universe-like region rather than a nested black hole interior. Spacetime Patching and the Plausibility Problem (2:48) The persistent disagreement among physicists regarding stellar collapse stems from the mathematical flexibility of general relativity. Einstein's equations allow theorists to excise the problematic interior of a collapsing star and mathematically patch on alternative geometries across the boundary, such as an expanding cosmos or a wormhole. Defaulting to the simplest assumptions yields a gravitational singularity of infinite curvature, an outcome physicists generally dismiss as unphysical. This impasse incentivizes theorists to formulate speculative alternative geometries. Although the study's derivation is mathematically valid, Hossenfelder assigns it a "9 out of 10 on the bullshit meter." She contends the geometry was artificially pieced together to achieve a predetermined outcome rather than a physically plausible scenario, noting that the mathematical framework can be made to splice in almost any arbitrary geometry. While general relativity mathematically accommodates scenarios where collapsing stellar matter gives rise to expanding baby universes, there is currently zero observational evidence favoring this specific model over numerous other mathematically permissible configurations.

Source quotes

[1:56] Sabine Hossenfelder: a black hole origin story without the black hole [2:48] Sabine Hossenfelder: some of them are [2:48] Sabine Hossenfelder: 9 out of 10 on the bullshit meter [2:48] Sabine Hossenfelder: fumbled together to give a result that they wanted to have, not a result that's remotely physically plausible [2:48] Sabine Hossenfelder: there are more things in mathematics, Horatio, than are dreamt of in your philosophy

Original transcript

[0:00] Do collapsing stars create universes? And if so, could our universe have been created this way? [0:08] This idea recently made headlines, and I got a lot of questions about it. Scientists propose that [0:14] entire universes can form inside collapsing stars. We may need new physics. Scientists say many [0:20] universes could form within dying stars. A dying star could trigger the birth of a new universe, [0:26] scientists say. So, let's have a look. Usually when a star collapses, it forms a black hole whose [0:33] defining property is the existence of an event horizon from within which nothing, not even light, [0:40] can escape. Black holes often portrayed as objects where a lot of mass is compressed into a small [0:47] volume, so a very high mass density. But this isn't true. The larger the radius of the black [0:52] hole, the smaller the average density. In fact, the density at which a black hole horizon forms [0:59] can be lower than the average density in our entire universe. This is why we might actually [1:06] sit within a huge black hole. We just haven't noticed because on the inside we can't see the [1:12] horizon. Mathematically, it's totally possible that we're inside a black hole. But it brings [1:18] up the question of, well, how did we get there? What does the math say about that? Again, the [1:25] mathematics says it's possible. There have been various proposals that demonstrate how it could [1:31] happen that the inside of a black hole generates a new universe, one that then undergoes a big bang [1:38] scenario similar to the one we think happened in our universe. The idea isn't even new. It's [1:44] been around since the 1970s. And it's appealing because it would solve two problems at once. [1:49] It did explain what happens inside black holes and it did explain the origin of our universe. Now, [1:56] what about the new paper? The authors of the new paper that just made headlines describe [2:02] a new solution to Einstein's field equations, the equations of general relativity. This new solution [2:09] describes matter that collapses under the pole of its own gravity. Normally, this matter will form a [2:16] black hole. In their setup, however, the inside of the collapsing matter begins to expand like [2:22] a universe would after the big bang. And because of this expansion, the horizon never forms. It's [2:29] basically a black hole origin story without the black hole. And this is what the headlines were [2:35] about. One does not get a new universe inside a black hole. You get something resembling [2:42] a temporarily expanding universe, but no black hole. Okay. But wait, you may ask, how can it be [2:48] that physicists don't agree on what happens when a star collapses? Are they just bad at maths? Well, [2:56] some of them are. But in this case, that isn't the issue. The issue is instead a general ambiguity in [3:02] our understanding of spacetime. You see, Einstein's equations tell you how spacetime behaves, [3:08] but you can patch together different regions of spacetime. You can basically remove the inside [3:14] of a collapsing star or a black hole and attach something else. For example, an expanding universe [3:21] or a wormhole to Andromeda or a bookshelf. Mathematically, you can make this all work [3:27] out. But which of them is physically correct? In a situation like this, physicists normally [3:34] default on the simplest possible solution, the one with the least extra assumptions. But for stellar [3:40] collapse, this gives you a singularity on the inside, a place where the curvature of spacetime [3:45] becomes infinitely large. Physicists don't believe that this is what's really going on. And this is [3:50] why you see so many speculations about other solutions like the one in the new paper. And [3:56] this is also why I give this paper a 9 out of 10 on the bullshit meter. It's mathematically fine, but [4:02] physically it's fumbled together to give a result that they wanted to have, not a result that's [4:09] remotely physically plausible. This is not illegal in theoretical physics. It is, however, the reason [4:15] the bullshit meter needs regular maintenance. That said, I want to be clear that this is indeed [4:21] possible that collapsing matter or black holes create new universes. It's also possible that this [4:28] is how our universe came about indeed. However, we currently have no good reason to think this is so [4:36] it's just one of many possible things that you can mathematically write down but that we can't tell [4:42] apart by observations. In summary, there are more things in mathematics, Horatio, than are dreamt of [4:50] in your philosophy. This video was sponsored by OpenStar. Thanks for watching. See you tomorrow.