<p>For distant galaxies to be accelerating away at equal speed in every direction, Earth would have to be at the centre of the universe. Since it is not, some region of the distant galaxies should appear to be retreating faster and this increased speed would be a function of how far the Earth is away from the centre.
Assuming light travels at the same speed in all directions, earth is at the center of the observable universe. Since we are part of the expanding universe, how far has &quot;earth&quot; travelled since the big bang?</p>
<p>The  distant galaxies around the observable universe periphery provide the references to access the relative  motion of the earth.</p>

CC BY-SA 4.0
2023-03-14T17:35:12.850Z
There is no centre. Please see (possible duplicate) https://astronomy.stackexchange.com/q/669/16685
PM 2Ring
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2023-03-14T21:49:13.627Z
Your first sentence is simply wrong.
Chenmunka
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2023-03-15T01:09:12.437Z
I'm not sure the downvotes are entirely fair and would ask members to reconsider them.  The OP seems to simply have a genuine misconception of how the expansion of the universe works (and why).  In fairness it's quite a difficult concept to grasp.
StephenG - Help Ukraine
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2023-03-15T12:54:45.540Z
Everywhere you go, there you are...
Jon Custer
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2023-03-17T23:35:24.277Z
How far has Earth traveled *with respect to which frame*? That is the basic problem. Every comoving observer (that is, observer moving only due to the expansion) has an equally good reference frame and is at rest with respect to their own frame. There's no universal reference frame with respect to which we can say how far an object has traveled due to the expansion of the universe.
Sten
CC BY-SA 4.0
2023-03-18T04:47:54.687Z
As Sten says, there is no universal reference frame. The closest thing we have to such a frame is the frame in which the CMB is isotropic, see  https://physics.stackexchange.com/q/411073/123208 However, points in that frame are *not* at rest with respect to each other, they are moving apart due to the Hubble flow. With respect to that frame, the Solar System is currently moving at roughly 600 km/s.
PM 2Ring
CC BY-SA 4.0
2023-03-18T08:57:25.350Z
Indeed, if you want to ask how far we've traveled with respect to the comoving observers, that is answerable. That's a question of how far we've moved *compared to the expansion*, not due to the expansion.
Sten
CC BY-SA 4.0
2023-03-23T13:53:26.290Z
I think you are wrong. There is a universal reference , in fact millions of them- not at the centre of the universe (wherever or if that exists) but at the periphery. Galaxies accelerating away from us in the same direction we are travelling, will seem to be accelerating more slowly while those travelling in the opposite direction will appear to be moving faster.  Calculation of these relative speeds vs direction would allow determination of earth's movement  and direction
Clifford Lingwood
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2023-03-28T17:08:16.853Z
What is the center of the *surface* of a ball?
planetmaker
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2023-03-28T17:52:45.937Z
There is no way to know and your question is nonsenseical
Starship
CC BY-SA 4.0
2023-03-28T17:55:07.273Z
@Clifford The CMB frame is similar to your shell of distant galaxies, except that the shell which emitted the CMB we're currently receiving (aka the surface of last scattering) is further than the galaxies, and more uniform.
PM 2Ring
CC BY-SA 4.0
2023-03-28T17:58:38.130Z
Note that cosmologically distant objects don't supply a well defined reference frame for us; see "[What does general relativity say about the relative velocities of objects that are far away from one another?](https://physics.stackexchange.com/q/400457/180843)". But the light reaching us from such objects does, as @PM2Ring notes. If that is the aim, then you are essentially asking about our motion with respect to the CMB frame (discussed in earlier comments).
Sten
CC BY-SA 4.0
2023-03-28T18:14:14.563Z
You may enjoy [this popular article on expansion](https://people.smp.uq.edu.au/TamaraDavis/papers/SciAm_BigBang.pdf) (PDF) by Tamara Davis & Charles Lineweaver. They have a formal paper on the topic [here](https://arxiv.org/abs/astro-ph/0310808), and there are numerous other resources on Professor Davis's [personal site](https://people.smp.uq.edu.au/TamaraDavis/research.html).
PM 2Ring
<cosmology><expansion><observable-universe>
where are we in the universe as compared to the observable universe?
Clifford Lingwood
# where are we in the universe as compared to the observable universe?

(Asked by: username_0 on 2023-03-14)

For distant galaxies to be accelerating away at equal speed in every direction, Earth would have to be at the centre of the universe. Since it is not, some region of the distant galaxies should appear to be retreating faster and this increased speed would be a function of how far the Earth is away from the centre.
Assuming light travels at the same speed in all directions, earth is at the center of the observable universe. Since we are part of the expanding universe, how far has "earth" travelled since the big bang?

The distant galaxies around the observable universe periphery provide the references to access the relative motion of the earth.

**Tags:** cosmology, expansion, observable-universe
> **Comments:**
> **username_1**: There is no centre. Please see (possible duplicate) https://astronomy.stackexchange.com/q/669/16685  
> **username_2**: Your first sentence is simply wrong.  
> **username_3**: I'm not sure the downvotes are entirely fair and would ask members to reconsider them.  The OP seems to simply have a genuine misconception of how the expansion of the universe works (and why).  In fairness it's quite a difficult concept to grasp.  
> **username_4**: Everywhere you go, there you are...  
> **username_5**: How far has Earth traveled *with respect to which frame*? That is the basic problem. Every comoving observer (that is, observer moving only due to the expansion) has an equally good reference frame and is at rest with respect to their own frame. There's no universal reference frame with respect to which we can say how far an object has traveled due to the expansion of the universe.  
> **username_1**: As Sten says, there is no universal reference frame. The closest thing we have to such a frame is the frame in which the CMB is isotropic, see  https://physics.stackexchange.com/q/411073/123208 However, points in that frame are *not* at rest with respect to each other, they are moving apart due to the Hubble flow. With respect to that frame, the Solar System is currently moving at roughly 600 km/s.  
> **username_5**: Indeed, if you want to ask how far we've traveled with respect to the comoving observers, that is answerable. That's a question of how far we've moved *compared to the expansion*, not due to the expansion.  
> **username_0**: I think you are wrong. There is a universal reference , in fact millions of them- not at the centre of the universe (wherever or if that exists) but at the periphery. Galaxies accelerating away from us in the same direction we are travelling, will seem to be accelerating more slowly while those travelling in the opposite direction will appear to be moving faster.  Calculation of these relative speeds vs direction would allow determination of earth's movement  and direction  
> **username_6**: What is the center of the *surface* of a ball?  
> **username_7**: There is no way to know and your question is nonsenseical  
> **username_1**: @Clifford The CMB frame is similar to your shell of distant galaxies, except that the shell which emitted the CMB we're currently receiving (aka the surface of last scattering) is further than the galaxies, and more uniform.  
> **username_5**: Note that cosmologically distant objects don't supply a well defined reference frame for us; see "[What does general relativity say about the relative velocities of objects that are far away from one another?](https://physics.stackexchange.com/q/400457/180843)". But the light reaching us from such objects does, as @PM2Ring notes. If that is the aim, then you are essentially asking about our motion with respect to the CMB frame (discussed in earlier comments).  
> **username_1**: You may enjoy [this popular article on expansion](https://people.smp.uq.edu.au/TamaraDavis/papers/SciAm_BigBang.pdf) (PDF) by Tamara Davis & Charles Lineweaver. They have a formal paper on the topic [here](https://arxiv.org/abs/astro-ph/0310808), and there are numerous other resources on Professor Davis's [personal site](https://people.smp.uq.edu.au/TamaraDavis/research.html).  

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## 0 answers

