<p>Semantics:  Some answers are saying &quot;no&quot; by definition since &quot;universe&quot; means everything, including multiple different parts of a larger existence.  However, that's not how the term is currently used and not how the question means it.  &quot;Universe&quot; is a domain with spacetime as we see it, and a <em>different</em> such domain would be a different universe, as in the video referenced.</p>
<p>The answer, and whether the questions is even meaningful at all, depends on the model of cosmology you are using.</p>
<hr />
<p>The question may be meaningless if different universes are totally separate and are not part of a larger structure that itself has space-like properties where things can move around, grow, and take up room.</p>
<p>One example of this is <a href="https://en.wikipedia.org/wiki/Cosmological_natural_selection" rel="noreferrer">Cosmological Natural Selection</a>.  Each daughter universe is in a different spacetime than the parent's, disconnected from it.  They are just <em>different</em>, not locations in a larger space that has coordinates.</p>
<hr />
<p>Different Big Bang universes are not separated by ordinary space; the BB takes up <em>all</em> the space.  However, the <a href="https://en.wikipedia.org/wiki/Eternal_inflation" rel="noreferrer">Eternal Inflation</a> model would have it that there is a different state of vacuum (space-time) that is inflating at a much faster rate, and when it decays at some point to <em>our</em> vacuum then that point grows outward at a slower rate.  Now the &quot;outside&quot; containing these bubble universes has a <em>different interpretation</em> of what is space and time dimensions than the bubble's spacetime inside a bubble.  But they are connected in a meaningful way.</p>
<p>These bubbles are growing at a much slower rate than the space between them, so they could never collide.</p>
<hr />
<p>A <a href="https://en.wikipedia.org/wiki/Brane_cosmology" rel="noreferrer">Braneworld</a> theory is that our 4D spacetime is structure that exists in higher dimensions, and other such &quot;branes&quot; also exist and they are floating around and might possibly come into contact.</p>
<p>The <a href="https://en.wikipedia.org/wiki/Ekpyrotic_universe" rel="noreferrer">Cyclic Ekpyrotic Universe</a> model <em>relies</em> on that, where two parallel branes (one of them being our universe) collide and bounce off each other, explaining the Big Bang (the collision) and Dark Energy (attraction between the two branes).</p>
<hr />
<p>Other models would have other answers, and different meanings for what such a collision actually represents.</p>

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2021-10-04T16:57:07.960Z
2021-10-04T17:05:35.733Z
2021-10-04T17:05:35.733Z
JDługosz
<p>Roger Penrose has posited that hot spots in the CMB are relics of  an &quot;earlier&quot; Universe.  Not widely accepted, perhaps, but he's an eccentric genius, not a quack. <a href="https://physicsworld.com/a/new-evidence-for-cyclic-universe-claimed-by-roger-penrose-and-colleagues/" rel="noreferrer">https://physicsworld.com/a/new-evidence-for-cyclic-universe-claimed-by-roger-penrose-and-colleagues/</a></p>
<p>It also bears mentioning that Brane Theory is a prominent feature of String Theory.  In (highly-simplified) Brane Theory our universe is resident upon, or is, a membrane (Brane) &quot;floating&quot; around in a higher geometry, along with other, perhaps infinitely other, Branes.  (As James K. says, &quot;floating&quot; is the least-worst visualization).  Collisions between Branes can, in Brane Theory, be responsible for Inflation, the perceived weakness of gravity and the creation of entire new universes.  <a href="https://www.nature.com/articles/news.2007.399" rel="noreferrer">https://www.nature.com/articles/news.2007.399</a></p>
<p>Some question whether String and Brane Theories are theories at all, because they appear to be untestable. Others believe that Inflation, for instance, will cause String-scale effects to be inflated to universe-scale effects, and so detected.</p>
<p>There are others here, fortunately, who can give a better take on these issues than I can, but there are, certainly, open lines of inquiry that are trying to address your question.</p>

