Can we identify the centre of the Universe?

Click For Summary

Discussion Overview

The discussion revolves around the concept of the center of the universe, particularly in the context of its expansion and the motion of galaxies. Participants explore the implications of the universe's expansion, the nature of singularities, and the possibility of identifying a central point from which galaxies are receding.

Discussion Character

  • Exploratory
  • Debate/contested
  • Conceptual clarification
  • Mathematical reasoning

Main Points Raised

  • Some participants propose that the universe has no center, suggesting that every point in the universe can be considered a center from its own perspective.
  • Others argue that while galaxies are moving away from each other due to expansion, they can still collide due to their own proper motion.
  • A participant questions whether the universe would contract to a singularity if time were reversed, leading to a discussion about the meaning of "singularity" and its implications.
  • There is a contention regarding the interpretation of singularity, with some asserting it does not imply a specific location but rather a breakdown of mathematical models.
  • Some participants express confusion about the relationship between galaxies moving away from each other and the possibility of collisions, suggesting a need for clarification on the dynamics involved.
  • A later reply introduces the concept of the observable universe and its limitations, emphasizing that our understanding is constrained by the finite speed of light and the age of the universe.
  • There is a discussion about the terminology used to describe singularities, with suggestions to use phrases like "approaches infinity" instead of "goes to infinity" to avoid implying infinite density.
  • One participant emphasizes the importance of Cantor's work on set theory in understanding the complexities of the universe's size at the moment of the big bang.

Areas of Agreement / Disagreement

Participants generally agree that the universe does not have a center, but multiple competing views remain regarding the implications of singularities and the dynamics of galaxy motion. The discussion remains unresolved on several points, particularly concerning the interpretation of singularities and the relationship between expansion and collision.

Contextual Notes

Limitations include the dependence on definitions of singularity and the observable universe, as well as unresolved mathematical interpretations regarding the universe's behavior at t=0.

  • #91
I think a better question would be "If the universe stopped expanding and started shrinking instead, where in space would end up being in the middle of the final clump of matter before it went singularity on us?" Though that would probably still be 'everywhere', more or less, I suppose.
 
Astronomy news on Phys.org
  • #92
Alexandra Fabiello said:
I think a better question would be "If the universe stopped expanding and started shrinking instead, where in space would end up being in the middle of the final clump of matter before it went singularity on us?" Though that would probably still be 'everywhere', more or less, I suppose.
Yes. If the universe is finite then having it become smaller does not help localize the center. It's still everywhere. If the universe is infinite then scaling it down does not help localize the center. It's still infinite. In any case, there is no "final time prior to the singularity" any more than there is a smallest real number greater than zero.
 
  • #93
mathman said:
In addition to expansion (significant only in large scale activity), galaxies have their own proper motion, so they can collide.

The universe has no center.

The solar sistem has a center of mass. Similar, a galaxy, a cluster of galaxies, etc, have a center of mass. What is the limit from where we cannot speak anymore about a center of a mass, in a finite Universe?
 
  • #94
Flo Tur said:
The solar sistem has a center of mass. Similar, a galaxy, a cluster of galaxies, etc, have a center of mass. What is the limit from where we cannot speak anymore about a center of a mass, in a finite Universe?
Even in a finite universe there is no size limit applicable (it sounds like you're saying size large enough it looks infinite). It's a geometry thing: the surface of the Earth has no center. The universe is like a 3D surface, curved in a higher dimension. It's hard to visualize, but just like flying around the world, you may be able to fly across the universe and end up where you started.
 
  • #95
So, can we say that, at a large enought scale, the vectors involved in calculating the center of mass are no longer liniar and cannot be added as usual anymore?
 
  • #96
Either that, or the universe is infinite and taking the limit (to cover an infinite volume) is not meaningful.
 
  • #97
I thought is a scientic fact that the universe is finite. Do you have a mathematical representation of a universe finit in time but infinite in volume?
 
  • #98
It could be finite or infinite, we don't know.
Flo Tur said:
Do you have a mathematical representation of a universe finit in time but infinite in volume?
The standard flat ΛCDM model is the easiest example.
 

Similar threads

Undergrad How fast were distant galaxies moving?
  • · Replies 7 ·
Replies
7
Views
2K
High School Is the Universe older than we think?
  • · Replies 40 ·
2
Replies
40
Views
7K
High School How did Earth get so far away from other galaxies?
  • · Replies 12 ·
Replies
12
Views
2K
Undergrad How Does the Balloon Analogy Explain the Expansion of the Universe?
  • · Replies 5 ·
Replies
5
Views
1K
Undergrad Why on Earth do we not see older stars close to us?
  • · Replies 3 ·
Replies
3
Views
2K
High School How does the observable Universe have meaning?
  • · Replies 25 ·
Replies
25
Views
4K
Undergrad Inflationary vs deflationary phase of Big Bang
  • · Replies 10 ·
Replies
10
Views
3K
High School Why Do We See Old Galaxies in Every Direction?
  • · Replies 12 ·
Replies
12
Views
2K
High School If the universe is expanding at an accelerating rate....
  • · Replies 3 ·
Replies
3
Views
2K
High School Is there more to the Red Shift than we think?
  • · Replies 18 ·
Replies
18
Views
4K