Big Bang: Definition of Universe Area

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Discussion Overview

The discussion revolves around the terminology used to describe the area of the Big Bang in relation to the bulk universe, exploring concepts within cosmology such as the observable universe and the Hubble volume.

Discussion Character

  • Debate/contested
  • Conceptual clarification
  • Technical explanation

Main Points Raised

  • Some participants inquire if there is a specific term for the area of the Big Bang to distinguish it from the bulk universe.
  • One participant suggests that no such term exists, as current mainstream beliefs hold that the bulk universe is essentially the Big Bang area stretched over time.
  • Another participant mentions the term "Hubble Volume" as commonly used in cosmology, but notes its limitations in accurately representing the observable universe.
  • It is argued that the observable universe is the best term to describe the region we can see, based on the age of the universe and its expansion history, although its properties beyond this region remain uncertain.
  • Some participants assert that the Big Bang was everywhere, aligning with the idea that the Hubble volume does not correspond exactly to the observable universe under current cosmological parameters.
  • There is a discussion about the Hubble volume being a term that describes the local universe, but it is clarified that it does not equate to the observable universe for any specific cosmological parameters.

Areas of Agreement / Disagreement

Participants express differing views on the terminology and conceptual understanding of the Big Bang area versus the bulk universe, with no consensus reached on a specific term or definition.

Contextual Notes

Participants highlight the limitations of current cosmological parameters and the uncertainty regarding the properties of regions beyond the observable universe.

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Is there a term for the area of the big bang to distingush it from the bulk universe?
 
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As far as I know no term like that exists, because no physical distinction is possible according to current mainstream beliefs- the bulk universe is simply the big bang "area", stretched out over time.
 
Pjpic said:
Is there a term for the area of the big bang to distingush it from the bulk universe?
Within cosmology, we usually use the term "Hubble Volume".
 
Chalnoth said:
Within cosmology, we usually use the term "Hubble Volume".

No, the Hubble volume is only equal to the observable Universe for a particular set of cosmological parameters, which are not those we find for our Universe.

To answer the OP, I'm not exactly sure what you are asking, but I think the best answer would be 'the observable Universe' which is what we conventionally call the patch of the Universe we can in principle see given the age of the Universe and the expansion history (which tells you how 'far' photons can travel from the Big Bang until now).

As MikeyW said, we have no reason to believe the regions beyond this are substantially different in nature, and in terms of the models we have for the Universe we assume that this region has on average the same kind of properites as the part of the Universe we can see, but of course since we can't see it we don't know for sure.
 
No such area. Big bang was everywhere you look, just as MikeyW said.
 
Wallace said:
No, the Hubble volume is only equal to the observable Universe for a particular set of cosmological parameters, which are not those we find for our Universe.
Well, not exactly. The Hubble volume is a word which is still bandied about to describe our local universe, though we understand it's not specifically talking about the universe out to the limits of our vision. The original poster didn't specifically say the observable universe.

As far as I know, there actually aren't any cosmological parameters for which the Hubble volume is exactly the size of the observable universe. But in De Sitter space it is the volume inside the future horizon.
 

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