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2021-10-03T18:16:32.293Z
2021-10-04T01:49:10.593Z
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JohnHunt
<p>This is difficult because we can only easily visualise 3D and space - the known universe we live in. Mathematically there could be any number - or an infinity - of universes, but they aren't parallel in an everyday sense. Maybe &quot;coexisting&quot; is a better word.</p>
<p>Cosmologists use the expression &quot;the universe&quot; to mean all of time and space, and all they contain. So by definition there isn't any space outside space, nor any time outside time.</p>
<p>So these parallel universes don't coexist like ink spreading out on blotting paper, that can overlap and collide.</p>
<p>The image you want is that they somehow coexist, if there is more than one, in multiple dimensions, each the only time and space in that dimension, each containing <strong>all</strong> the time and space in that dimension. They don't &quot;collide&quot;, or at least don't collide in any sense we usually use the word.</p>
<p>This is quite possible, but extremely hard to imagine.</p>

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2021-10-03T19:07:45.853Z
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Stilez
<p>The Universe <em>is</em> space and time.  If there are other universes they can't be &quot;next to&quot; ours, as &quot;next to&quot; is a statement about the relationship between things <em>in</em> space, and the Universe is not in space. It <em>is</em> space.</p>
<p>You can't have two universes colliding at a particular time, because time is a property of the universe.</p>
<p>Your mental image of universes as spherical bubbles floating in space is wrong. Unfortunately, there isn't a better visual image. The notion of being outside the Universe and looking at it seems to be fundamentally impossible, because &quot;outside&quot; is a property of space, and space only exists inside a universe.</p>
<p>The last part of the video does show &quot;bubbles floating in space&quot; but this is not intended to be a representation of the multiverse (if it exists) but a metaphorical symbolisation of it. It is something that is fundamentally unknown and unknowable. It is beyond our ability to visualise in a realistic way, so it must be visualised in an unrealistic way.</p>
<p>This is, at least, our best guess.  In fact questions of &quot;outside the universe&quot; are unanswerable.  If we could know about something outside the universe, then it wouldn't be outside, it would be part of our universe.</p>
<p>So ultimately, Mick is right: Nobody knows.</p>

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2021-10-03T20:04:54.537Z
Universes (as plural of Universe) need to exist in a higher dimensional space, otherwise we'd talk about our own universe. If there was a higher dimensional space, we couldn't (yet) tell if we're close to another "3,5d-universe". So there is no physics based answer to this question to me.

Either the question is wrong or your answer is wrong, it seems to me. But i'd love to be corrected :)
Alex B
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2021-10-03T20:12:26.397Z
Or to put it another way: suppose there are two 2-dimensional universes, but their x/y plane is tilted 45° in 3d space. They definitely could collide, but neither could understand from the 2d point of view what's happening. To me, this is the gist of the question.
Alex B
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2021-10-03T20:32:28.267Z
Just imagine the 2d scenario. You have two slices of 2d universes tilted in 3d space, and intersecting.
Alex B
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2021-10-03T22:25:57.383Z
@AlexB That's not two 2d universes, it's one 3d universe with two 2d planes inside it. The point this answer makes is that space is a property of the universe. In your scenario you can't describe your two planes without using co-ordinates from your 3d space.
JBentley
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2021-10-04T16:58:00.340Z
"The notion of being outside the Universe and looking at it seems to be fundamentally impossible,"  Isn't that what Anti-DeSitter Space is _for_?
JDługosz
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2021-10-04T20:52:23.167Z
@JBentley If there were not just one universe, but more, the term universe would be wrong from the start. And if there were more, the correct term would be multiverse. If we'd be living in one of multiple universes, there needs to be a separation amongst them. I follow science closely, but I'm not a physicist, but where don't you agree that multiple "universes" need to be separated by currently unknown dimensions(1), *if they would exist*?

