# How plausible is my pet theory that our universe is inside a black hole? **URL:** \ **Category:** Factual Questions\ **Created:** [September 21, 2018, 3:27pm UTC](https://boards.straightdope.com/t/how-plausible-is-my-pet-theory-that-our-universe-is-inside-a-black-hole/821682 "2018-09-21T15:27:21Z")\ **Posts on this page:** 12\ **Page:** 2
**Author:** ![scabpicker](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/scabpicker/32/8268_2.png) [@scabpicker](https://boards.straightdope.com/u/scabpicker)\ **Post date:** [September 23, 2018, 5:48am UTC](https://boards.straightdope.com/t/how-plausible-is-my-pet-theory-that-our-universe-is-inside-a-black-hole/821682/21 "2018-09-23T05:48:55Z")
> [@Exapno\_Mapcase](#): > > I don’t understand your question. Where did I say our universe is special? Ok, I’ll quote the whole thing this time. > [@Exapno\_Mapcase](#): > > The singularity is a viewpoint? We’re crushed inside an “infinitely small point” and that magically allows us to … something? Infinitely small becomes infinitely large? Whoa. Heavy, man. > > That black holes may seed other universes is conjecture but hugely more plausible than we’re seeing the universe from inside of a singularity. Nor are the two hypotheses remotely similar or interchangeable. We’re not talking about seeding other universes here. That’s a different discussion. How would our universe be different from the other universes that might be seeded by black holes in our universe? How would you know that it was? We’re talking about crossing a singularity, after all. Additionally how would being “seeded” by a black hole be different from being inside one? ---
**Author:** ![Exapno\_Mapcase](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/exapno_mapcase/32/1051_2.png) [@Exapno\_Mapcase](https://boards.straightdope.com/u/Exapno_Mapcase)\ **Post date:** [September 23, 2018, 4:08pm UTC](https://boards.straightdope.com/t/how-plausible-is-my-pet-theory-that-our-universe-is-inside-a-black-hole/821682/22 "2018-09-23T16:08:10Z")
> [@scabpicker](#): > > Ok, I’ll quote the whole thing this time. > > How would our universe be different from the other universes that might be seeded by black holes in our universe? How would you know that it was? We’re talking about crossing a singularity, after all. > > Additionally how would being “seeded” by a black hole be different from being inside one? First, it’s the OP who keeps insisting that we are “inside” a black hole. Second, any universe that is created by energy from a black hole - seeded, as I put it - is by definition not inside a black hole but its own entity, which may be unbounded according to current theory. It is not “inside” anything. The OP has never explained whether seeding is what is being described. It seems not. The claim is that we are inside a black hole. That can’t be true. “Our universe” - the one the OP specifically references - isn’t, as several people have pointed out. Whether it formed from a black hole in another universe or not, we are not “inside” a black hole. Our universe may be unique or it may be one of an infinite number of examples or anywhere in between. I don’t know and made no claim about specialness. ---
**Author:** ![scabpicker](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/scabpicker/32/8268_2.png) [@scabpicker](https://boards.straightdope.com/u/scabpicker)\ **Post date:** [September 24, 2018, 11:15am UTC](https://boards.straightdope.com/t/how-plausible-is-my-pet-theory-that-our-universe-is-inside-a-black-hole/821682/23 "2018-09-24T11:15:01Z")
> [@Exapno\_Mapcase](#): > > The OP has never explained whether seeding is what is being described. It seems not. The claim is that we are inside a black hole. That can’t be true. “Our universe” - the one the OP specifically references - isn’t, as several people have pointed out. Whether it formed from a black hole in another universe or not, we are not “inside” a black hole. Actually, at least in this thread, others are wisely saying we “probably” aren’t inside a black hole. You’re the only person who seems to be certain what’s going on on the other side of a singularity. If you have evidence to back this up, I’d be interested in seeing it. ---
**Author:** ![Exapno\_Mapcase](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/exapno_mapcase/32/1051_2.png) [@Exapno\_Mapcase](https://boards.straightdope.com/u/Exapno_Mapcase)\ **Post date:** [September 24, 2018, 2:43pm UTC](https://boards.straightdope.com/t/how-plausible-is-my-pet-theory-that-our-universe-is-inside-a-black-hole/821682/24 "2018-09-24T14:43:03Z")
> [@scabpicker](#): > > Actually, at least in this thread, others are wisely saying we “probably” aren’t inside a black hole. You’re the only person who seems to be certain what’s going on on the other side of a singularity. If you have evidence to back this up, I’d be interested in seeing it. They are not saying probably. > [@ftg](#): > > Also … > > There’s a simple relationship between the mass of a black hole and it’s size (and therefore it’s density). Years ago I’d sometimes come across a back-of-the envelope calculation as to what the density of an observable universe-sized black hole would be and it turned out to be surprisingly similar to the density of our Universe. > > Then dark matter turned up. Throw in the increase in the rate of expansion of the Universe (probably no Big Crunch) and all that gets thrown out. > [@Chronos](#): > > 20 years ago or so, your idea was _extremely_ plausible, and in fact was one of the three main competing models for the Universe. As **Lemur866** says, a Big Crunch universe is, in every way that matters, the same thing as a black hole. But it wouldn’t have been a black hole resulting from the collapse of a single star; it would have been a black hole resulting from the collapse of _everything_. > > But then dark energy was discovered, which throws a real monkey wrench into everything. ---
