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Astronomy and Cosmology
Astronomy and Astrophysics
How can the Universe be flat? Ridiculous
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[QUOTE="Ibix, post: 6899949, member: 365269"] There are three types of universe described by the Einstein field equations, called open, flat and closed. Which type you have depends on the average density of matter in the universe. Note that all of these are four dimensional structures, and while you may see them illustrated as sheets of paper or the surface of a beach ball this is because drawing 4d structures always requires some simplification - in this case to just 2d. Don't mistake such sketches for the actual models. In open universes initially parallel lines diverge, in flat universes they remain parallel, and in closed universes they converge and eventually cross twice before returning to where they started (the similarity to lines of longitude on a globe is not coincidental). Closed universes are finite in size but boundaryless (did I get the terminology right that time [USER=399360]@Bandersnatch[/USER]?) and can eventually collapse into a Big Crunch (depending on the dark energy content), but the other two are infinite in size and expand forever. Our best measurements suggest we live in a flat universe, but we could live in one of the others if the scale of the curvature is so large that the observable universe is too small a patch for us to detect the deviation from flatness. [/QUOTE]
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How can the Universe be flat? Ridiculous
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