<p>This is an intriguing proposition, but I would ask how your hypothesis explains that the universe appears to be <strong>flat</strong>? That is with <span class="math-container">$\Omega_M + \Omega_\Lambda = 1$</span>. The evidence for this comes from measurements of the cosmic microwave background, yet if we sum up all the matter (including dark matter), we only arrive at <span class="math-container">$\Omega_M \sim 0.3$</span>.</p>
<p>I do not think that your proposed arrangement both allows an accelerating expansion of the visible part of the universe (which note, can only be gravitationally influenced by &quot;outside regions&quot; that are within causal contact with it) and for it to be geometrically flat.</p>
<p>In addition, I note you are attempting to explain the expansion in some sort of Newtonian sense - I suppose your clumps of far-away dark matter are meant to be &quot;stretching&quot; the observable universe? But that isn't what happens in GR and any Newtonian interpretation would have to counter the problem that if the matter outside the observable universe was uniformly distributed (i.e. in a spherical shell), then it would exert exactly zero force on everything inside it (the shell theorem); but if it were not symmetric then you have to explain why the expansion of the universe appears to be (very close to) isotropic observationally.</p>

CC BY-SA 4.0
2016-05-16T17:34:44.690Z
2020-10-17T12:51:23.403Z
2020-10-17T12:51:23.403Z
ProfRob
<p>As is always the case in physics, there is no proof.</p>

<p>But if your scenario were true, it would have to be rather fine-tuned in order to create the observed expansion of the Universe.</p>

<p>First of all, the expansion is observed to be highly <em>isotropic</em>, i.e. the expansion rate is the same in all directions. Hence, your lumps couldn't really look like your drawing, but would have to lie in a shell around our Universe.</p>

<p>Second, the matter farthest from us would achieve a larger acceleration since it were closer your surrounding matter. In fact the opposite is observed; in the "local" Universe, the expansion accelerates, whereas in the distant Universe (which due to the finite speed of light also means the <em>early</em> Universe), the expansion actually <em>de</em>celerated.</p>

<p>Third, we would have to be located near the center of the Universe which, while not impossible, would be regarded as a highly improbable coincidence.</p>

<p>Fourth, preferably you would have to come up with some mechanism that could result in such a configuration of matter.</p>

<p>Dark energy, at least in the form of the cosmological constant which is usually assumed, is so far (!) the simplest explanation for the observed fact that the expansion of the Universe is accelerating, and that the geometry of space seems to be flat. But several other models that fit the observations exist, and although I personally think dark energy makes the most sense — partly because this is so far from my field that I'll have to rely on what I read — I think most cosmologists are rather open to the possibility that we may one day have to severely reshape or even reject this model.</p>

