/sci/ - Science & Math

>>2638264
Since space and time are like a fabric, space-time can have curvature locally, like the distortions caused by the sun or "globally" a curvature for the entire universe. It is something like our own Earth. Locally the surface of the Earth has peaks and valleys, rolling hills and crevasses, little lumps and divots that affect a small area on the surface. But zoom out far enough and you see that the Earth is a sphere, even though the curvature is all but imperceptible across small distances. It is the same with the universe as a whole. Locally, the fabric of space-time can be flat, or it can have ripples; it can even have immense, seemingly bottomless pits. The universe as a whole, however, also has a shape. It might be flat, or it might have a *positive curvature* like a ball, or *negative curvature* like a saddle. All of these shapes are in FOUR DIMENSIONS, of course, so they are very difficult to visualize, even with training. Nonetheless, the three-dimensional versions- a plane, sphere or enormous saddle- are reasonable approximations of what is happening in our 4-D universe.