Parsec Parsec The parsec (symbol: pc) is a unit of length used to measure large distances to astronomical objects outside the Solar System. A parsec is defined as the distance at which one astronomical unit subtends an angle of one arcsecond, which corresponds to astronomical units. One parsec is equal to about 3.26 light-years (30 trillion km or 19 trillion miles) in length. The nearest star, Proxima Centauri, is about from the Sun. Most of the stars visible to the unaided eye in the night sky are within 500 parsecs of the Sun. The parsec unit was probably first suggested in
Wolfram's 2-state 3-symbol Turing machine a LBA would require to be restarted manually to become universal using the same initial configuration, while his construction restarts the Turing machine automatically with no external intervention. Discussions about the proof continued for some time between Alex Smith, Vaughan Pratt, and others. Wolfram's 2-state 3-symbol Turing machine In his book "A New Kind of Science", Stephen Wolfram described a universal 2-state 5-symbol Turing machine, and conjectured that a particular 2-state 3-symbol Turing machine (hereinafter (2,3) Turing machine) might be universal as well. On May 14, 2007, Wolfram announced a $25,000 prize to be won by the first person to