Quantum Gravity and Logical Type: The Graviton Is Real and the Standard Programmes Are Correct

Abstract

The graviton is the superposition of metric perturbations across a class of relativistic worlds. The gravitational reality of the quasi-classical world is the quantum superposition of the complete determinate spacetimes of these worlds: global quantum gravity. Worlds that instantiate the same correlation record differ only in respects the record does not specify. By the principle of indistinguishability, they therefore constitute a single physical state: a 'class-of-worlds-as-a-world'. Quantum phenomena are not strange entities in an ordinary world. The quasi-classical world is a higher-logical-type domain, literally a metaworld. It is quantum at every scale. The direct evidence is the formalism itself: it is class arithmetic throughout.The dual ontology identifies quantisation as a phenomenon of higher logical type. A quantum is the phase-weighted superposition of determinate element-level configurations of a given field. The photon, gluon and weak bosons share this architecture, each superposing the configurations of the corresponding field across the worlds. So too does the graviton, superposing metric perturbations. The four forces are thereby unified under this one quantum architecture, differing only in the specific element-level field superposed.Perturbative quantum gravity correctly identifies the graviton. Its fixed background is the solution of general relativity matching the geometry already measured for the situation. A measurement result is part of the correlation record, so this is the geometry the correlation record fixes in every world of the class. To the resolution of the record, the programme computes the genuine graviton, and is predictive. Beyond that resolution, the backgrounds of the worlds differ, and the single fixed background loses its warrant. That limitation belongs to the representation, not to gravity. The graviton is real.Background-independent approaches to quantum gravity have precisely the formal structure of quantisation in the dual ontology. In their covariant form, they construct the phase-weighted superposition of complete four-geometries, and make predictions by sorting them into classes by outcome. Here again, the difficulties belong to the representation, not to the formalism: the superposition is read as the state of a single world. One version, the 'generalised quantum mechanics of spacetime', selects histories by records. Read as one world, it leaves open which classes describe the world. Read as a class of worlds, the classes the record selects constitute the quasi-classical world, and the sum of their solutions of general relativity is global quantum gravity.The formalism stands unchanged: it is the class arithmetic of the metaworld. Quantum gravity is the superposition of the gravitational fields of the worlds in the class: the gravity of general relativity at the class level.