  A communication theory for a transmitter broadcasting to many receivers is
presented. In this case energetic considerations cannot be neglected as in
Shannon theory. It is shown that, when energy is assigned to the information
bit, information theory complies with classical thermodynamic and is part of
it. To provide a thermodynamic theory of communication it is necessary to
define equilibrium for informatics systems that are not in thermal equilibrium
and to calculate temperature, heat, and entropy with accordance to Clausius
inequality. It is shown that for a binary file the temperature is proportional
to the bit energy and that information is thermodynamic entropy. Equilibrium
exists in random files that cannot be compressed. Thermodynamic bounds on the
computing power of a physical device, and the maximum information that an
antenna can broadcast are calculated.
