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Happiness

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"the universe expands at about 70 kilometers per second per megaparsec. This means that a galaxy 1 megaparsec away from us is receding at about 70 km/s, another galaxy 2 megaparsecs away from us is receding at 140 km/s, and so on. This is Hubble's law. Following the same logic, one could do the math to compute how far a galaxy has to be in order to move away at the speed of light. It turns out, galaxies 4300 megaparsecs away from us recede faster than light. This distance defines the "Hubble sphere", an imaginary sphere centered at us, outside which everything recedes faster than the speed of light. Note that, since the universe expands at an accelerated rate, the Hubble sphere increases its radius as time goes by."

Source: http://curious.astro.cornell.edu/ab...peed-of-light-disappear-from-our-observations