Of course, the observable universe may be many orders of magnitude smaller than the whole universe. Measurements from the Wilkinson Microwave Anisotropy Probe (WMAP) have shown the observable universe to have a density very close to the critical density (within a 0.4% margin of error). According to Einsteins theory of General relativity, space-time is a fabric that can be stretched and curved by massive objects like the Sun, and it is that.
And if the universe’s density is less than the critical density, then the universe is open and has negative curvature, like the surface of a saddle. A universe with density greater than the critical density has positive curvature, creating a closed universe that can be imagined like the surface of a sphere. You can imagine a flat universe like a sheet of paper that extends infinitely in all directions. The Curvature of the space curve C at c(s) is the scalar. If the density is equal to the critical density, then the universe has zero curvature it is flat. This is the arc length of the portion of graph of r(t) between r(a) and r(t), and by the. The density of matter and energy in the universe determines whether the universe is open, closed, or flat. Mass also has an effect on the overall geometry of the universe. Overall Curvature of Space Closed universe (top), open universe (middle), and flat universe (bottom). So, locally, spacetime is curved around every object with mass. According to Einstein’s theory of general relativity, massive objects warp the spacetime around them, and the effect a warp has on objects is what we call gravity.