If you could somehow manage to step outside of the universe, what would it look like? Scientists have struggled with this question, taking several different measurements in order to determine the geometry of the cosmos and whether or not it will come to an end. How do they measure the shape of the universe? And what have they found?
According to Einstein's theory of General Relativity, space itself can be curved by mass. As a result, the density of the universe 14 how much mass it has spread over its volume 14 determines its shape, as well as its future.
Scientists have calculated the "critical density" of the universe. The critical density is proportional to the square of the Hubble constant, which is used in measuring the expansion rate of the universe. Comparing the critical density to the actual density can help scientists to understand the cosmos.
If the actual density of the universe is less than the critical density, then there is not enough matter to stop the expansion of the universe, and it will expand forever. The resulting shape is curved like the surface of a saddle. This is known as an open universe.
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