A new proposal to tweak general relativity, if it is correct (and it is consistent with observations), would break down the main barrier to developing a working quantum gravity theory.
Asymptotically Weyl-invariant gravity (AWIG) is further developed within the Palatini formalism as a power-counting renormalizable alternative to general relativity (GR). An expression for the dimensionless exponent n(R) is derived based on dynamical dimensional reduction. We show that this version of AWIG naturally resolves several theoretical issues normally associated with the Palatini formalism.
A falsifiable prediction regarding the frequency of gravitational waves from binary black hole mergers is made. A preliminary analysis of gravitational wave GW150914 yields a maximum tension of 0.9 sigma with GR and marginally favours AWIG. A similar analysis of gravitational wave GW151226 yields a maximum tension of 2.7 sigma with GR and favours AWIG more significantly.
Daniel Coumbe, Aria Rahmaty, "A Falsifiable Alternative to General Relativity" arXiv:2505.15399 (May 21, 2025).
6 comments:
Have you blogged about "quadratic gravity"? It appears to be the minimal renormalizable extension to general relativity.
arXiv:2505.17014 [pdf, ps, other] gr-qc hep-th
Emergent Gravity from Topological Quantum Field Theory: Stochastic Gradient Flow Perspective away from the Quantum Gravity Problem
Authors: Andrea Addazi, Salvatore Capozziello, Jinglong Liu, Antonino Marciano, Giuseppe Meluccio, Xuan-Lin Su
Abstract: We propose a scenario according to which the ultraviolet completion of General Relativity is realized through a stochastic gradient flow towards a topological BF theory. Specifically, we consider the stochastic gradient flow of a pre-geometric theory proposed by Wilczek. Its infrared limit exists, and corresponds to a fixed point where stochastic fluctuations vanish. Diffeomorphism symmetries are restored in this limit, where the theory is classical and expressed by the Einstein-Hilbert action. The infrared phase then corresponds to the classical theory of General Relativity, the quantization of which becomes meaningless. Away from the infrared limit, in the pre-geometric phase of the stochastic gradient flow, the relevant fields of the Wilczek theory undergo stochastic fluctuations. The theory can be quantized perturbatively, generating corrections to the classical Einstein-Hilbert action. The stochastic gradient flow also possesses an ultraviolet fixed point. The theory flows to a topological BF action, to which general non-perturbative quantization methods can be applied. Two phase transitions occur along the thermal time dynamics, being marked by: i) the breakdown of the topological BF symmetries in the ultraviolet regime, which originates the pre-geometric phase described by the Wilczek theory; ii) the breakdown of the parental symmetries characterizing the Wilczek theory, from which General Relativity emerges. The problem of quantizing the Einstein-Hilbert action of gravity finally becomes redundant. △ Less
Submitted 22 May, 2025; originally announced May 2025.
So if a theory is renormalizable, one has certain ways of calculating. But the gravitational potential is long ranged and attractive. It is thermodynamically unstable. Given a way to loose energy, such systems collapse. Maybe nonrenormalizable is correct? Or is there some fundamental reason one wants renormalization?
"Have you blogged about "quadratic gravity"?" Not in any real focused way, although I may have cited papers discussing it in passing.
"is there some fundamental reason one wants renormalization?" Because a viable quantum gravity theory needs to be renormalizable, and as currently formulated, classical GR and the Standard Model of Particle Physics (which is a renormalizable quantum theory of the other fundamental forces), is theoretically incompatible. Fortunately, there aren't many places where both GR and the SM are relevant at the same time, so this incompatibility isn't a huge practical problem, but it implies that one of the theories is flawed, and the conventional wisdom is that this is far more likely to be GR and that the most plausible resolution of the internal inconsistency in the two most fundamental physical theories is to formulate GR in a quantum physical matter. One possible resolution is that it has been impossible to quantize GR because the true theory of gravity is something that looks very like GR in all circumstances where it has been experimentally tested but has some very subtle differences that make it possible to quantize in a way that you can't with GR.
@neo Thanks for noting that paper.
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