# Big Bang Theory and Shape of the Universe

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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DaveC426913
Gold Member
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.

Chronos
Gold Member
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.

Chalnoth
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.

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.