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Originally Posted by GUILLE Who invented the idea of the universe being flat? |
the flatness problem wasn't invented. It's an experimental fact from astronomical observations. At the present epoch of the universe, the equilibrium between gravitational energy and expansion energy is undeniable and incontestable. The spacetime structure of the universe is very nearly Euclidean, and not Riemannian (closed - elliptic), nor Gaussian (open - hyperbolic).
Euclidean spacetime allows the metric components of nonzero values for equal values of index. g11, g22, g33, g44, g55, g66, g77, g88, g99,...And the 2D analoque is the Pythagorean theorem for determining distances.
Note: the flatness problem has been resolved by the inflationary model of the universe. There are many cosmological models in the hopper at the moment. All of them can be based on Einstein's general relativistic field equations with or without the cosmological constants.