Self-Gravitation of Mode Quanta in a Causal Resonator: One-Loop Finiteness in Linearized Quantum Gravity and the Emergence of the Dark-Energy Scale
Perturbative quantum gravity is ultraviolet divergent and, as shown by 't Hooft and Veltman, non-renormalizable. A recent object-relative, Lorentz-invariant weighting of internal electromagnetic modes renders selected one-loop contributions of quantum electrodynamics finite without counterterms. Here that weighting is derived rather than postulated: causality defines a mode resonator bounded by the Hubble radius and re-defined in every inertial frame, and the self-gravitation of each mode quantum deforms its spectrum. Applied to linearized gravity, the graviton self-coupling reaches order unity at the Planck wave number, so that the mode content available to a loop is suppressed beyond it. Any suppression exceeding a threshold fixed by the diagram renders the one-loop integrals finite; no cutoff is imposed and no mode structure above the Planck scale need be derived. For pure gravity the same power counting extends to every loop order, and the leading suppression already meets the resulting condition for every topology with more than one vertex; a single class of single-vertex insertions is excluded. The Bianchi identity takes the role of the Ward identity at one loop, and the transformation between the resonators of two inertial frames is unitary. The same finite mode content yields a vacuum energy density of order H^2/G, of the observed sign and magnitude, from the Planck and causal infrared wave numbers alone. A contribution tracking the instantaneous expansion rate is an exact rescaling of the gravitational constant and is excluded by primordial nucleosynthesis, so the mode basis must be frozen in any inertial system; referring it to the stationary de Sitter horizon fixes the remaining coefficient to the geometric value 6/pi and makes a value for the energy density of gravitational vacuum fluctuations possible which can be interpreted as origin of the dark-energy effect.