**Author:** ![septimus](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/septimus/32/410_2.png) [@septimus](https://boards.straightdope.com/u/septimus)\ **Post date:** [September 24, 2018, 2:50pm UTC](https://boards.straightdope.com/t/how-plausible-is-my-pet-theory-that-our-universe-is-inside-a-black-hole/821682/25 "2018-09-24T14:50:28Z")
With all this talk about peering _inside_ a singularity, perhaps we should recall [the thoughts of Sir Winston Churchill on the topic](https://books.google.co.th/books?id=ooFGl74WbXsC): > [@Winston S. Churchill](#): > > I had a feeling once about Mathematics - that I saw it all. Depth beyond depth was revealed to me - the Byss and Abyss. I saw - as one might see the transit of Venus or even the Lord Mayor’s Show - a quantity passing through infinity and changing its sign from plus to minus. I saw exactly why it happened and why the [tergiversation](http://media.merriam-webster.com/audio/prons/en/us/mp3/t/tergiv04.mp3) was inevitable but it was after dinner and I let it go. ---
**Author:** ![scabpicker](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/scabpicker/32/8268_2.png) [@scabpicker](https://boards.straightdope.com/u/scabpicker)\ **Post date:** [September 25, 2018, 12:35am UTC](https://boards.straightdope.com/t/how-plausible-is-my-pet-theory-that-our-universe-is-inside-a-black-hole/821682/26 "2018-09-25T00:35:57Z")
> [@Exapno\_Mapcase](#): > > They are not saying probably. To me, those are not saying the proposal is impossible. In essence, they’re saying it’s not very likely given what we understand now, and the world would be a strange place if the proposed theory were true - but it could be. And if you are certain of what you are saying, why try to discredit that part of my question? It seems easier to provide your cite, and be done with me. After all, I’m certainly not saying you’re wrong. I’m saying I don’t know how you can claim certainty in your belief. ---
**Author:** ![Exapno\_Mapcase](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/exapno_mapcase/32/1051_2.png) [@Exapno\_Mapcase](https://boards.straightdope.com/u/Exapno_Mapcase)\ **Post date:** [September 25, 2018, 2:52am UTC](https://boards.straightdope.com/t/how-plausible-is-my-pet-theory-that-our-universe-is-inside-a-black-hole/821682/27 "2018-09-25T02:52:44Z")
> [@scabpicker](#): > > To me, those are not saying the proposal is impossible. In essence, they’re saying it’s not very likely given what we understand now, and the world would be a strange place if the proposed theory were true - but it could be. > > And if you are certain of what you are saying, why try to discredit that part of my question? It seems easier to provide your cite, and be done with me. After all, I’m certainly not saying you’re wrong. I’m saying I don’t know how you can claim certainty in your belief. My understanding is that it’s based on simple math. If the amount of mass-energy in the universe is 20 times what was previously thought (which is what you get when you add dark matter and dark energy to normal matter), then the black hole calculation simply doesn’t work. If you don’t like it, take it up with the physicists, two of whom I’ve already cited _because they posted in this thread_. As for your question, I didn’t “discredit it,” I asked you what the hell you were talking about since you put words in my mouth I never said. I’ve never gotten an apology for that either. I’m 100% certain that I never will. Want to prove me wrong about that? ---
**Author:** ![rat\_avatar](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/rat_avatar/32/255_2.png) [@rat\_avatar](https://boards.straightdope.com/u/rat_avatar)\ **Post date:** [September 25, 2018, 3:58am UTC](https://boards.straightdope.com/t/how-plausible-is-my-pet-theory-that-our-universe-is-inside-a-black-hole/821682/28 "2018-09-25T03:58:47Z")
In the real universe, black holes contain probably don’t contain physical singularities that we know of. They would be light-like in a charged rotating one so that will pose a problem too. Physics in general tends to use Perturbation Theory. You start with a simplified problem that you can solve exactly, then you move on to the next “perturbed” or solvable chunk by adding terms then…rinse and repeat as needed. The singularity in a black hole is just the point were the mathematics of a known incomplete theory breaks down. In this case when you reach the “singularity” differential geometry fails and the entire premise of the theory are violated. The theory just cannot make any predictions at that point. At that point there simply is no theory and the GR makes no predictions about physics there. Contrast this with the singularity at the start of time. Penrose-Hawking theories show that the start of time singularity is geometrical and physical, not topological. Another important part here. Observers outside the event horizon will _never_ see the singularity never form even if they could break the rules and see inside. Because from an outside observer it just won’t exist in a finite amount of time. That central point source singularity is a limitation in the current math that will be reach at a finite amount of time for someone who does fall in past the event horizon. Singularities are problems for doing the math and math is the language of physics so they are very real for those who are working on these problems. It is not safe to assume that the singularity is a literal physical things or places or that they are even similar in the challenges they pose. ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [September 25, 2018, 7:03am UTC](https://boards.straightdope.com/t/how-plausible-is-my-pet-theory-that-our-universe-is-inside-a-black-hole/821682/29 "2018-09-25T07:03:10Z")
