# Is our universe included inside a black hole? [duplicate]

This question repetitively comes to my mind but I've never found any good scientist article to argue about it, only esoteric or speculative web articles without much valuable background.

So let's suppose we're in the middle of a "black hole" ...

To me, here is why this would make sense:

• Big bang

The word big bang itself may be inapproriate, indeed it is said to be an "explosion" but an "explosion" without any center.

With the idea of being inside a black-hole, it is easier to represent this as being the matter entering the black-hole. From our position, and as we are attracted by the singularity, everything seems to expand wherever we look at. And as far as we can look at, we can only see the cosmic background radiation.

• Dark matter

On the contrary of matter entering the black-hole, dark matter is the matter already in front of us and we'll never be able to access it as its light (i.e. information) cannot go backward within the singularity.

• Time/Gravitation

Time is a dimension like any other and as we feel x,y,z dimensions as a field of view, we fell time as an irrepressible attraction toward the singularity. Gravity may be see also as a less irrepressible dimension (depending on mass around).

• Other black holes

Other black-hole we "see" may let us envision the shape of the universe not as simple torus, but higher dimensional "toric" shape with "connections" everywhere (maybe shapes like high order atomic orbitals ?).

• – HDE 226868 Jun 6 '15 at 17:23
• I think at least the "dark matter" and "time/gravitation" parts are cloudy. – peterh Oct 10 '20 at 19:55

There's a lot to pick apart in everything you try to propose, as it includes a lot of far fetched (or at least rather non-standard) claims. I am frankly not up to attempting to address every one of them, if for no other reason than that it makes the question as a whole rather too broad for my taste (and perhaps more in the territory of Physics.SE, which has quite a lot of answered questions concerning black holes).

There is, however, the following simple and amusing observation: current estimates of the mass-energy of the observable universe tell us that it is too dense to be a black hole. That might sound a little weird if you're not familiar with black holes. In fact, the density of a (non-rotating, Schwarzchild) blackhole is inversely proportional to the square of its mass, and the radius is directly proportional to the mass. More explicitly: $$r=\frac{2 G M}{c^2},$$ $$\rho(M) = \frac{3 c^6}{32 \pi G^3}\cdot \frac{1}{M^2},$$ where $r$ is the radius, $\rho$ is the density, $M$ is the mass, $c$ is the speed of light, and $G$ is the gravity constant.

The order of magnitude estimate for $M$ is $10^{54}$ (and $M\geq 10^{54}$ in particular), which makes the universe ~3 times too small at least.

A key fact here is that the universe is not static with respect to itself. See this Physics.SE Q&A in particular. I'll quote the end of Lubos Motl's answer, in particular:

Our Universe, dominated by the dark energy, is already rather close to an empty de Sitter space which is, from many viewpoints, analogous to a black hole except that the interior of the visible part of the de Sitter space is analogous to the exterior of a normal black hole, and the analogy of the interior of a black hole is everything that is behind the cosmic horizon - where we don't see. It is misleading to create the analogy with the static black holes directly because our Universe is not static in the normal cosmological coordinates.

In other words, there are lots of important and sometimes subtle issues with the whole "the universe is a black hole" concept.

No, since any matter inside a black hole will not be in a stable solid state. This happens because the gravitational force at the inside of a black hole is huge and powerful, because it's formed by the collapse of a star under its own mass.

So say for your question there might have been a immensely huge supernova, which became a black hole. In turn, the Big Bang happened to form our universe. Would not that be reverting the black hole laws?

• Actually not, the density of a black hole may be smaller than our own Universe's. It has a huge gravitational pull on the outside, but not necessarily inside (just like the gravitational pull on the center of a star would be zero). – Rodrigo Mar 9 '18 at 0:15
• @Benjamin That's a question with 2 different answers. What exactly is your point? – Rodrigo Aug 21 '19 at 23:59
• @Rodrigo That black holes always collapse into a singularity. Within the event horizon all of the geodesics point inexorably toward the singularity so our universe cannot be a black hole because it's not a singularity. – SurpriseDog Aug 22 '19 at 0:28
• @Benjamin That's not what one of the answers say. – Rodrigo Aug 22 '19 at 1:47