For simplicity's sake let us consider the case of a spatially uni-dimensional closed universe. What would be the simplest shape that would define such a universe? It would, of course, be a circle (or ring) of zero thickness. Now let us introduce the dimension of Time and see how this universe would behave from the point of creation from Nothingness, to growth and expansion, to decline and implosion, and finally completing the cycle by merging into that Nothingness. How would Space and Time behave here?
The illustration shown below plots the cyclical birth, growth, decline and final dissolution of this universe:
As can be seen from the above illustration, in order to understand the behavior of a spatially uni-dimensional closed universe we need to imagine a three dimensional toroidal shape with a central hole of zero diameter. This point of zero diameter is the point Zero/the Primordial Point/the Origin of Creation/Nothingness/the Super-Singularity or the Mother of all Singularities.
This three dimensional toroidal shape can be imagined as that obtained if the polar axis of the Earth was suddenly shrunk to zero length thus merging the North and South poles to one point (in the centre of the Earth) without any reduction in the volume of the planet. Then the Latitudinal lines would be the two dimensional universe at various stages in the Longitude of Time. Once again, it is interesting to note that in order to define this spatially one-dimensional universe we need to imagine a three dimensional shape. Then what would it be like to define the spatially three-dimensional universe in which we live in? Would it require us to imagine a spatially five-dimensional shape?