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Time-Reversal Symmetry

  1. Oct 10, 2015 #1
    I completely have no idea what time-reversal mean.
    Why does, by substituting -t into an equation and if the result is the same as the original equation, then the equation is said to be time-reversal symmetry?
    Also, what does that 'symmetry' mean there? An even function?
  2. jcsd
  3. Oct 10, 2015 #2

  4. Oct 10, 2015 #3
    Time reversal symmetry means that the physical laws governing a dynamical system would be equally descriptive if that system was played in reverse. For instance, if you showed a movie of the motion of the planets in some solar system to a physicist, and then showed the same movie in reverse, it would be impossible for her/him to decide which of the movies was played forwards and which was played backwards, because both would be equally consistent with Newton's equations.
    Last edited: Oct 10, 2015
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