> [@Moriarty](#): > > … fits with my other non-scientific science theory that the universe is teeming with life, although it is so damn big - or we are so damn small - that we have simply never encountered it. We’re the proverbial ant hill in an abandoned parking lot wondering if there are other ants across the street in the grassy park - dude, ants are everywhere, but how can an ant even begin to conceive of all of those other habitats?) Regardless whether it is inside a black hole or not, our universe is pretty damn big. I agree that the occurrence of life in the universe may be spaced out too thinly in both space and across time, that meeting others may be incredibly unlikely, but I don’t see how this relates to the universe-in-a-black-hole thing. We haven’t even properly explored our own solar system, which is a teeny-tiny speck in the universe we do live in - it’s not as if we are even remotely close to being able to look in all the places in our own universe. ---
**Author:** ![Asympotically\_fat](https://avatars.discourse-cdn.com/v4/letter/a/e47c2d/32.png) [@Asympotically\_fat](https://boards.straightdope.com/u/Asympotically_fat)\ **Post date:** [September 25, 2018, 4:03pm UTC](https://boards.straightdope.com/t/how-plausible-is-my-pet-theory-that-our-universe-is-inside-a-black-hole/821682/30 "2018-09-25T16:03:21Z")
> [@ftg](#): > > Also … > > There’s a simple relationship between the mass of a black hole and it’s size (and therefore it’s density). Years ago I’d sometimes come across a back-of-the envelope calculation as to what the density of an observable universe-sized black hole would be and it turned out to be surprisingly similar to the density of our Universe. > > Then dark matter turned up. Throw in the increase in the rate of expansion of the Universe (probably no Big Crunch) and all that gets thrown out. Trivially, the Schwarzschild radius corresponding to a universe at critical density is the Hubble radius and our Universe is very, very close to critical density (see the ‘flatness problem’). The Hubble ‘horizon’ though is not generally speaking an event horizon, except in two cases: in a critical density radiation-only Universe without a cosmological constant/dark energy, the observable Universe is the same as the Hubble sphere; and in a dark energy-only Universe the Hubble horizon is the same as the cosmological event horizon. Our observable Universe is several times larger than the Hubble sphere (the ‘Schwarzschild radius’ for a critical density universe), however, the cosmological event horizon is only slightly larger than the Hubble sphere as which is related to the fact that dark energy is currently the dominant form of energy in our Universe. The coincidence or non-coincidence of cosmological horizons and the Schwarzschild radius though does not mean the Universe is a black hole: the Schwarzschild solution describes the vacuum around a spherically-symmetric mass and more generally, a black hole only has a precise definition when dealing with a vacuum-surrounded region, and there is no vacuum surrounding our Universe, even approximately. Now there are more advanced ideas that see possible fundamental relationships between our Universe and black holes, but the simple idea that our Universe has some fundamental relationship to a black hole due to its density is always a non-starter. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [September 25, 2018, 8:15pm UTC](https://boards.straightdope.com/t/how-plausible-is-my-pet-theory-that-our-universe-is-inside-a-black-hole/821682/31 "2018-09-25T20:15:52Z")
Dark matter isn’t a problem at all for the idea. Dark matter was certainly known as of when the Big Crunch model was still taken seriously; the difficulty was just that we didn’t know precisely how much of it there was. And there being more of it would be support for the Big Crunch model, not refutation. The problem is dark energy. And even there, we can come up with mathematical descriptions similar to those for black holes, but which include dark energy: That’s the Schwarzschild-de Sitter solution. It’s just not clear whether such an object can meaningfully be described as a “black hole” any more. ---
**Author:** ![scabpicker](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/scabpicker/32/8268_2.png) [@scabpicker](https://boards.straightdope.com/u/scabpicker)\ **Post date:** [September 26, 2018, 1:33am UTC](https://boards.straightdope.com/t/how-plausible-is-my-pet-theory-that-our-universe-is-inside-a-black-hole/821682/32 "2018-09-26T01:33:53Z")
Thank you for clarifying your statement, **Chronos**. Other than I had somehow gotten the idea in my head that the dark matter was [DEL]doing the pushing[/DEL] expanding space (which was cleared up by reading the wiki articles on it and dark energy yesterday), that was largely how I understood it. [Previous page](https://boards.straightdope.com/t/how-plausible-is-my-pet-theory-that-our-universe-is-inside-a-black-hole/821682.md?page=1)