“Man is something that shall be overcome. Man is a rope,tied between beast and overman - a rope over an abyss.What is great in man is that he is a bridge and not an end.” -Friedrich Nietzsche

There are only two types of singularities that General Relativity predicts the existence of in our Universe: one at the centers of black holes, which form from the collapse of matter, and one at the very birth of space and time, at the origin of it all. All of the information that falls into a black hole from our 3D Universe gets encoded on the black hole’s 2D event horizon, which is both fascinating and one of the main components of the black hole information paradox.

But it makes one wonder, with a little creative thinking, whether our 3D Universe didn’t result from the formation of a much more massive black hole in higher-dimensional space? Although the idea sounds a little bit out there, there’s a lot of theoretical reasons to believe this might be legitimate. And the closer we get to quantum gravity, the closer we get to testing whether this might actually reflect our reality.

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So if this theory holds water: An N dimensional universe which creates blackholes, creates N-1 dimensional universes.

So perhaps the 4D universe was in turn created by a 5-D universe/BH?

I've always loved this idea, but I know that I had first heard about it farther back than 2014. For instance here is a paper from Indiana University's Nikodem J. Poplawski discussing it in 2010 and I know there have been more since then. What is it about Afshordi, Pourhasan and Mann that make them the founders of the idea in 2014?

https://arxiv.org/abs/1007.0587

@Denier #2/#3: They are different ideas. Poplawski's 2010 paper is specifically in conventional 4D GR, and makes an argument for how to avoid a singularity by way of a minimum radius "bounce."

The paper Ethan is discussing makes use of the same sort of ideas as those behind the "holographic principle," projecting the behaviour of an N-dimensional spacetime into N-1 dimensions.

This sounds like a Liu Cixin novel. In "The Three-Body Problem" trilogy something very similar is a major plot point of the third book whose translation came out last month.

If our universe is the event horizon of a 4d BH, what happens if "our" BH merges with another 4D BH? Are there any observable effects? Would they be catastrophic? Would merger activity show up as something like dark energy?

I still haven't read the paper, but reading the article, the first thought I got is that this might end up like "turtles all the way down". If we assume that this is true, the question comes up of how did the BH in +1 dimension come to be in the first place? Is there a 5d universe that needed to begin and evolve to the point of having 5d BHs in order for one to create our 4d universe? Then before that a 6d one to create a 5d one to create a 4d one to create a 3d one?

In other words, this has the same problem that we use for god argument. What created a BH in higher dimension in the first place?

@ Ethan . in your article.. this sentence: "If you were to take a photon’s wavelength and convert it into mass, via Einstein’s E = mc2, you’d get a massive particle’s Compton wavelength."

one IMO important part was left out. Photon's energy needs to be the same as rest energy of the massive particle that you are interested in.. then the transformation makes sense. Without that part, it's a bit ambiguous.

Glossed over their paper just now

https://arxiv.org/abs/1309.1487

what is strange to me, is they focus so much on weather you can do this in GR, that they don't even notice that they just created a new universe which had to evolve for at least half a billion years (and obey same laws of physics as our own, just has more spatial dimensions).. in order to reach a starting point for our BB out of some BH in that universe.

so it doesn't do anything really to answer how universe came to be... it really is turtles all the way down.. but in this sense it's turtles all around.. since every BH in any universe will create a -1 dimension holographic universe. talk about a mess :D

1. If this is true, shouldn't we be able to look at the event horizon of a BH in our space and watch the development of 2-D singularities on it, producing 1-D universes as their event horizons? Or does geometry prevent the density from reaching BH levels?

2. If so, wouldn't those 1-D ring event horizons around the 2-D holes (sitting on the horizon of a 3-D BH) contain yet another copy of the subset of particles that fall into the 3-D BH and then into the 2D BH within it?

3. OTOH if geometry prevents the formation of any more derivative BHs in lower dimensional space, this might also mean that geometry impacts the ability of higher dimensional spaces to create the same stable BH phenomena. In which case, maybe not turtles all the way down.

@ eric

re #3 .. that might be, but it still leaves the elephant in the room. Namely, that the focus is now just shifted to a new universe with the same un-answered question of how it came to be. just not our 4d universe but a 5d universe in who's BH we are and which is clearly older than 13.7 b.y.

@11: well agreed that it doesn't really answer 'origin of everything.' However, if 2-D black holes are geometrically possible, then we can at least test this theory with observation. We look at BH event horizons. If we see anomalies consistent with a 2-D BH, then I would take that as pretty confirming evidence that our 3-D space could be the event horizon of a 4-D BH. At that point the work has gone from "interesting idea that's hypothetically possible" to "we should start taking this seriously and see what else it implies."

Another thing I find fascinating about the idea is: what does a 2-D BH on a 3-D event horizon look like? Does our extra dimensionality allow us to see past its event horizon (technically, I guess, we are looking "sideways" not "past")? If so, does looking at the inner workings of a 2-D BH help us understand the inner workings of a 3-D BH? And if it

does, does it also lead to testable ideas about any higher-dimensional BH we might be part of?Mitosis of the universe…… Think of space as a living organism internally populated with each individual universe representing cells and those cells undergoing cell division. There are temporary connections between one universe and the next but this connection is severed once the universe matures. Once the “offspring” universe have matured further, they will also divide through what we perceive as black holes and begin there mitosis.