CC BY-SA 3.0
2016-05-16T14:38:40.847Z
"Third, we would have to be located near the center of the Universe" Don't you mean at the center of the dark matter shell? Since the Universe doesn't have a center, and we are by definition at the center of the observable universe.
called2voyage
CC BY-SA 3.0
2016-05-16T16:54:47.830Z
Thanks Pela for your response. I am intrigued by this part, though: "Second, the matter farthest from us would achieve a larger acceleration since it were closer your surrounding matter. In fact the opposite is observed; in the "local" Universe, the expansion accelerates, whereas in the distant Universe (which due to the finite speed of light also means the early Universe), the expansion actually decelerated."
Cătălin Rădoi
CC BY-SA 3.0
2016-05-16T16:57:30.000Z
Also, couldn't it be that we're surrounded by so much matter in all directions, Graham's numbers * matter in our universe, that it seems that it is fined tuned and the expansion rate seems to be the same in all directions, but actually, we will never have the instruments to measure it
Cătălin Rădoi
CC BY-SA 3.0
2016-05-16T17:54:04.993Z
@called2voyage: Well, in principle we don't know if the Universe has a center. In Proka's scenario — where according to the drawing there is the visible (=observable) Universe, surrounded by a void with lumps a dark matter — there _is_ a center, so to observe an isotropic Universe, we would have to be at the center. So I did mean the center of the Universe, but I agree that it should _also_ be in the center of the shell.
pela
CC BY-SA 3.0
2016-05-16T17:54:30.633Z
@Proka: No matter how much matter we were surrounded by, if it were notably clumpy, it would produce inhomogeneous acceleration. By the way, you also need to come up with a mechanism that prevented the shell itself from gravitational collapse.
pela
CC BY-SA 3.0
2016-05-16T17:56:15.630Z
@pela I don't see how Proka's scenario necessitates a Universal center. It could be there is other stuff out there that is far enough away that the influence of its gravity is negligible on what is pictured.
called2voyage
CC BY-SA 3.0
2016-05-16T18:00:10.553Z
@called2voyage: Okay, I see. I think I interpreted the scenario as the black sphere being not only the observable Universe, but all of the Universe, while the lumps/shell of DM were something "outside" the Universe.
pela
CC BY-SA 3.0
2016-05-16T18:02:10.240Z
@pela I can see how you might have understood it that way. Regardless, I agree with you that a shell of DM perfectly oriented around us seems too fine-tuned.
called2voyage
CC BY-SA 3.0
2016-05-16T12:31:41.753Z
2016-05-16T12:31:41.753Z
pela
<p>Is there any proof for space being created?</p>

<p>Because I guess <strong>an explanation for the dark energy</strong> (dark = our understanding of it) could be that <em>there is a gigantic amount of matter/dark matter that we cannot see (the gray clumps in the picture) that are attracting our matter (the known universe in the middle) => of course the universe is "expanding" with an acceleration.</em> </p>

<p>Am I talking non-sense?</p>

<p><a href="https://i.sstatic.net/LUuBH.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/LUuBH.png" alt="enter image description here"></a></p>

CC BY-SA 4.0
2020-10-17T13:28:38.927Z
Sorry but I believe it is non-sense. Please read more about dark matter or dark energy, for example on the Wikipedia.
peterh
CC BY-SA 4.0
2020-10-17T15:07:19.330Z
@peterh-ReinstateMonica consider the amount of work put into writing several well-received answers by very active members here, this is probably not dismissible as non-sense, nor should additional answers be prevented by closing. Seems fine to me!
uhoh
CC BY-SA 4.0
2020-10-17T16:42:54.360Z
@uhoh Yes, it is the case as the answers saved the question.
peterh
<universe><expansion><dark-energy><matter>
Is there any proof of space being created?
Cătălin Rădoi
# Is there any proof of space being created?

(Asked by: username_0 on 2016-05-16)

Is there any proof for space being created?

Because I guess **an explanation for the dark energy** (dark = our understanding of it) could be that *there is a gigantic amount of matter/dark matter that we cannot see (the gray clumps in the picture) that are attracting our matter (the known universe in the middle) => of course the universe is "expanding" with an acceleration.*

Am I talking non-sense?

[![enter image description here](https://i.sstatic.net/LUuBH.png)](https://i.sstatic.net/LUuBH.png)

**Tags:** universe, expansion, dark-energy, matter

> **Comments:**
> **username_1**: Sorry but I believe it is non-sense. Please read more about dark matter or dark energy, for example on the Wikipedia.  
> **username_2**: @username_1-ReinstateMonica consider the amount of work put into writing several well-received answers by very active members here, this is probably not dismissible as non-sense, nor should additional answers be prevented by closing. Seems fine to me!  
> **username_1**: @username_2 Yes, it is the case as the answers saved the question.  

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## 2 answers

### Answer by username_3 on 2016-05-16. Score: 9

This is an intriguing proposition, but I would ask how your hypothesis explains that the universe appears to be **flat**? That is with $\Omega\_M + \Omega\_\Lambda = 1$. The evidence for this comes from measurements of the cosmic microwave background, yet if we sum up all the matter (including dark matter), we only arrive at $\Omega\_M \sim 0.3$.