(1) dimension as another free parameter, not necessarily in the sense of 2d/3d/4d
Alex B
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2021-10-04T21:54:32.587Z
No, because your language is spacial ("separated") and temporal ("from the start", "exist" (in the present tense))  Of course your language is spacial and temporal.  All languages are!  You can't talk about any of this, because human language is fundamentally incapable of not using spacial and temporal expressions.  As an exercise, try to imagine a topological circle S¹ without imagining the space around it.  It can be described mathematically, but we can't imagine it, nor can we visualise it. We can't describe what such a circle is like, our language is not up to the task.
James K
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2021-10-06T10:41:18.067Z
Except if we assume consciousness is outside space and time, thus it can perceive such disconnected universes in case it is capable of dis-identifying itself with physical senses. We are going in the domain of yoga ;)
akostadinov
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2021-10-02T23:11:21.163Z
2021-10-03T14:45:40.277Z
2021-10-03T14:45:40.277Z
James K
<p>I just watched one of those videos that shows the scale of the universe, zooming out from one thing all the way out to the sphere that is thought to be the universe. However, they also showed other universes outside our own, and they made it seem like a universe is right next to others in space. I have often heard that our universe is expanding, so I just want to ask: What would happen if one universe expanded enough to collide with another, and what would this look like from inside one of the universes?</p>
<p>Source: <div class="youtube-embed"><div>
                <iframe width="640px" height="395px" src="https://www.youtube.com/embed/kLcrBXl37BQ?start=0"></iframe>
            </div></div></p>

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2021-10-02T22:32:40.810Z
It will be great if you include the link to the video you've mentioned. There may be some factual errors, omissions, or ambiguities in it that need to be pointed out. It's not like there are multiple universes *in space* that can expand, touch, and overlap. If it was explained that way, it was probably a misleading picture.
uhoh
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2021-10-02T22:41:06.257Z
Short answer: no one knows.
Mick
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2021-10-03T04:00:24.870Z
So sorry for the late response: here's the video.
Margorp13
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2021-10-03T04:00:28.350Z
https://www.youtube.com/watch?v=kLcrBXl37BQ
Margorp13
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2021-10-03T09:21:55.047Z
[The universe is probably infinite](https://astronomy.stackexchange.com/a/31795/16685). But even if it is infinite, there could still be other universes.
PM 2Ring
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2021-10-03T11:58:01.713Z
Thanks for the link!
uhoh
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2021-10-04T09:38:25.820Z
The spheres you have in mind are the visibile and the observable Universe. Actually beyond them there is still our Universe. According to current knowledge it goes far far away, perhaps it is infinite. There might be other universes but they should not be out there. They should be other universes in their own spaces.
Alchimista
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2024-07-04T06:17:00.273Z
Actually if you imagine that we live inside an atom, nothing exists outside the atom. This is our universe everything we know exists inside it. So if we can broaden our minds and that outside of our universe is an other type of matter that we have not yet discovered. So the possibility of other universes makes everything infinite. No beginning, no end.
chris fraser
<universe>
Will there be collision between universes?
Margorp13
# Will there be collision between universes?

(Asked by: username_0 on 2021-10-02)

I just watched one of those videos that shows the scale of the universe, zooming out from one thing all the way out to the sphere that is thought to be the universe. However, they also showed other universes outside our own, and they made it seem like a universe is right next to others in space. I have often heard that our universe is expanding, so I just want to ask: What would happen if one universe expanded enough to collide with another, and what would this look like from inside one of the universes?