@ eric

" what does a 2-D BH on a 3-D event horizon look like?.."

I would venture and say (since it's the swartzschild solution.. meaning spherical and symmetrical).. that in 2D it's a circle :)

What about the holographic principle? Does that idea enter into this? I'm just an interested by-stander, not a theoretical physicist. But I've read a lot of interesting stuff on the notion of a potential equivalence between a 2-D world following quantum dynamics and a 3-D world subject to gravity. IIRC, the celebrated AdS/CFT correspondence was a clue that there might be a holographic equivalence even in deSitter space. So, here's my stupid wild-assed guess question -- could the 2-dimentional thing being born from the 3-D black hole just be the holographic "blueprint" for a 3-D world with gravity, pretty much like our universe?

@14: well yeah, I'd expect the perimeter to be circular. I meant: what does the

insidelook like? Because we should be able to see it.If it's on the event horizon, I don't think we could see it.

re 16

Am not sure we would be able to see inside, since it's still a black hole. I don't think there are light cones that can come from it to us if you look at a solution for a far away observer. If you are there close by, then maybe.

It's only a black hole in two dimensions, but we are looking at it "top down" from the third dimension. There is no event horizon in the third dimension because its a 2-D object, so why wouldn't we be able to see into it? And since we are talking about a phenomena

onthe event horizon of a 3-D BH, not somethinginit, it should be just as observable as your standard infalling object that appears to our external view to be 'stuck' on the event horizon.Or was your point that we are not technologically advanced to see those images of infalling objects yet? I agree there. We have the fairly insurmountable engineering challenges of (1) travel to BH and (2) set up observatory around it before we could try the experiment. But if we ever accomplish 1-2, I would certainly suggest we spend some telescope time looking for 2-D BHs on the surface...and looking inside the circular (not spherical) boundary that describes their event horizons if we find them.

@ eric

"It’s only a black hole in two dimensions,"

sorry, then we were talking about different things. I am thinking about the paper and article where n-dimensional BH creates a (n-1)-dimensional universe. Not a BH on a horizon of a higher dimensional BH. So in an example above I was thinking of a 2D universe being made within 3D BH... and I was thinking that view of that 2D would be obstructed by the 3D BH.

Don't know how we would have a 2d bh on a horizon of a 3d BH. If gravity works in all dimensions, then 2d BH would end up inside 3D one, assuming 3D one is larger.

I think we're close. I'm talking about the 2-D preserved information on the surface of a 3-D BH. Using the original article's logic, that is a "universe" which could have 2-D BH's in it. If so, they should be accessible to our observation just like a frozen image of infalling matter should be accessible to our observation. In that 2-D universe, the 2-D BH's event horizon is an observationally impassible barrier. But we don't look through that barrier from our 3-D perspective; we look down into the 2-D BH the same way we can look down on the inside of a circle inscribed on the surface of a sphere.

" I’m talking about the 2-D preserved information on the surface of a 3-D BH..."

but here's the thing. There is no "surface" of the BH as such. "Physical" surface... if it exists, is well inside the event horizon. Event horizon as such is not a physical thing since it depends on the coordinate frame you choose. That's why I said that if you choose the reference frame for a far away observer and look at that event horizon. You wouldn't see anything. Not because of technology, but because photons coming from it are infinitely red shifted.

I was referring to what Ethan says here (emphasis in the original):

A 2-D BH

onthe boundary should be just as visible to us as anything elseonthe boundary. But for us it would be a particularly interesting phenomenon because we could see past its event horizon because we're higher dimensional (compared to it).Maybe Ethan's wrong about the boundary being visible at all? I'll admit that for my posts I assumed that what Ethan said above was true.

Don't think that Ethan is wrong, but think that it's the interpretation of what was written. We can calculate what happens at the event horizon yes, but that doesn't mean we can see it, nor does it mean that it actually happens. We still have very little observational verification to most of what we think happens at/in/around BH's. But that aside, one important distinction IMO is between two things that we mentioned.. one is an object falling into the BH (the text you quoted from Ethan), and the hypothetical 2d universe which is created from the 3d black hole's singularity. In the first case you do see the object in our universe emitting photons to you as it approaches the BH... and you (as a far away observer) see it's clock slowing down and photons from it getting redshifted more and more until you see a "shadow" frozen in time of the object that fell into the BH. The area of spacetime just beyond those "shadows" is what we call event horizon. But it's not a physical thing.... it's like Bermuda triangle... just a name for the set of coordinates.

In the second case... that new object (a 2d universe.. or a 2d black hole in your case)... gets created from within the BH.. it might be projected to the event horizon.. but it's projected inverted (so to say) in reference to us. Meaning no photons from it will ever reach you, because they are causally disconected from the stuff beyond their event horizon. It's like a world within the BH's horizon.