Does the universe have a definite "size"?

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Discussion Overview

The discussion revolves around the concept of the universe's size, particularly whether it has a definite size or edge. Participants explore the implications of the observable universe being 92 billion light years across and the nature of space itself, including ideas of finiteness and infiniteness in the context of cosmology.

Discussion Character

  • Exploratory
  • Debate/contested
  • Conceptual clarification

Main Points Raised

  • Some participants express confusion over the concept of "space expanding" and the implications of a finite universe, suggesting it leads to paradoxical scenarios.
  • One participant states that the observable universe is 92 billion light years across, but this does not imply an edge if the universe is not flat.
  • Another participant argues that if the universe is analogous to a three-dimensional sphere, it could be much larger than the observable universe, which is only a sphere defined by the limits of light travel since the beginning of time.
  • There is a suggestion that the observable universe is bounded due to the finite speed of light and the age of the universe, rather than indicating a physical edge to the universe itself.

Areas of Agreement / Disagreement

Participants generally agree that the observable universe is 92 billion light years across, but there is disagreement regarding the implications of this size, particularly whether it suggests a finite edge or if the universe is infinite in extent.

Contextual Notes

Participants note that the observable universe is defined by the limitations of light travel and the age of the universe, which may not fully capture the true nature of the universe's size or structure.

ScottVal
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TL;DR
There's a YouTube video which says the universe is 92 billion light years wide; is this true?
Hello-
I just watched (or tried to watch) a YouTube video by Fermilab, in which the speaker states that the universe has a definite "width" of 92 billion light years. I could only watch about half of it because more and more terms were used which it am not familiar with. Besides, his pedantic nature is very annoying. I made the following comment on YouTube:

You lost me when you talked about "space expanding." I guess the video is meant for people who already understand that concept (which I don't). However, I pondered the idea of the universe having finite size several years ago, and got some help from some people on a physics forum, and I concluded that the question is sort of a paradox, because, if the universe had a finite size, you could imagine an inhabited planet on the edge of the universe, and the people who lived there would see the cosmos only on one side of their celestial sphere, which wouldn't make much sense. I think it makes more sense to consider the universe as having an indefinite size. I.e., you see galaxies in all directions, no matter where you are.

The video has about 4000 comments, so I'm not expecting anyone to reply to my comment. However, this forum seems like a smaller group, and I was wondering what you all think of this...
-Scott V.
 
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The observable universe is 92 billion lightyears across.
 
Your assumption that the size is finite implies there is an edge. However if the universe is not flat, like a three dimensional analog of the surface of a sphere, there will not be an edge.
 
mathman said:
Your assumption that the size is finite implies there is an edge. However if the universe is not flat, like a three dimensional analog of the surface of a sphere, there will not be an edge.
Based on current observations, if this is the case this 3-sphere is significantly larger than 92 billion lightyears. The statement in the video is about the observable universe.
 
From what we understand, space is infinite in every direction. The video from Fermilabs was indeed talking about the observable universe, which is a sphere of about 92 billion light years. The reason that the observable universe is this size is because the speed of light is finite and there was a beginning of time. We simply can't see things further away than that because there hasn't been enough time for light from beyond that edge to reach us, but it's still out there.

This would be true regardless of whether or not space is expanding (which it is.)
 
I think I see now, that the implication is not that there is an "edge" to the universe 92 billion light years away (which wouldn't make sense), but that the "observable" universe seems to be bounded by a sphere 92 BLY in radius, simply because of the age of the universe, etc. Thanks.
 

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