Cosmologists Model Big Bang as Rebound Inside Parent Black Hole

This Black Hole Could be Bigger Than The Universe — Kurzgesagt – In a Nutshell

Kurzgesagt – In a Nutshell

Collapsing black holes trigger interior cosmic bounces that birth daughter universes, driving an evolutionary selection process that favors star formation and inadvertently produces the conditions for life.

AI-assisted summary of This Black Hole Could be Bigger Than The Universe — original source. Check the original for full context.

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Key ideas

  • Black hole density decreases as mass increases, meaning ultra-massive black holes can match the density of ambient air, and a cosmic-sized mass could theoretically create an event horizon larger than the observable universe. (0:00)
  • Inside an event horizon, spacetime inverts: space becomes infinite while time becomes finite, converting the singularity from a spatial point into an unavoidable future moment. (4:00)
  • A collapsing black hole interior could experience a 'Big Bounce,' sparking a Big Bang and creating an expanding daughter universe nested within the horizon. (5:13)
  • Under cosmological natural selection, universes with physical constants optimized to maximize black hole reproduction inevitably produce stars, galaxies, and the accidental conditions for organic life. (7:13)

Detailed notes

## Background Published on YouTube by Kurzgesagt – In a Nutshell on May 21, 2024, the video investigates the counterintuitive physics of black holes and the mind-bending possibility that our universe exists inside one. The channel's description introduces the premise that black holes could spawn infinite nested universes, starting the thought experiment by building a black hole out of ambient air, while also promoting their interactive Curiosity Guide.

## TL;DR Contrary to common intuition, black holes decrease in average density as they grow larger, meaning a black hole the size of the observable universe would require an average density of just a few atoms per cubic meter to form an event horizon. Inside a black hole, space and time invert, transforming the central singularity from a physical destination into an unavoidable moment in time where all matter collapses. Theoretical physics suggests this collapse could trigger a Big Bounce, birthing a new expanding daughter universe inside the horizon. Under a model of cosmological natural selection, universes fine-tuned to produce abundant stars and black holes reproduce the most prolifically, accidentally creating the precise cosmic conditions necessary for biological life to emerge.

## Atmosphere & style The presentation delivers Kurzgesagt's signature blend of colorful, whimsical animation and disorienting cosmic wonder. Steve Taylor's calm, measured narration walks the viewer through increasingly bizarre spacetime paradoxes, grounding mind-melting concepts like inverted dimensions and cosmological reproduction in approachable thought experiments. The emotional trajectory shifts from playful curiosity to existential awe, transforming potentially terrifying concepts of gravitational collapse and cosmic insignificance into a poetic, comforting meditation on the endurance of life across an infinite multiverse.

## Bulletin - [00:00](https://www.youtube.com/watch?v=71eUes30gwc&t=0s) Black hole density decreases as mass increases, meaning ultra-massive black holes can match the density of ambient air, and a cosmic-sized mass could theoretically create an event horizon larger than the observable universe. - [04:00](https://www.youtube.com/watch?v=71eUes30gwc&t=240s) Inside an event horizon, spacetime inverts: space becomes infinite while time becomes finite, converting the singularity from a spatial point into an unavoidable future moment. - [05:13](https://www.youtube.com/watch?v=71eUes30gwc&t=313s) A collapsing black hole interior could experience a 'Big Bounce,' sparking a Big Bang and creating an expanding daughter universe nested within the horizon. - [07:13](https://www.youtube.com/watch?v=71eUes30gwc&t=433s) Under cosmological natural selection, universes with physical constants optimized to maximize black hole reproduction inevitably produce stars, galaxies, and the accidental conditions for organic life.

