  I propose here a new concept of information based on two relevant aspects of
its expression. The first related to the undeniable fact that the expression of
information modifies the physical state of its receiver. The second to the
arbitrariness of such physical changes. In fact, these changes are not
deducible from physical laws but from a code established arbitrarily. Thus,
physical information is proposed here as the capacity of producing arbitrary
changes. Once defined physical information from this physical point of view, I
deduce some basic properties of informed systems. These properties (renewal,
self-reproducing, evolution, diversification) are immediately recognized as the
attributes most characteristic of living beings, the only natural informed
systems we know. I also propose here a double evaluation of information. The
former is an absolute measure of the physical effects of its expression based
on Einstein's probability. The second is a functional measure based on the
probability that an informed systems attain a given objective as consequence of
the expression of its information.
