If I consider an isolated system, e.g. two masses, i know I can apply the energy conservation principle considering the kinetic energy and the gravitational potential energy of the two masses. But to be more precise, the energy is exchanged between the two masses and the gravitational field. So I should consider the system as composed by (mass1 + mass2 + field).
BUT the field itself will interact with any mass (not only the two masses of my system). Does this mean that my system is not isolated anymore?