## Key takeaways - [00:00](https://www.youtube.com/watch?v=71eUes30gwc&t=0s) Black holes do not require infinitely compressed matter to form; their average density drops significantly as mass and radius scale upward. - [00:42](https://www.youtube.com/watch?v=71eUes30gwc&t=42s) While a solar-mass black hole has the density of a mountain range squeezed into a cubic meter, an ultramassive black hole like IRAS 20100−4156 matches the density of room-temperature air. - [02:31](https://www.youtube.com/watch?v=71eUes30gwc&t=151s) The mass of the observable universe (roughly 10²⁴ solar masses) has an average density of just five hydrogen atoms per cubic meter, which is mathematically enough to generate a black hole ten times larger than observable space. - [03:31](https://www.youtube.com/watch?v=71eUes30gwc&t=211s) The simple hypothesis that we inhabit a static black hole fails because the universe is expanding rather than undergoing inward collapse. - [04:00](https://www.youtube.com/watch?v=71eUes30gwc&t=240s) Crossing an event horizon inverts the roles of space and time: internal space becomes infinite without a center, while time becomes finite and runs out. - [04:44](https://www.youtube.com/watch?v=71eUes30gwc&t=284s) The singularity inside a black hole is not a location in space, but an inevitable event in the future of any matter crossing the event horizon. - [05:13](https://www.youtube.com/watch?v=71eUes30gwc&t=313s) The inward collapse of a black hole interior resembles a Big Crunch, which theoretical physics suggests could rebound via a 'Big Bounce' into a new Big Bang. - [06:12](https://www.youtube.com/watch?v=71eUes30gwc&t=372s) To an outside observer, a black hole remains a quiet sphere, while internally it can birth a distinct, rapidly expanding nested universe. - [07:13](https://www.youtube.com/watch?v=71eUes30gwc&t=433s) Chaotic Big Bounces could introduce variations in physical constants, creating an evolutionary branching process across daughter universes. - [07:45](https://www.youtube.com/watch?v=71eUes30gwc&t=465s) Universes with physical laws unable to form stars become evolutionary dead ends with no black hole progeny. - [08:21](https://www.youtube.com/watch?v=71eUes30gwc&t=501s) Our universe has produced over 10¹⁷ black holes, suggesting its physical constants are finely tuned through cosmological natural selection for black hole reproduction. - [08:46](https://www.youtube.com/watch?v=71eUes30gwc&t=526s) Because generating black holes requires massive stars and complex cosmic chemistry, the conditions necessary for biological life arise as a natural byproduct of cosmological reproduction. - [09:11](https://www.youtube.com/watch?v=71eUes30gwc&t=551s) While cosmologically compelling, nested black hole universe models remain speculative, currently untestable, and do not resolve the philosophical question of why existence began.

## Detailed walkthrough ### [00:00](https://www.youtube.com/watch?v=71eUes30gwc&t=0s) Building a Black Hole Out of Air

Common intuition holds that creating a black hole requires violently squeezing massive amounts of matter into impossibly small spaces. Under this standard view, Earth would have to be crushed down to the size of a coin to form a black hole, while the Sun would need to compress into an area the size of a small city. While it is true that packing immense mass into a tiny space creates extreme density, black holes do not actually require ultra-dense matter to exist. The governing physics reveals an unexpected relationship: the larger a black hole becomes, the lower its overall average density within its event horizon.

As black holes scale upward in mass and radius, they become increasingly "thin." A stellar-mass black hole with the mass of our Sun measures roughly 6 kilometers across and packs a density comparable to one Himalayan mountain range compressed into a single cubic meter. Scaling up to supermassive black holes, Sagittarius A* at the core of the Milky Way contains the mass of 4 million suns across a diameter of 24 million kilometers, yielding an average density of just six blue whales per cubic meter. Pushing further to the ultramassive scale, the black hole IRAS 20100−4156 holds a mass equal to 3.8 billion suns and spans an area as broad as an entire solar system. At that vast scale, its average density drops down to match the density of ordinary room-temperature air. Consequently, if you could fill a solar-system-sized balloon with undecillions of tons of ordinary air, an event horizon would naturally emerge without requiring any violent compression whatsoever.

