The Torus: A Great Concept That Is Rarely The Right Answer

 

The image above is silly, because it is easy to understand and the truth is readily observable. 

But, mathematicians and physicists absolute love to propose cosmology models with torus (i.e. donut shaped) structures in them in theoretical papers, because their topological properties are quite similar to those of more common sense space-times if you make the scale of the torus large enough.

The problem is that toroidal models are almost never good solutions to these problems that make sense. Nature just doesn't like donuts as much as mathematical physicists do.