<p>If so, there would be an area in the middle of the sphere/ring where the galaxies are not moving away from each other, and it would be easy to detect the gradient of movement from the center of the ring to the periphery. In reality everything is moving away from everything else at an equal ratio.</p>

CC BY-SA 4.0
2023-04-22T21:35:41.910Z
is the sun also redshifted?
Hisham
CC BY-SA 4.0
2023-04-24T10:52:39.810Z
The sun is redshifted relative to other stars, because they are redshifted to the sun's region. Actually the galaxy's 100bn stars are not caught in the expansion because they have local gravitation, and planets are not expanding either. Only gravitationally unbound structures are expanding. If you want, start a new question to ask about the different ways that measure that the expansion is the same locally as it is far away.
bandybabboon
CC BY-SA 4.0
2023-04-21T17:20:39.947Z
2023-04-21T17:20:39.947Z
bandybabboon
<p>You have identified the issues.</p>
<p>The model does not explain the redshift-distance relationship, which is one of the primary pieces of evidence.</p>
<p>Simply to say &quot;our ideas about gravity are wrong&quot;, so we invent some magic which makes things work isn't how science is done. We already have good evidence that our ideas about gravity <em>do</em> work very well, even in extremely strong gravity situations near black holes.</p>
<p>Perhaps more fundamentally, the model doesn't produce any redshift at all!
The gravitational redshift due to concentrations of mass is proportional to their relative gravitational potential. <a href="http://hyperphysics.phy-astr.gsu.edu/hbase/Mechanics/sphshell2.html" rel="noreferrer">Newton's shell theorem</a> tells us that the gravitational field everywhere inside a spherically symmetric shell is identically <em>zero</em>. Therefore there is no gradient in gravitational potential and no gravitational redshift caused by this arrangement anywhere inside the shell.</p>

CC BY-SA 4.0
2023-04-21T11:10:54.433Z
The latter paragraph's point is IMHO the better one: the suggested solution is no solution at all.
planetmaker
CC BY-SA 4.0
2023-04-21T14:41:34.777Z
Doesn't it also violate the mediocrity principle, that we're not located in a special place? For the effect to be the same in all directions, we'd presumably have to be in the center of that ring, right?
Barmar
CC BY-SA 4.0
2023-04-22T05:29:58.583Z
@Barmar; I suspect that your objection might be a central aim of the proposition, i.e. to promote the idea that Earth -is- in a privileged position, privileged by the sanction of some "higher power".  I don't know that, of corse, but I've seen such arguments before.
JohnHunt
CC BY-SA 4.0
2023-04-22T05:30:55.850Z
@JohnHunt Good point -- we really *are* the center of the universe, that's why everything is expanding away from us.
Barmar
CC BY-SA 4.0
2023-04-22T07:09:48.210Z
“we invent some magic which makes things work isn't how science is done” I would argue that is exactly how science is done, often with success and sometimes without direct evidence: antimatter, neutrinos, inflation, dark matter, dark energy, etc.
Matt
CC BY-SA 4.0
2023-04-22T08:36:40.227Z
The last paragraph completely buries my idea, thanks
Hisham
CC BY-SA 4.0
2023-04-21T05:43:27.470Z
2023-04-21T05:57:28.800Z
2023-04-21T05:57:28.800Z
ProfRob
<p>ChatGPT and wikipedia have informed me that the primary evidence for the theory that the universe is expanding is the fact that photons that arrive to our planet from all directions are being redshifted, and this redshift is directly proportional to the distance from our earth to the origin of the source of the light.</p>
<p>Although universal expansion does explain this observation</p>
<p>Could it also be explained by having a ring of unimaginably dense concentrations of matter all around us, far away from what we can observe, which cause the redshift of the photons we detect by pulling the sources of those photons, (stars, galaxies whatever they may be) by gravitation?</p>
<p>this would imply two main problems of course:</p>
<p>(1) The issue that the amount of redshift is approximately proportional to the distance of the source. Perhaps the current model of gravitation breaks down at such scales and gravity behaves differently, if so this would also explain why the redshift we can determine of incoming photons is greater the further the origin is, because the net gravitational effects and thus the acceleration on that photon source would be greater as it moves closer and closer to a particular section of the perimeter, thus intensifying the doppler effect</p>
<p>(2) Why don't we or other observable astronomical bodies accelerate away too?
Perhaps we are in a sweet spot where the gravitational effects by this ring of masses roughly cancel out.</p>
<p>Or perhaps we are accelerating towards a particular section on the perimeter of this  ring, along with our entire galaxy we just don't realise it.</p>
<p>I look forward to a retort to this idea which has sat in my brain for a while now, googling didn't really help because I could not think of a &quot;googlable&quot; way of formulating it.</p>

CC BY-SA 4.0
2023-04-21T18:52:39.613Z
Aside from the highly contrived nature of this idea and the fact that it wouldn't work... it's not even an alternative to cosmic expansion. If it worked, it would just be a source for cosmic expansion.
Sten
CC BY-SA 4.0
2023-04-22T19:39:42.803Z
How would it cause expansion?
Hisham
CC BY-SA 4.0
2023-04-22T20:15:54.850Z
If the idea is to pull everything away from us, that's just accelerating cosmic expansion (albeit in an inhomogeneous way). That's all cosmic expansion means: everything is separating.
Sten
CC BY-SA 4.0
2023-04-22T20:58:33.503Z
(sitting here, whetting Occam's razor ...) ;)
Karl
CC BY-SA 4.0
2023-04-22T21:27:16.253Z
@sten I thought the defining feature of universal expansion is that... the universe expands, not just things getting further away. me and you and sit in a room of fixed volume and decide to walk away from each other that doesn't mean the room got bigger
Hisham
CC BY-SA 4.0
2023-04-22T23:30:30.327Z
why am i being downvoted
Hisham
<expansion><redshift><space><observable-universe>
Could the redshift of all incoming photons be explained by a massive ring of distant masses pulling the sources of the photons away?
Hisham
# Could the redshift of all incoming photons be explained by a massive ring of distant masses pulling the sources of the photons away?