- **Earth into a black hole:** Requires compression down to the size of a coin. - **Sun into a black hole:** Requires compression down to the size of a small city (~6 km diameter, density of ~1 Himalayan mountain range per cubic meter). - **Sagittarius A* (Milky Way center):** Mass of 4 million suns, diameter of 24 million kilometers, density equal to 6 blue whales per cubic meter. - **IRAS 20100−4156:** Mass of 3.8 billion suns, width of a solar system, density equal to ambient air.

> “The larger black holes get, the less dense they are.”

---

[02:31](https://www.youtube.com/watch?v=71eUes30gwc&t=151s) A Universe-Sized Black Hole

Taking this scaling logic to its absolute extreme raises the question of what would happen if a black hole were constructed on the scale of the entire cosmos. The observable universe visible from Earth spans a sphere with a radius of roughly 45 billion light-years, housing hundreds of billions of galaxies, enormous reservoirs of gas, and energetic fields. Summing all of this matter and energy produces an estimated mass equal to roughly a million billion billion suns. Spread evenly across the vast volume of observable space, this yields an average cosmic density of only about five hydrogen atoms per cubic meter—an ultra-dilute "cosmic air."

If that entire observable volume were treated as a balloon filled with this cosmic air, the total contained mass would not merely be sufficient to form a black hole; it would actually be enough to generate an event horizon ten times larger than the observable universe itself. This mathematical reality leads to the startling initial deduction that we ought to be living deep inside a cosmic-sized black hole. However, a major contradiction immediately challenges this straightforward picture: observations prove that our universe is actively expanding, whereas the interior of a traditional black hole is characterized by inexorable collapse. While this rules out living in a simplistic, static black hole, a much stranger cosmic mechanism resolves the contradiction.

```mermaid flowchart TD accTitle: Mass and Density Scaling to Universe Scale accDescr: Diagram showing how increasing mass leads to decreasing black hole density until cosmic scales are reached.

subgraph Scaling["Black Hole Mass vs. Density"] A["Sun-Mass Black Hole<br/>Size: Small city (~6 km)<br/>Density: 1 Himalaya / m³"] --> B["Supermassive: Sgr A*<br/>Mass: 4M Suns<br/>Density: 6 Blue Whales / m³"] B --> C["Ultramassive: IRAS 20100−4156<br/>Size: Solar System<br/>Density: Ambient Air"] C --> D["Observable Universe<br/>Radius: 45B light-years<br/>Density: 5 hydrogen atoms / m³"] end

subgraph Implication["Cosmic Scale Horizon"] D --> E["Mass exceeds threshold for a black hole<br/>10x larger than the observable universe"] E --> F{"Is the universe a black hole?"} F -->|"Problem: Universe is expanding"| G["Requires interior spacetime inversion"] end ```

- **Observable universe radius:** 45 billion light-years. - **Total observable mass:** Approximately $10^{24}$ (one million billion billion) solar masses. - **Average cosmic density:** Roughly 5 hydrogen atoms per cubic meter. - **Calculated horizon size:** Mass of the observable universe can support a black hole 10 times larger than the observable universe itself.

> “Actually, it's enough to make a black hole 10 times larger than the observable universe.”

---

[04:00](https://www.youtube.com/watch?v=71eUes30gwc&t=240s) A Whole Universe Born Inside a Black Hole

The popular visualization of a black hole—a 3D sphere with an infinitely dense point singularity sitting fixed at its physical center—is a misleading simplification. From the outside, a black hole appears as an ordinary spherical shadow, but crossing the event horizon completely upends the rules of geometry and physics. At the horizon boundary, the roles of space and time invert. In ordinary reality outside, spatial dimensions are finite and traversable while time marches forward forever in one direction. Inside the horizon, space becomes infinite while time becomes strictly finite. An observer inside would perceive an endless universe devoid of any spatial center; one could theoretically travel endlessly in one direction or loop back around to where they started.