I do not think that your proposed arrangement both allows an accelerating expansion of the visible part of the universe (which note, can only be gravitationally influenced by "outside regions" that are within causal contact with it) and for it to be geometrically flat.

In addition, I note you are attempting to explain the expansion in some sort of Newtonian sense - I suppose your clumps of far-away dark matter are meant to be "stretching" the observable universe? But that isn't what happens in GR and any Newtonian interpretation would have to counter the problem that if the matter outside the observable universe was uniformly distributed (i.e. in a spherical shell), then it would exert exactly zero force on everything inside it (the shell theorem); but if it were not symmetric then you have to explain why the expansion of the universe appears to be (very close to) isotropic observationally.


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### Answer by username_4 on 2016-05-16. Score: 4

As is always the case in physics, there is no proof.

But if your scenario were true, it would have to be rather fine-tuned in order to create the observed expansion of the Universe.

First of all, the expansion is observed to be highly *isotropic*, i.e. the expansion rate is the same in all directions. Hence, your lumps couldn't really look like your drawing, but would have to lie in a shell around our Universe.

Second, the matter farthest from us would achieve a larger acceleration since it were closer your surrounding matter. In fact the opposite is observed; in the "local" Universe, the expansion accelerates, whereas in the distant Universe (which due to the finite speed of light also means the *early* Universe), the expansion actually *de*celerated.

Third, we would have to be located near the center of the Universe which, while not impossible, would be regarded as a highly improbable coincidence.

Fourth, preferably you would have to come up with some mechanism that could result in such a configuration of matter.

Dark energy, at least in the form of the cosmological constant which is usually assumed, is so far (!) the simplest explanation for the observed fact that the expansion of the Universe is accelerating, and that the geometry of space seems to be flat. But several other models that fit the observations exist, and although I personally think dark energy makes the most sense — partly because this is so far from my field that I'll have to rely on what I read — I think most cosmologists are rather open to the possibility that we may one day have to severely reshape or even reject this model.

> **Comments:**
> **username_5**: "Third, we would have to be located near the center of the Universe" Don't you mean at the center of the dark matter shell? Since the Universe doesn't have a center, and we are by definition at the center of the observable universe.  
> **username_0**: Thanks Pela for your response. I am intrigued by this part, though: "Second, the matter farthest from us would achieve a larger acceleration since it were closer your surrounding matter. In fact the opposite is observed; in the "local" Universe, the expansion accelerates, whereas in the distant Universe (which due to the finite speed of light also means the early Universe), the expansion actually decelerated."  
> **username_0**: Also, couldn't it be that we're surrounded by so much matter in all directions, Graham's numbers * matter in our universe, that it seems that it is fined tuned and the expansion rate seems to be the same in all directions, but actually, we will never have the instruments to measure it  
> **username_4**: @username_5: Well, in principle we don't know if the Universe has a center. In Proka's scenario — where according to the drawing there is the visible (=observable) Universe, surrounded by a void with lumps a dark matter — there _is_ a center, so to observe an isotropic Universe, we would have to be at the center. So I did mean the center of the Universe, but I agree that it should _also_ be in the center of the shell.  
> **username_4**: @Proka: No matter how much matter we were surrounded by, if it were notably clumpy, it would produce inhomogeneous acceleration. By the way, you also need to come up with a mechanism that prevented the shell itself from gravitational collapse.  
> **username_5**: @username_4 I don't see how Proka's scenario necessitates a Universal center. It could be there is other stuff out there that is far enough away that the influence of its gravity is negligible on what is pictured.  
> **username_4**: @username_5: Okay, I see. I think I interpreted the scenario as the black sphere being not only the observable Universe, but all of the Universe, while the lumps/shell of DM were something "outside" the Universe.  
> **username_5**: @username_4 I can see how you might have understood it that way. Regardless, I agree with you that a shell of DM perfectly oriented around us seems too fine-tuned.  

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