If the universe were a musical instrument, it would be inexplicably missing its low notes, perhaps, some cosmologists have suggested, because it is too small to play them. The universe is finite rather than infinite, they speculate. Like a violin that cannot produce deep cello notes, the universe cannot produce waves larger than itself.<p>In such a universe, if you went far enough in one direction, you would find yourself back where you started, on the other side of the universe, like a cursor disappearing off the left side of a screen and reappearing on the right.<p>One simple example of this is a bagel, which is what you get when you wrap the left and right and top and bottom sides of the screen around so that they meet.<p>In the model proposed by Dr. Weeks and his colleagues, three-dimensional space has 12 sides, like a soccerball, or more technically a dodecahedron. ...
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