Because time becomes finite inside the horizon, time itself is actively running out for anything trapped within. As the temporal clock counts down, the internal geometry warps dramatically: space is stretched along one direction while simultaneously contracting along the others, deforming everything into a collapsing cosmic spaghetto. Ultimately, the entire internal spatial fabric contracts toward a singularity. Crucially, this means the singularity is not a physical place located at the center of the interior space; rather, it is a specific, unavoidable moment in the future of anything that crosses the horizon. When this temporal destination arrives, all trapped matter, space, and time are compressed into an infinitely dense, high-energy state where standard physics ceases to operate.

Yet this catastrophic inward collapse closely mirrors a theoretical cosmic finale: the Big Crunch, where an entire universe ceases expanding and contracts back into a primordial singularity. If a collapsing interior undergoes a Big Crunch, theoretical physics allows for a subsequent "Big Bounce"—a rebound where compressed space violently expands outward once again like an over-squeezed rubber ball. To an outside observer, nothing changes; the black hole remains a quiet, static black sphere of frozen geometry. On the inside, however, that rebound acts as a Big Bang, birthing an entire expanding universe within the horizon. If our universe originated through such an interior bounce, it suggests a recursive cosmological architecture: a nested hierarchy of universes inside black holes, which themselves reside inside parent universes, potentially continuing endlessly without a single prime origin.

> “So the singularity is not a place where you can go – it's an event in time that happens.”

---

[07:13](https://www.youtube.com/watch?v=71eUes30gwc&t=433s) Infinite Black Hole Universes and Cosmological Natural Selection

If collapsing black holes routinely trigger Big Bounces that give birth to infant universes, the cosmos would operate under a mechanism akin to Darwinian natural selection. A Big Bang is inherently turbulent and chaotic, meaning newborn daughter universes might not inherit identical physical constants from their parent universes. Slight variations in fundamental forces and cosmological parameters would arise. Some universes might inherit physical laws that produce a featureless, uniform soup of particles, never cooling or clumping sufficiently to form stars, galaxies, or black holes. Such infertile universes would represent evolutionary dead ends, failing to reproduce.

Conversely, daughter universes possessing the precise physical laws required to produce long-lived stars will inevitably forge vast numbers of black holes. Over cosmic time, these prolific universes produce the overwhelming majority of daughter universes, dominating the multiverse population. Our own observable universe has already generated at least $10^{17}$ black holes, strongly suggesting that its laws are finely tuned for black hole fecundity because it is the descendant of a lineage optimized across generations of cosmological selection.

```mermaid flowchart LR accTitle: Cosmological Natural Selection Loop accDescr: Cycle illustrating how universes evolve through black hole reproduction and selection for life-supporting parameters.

subgraph Generation["Universe Lifecycle"] U["Parent Universe"] -->|"Collapse & Big Bounce"| BH["Black Hole Interior"] BH -->|"Chaotic Big Bang"| D["Daughter Universe<br/>(Mutated constants)"] end

subgraph Selection["Cosmological Selection"] D -->|"Infertile parameters"| DeadEnd["Uniform Particle Soup<br/>(0 Black Holes formed = Extinction)"] D -->|"Fertile parameters"| StarRich["Star & Galaxy Rich<br/>(Creates 10¹⁷+ Black Holes)"] StarRich -->|"Accidental byproduct"| Life["Conditions for Life Emergence"] StarRich -->|"Spawns next generation"| U end ```

A profound byproduct of this cosmological selection model is its natural explanation for the emergence of life. A universe optimized to maximize black hole reproduction must first produce trillions of stars, complex chemical synthesis, and sprawling galaxies—the exact prerequisites required for chemistry and organic life. While compelling on paper, these cyclic and nested models remain speculative, unproven, and currently untestable by empirical science. Furthermore, they do not resolve the ultimate philosophical dilemma of why existence exists at all, instead replacing one mystery with an infinite regression of questions. Nevertheless, the idea offers a poetic perspective on our place in nature: if black hole universe generation is continuous, life across the multiverse may endure indefinitely.

