The derivations utilize the mathematical principle of extreme physical information (EPI). This principle builds on the well known idea that the observation of a "source" phenomenon is never completely accurate. That is, information is inevitably lost in transit from source to observation. Furthermore, the random errors that creep in are presumed to define the distribution function of the source phenomenon. That is, "the physics lies in the fluctuations." Finally, the information loss may be shown to be an extreme value. Thus, if the observed level of Fisher information in the data has value I, and the level of Fisher information that existed at the source has value J, the EPI principle states that I − J = extremum. The extremum is a minimum in most problems, meaning that there is a tendency for any observation to faithfully match up with its source. The physical and mathematical correctness of Frieden's ideas have been characterized as highly dubious by several knowledgeable observers; see, for example, Raymond F. Streater's Lost Causes in Theoretical Physics: Physics from Fisher Information, and Cosma Shalizi's review of Physics from Fisher Information.
The EPI principle is a variational principle that has been used to derive most fundamental laws of physics, as well as laws of biology, cancer growth, chemistry, and economics. These include new laws and concepts as well. In this way, Fisher information, and in particular its loss I − J during observation, provides a bridge for deriving laws of nature in general.
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