In a theory developed by B. Roy Frieden, “physical information” is defined as the loss of Fisher information that is incurred during the observation of a physical effect. Thus, if the effect has an intrinsic information level J but is observed at information level I, the physical information is defined to be the difference I − J. This defines an information Lagrangian. Frieden’s principle of extreme physical information or EPI states that extremalizing I − J by varying the system probability amplitudes gives the correct amplitudes for most or even all physical theories. The EPI principle was recently proven. It follows from a system of mathematical axioms of L. Hardy defining all known physics.

— Wikipedia on Physical information

2014.08.31 Sunday ACHK