- **Observed black hole abundance:** The observable universe contains upwards of $10^{17}$ black holes. - **Mechanism of selection:** Universes with constants favoring stellar collapse produce the highest volume of progeny. - **Cosmic byproduct:** Maximizing stellar collapse accidentally optimizes the exact environments required for biological life.

> “If universes are optimized to create as many new black hole universes as possible, they're optimized to create loads of galaxies and stars. And thereby also, by accident, the conditions for life to emerge.”

---

[09:46](https://www.youtube.com/watch?v=71eUes30gwc&t=586s) The Kurzgesagt Curiosity Guide

The closing segment introduces Kurzgesagt's interactive release, *The Kurzgesagt Guide to Curiosity*, framed through the channel's signature avian mascot lore. The book is presented as an artifact designed to unlock the reader's latent capacity for curiosity—the same foundational drive the production team relies on to research cutting-edge science and construct animated narratives. The team poses the question of whether the reader might be the "chosen birb" capable of using curiosity to illuminate the mysteries of the natural world.

The publication spans 160 illustrated, interactive pages featuring 18 dedicated "curiosity quests" conceptualized and refined at Kurzgesagt headquarters after hundreds of hours of research and experimentation. The activities prompt readers to explore external environments to find unusual organisms, assemble novel structures, experiment with creative cooking, and solve analytical riddles to uncover scientific truths. The guide accommodates solo readers or pairs collaborating with a friend, with sales directly funding the channel's ongoing video production and research pipeline.

- **Title:** *The Kurzgesagt Guide to Curiosity* - **Format:** 160-page interactive adventure book featuring 18 structured curiosity quests. - **Core themes:** Guided scientific inquiry, real-world exploration challenges, observational puzzles, and creative experiments. - **Support role:** Book purchases directly subsidize future research and video production for the Kurzgesagt channel.

> “Every kurzgesagt product you buy directly funds another moment we get to spend working on our videos – and you get a special piece of kurzgesagt in return.”

## Notable quotes > [00:00](https://www.youtube.com/watch?v=71eUes30gwc&t=0s) The larger black holes get, the less dense they are.

> [04:00](https://www.youtube.com/watch?v=71eUes30gwc&t=240s) So the singularity is not a place where you can go – it's an event in time that happens.

> [07:13](https://www.youtube.com/watch?v=71eUes30gwc&t=433s) If universes are optimized to create as many new black hole universes as possible, they're optimized to create loads of galaxies and stars. And thereby also, by accident, the conditions for life to emerge.

## Mentioned Kurzgesagt – In a Nutshell, Sagittarius A*, IRAS 20100−4156, The Kurzgesagt Guide to Curiosity, Steve Taylor, Epic Mountain

## Video description Get your ✨Curiosity Guide✨ now on the kurzgesagt shop here: https://shop.kgs.link/Curiosity and unlock your inner curiosity power! It’s packed with adventures, cute birbs, and all you need to discover new perspectives on the world.

Sources & further reading: https://sites.google.com/view/sources-black-hole-universe/

Black holes might create infinite universes while destroying time and space. Everything in existence could be black holes, all the way down. We might live inside a black hole that is inside a black hole, that is inside a black hole. But let’s start at the beginning and build a black hole out of air.

