I am only a beginner in physics and have been reading popular books.(adsbygoogle = window.adsbygoogle || []).push({});

I read that the average mass-energy density of the universe determines its shape such as having uniform positive curvature, uniform negative curvature, or zero curvature if it equals the critical density. However, if spacetime is expanding, does that mean the mass-energy density of the universe is changing and the shape of the universe is changing? Moreover, if we speak of the universe having an infinite spatial extent and a finite amount of mass-energy, doesn't the mass-energy density of the universe be equal to zero?

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# Critical density in our expanding universe

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