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The EPI principle builds on the well known idea that the observation of a "source" phenomenon is never completely accurate. That is, information present in the source is inevitably lost when observing the source. Moreover, the random errors that contaminate the observations are presumed to define the probability distribution function of the source phenomenon. That is, "the physics lies in the fluctuations." Finally, the information loss can be shown to be an extreme value. Thus, if the Fisher Information in the data is ''I'', and the Fisher information in the source is ''J'', the EPI principle states that ''I - J'' = ''extremum''. The extremum for most situations is a minimum, meaning that there is a comforting tendency for any observation to describe its source faithfully. EPI can also be seen as a Game against nature. While this game-theoretic structure is only a manner of speaking, Frieden shows that it has explanatory power.

Frieden (2004: 81-84) grounds EPI in three axioms:
  • ''Law of Conservation of information change''. Let an act of observation perturb a source and the data gathered from that source. Let the perturbed information be δ''I'' and δ''J''. Then δ''I'' = δ''J''.

  • There exist sequences of functions i_{n}(x) and j_{n}(x) such that I = \int \sum_{n} i_{n}(x)dx and J = \int \sum_{n} j_{n}(x)dx.

  • ''Microscopic zero condition''. \exist \kappa, 0<\kappa<1, such that i_{n}(x) - \kappa j_{n}(x) = 0.


Frieden (2004) employs EPI to derive a number of fundamental laws of physics, as well as some established principles and new laws of Biology , the Biophysics of Cancer growth, Chemistry , and Economics . Fisher information, in particular the loss ''I'' - ''J'' resutling from observation, is a powerful new method for deriving laws governing many aspects of nature and human society.


REFERENCE

  • B. Roy Frieden , 2004. ''Science from Fisher Information'', 2nd ed. Cambridge University Press.



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