Big Bang Theory and Shape of the Universe

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Discussion Overview

The discussion revolves around the compatibility of the Big Bang theory with various models of the universe's shape and topology, exploring whether a finite universe can exist in forms other than spherical. Participants examine theoretical implications and the constraints of General Relativity (GR) regarding the universe's geometry.

Discussion Character

  • Debate/contested
  • Exploratory
  • Technical explanation

Main Points Raised

  • Some participants suggest that the Big Bang theory implies a finite universe, which they believe must be spherical or elliptical in shape.
  • Others point out that there are competing theories regarding the universe's shape, including hyperbolic, flat, and spherical geometries, depending on certain variables in GR equations.
  • One participant argues that GR does not impose strict constraints on global topology, allowing for the possibility of nontrivial topologies compatible with the Big Bang.
  • Another participant introduces the concept of toroidal topology as a feasible alternative, likening it to the mechanics of the arcade game Asteroids.
  • There is a suggestion that while the observable universe is finite, the existence of additional unobservable regions remains a possibility, though difficult to prove.
  • Some participants express uncertainty about the limitations imposed by the Big Bang theory on the universe's shape, acknowledging that imagination does not equate to possibility.

Areas of Agreement / Disagreement

Participants do not reach a consensus; multiple competing views regarding the shape and topology of the universe remain, with ongoing debate about the implications of the Big Bang theory.

Contextual Notes

Participants note the complexity of the relationship between the Big Bang theory and the universe's topology, highlighting the dependence on specific variables in GR equations and the ambiguity surrounding the nature of the universe beyond the observable limits.

Vorde
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Is the big bang (referring to the well-established theory of post-Planck time evolution) compatible with any model of a finite universe that isn't spherical in topology?

It seems to me that the big bang theory requires that the universe be finite in volume and the only way that seems feasible to me is if it is spherical/elliptical in shape.
 
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What other shape would you expect?
 
Well it was my understanding that there are competing theories for the shape of the universe, Ranging from hyperbolic to flat to spherical depending on a value of a variable in the GR equations (I want to say eccentricity but I know that's different). And that we don't know which (if any) is correct.
 
It seems to me that the big bang theory requires that the universe be finite in volume and the only way that seems feasible to me is if it is spherical/elliptical in shape.[/QUOTE]

I think that right on both counts.
 
GR does not put much constraint on the global topology. You could in principle have nontrivial topology and still be compatible with the big bang.
 
The observable universe is, of course, finite - and always has been. If there is more to it than is observable - that is difficult to prove, but, possible.
 
Vorde said:
Is the big bang (referring to the well-established theory of post-Planck time evolution) compatible with any model of a finite universe that isn't spherical in topology?
Certainly! You could have toroidal topology, for one. Or a mixture of spherical and toroidal topology.

A quick example of toroidal topology, by the way, would be the example of the classic arcade game Asteroids. When you go off one edge of the screen, you come back on the other. A toroidal topology is like that.

You could also have one where two dimensions are like the surface of a sphere, while the third dimension is flat but wraps back on itself.

Vorde said:
It seems to me that the big bang theory requires that the universe be finite in volume and the only way that seems feasible to me is if it is spherical/elliptical in shape.
I'm not so sure there is any such limitation. It's hard to imagine how it could be other than finite, but an inability to imagine it doesn't mean it isn't possible.
 

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