Source:

**Tags:** universe

> **Comments:**
> **username_1**: It will be great if you include the link to the video you've mentioned. There may be some factual errors, omissions, or ambiguities in it that need to be pointed out. It's not like there are multiple universes *in space* that can expand, touch, and overlap. If it was explained that way, it was probably a misleading picture.  
> **username_2**: Short answer: no one knows.  
> **username_0**: So sorry for the late response: here's the video.  
> **username_0**: https://www.youtube.com/watch?v=kLcrBXl37BQ  
> **username_3**: [The universe is probably infinite](https://astronomy.stackexchange.com/a/31795/16685). But even if it is infinite, there could still be other universes.  
> **username_1**: Thanks for the link!  
> **username_4**: The spheres you have in mind are the visibile and the observable Universe. Actually beyond them there is still our Universe. According to current knowledge it goes far far away, perhaps it is infinite. There might be other universes but they should not be out there. They should be other universes in their own spaces.  
> **username_5**: Actually if you imagine that we live inside an atom, nothing exists outside the atom. This is our universe everything we know exists inside it. So if we can broaden our minds and that outside of our universe is an other type of matter that we have not yet discovered. So the possibility of other universes makes everything infinite. No beginning, no end.  

---

## 4 answers

### Answer by username_9 on 2021-10-02. Score: 60 | Accepted answer

The Universe *is* space and time. If there are other universes they can't be "next to" ours, as "next to" is a statement about the relationship between things *in* space, and the Universe is not in space. It *is* space.

You can't have two universes colliding at a particular time, because time is a property of the universe.

Your mental image of universes as spherical bubbles floating in space is wrong. Unfortunately, there isn't a better visual image. The notion of being outside the Universe and looking at it seems to be fundamentally impossible, because "outside" is a property of space, and space only exists inside a universe.

The last part of the video does show "bubbles floating in space" but this is not intended to be a representation of the multiverse (if it exists) but a metaphorical symbolisation of it. It is something that is fundamentally unknown and unknowable. It is beyond our ability to visualise in a realistic way, so it must be visualised in an unrealistic way.

This is, at least, our best guess. In fact questions of "outside the universe" are unanswerable. If we could know about something outside the universe, then it wouldn't be outside, it would be part of our universe.

So ultimately, username_2 is right: Nobody knows.

> **Comments:**
> **username_10**: Universes (as plural of Universe) need to exist in a higher dimensional space, otherwise we'd talk about our own universe. If there was a higher dimensional space, we couldn't (yet) tell if we're close to another "3,5d-universe". So there is no physics based answer to this question to me.  Either the question is wrong or your answer is wrong, it seems to me. But i'd love to be corrected :)  
> **username_10**: Or to put it another way: suppose there are two 2-dimensional universes, but their x/y plane is tilted 45° in 3d space. They definitely could collide, but neither could understand from the 2d point of view what's happening. To me, this is the gist of the question.  
> **username_10**: Just imagine the 2d scenario. You have two slices of 2d universes tilted in 3d space, and intersecting.  
> **username_11**: @AlexB That's not two 2d universes, it's one 3d universe with two 2d planes inside it. The point this answer makes is that space is a property of the universe. In your scenario you can't describe your two planes without using co-ordinates from your 3d space.  
> **username_6**: "The notion of being outside the Universe and looking at it seems to be fundamentally impossible,"  Isn't that what Anti-DeSitter Space is _for_?  
> **username_10**: @username_11 If there were not just one universe, but more, the term universe would be wrong from the start. And if there were more, the correct term would be multiverse. If we'd be living in one of multiple universes, there needs to be a separation amongst them. I follow science closely, but I'm not a physicist, but where don't you agree that multiple "universes" need to be separated by currently unknown dimensions(1), *if they would exist*?  (1) dimension as another free parameter, not necessarily in the sense of 2d/3d/4d  
> **username_9**: No, because your language is spacial ("separated") and temporal ("from the start", "exist" (in the present tense))  Of course your language is spacial and temporal.  All languages are!  You can't talk about any of this, because human language is fundamentally incapable of not using spacial and temporal expressions.  As an exercise, try to imagine a topological circle S¹ without imagining the space around it.  It can be described mathematically, but we can't imagine it, nor can we visualise it. We can't describe what such a circle is like, our language is not up to the task.  
> **username_12**: Except if we assume consciousness is outside space and time, thus it can perceive such disconnected universes in case it is capable of dis-identifying itself with physical senses. We are going in the domain of yoga ;)  

---

### Answer by username_6 on 2021-10-04. Score: 10

Semantics: Some answers are saying "no" by definition since "universe" means everything, including multiple different parts of a larger existence. However, that's not how the term is currently used and not how the question means it. "Universe" is a domain with spacetime as we see it, and a *different* such domain would be a different universe, as in the video referenced.

