Is There a Reference Point for the Expansion of the Universe?

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Discussion Overview

The discussion centers on the concept of the expansion of the universe and whether there exists a reference point for this expansion. Participants explore analogies, particularly the balloon analogy, to understand the nature of expansion and the implications of having or not having a center of expansion.

Discussion Character

  • Exploratory
  • Debate/contested
  • Conceptual clarification

Main Points Raised

  • Some participants propose that the universe does not have a center of expansion, similar to a balloon, but question how the expansion occurs without a reference point.
  • One participant argues that a reference point for expansion would imply a preferred frame of reference, which is not supported by evidence.
  • Another participant challenges the balloon analogy, stating that it does not have an axis of rotation when considered as a two-dimensional surface, rather than in three-dimensional space.
  • A later reply clarifies that the discussion about the balloon's axis pertains to its surface, not its entire volume, suggesting a need for careful consideration of the analogy used.

Areas of Agreement / Disagreement

Participants express differing views on the validity of the balloon analogy and the implications of having a center of expansion. There is no consensus on the existence of a reference point for the expansion of the universe.

Contextual Notes

Participants reference prior discussions on the topic, indicating that the concept of expansion has been debated extensively. There may be limitations in the analogies used and assumptions about dimensionality that are not fully resolved.

Sarthak1221
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I once read somewhere a long time ago (and so I am not sure if this is true, let me know if it isn't) that the universe doesn't have a center of expansion. I get it. Neither does a typical balloon. But a balloon has an axis about which it is symmetrically expanding. Obviously that is not the case with the universe. So how exactly is the expansion taking place? Is there nothing that can be taken as a reference point for the expansion?
 
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Sarthak1221 said:
I once read somewhere a long time ago (and so I am not sure if this is true, let me know if it isn't) that the universe doesn't have a center of expansion. I get it. Neither does a typical balloon. But a balloon has an axis about which it is symmetrically expanding. Obviously that is not the case with the universe. So how exactly is the expansion taking place? Is there nothing that can be taken as a reference point for the expansion?
A reference point for the expansion would imply a preferred frame of reference and there is not only zero evidence for such, there is overwhelming evidence to the contrary.

Expansion has been beaten to death numerous times here on PF. I suggest a forum search.

I also recommend the link in my signature.
 
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Sarthak1221 said:
But a balloon has an axis about which it is symmetrically expanding.
No, it does not. You have to disregard any embedding of the balloon into three-dimensional space and just consider it as a two-dimensional surface. Anything outside of that surface is unphysical.
 
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@Sarthak1221 I believe that you are referencing the entire volume of the balloon when you make your statement that it has an axis of rotation. What Ordruin is referencing when he says it doesn't have such an axis is the SURFACE of the balloon, which is what has to be considered if you are using the balloon analogy. Again, I suggest the link in my signature, which will explain that.
 
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