Astro-physicists think that maybe the universe is in the shape of a torus, i.e. a doughnut.
This is known as the Krispy Kreme theory of the universe. This would satisfy the need to have time travel perpendicularly to space, and allow space to still be curved, all of which apparently is necessary to allow for a flat universe without folds and ripples. Albert the prophet taught us better, but we didn’t listen, still treating time and space like plumbing and wiring, sharing the same continuum but diametrically opposed, constantly at odds, still treating gravity like a Newtonian force, commanding the troops and craving attention. With all due respect to the many Cambodians in the business of frying ring-shaped doughy fritters in order to feed their families, I remain skeptical. I tend to view Nature as a unit, as in microcosm so in macrocosm. I see many more spheres in Nature than rings, and even fewer aspiring to such. I think the universe is round like a ball, albeit a lumpy one. The only question is, are we on the edge looking out to the future or looking back to the past?