(Asked by: username_0 on 2023-04-21)

ChatGPT and wikipedia have informed me that the primary evidence for the theory that the universe is expanding is the fact that photons that arrive to our planet from all directions are being redshifted, and this redshift is directly proportional to the distance from our earth to the origin of the source of the light.

Although universal expansion does explain this observation

Could it also be explained by having a ring of unimaginably dense concentrations of matter all around us, far away from what we can observe, which cause the redshift of the photons we detect by pulling the sources of those photons, (stars, galaxies whatever they may be) by gravitation?

this would imply two main problems of course:

(1) The issue that the amount of redshift is approximately proportional to the distance of the source. Perhaps the current model of gravitation breaks down at such scales and gravity behaves differently, if so this would also explain why the redshift we can determine of incoming photons is greater the further the origin is, because the net gravitational effects and thus the acceleration on that photon source would be greater as it moves closer and closer to a particular section of the perimeter, thus intensifying the doppler effect

(2) Why don't we or other observable astronomical bodies accelerate away too?
Perhaps we are in a sweet spot where the gravitational effects by this ring of masses roughly cancel out.

Or perhaps we are accelerating towards a particular section on the perimeter of this ring, along with our entire galaxy we just don't realise it.

I look forward to a retort to this idea which has sat in my brain for a while now, googling didn't really help because I could not think of a "googlable" way of formulating it.

**Tags:** expansion, redshift, space, observable-universe
> **Comments:**
> **username_1**: Aside from the highly contrived nature of this idea and the fact that it wouldn't work... it's not even an alternative to cosmic expansion. If it worked, it would just be a source for cosmic expansion.  
> **username_0**: How would it cause expansion?  
> **username_1**: If the idea is to pull everything away from us, that's just accelerating cosmic expansion (albeit in an inhomogeneous way). That's all cosmic expansion means: everything is separating.  
> **username_2**: (sitting here, whetting Occam's razor ...) ;)  
> **username_0**: @sten I thought the defining feature of universal expansion is that... the universe expands, not just things getting further away. me and you and sit in a room of fixed volume and decide to walk away from each other that doesn't mean the room got bigger  
> **username_0**: why am i being downvoted  

---

## 2 answers

### Answer by username_4 on 2023-04-21. Score: 18 | Accepted answer

You have identified the issues.

The model does not explain the redshift-distance relationship, which is one of the primary pieces of evidence.

Simply to say "our ideas about gravity are wrong", so we invent some magic which makes things work isn't how science is done. We already have good evidence that our ideas about gravity *do* work very well, even in extremely strong gravity situations near black holes.

Perhaps more fundamentally, the model doesn't produce any redshift at all!
The gravitational redshift due to concentrations of mass is proportional to their relative gravitational potential. [Newton's shell theorem](http://hyperphysics.phy-astr.gsu.edu/hbase/Mechanics/sphshell2.html) tells us that the gravitational field everywhere inside a spherically symmetric shell is identically *zero*. Therefore there is no gradient in gravitational potential and no gravitational redshift caused by this arrangement anywhere inside the shell.

> **Comments:**
> **username_5**: The latter paragraph's point is IMHO the better one: the suggested solution is no solution at all.  
> **username_6**: Doesn't it also violate the mediocrity principle, that we're not located in a special place? For the effect to be the same in all directions, we'd presumably have to be in the center of that ring, right?  
> **username_7**: @Barmar; I suspect that your objection might be a central aim of the proposition, i.e. to promote the idea that Earth -is- in a privileged position, privileged by the sanction of some "higher power".  I don't know that, of corse, but I've seen such arguments before.  
> **username_6**: @JohnHunt Good point -- we really *are* the center of the universe, that's why everything is expanding away from us.  
> **username_8**: “we invent some magic which makes things work isn't how science is done” I would argue that is exactly how science is done, often with success and sometimes without direct evidence: antimatter, neutrinos, inflation, dark matter, dark energy, etc.  
> **username_0**: The last paragraph completely buries my idea, thanks  

---

### Answer by username_3 on 2023-04-21. Score: 4

If so, there would be an area in the middle of the sphere/ring where the galaxies are not moving away from each other, and it would be easy to detect the gradient of movement from the center of the ring to the periphery. In reality everything is moving away from everything else at an equal ratio.

> **Comments:**
> **username_0**: is the sun also redshifted?  
> **username_3**: The sun is redshifted relative to other stars, because they are redshifted to the sun's region. Actually the galaxy's 100bn stars are not caught in the expansion because they have local gravitation, and planets are not expanding either. Only gravitationally unbound structures are expanding. If you want, start a new question to ask about the different ways that measure that the expansion is the same locally as it is far away.  

---

