> In the theory we present here, the status of information in physics is analogous to that of (say) energy: given the laws of motion of physical objects, neither the concept of energy nor the conservation law for the energy-momentum tensor are necessary for making any prediction from initial data, yet our understanding of the physical world would be radically incomplete without them. The conservation law explains some aspects of motion as consequences of a deeper regularity in nature – which is why we expect as-yet-undiscovered laws of motion to conserve the energy-momentum tensor too; but we don’t expect to derive new laws of motion from it. It is a principle – a law of physics that constrains other laws rather than the behaviour of physical objects directly.