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BentonD_Struckcheon t1_jakhyfp wrote

Reply to comment by everythingist in Why do cosmologists say that gravity should "slow down" the expansion of the universe? by crazunggoy47

Yeah I haven't thought much about this since college but I do remember curved geometries being introduced and the idea that the issue with whether or not the universe would eventually collapse in on itself was a function of which way the universe was curved.

Probably not remembering it right, but your comment jogged my memory.

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Aseyhe t1_jaliccb wrote

That's a bit different because that idea refers to the curvature of space, not spacetime. Space is a 3D surface in 4D spacetime. There are lots of possible choices of spatial surface, but there is a unique choice that makes the universe homogeneous (statistically the same everywhere on the surface). The curvature of this particular choice of spatial surface can indeed inform us as to whether the universe will eventually collapse.

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