<p>That all depends on how gravity works in your hypothetical universe. Let's imagine a Flatland black hole.</p>
<p>In flatland (a two dimensional world embedded in a three dimensional one) a two dimensional star collapses and forms a black hole.  What happens next?  Well it is at least possible to imagine that in flat land, gravity does not pass out of the 2-d universe into the 3d one. This means that particle in the 3d world could pass through the disc of the 2d black hole. It would only be &quot;in&quot; the black hole for an instant.</p>
<p>It is equally plausible that gravity causes a curvature of the spacetime not only in the the 2-d flatland world, but in the 3d world which contains it.  Then the black hole would appear as a sphere, and a particle in the 3d world could not pass through the disc.</p>
<p>There are string theories with more than 3 dimensions.  But in these theories, we are not like a flatland universe, because the other dimensions are curlled up tighter than a proton.  (You can use the metaphor of a long thin straw:  It looks one dimensional, but the surface of the straw is in fact 2d. It is flat in one direction but highly curved in another)  In such universes the black hole does pass through all dimensions (as does everything else) and you can't escape it by &quot;going up a dimension&quot;.</p>
<p>Even if there was a large flat 4th dimension, that was not affected by gravity, getting into it would be at least as hard as escaping a black hole. Just as a flatlander can't get into the 3d world except with help from that world.</p>

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2021-02-13T10:32:15.513Z
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2021-02-13T20:09:11.327Z
James K
<p>Multidimensional black holes are actually studied, mostly because of theories where there are <a href="https://en.wikipedia.org/wiki/Compactification_(physics)" rel="nofollow noreferrer">extra (usually very small) dimensions</a> or <a href="https://en.wikipedia.org/wiki/Brane_cosmology" rel="nofollow noreferrer">our world is a lower-dimensional brane inside a bulk space</a>. In these cases gravity propagates in the extra dimensions and one cannot escape the black hole by moving at right angles to normal reality.</p>
<p><a href="https://link.springer.com/article/10.12942/lrr-2008-6" rel="nofollow noreferrer">There are a lot of black hole-like solutions in higher dimensions, with very different properties</a>. However, if you have a d-dimensional black hole with some metric <span class="math-container">$ds^2=g^{ij} dx_i dx_j$</span> (<span class="math-container">$0\leq i,j\leq d$</span>) you can always add an extra flat dimension <span class="math-container">$x_{d+1}$</span> that just extends the black hole horizon <span class="math-container">$\Sigma$</span> to <span class="math-container">$\Sigma \times \mathbb{R}$</span>, commonly called a black string. In this case jumping along  <span class="math-container">$x_{d+1}$</span> will not save you. Generally <a href="https://arxiv.org/abs/hep-th/0204005" rel="nofollow noreferrer">higher-dimensional black holes also have trapped surfaces</a>, and are hence inescapable.</p>

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Anders Sandberg
<p>I imagine if there was a 2D black hole on a piece of paper, and something was inside the black hole had access to the 3rd dimension, they could just go &quot;upwards&quot; out of the black hole. Could it be possible, that if there were something, perhaps a particle that was inside a blackhole, escape it by going into the 4th dimension and back into the 3rd dimension elsewhere in space?</p>

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2021-02-13T20:08:24.260Z
Welcome on the Astronomy SE! Note, we are real humans, not some search engine or so. Please honor us by using capital letters and sentences.
peterh
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2021-02-13T20:11:38.350Z
FYI: currently there is nothing, not even a minuscule experimental estimation, for the existence of any 4th space dimension. Most of the current physics formulas could work in any number of dimensions, and general relativity would look much better if our 3d world would be embedded into a higher d one. Side note: the formulas of the General Relativity somehow do not require it.
peterh
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2021-02-13T20:19:21.887Z
I see. I guess i was just wondering how things might work assuming that there does exist a 4th (or higher) dimension. I didn't think that gravity from a black hole (or any object) could reach those higher dimensions as well.
user289602
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2021-02-13T21:17:09.903Z
Gravity decreases quadratically by the distance. This makes likely that it works only in 3D. In a 4d sphere ("4-sphere"), the surface area increases with the third power of the radius, so gravity would likely decrease cubically with the distance. It would have interesting side-effects, for example there would be no stable planetary orbits.
peterh
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2021-02-13T23:27:08.223Z
While it's not a good question for this site, I like your flatland approach to this.   In Flatland, it's impossible for a 2d object to see, much less move into the 3rd dimension.  If we take that approach, then a 3d object couldn't escape a black hole that way, and this is all theoretical. Could a 4 dimensional being reach inside a black hole and pick something out of it . . . That's getting into the theoretical and hypothetical quite a bit.  Fun idea, but no real answer.
userLTK
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2021-02-15T23:41:36.743Z
I’m voting to close this question because it's about an imaginary/hypothetical 4th spatial dimension inconsistent with mainstream physics, and is therefore off-topic.
Chappo Hasn't Forgotten
<black-hole>
Can you escape a black hole by going into another (4th) dimension?
user289602
# Can you escape a black hole by going into another (4th) dimension?

