Can Unbounded 3D Space Truly Exist?

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Discussion Overview

The discussion revolves around the concept of unbounded three-dimensional space, exploring whether such a space can exist and how it relates to boundedness and boundaries in mathematical terms. Participants examine examples from geometry and topology, including the properties of spheres and manifolds.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant questions the existence of unbounded three-dimensional space, referencing the concept of unbounded surfaces in two-dimensional space.
  • Another participant suggests that the surface of a four-dimensional sphere could serve as an example of unbounded space.
  • A different viewpoint asserts that R3 (three-dimensional Euclidean space) is unbounded, and proposes that the original poster may be seeking the concept of "finite but unbounded."
  • One participant expresses confusion, stating that an n-sphere is bounded as a metric space and suggests that "boundaryless" might be the correct term for a manifold without boundaries.
  • Another participant describes the surface of a sphere as "bounded but having no boundary," indicating that while distances are limited, there is no edge to the space.
  • A later reply proposes that "boundaryless and compact" may align more closely with the original poster's inquiry.
  • One participant emphasizes the importance of defining terms, questioning whether "bounded" refers to size or the presence of an edge.

Areas of Agreement / Disagreement

Participants express differing views on the definitions of boundedness and boundaries, with no consensus reached on the terminology or the existence of unbounded three-dimensional space.

Contextual Notes

There are unresolved assumptions regarding the definitions of "bounded," "unbounded," and "boundaryless," which may affect the clarity of the discussion.

touqra
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Can there be any unbounded 3 dimensional space? For example, for a 2-dimensional space, we have an unbounded surface that resides on a sphere.
How about three-dimensional space?
 
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Sure. For example, the surface of a 4-dimensional sphere!


(PS: I'm not sure if "unbounded" is the word you're looking for... though it might be)
 
R3 is unbounded.
Maybe he is looking for "finite but unbounded".
Another example is the analog of a torus (The Asteroids topology :-p ).
 
Now this is what has confused me, surely an n-sphere is bounded as a metric space, I think the correct matehamtical term is 'boundaryless' i.e. a manifold without boundaries.
 
The example he gives (surface of a sphere) is what I would call (perhaps "paradoxically) "bounded but having no boundary".

That is, the set of all possible distances between points has an upper bound but there is no boundary: points such that every neighborhood contains some points in the set and some points not in the set.

Of course, there exist 3 dimensional bounded sets that have no boundary- but you have to imagine them embedded in 4 dimensional space. The surface of a 4-sphere is an example.
 
Actually now I think a little more, boundaryless and compact is probably what the OP was looking for.
 
it always helps to define your terms. i.e. does "bounded" mean not very big, or having an edge?
 

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