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[Source](https://www.youtube.com/watch?v=71eUes30gwc)

中文简报

宇宙学家将大爆炸建模为母黑洞内部的反弹 坍缩的黑洞会触发内部宇宙反弹并孕育出子宇宙，从而推动一种偏向恒星形成的演化选择过程，并附带产生生命所需的条件。 与常规直觉相反，黑洞的平均密度随着质量增大而降低，这意味着一个与可观测宇宙同样大小的黑洞，仅需每立方米几个原子的平均密度即可形成事件视界。在黑洞内部，空间与时间发生倒置，使中心奇点从一个物理目的地转变为所有物质坍缩时不可避免的时间节点。理论物理学表明，这种坍缩可能会触发“大反弹”，在视界内部孕育出一个膨胀的新子宇宙。在宇宙自然选择模型下，经过精细调节以产生大量恒星与黑洞的宇宙其繁殖效率最高，这也附带创造了生物生命出现所需的精确宇宙条件。 黑洞密度随质量增加而降低，这意味着超大质量黑洞的密度可以与周围空气相近，而在理论上，具有宇宙级尺度的质量可产生一个大于可观测宇宙的事件视界。 (0:00) 在事件视界内部，时空发生倒置：空间变得无限，而时间变得有限，从而将奇点从一个空间点转变为一个不可避免的未来时刻。 (4:00) 坍缩的黑洞内部可能会经历一次“大反弹”，从而引发大爆炸，并在视界内部创造出一个嵌套的膨胀子宇宙。 (5:13) 在宇宙自然选择机制下，物理常数经过优化以最大化黑洞繁殖的宇宙，必然会产生恒星、星系以及有机生命所需的附带条件。 (7:13)

Source quotes

[0:00] The larger black holes get, the less dense they are. [4:00] So the singularity is not a place where you can go – it's an event in time that happens. [7:13] If universes are optimized to create as many new black hole universes as possible, they're optimized to create loads of galaxies and stars. And thereby also, by accident, the conditions for life to emerge.

