If the universe's space-time is positively curved, like the surface of a sphere, parallel beams would come together.

如果宇宙的时空像球体表面一样正向弯曲，平行的光线就会交合在一起。

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A two-dimensional model of such a universe would look like a sphere. It's impossible to have parallel geodesics (straight lines on a curved surface) — the two lines will cross at some point.

这样的2维宇宙模型就像是球体，不可能出现平行的测地线(测地线是曲面上的直线)——两直线必然在某点相交。

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The density profile of hard sphere fluid confined in two parallel hard walls was studied by using Rosenfeld density Functional Theory (DFT) and Molecular Dynamics (MD) simulation method.

利用密度泛函理论和分子动力学方法，对处于两平行硬墙之间的硬球流体的密度分布进行了计算。

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