Is singularity resolution trivial?

Di, Jia

doi:10.48550/arxiv.2204.12304

Cited by 4 publications

(6 citation statements)

References 22 publications

(34 reference statements)

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Last but certainly not least, let us not forget that quantum gravitational light ray fluctuations are not just computable, but also potentially measurable. To realize this potential, we should probably look at highly non-perturbative effects such as quantum gravitational tunneling around would-be singularities [22]. It is worth investigating light ray fluctuations for the boundary conditions of these events.…”

Section: Outlooksmentioning

confidence: 99%

Light ray fluctuation and lattice refinement of simplicial quantum gravity

Jia

2023

Class. Quantum Grav.

View full text Add to dashboard Cite

In several approaches of non-perturbative quantum gravity, a major outstanding problem is to obtain results valid at the infinite lattice refinement limit. Working with Lorentzian simplicial quantum gravity, we compute light ray fluctuation probabilities in 3D and 4D across different lattices. In a simplified refined box model with the Einstein- Hilbert action, numerical results show that lattice refinement does not simply suppress or simply enhance light ray fluctuations, but actually drives very wide and very narrow light probability distributions towards intermediate ones. A comparison across lattices and across couplings reveals numerical hints at a lattice refinement fixed point associ- ated with a universality class of couplings. The results fit the intuition that quantum spacetime fluctuations reflected by light ray fluctuations start wild microscopically and become mild macroscopically. The refined box model is limited by the assumption of a rigid frame at all scales. The present results suggest further studies around the zero-coupling limit to relax the simplifying assumptions of the model.

show abstract

Section: Outlooksmentioning

confidence: 99%

Light ray fluctuation and lattice refinement of simplicial quantum gravity

Jia

2023

Class. Quantum Grav.

View full text Add to dashboard Cite

show abstract

“…Last but certainly not least, let us not forget that quantum gravitational light ray fluctuations are not just computable, but also potentially measurable. To realize this potential, we should probably look at highly non-perturbative effects such as quantum gravitational tunnelling around would-be singularities [22]. It is worth investigating light ray fluctuations for the boundary conditions of these events.…”

Section: Outlooksmentioning

confidence: 99%

Light ray fluctuations in simplicial quantum gravity

Jia¹

2022

Class. Quantum Grav.

Self Cite

View full text Add to dashboard Cite

A non-perturbative study on the quantum fluctuations of light ray propagation through a quantum region of spacetime is long overdue. Within the theory of Lorentzian simplicial quantum gravity, we compute the probabilities for a test light ray to land at different locations after travelling through a symmetry-reduced box region in 2,3 and 4 spacetime dimensions. It is found that for fixed boundary conditions, light ray fluctuations are generically large when all coupling constants are relatively small in absolute value. For fixed coupling constants, as the boundary size is decreased light ray fluctuations first increase and then decrease in a 2D theory with the cosmological constant, Einstein-Hilbert and R-squared terms. While in 3D and 4D theories with the cosmological constant and Einstein-Hilbert terms, as the boundary size is decreased light ray fluctuations just increase. Incidentally, when studying 2D quantum gravity we show that the global time-space duality with the cosmological constant and Einstein-Hilbert terms noted previously also holds when arbitrary even powers of the Ricci scalar are added. We close by discussing how light ray fluctuations can be used in obtaining the continuum limit of non-perturbative Lorentzian quantum gravity.

show abstract

“…However, there is a trivial alternative. A gravitational path integral may simply not include singular spacetimes in its sum [50].…”

Section: Singularity Avoidance 71 Is Singularity Avoidance Trivial?mentioning

confidence: 99%

“…In a general non-perturbative setting, simplicial manifold models provide a systematic way to incorporate inhomogeneity and anisotropy in quantum cosmology [10,11,12,75,76,77,78,79,80,81,82]. Traditionally, simplicial quantum gravity is studied with respect to an Euclidean contour or an ad hoc complex contour, but there has been growing attention towards the Lorentzian case [4,83,5,70,59,84,50,85,86,87]. In particular, the generalized thimble method employed here and in [70] may be applicable in studies of inhomogeneity and anisotropy.…”

Section: Inhomogeneity Anisotropy and Matter Couplingmentioning

confidence: 99%

See 1 more Smart Citation

Truly Lorentzian quantum cosmology

Di¹

2022

Preprint

View full text Add to dashboard Cite

Quantum cosmology based on Lorentzian path integrals is a promising avenue. However, many previous works allow non-Lorentzian configurations by integrating the squared scale factor over the whole real line. Here we show that restricting the minisuperspace path integral to Lorentzian configurations with positive squared scale factor can significantly change the expectation values. In addition, this enables the study of causal horizons and their quantum fluctuations, and achieves singularity avoidance trivially by excluding singular minisuperspace geometries as non-Lorentzian. The results indicate that semiclassical saddle point approximation is not always valid in truly Lorentzian quantum cosmology. As a consequence, related works on the tunnelling and no-boundary proposals, bouncing cosmology, and the quantum origin of inflation etc. need to be reexamined.

show abstract

Is singularity resolution trivial?

Cited by 4 publications

References 22 publications

Light ray fluctuation and lattice refinement of simplicial quantum gravity

Light ray fluctuation and lattice refinement of simplicial quantum gravity

Light ray fluctuations in simplicial quantum gravity

Truly Lorentzian quantum cosmology

Contact Info

Product

Resources

About