Original transcript

[0:00] We proudly present to you: The  kurzgesagt Guide to Curiosity. [0:06] Join us on an interactive adventure across  160 thrilling pages that will change your [0:11] perspective on the world forever. Available now on the kurzgesagt shop. [0:18] You might be inside a black hole that's inside a black hole that is inside a black hole. [0:24] Everything in existence could be black holes all the way down. [0:28] It turns out black holes are much weirder than  you think and they break the universe much more [0:33] than is usually explained, destroying time and  space – and they may actually create infinite [0:39] universes in the process. But before we can get to that, let’s first build a black hole out of air. [0:48] Everything can become a black hole if you  squeeze it to a critical limit. [0:53] You'd need to squeeze Earth down to the size of a coin for it to turn into a black hole. [0:59] The Sun needs  to be squeezed down to the size of a small city to become a black hole. [1:05] And if a lot of  mass is concentrated in a really tiny space, you get something super dense. [1:11] This is usually how black holes are explained.  Stuff becomes super dense and collapses into [1:16] a black hole. But actually you don’t  need any ultra dense stuff to make them! [1:22] We're ignoring some math here, but all  you really need to know is one thing: [1:25] The larger black holes get, the less dense they  are. So really large black holes are kind of thin. [1:33] A sun-mass black hole is only about 6 km wide  and has a density of about one Himalayan range [1:39] per cubic meter. The supermassive black hole  at the center of the Milky Way has a mass of 4 [1:44] million suns, a diameter of 24 million kilometers,  and a density of 6 blue whales per cubic meter. [1:51] The ultramassive black hole IRAS 20100−4156  has a mass of 3.8 billion suns and is as wide [2:00] as a solar system. But because it's  so large, it is only as dense as air! [2:06] This means, at least in theory, that if you take  a gigantic balloon and fill it with undecillions [2:11] of tons of air, the moment it gets to the size  of a solar system, an event horizon suddenly [2:17] forms and it turns into a supermassive  black hole. Without violence or squeezing. [2:23] So now let’s think big. What do we need to  make a black hole the size of the universe? [2:31] A Universe-Sized Black Hole [2:33] The chunk of the universe that we can see  from Earth is a sphere with a radius of 45 [2:38] billion light-years, filled with hundreds of  billions of galaxies, lots of gas and a bunch [2:43] of other things. If you add them up, it has the  mass of about a million billion billion suns. [2:49] Which sounds a lot – but on average, the  universe is not very dense. If we break up all [2:55] the galaxies, stars, gas and energy, and spread  them equally inside the volume of the universe, [3:00] we get an average density of about 5  hydrogen atoms per cubic meter. You [3:05] can imagine this as the sort of ultra thin  “cosmic air” that makes up the universe. [3:11] What would happen if we take a balloon as big as [3:13] the observable universe and  fill it with “cosmic air”? [3:17] Well, it turns out that all the mass in the  observable universe is more than enough to [3:21] create a black hole. Actually, it's  enough to make a black hole 10 times [3:25] larger than the observable universe.  But that can only mean one thing – we [3:30] should be living deep inside a truly  gargantuan, cosmic-sized black hole! [3:36] There is one catch though. We know that our  universe is expanding – and an expanding [3:41] universe is not what you'd expect to  see if you were inside a black hole. So [3:45] our universe can’t be a black hole – at least  not in the naive way we’ve just described. [3:50] Except there is a wild and mind-bending  trick the universe could play on us. [3:55] To find out how, let's jump  into a black hole and die! [4:00] A Whole Universe Born Inside a Black Hole [4:04] We usually imagine black holes as spheres  with a singularity at their center, [4:09] a point where all their mass  is concentrated so much that [4:12] our math breaks down. But this is  a lie – they are SO much weirder. [4:18] From the outside a black hole looks like  a normal black sphere. But the inside is [4:22] where things stop making sense. [4:26] Black holes warp the universe so much that, at the event horizon, [4:30] space and time switch their roles. Inside a normal  sphere, space is finite but time goes on forever. [4:37] But inside a black hole it's the other way around  – space goes on forever but time is finite. [4:44] So once inside, you see an infinite universe  with no center. The geometry is too complicated, [4:50] so we're simplifying. But basically  you could walk forever in one direction [4:55] or walk in another direction and  arrive at the same place again. [4:59] But not only that. Inside a black hole time  is finite, and it's now running out. [5:04] So after a while you start to notice that  space itself is slowly changing. In one [5:08] direction space is being stretched, while in  all other directions space is shrinking – the [5:13] whole universe is being squeezed, kind  of turning into a collapsing spaghetti. [5:18] Sooner or later, the whole black hole  universe collapses into itself. All of space, [5:23] every single part of it, is turning into a  singularity. So the singularity of a black [5:28] hole is not at its center or in any  direction at all. It's in the future [5:33] of whatever falls inside. We made a whole  video about this if you want to learn more. [5:38] So the singularity is not a place where you  can go – it's an event in time that happens. [5:45] Once it happens, you and everything else that  fell inside the black hole will be mercilessly [5:50] crushed