Space can have positive curvature, like the surface of a sphere, or negative curvature, like the surface of a saddle.

空间可以向球面一样有正的曲率，也可以像马鞍面一样有负的曲率。

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This artist's depiction shows a possible Earth-like planet with a rocky surface, oceans and an atmosphere. See more space tourism images.

模拟图描绘了类地行星，有岩石表面、海洋和大气。

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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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