Proxima Centauri b Proxima Centauri b Proxima Centauri b (also called Proxima b or Alpha Centauri Cb) is an exoplanet orbiting in the habitable zone of the red dwarf star Proxima Centauri, which is the closest star to the Sun and part of a triple star system. It is located about 4.2 light-years (1.3 parsecs, 40 trillion km, or 25 trillion miles) from Earth in the constellation of Centaurus, making it the closest known exoplanet to the Solar System. Proxima Centauri b orbits the star at a distance of roughly with an orbital period of approximately 11.2 Earth days, and has an estimated
Wolfram's 2-state 3-symbol Turing machine universal, though the proof was initially disputed. The following table indicates the actions to be performed by the Turing machine depending on whether its current state is A or B, and the symbol currently being read is 0, 1 or 2. The table entries indicate the symbol to be printed, the direction in which the tape head is to move, and the subsequent state of the machine. The (2,3) Turing machine: Minsky (1967) briefly argued that standard (2,2) machines cannot be universal and M. Margenstern (2010) provided a mathematical proof based on a result by L. Pavlotskaya in 1973 (not