Unimodular loop quantum gravity and the problems of time

  title={Unimodular loop quantum gravity and the problems of time},
  author={Lee Smolin},
  journal={Physical Review D},
  • L. Smolin
  • Published 10 August 2010
  • Physics
  • Physical Review D
We develop the quantization of unimodular gravity in the Plebanski and Ashtekar formulations and show that the quantum effective action defined by a formal path integral is unimodular. This means that the effective quantum geometry does not couple to terms in the expectation value of energy proportional to the metric tensor. The path integral takes the same form as is used to define spin foam models, with the additional constraint that the determinant of the four metric is constrained to be a… 

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  • Kodama
  • Physics, Mathematics
    Physical review. D, Particles and fields
  • 1990
The analysis of the quantum Robertson-Walker universe indicates that if the superspace is extended to such a classically forbidden region, the holomorphic representation picks up some restricted class of solutions in general, which leads to a new ansatz on the boundary condition of the Universe.

Time and the interpretation of canonical quantum gravity.

  • UnruhWald
  • Physics
    Physical review. D, Particles and fields
  • 1989
It is argued that the interpretive problems of quantum gravity are not alleviated by the incorporation of observers into the theory, and a proposal for a formulation of canonical quantum gravity in which an appropriate nondynamical time parameter is present is made.

Role of time in the sum-over-histories framework for gravity

I sketch a self-contained framework for quantum mechanics based on its path-integral or “sum-over-histories” formulation. The framework is very close to that for classical stochastic processes like

Possible solution to the cosmological-constant problem.

A modified-gravity-type model of two hypothetical massless vector fields are presented, which give rise to a standard Friedmann-Robertson-Walker universe and standard Newtonian gravitational dynamics of small systems.

On the Role of Time in the Sum-over-histories Framework for Gravity, paper presented to the conference on The History of Modern Gauge The- ories, held Logan, Utah

  • published in Int. J. Theor. Phys
  • 1987