The answer, and whether the questions is even meaningful at all, depends on the model of cosmology you are using.

---

The question may be meaningless if different universes are totally separate and are not part of a larger structure that itself has space-like properties where things can move around, grow, and take up room.

One example of this is [Cosmological Natural Selection](https://en.wikipedia.org/wiki/Cosmological_natural_selection). Each daughter universe is in a different spacetime than the parent's, disconnected from it. They are just *different*, not locations in a larger space that has coordinates.

---

Different Big Bang universes are not separated by ordinary space; the BB takes up *all* the space. However, the [Eternal Inflation](https://en.wikipedia.org/wiki/Eternal_inflation) model would have it that there is a different state of vacuum (space-time) that is inflating at a much faster rate, and when it decays at some point to *our* vacuum then that point grows outward at a slower rate. Now the "outside" containing these bubble universes has a *different interpretation* of what is space and time dimensions than the bubble's spacetime inside a bubble. But they are connected in a meaningful way.

These bubbles are growing at a much slower rate than the space between them, so they could never collide.

---

A [Braneworld](https://en.wikipedia.org/wiki/Brane_cosmology) theory is that our 4D spacetime is structure that exists in higher dimensions, and other such "branes" also exist and they are floating around and might possibly come into contact.

The [Cyclic Ekpyrotic Universe](https://en.wikipedia.org/wiki/Ekpyrotic_universe) model *relies* on that, where two parallel branes (one of them being our universe) collide and bounce off each other, explaining the Big Bang (the collision) and Dark Energy (attraction between the two branes).

---

Other models would have other answers, and different meanings for what such a collision actually represents.


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### Answer by username_7 on 2021-10-03. Score: 8

Roger Penrose has posited that hot spots in the CMB are relics of an "earlier" Universe. Not widely accepted, perhaps, but he's an eccentric genius, not a quack. <https://physicsworld.com/a/new-evidence-for-cyclic-universe-claimed-by-roger-penrose-and-colleagues/>

It also bears mentioning that Brane Theory is a prominent feature of String Theory. In (highly-simplified) Brane Theory our universe is resident upon, or is, a membrane (Brane) "floating" around in a higher geometry, along with other, perhaps infinitely other, Branes. (As username_9. says, "floating" is the least-worst visualization). Collisions between Branes can, in Brane Theory, be responsible for Inflation, the perceived weakness of gravity and the creation of entire new universes. <https://www.nature.com/articles/news.2007.399>

Some question whether String and Brane Theories are theories at all, because they appear to be untestable. Others believe that Inflation, for instance, will cause String-scale effects to be inflated to universe-scale effects, and so detected.

There are others here, fortunately, who can give a better take on these issues than I can, but there are, certainly, open lines of inquiry that are trying to address your question.


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### Answer by username_8 on 2021-10-03. Score: 2

This is difficult because we can only easily visualise 3D and space - the known universe we live in. Mathematically there could be any number - or an infinity - of universes, but they aren't parallel in an everyday sense. Maybe "coexisting" is a better word.

Cosmologists use the expression "the universe" to mean all of time and space, and all they contain. So by definition there isn't any space outside space, nor any time outside time.

So these parallel universes don't coexist like ink spreading out on blotting paper, that can overlap and collide.

The image you want is that they somehow coexist, if there is more than one, in multiple dimensions, each the only time and space in that dimension, each containing **all** the time and space in that dimension. They don't "collide", or at least don't collide in any sense we usually use the word.

This is quite possible, but extremely hard to imagine.


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