What is Shannon information?

entity; it is always tied to a physical representation. It is represented by engraving on a stone tablet, a spin, a charge, a hole in a punched card, a mark on a paper, or some other equivalent.” (1996, p. 188; see also Landauer 1991). This view is also adopted by some philosophers of science; for instance, Peter Kosso states that “information is transferred between states through interaction.” (1989, p. 37). The need of a carrier signal sounds natural in the light of the generic idea that physical influences can only be transferred through interactions. On this basis, information is conceived by many physicists as a physical entity with the same ontological status as energy; it has also been claimed that its essential property is the power to manifest itself as structure when added to matter (Stonier 1990, 1996). As we argued above, pace Timpson, the abstract nature of information is not an obstacle to a physical interpretation of the concept. Nevertheless, it might be thought that the neutrality of Shannon information with respect to the physical theory −or theories− involved in the implementation of the communication arrangement is really a trouble for the physical interpretation. However, this conclusion is not unavoidable. In fact, many physical concepts, through the evolution of the discipline, have experienced a process of abstraction and generalization in such a way that, at present, they are no longer tied to a specific theory but permeate the whole of physics. Again, energy is the most conspicuous example: since essentially present in all the theories of physics, it is not tied to one in particular; it has different physical manifestations in different domains; nevertheless, the concept of energy is perhaps the physical concept par excellence. Mutatis mutandis, the same can be said of information, and therefore its theoretical neutrality is not an insurmountable obstacle to interpret the concept in physical terms. The difference between the epistemic and the physical interpretations of information is not merely nominal, but may yield different conclusions regarding certain common physical situations. For instance, in the influential philosophical tradition that explains scientific observation in terms of information (Shapere 1982, Brown 1987, Kosso 1989), the way in which information is conceived leads to very different consequences regarding observation. This turns out to be particularly clear in the so-called ‘negative experiments’ (see Jammer 1974), in which it is assumed that an object or event has been observed by noting the absence of some other object or event. From the informational view of scientific observation, observation without a direct physical interaction between the observed object and an appropriate destination is only