into an infinitely small region with  infinite gravity and infinite energy. Time, [5:55] space, none of it matters anymore, both kind of  stop existing in ways that we would recognize. [6:01] And then? Is this the end? Well, maybe not. [6:06] This collapse of the black hole universe  into a singularity looks like one of the [6:10] scenarios for the end of our universe: The Big  Crunch, where long after the Big Bang the whole [6:14] universe collapses into a singularity again. [6:18] But if there is a Big Crunch,  there might be a Big Bounce – [6:22] like a rubber ball that you’ve squeezed too much and that suddenly [6:24] rebounds, space might expand again. So a new  universe could be born inside a black hole. [6:31] The funny thing about this  scenario is that nothing has [6:34] changed in the slightest outside the  black hole. Watching from the outside, [6:38] it's still a black sphere of nothingness. And  yet, on the inside a new universe has been born. [6:44] So maybe our universe was born like  this and we are all actually inside [6:49] a black hole. But if our universe can also  create black holes, they might give birth [6:54] to new universes. Is our black hole universe  also just part of a universe “further up”, [7:00] that's also a black hole inside another  universe? Is there an end to it? Is there [7:05] one original universe? Is the cosmos black  holes inside black holes inside black holes? [7:13] Infinite Black Hole Universes [7:16] If the universe creates black  holes that create universes, [7:20] that then create new black holes that create  new universes, this cosmic self-reproduction [7:25] would be subject to natural selection.  A Big Bang is a chaotic and messy event, [7:29] so it’s possible that the new daughter universes  would not always be fully identical to their mums. [7:35] Sometimes physics may be slightly different,  with some fundamental values higher or lower. [7:40] And so some universes might be able to create  loads of stars, planets and black holes. Others [7:46] might not, maybe creating a uniform cosmic soup  where no stars, planets and black holes form. [7:53] But if all universes are born inside black  holes, in the long run all universe lines [7:58] that don’t create loads of black holes  would die out. The universes with the [8:02] conditions for loads of black holes would  become the most common and spawn the most [8:06] daughter universes. Survival of the fittest,  but with universes instead of organisms. [8:12] Our observable universe alone has created at  least 1017 black holes so far. So maybe our [8:18] universe has the physics and laws it has,  because it was born after a long process [8:23] of cosmological selection that favored  the production of tons of black holes. [8:27] And that would have a lovely side effect. [8:30] If universes are optimized to create as  many new black hole universes as possible, [8:34] they're optimized to create loads of galaxies  and stars. And thereby also, by accident, [8:41] the conditions for life to emerge. So universes  that are the best at creating new universes are [8:47] also the best at creating life. If this scenario  is true, who knows how many bazillions of black [8:54] hole universes might be out there. All with stars  and planets, potentially home to others like us. [9:01] So. Is our universe like this? The  truth is we don’t know. While these [9:06] ideas are based on real science and work on paper, [9:09] they're speculative and not testable. Also  cyclic universes don’t actually explain why [9:14] the universe exists in the first place or why it  is the way it is. Instead of providing answers, [9:20] these are really just new questions in disguise,  so keep that in mind before getting too excited. [9:25] But isn’t it just wonderful and  heartwarming that we're living [9:28] in a universe where ideas as big as this  one are even thinkable? There might be so [9:34] much life. And if new universes are created  constantly, maybe life will go on forever. [9:46] We’ve heard rumors of a chosen one. A special birb who has the power to [9:51] illuminate the vast darkness of the universe,  uncovering the great mysteries of the world. [9:57] We are all born with this power.  But only few are able to master it. [9:57] We use the same power here at kurzgesagt to find [9:57] the latest science and come up  with the most exciting videos. [9:57] This special power is called: curiosity. And the special birb… could be you! [10:03] Our Guide to Curiosity is now available on  our shop. It’s an adventure that will help [10:09] you to think like a kurzgesagt birb  and unlock your curiosity potential. [10:14] Join us across 160 thrilling, interactive  pages designed to awaken your curiosity, [10:21] changing your perspective on the world forever. [10:23] But be prepared! We will send you on  epic quests to find incredible creatures, [10:29] challenge you to build unprecedented structures, [10:32] ask you to cook up something surprising, and solve  riddles to unveil hidden truths about the world. [10:39] But don’t worry, the birbs will be with you every  step of the way. And you can also bring a friend! [10:45] The 18 curiosity quests were developed  right here at the kurzgesagt headquarters. [10:50] After hundreds and hundreds of hours of  research and lots of trial and error, [10:54] we created the ultimate curiosity adventure. It was the most fun we ever had making [10:59] a product – and we are so excited to  finally share this experience with you. [11:04] So head over to the kurzgesagt shop and  find out if you are the chosen birb. [11:09] Every kurzgesagt product you buy  directly funds another moment we [11:13] get to spend working on our videos – and you  get a special piece of kurzgesagt in return. 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