(Asked by: username_0 on 2021-02-13)

I imagine if there was a 2D black hole on a piece of paper, and something was inside the black hole had access to the 3rd dimension, they could just go "upwards" out of the black hole. Could it be possible, that if there were something, perhaps a particle that was inside a blackhole, escape it by going into the 4th dimension and back into the 3rd dimension elsewhere in space?

**Tags:** black-hole

> **Comments:**
> **username_1**: Welcome on the Astronomy SE! Note, we are real humans, not some search engine or so. Please honor us by using capital letters and sentences.  
> **username_1**: FYI: currently there is nothing, not even a minuscule experimental estimation, for the existence of any 4th space dimension. Most of the current physics formulas could work in any number of dimensions, and general relativity would look much better if our 3d world would be embedded into a higher d one. Side note: the formulas of the General Relativity somehow do not require it.  
> **username_0**: I see. I guess i was just wondering how things might work assuming that there does exist a 4th (or higher) dimension. I didn't think that gravity from a black hole (or any object) could reach those higher dimensions as well.  
> **username_1**: Gravity decreases quadratically by the distance. This makes likely that it works only in 3D. In a 4d sphere ("4-sphere"), the surface area increases with the third power of the radius, so gravity would likely decrease cubically with the distance. It would have interesting side-effects, for example there would be no stable planetary orbits.  
> **username_2**: While it's not a good question for this site, I like your flatland approach to this.   In Flatland, it's impossible for a 2d object to see, much less move into the 3rd dimension.  If we take that approach, then a 3d object couldn't escape a black hole that way, and this is all theoretical. Could a 4 dimensional being reach inside a black hole and pick something out of it . . . That's getting into the theoretical and hypothetical quite a bit.  Fun idea, but no real answer.  
> **username_3**: I’m voting to close this question because it's about an imaginary/hypothetical 4th spatial dimension inconsistent with mainstream physics, and is therefore off-topic.  

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## 2 answers

### Answer by username_4 on 2021-02-13. Score: 2 | Accepted answer

That all depends on how gravity works in your hypothetical universe. Let's imagine a Flatland black hole.

In flatland (a two dimensional world embedded in a three dimensional one) a two dimensional star collapses and forms a black hole. What happens next? Well it is at least possible to imagine that in flat land, gravity does not pass out of the 2-d universe into the 3d one. This means that particle in the 3d world could pass through the disc of the 2d black hole. It would only be "in" the black hole for an instant.

It is equally plausible that gravity causes a curvature of the spacetime not only in the the 2-d flatland world, but in the 3d world which contains it. Then the black hole would appear as a sphere, and a particle in the 3d world could not pass through the disc.

There are string theories with more than 3 dimensions. But in these theories, we are not like a flatland universe, because the other dimensions are curlled up tighter than a proton. (You can use the metaphor of a long thin straw: It looks one dimensional, but the surface of the straw is in fact 2d. It is flat in one direction but highly curved in another) In such universes the black hole does pass through all dimensions (as does everything else) and you can't escape it by "going up a dimension".

Even if there was a large flat 4th dimension, that was not affected by gravity, getting into it would be at least as hard as escaping a black hole. Just as a flatlander can't get into the 3d world except with help from that world.


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### Answer by username_5 on 2021-02-13. Score: 2

Multidimensional black holes are actually studied, mostly because of theories where there are [extra (usually very small) dimensions](https://en.wikipedia.org/wiki/Compactification_(physics)) or [our world is a lower-dimensional brane inside a bulk space](https://en.wikipedia.org/wiki/Brane_cosmology). In these cases gravity propagates in the extra dimensions and one cannot escape the black hole by moving at right angles to normal reality.

[There are a lot of black hole-like solutions in higher dimensions, with very different properties](https://link.springer.com/article/10.12942/lrr-2008-6). However, if you have a d-dimensional black hole with some metric $ds^2=g^{ij} dx\_i dx\_j$ ($0\leq i,j\leq d$) you can always add an extra flat dimension $x\_{d+1}$ that just extends the black hole horizon $\Sigma$ to $\Sigma \times \mathbb{R}$, commonly called a black string. In this case jumping along $x\_{d+1}$ will not save you. Generally [higher-dimensional black holes also have trapped surfaces](https://arxiv.org/abs/hep-th/0204005), and are hence inescapable.


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