Abstract
Dark energy accounts for most of the matter-energy content of our universe, yet current theories of its origin rely on radical physical assumptions such as the holographic principle or controversial anthropic arguments. We give a better motivated explanation for dark energy, claiming that it arises from a small negative scalar-curvature present even in empty spacetime. The vacuum has this curvature because spacetime is fundamentally discrete and there are more ways for a discrete geometry to have negative curvature than positive. We explicitly compute this effect using a variant of the well known dynamical-triangulations (DT) model for quantum gravity. Our model predicts a time-varying non-zero cosmological constant with a current value, in natural units, in agreement with observation. This calculation is made possible by a novel characterization of the possible DT action values combined with numerical evidence concerning their degeneracies.
Highlights
Multiple independent sets of empirical data [1,2,3,4] indicate that about 70% of the matter and energy in our universe comes from a mysterious repulsive gravitational effect known as ‘‘dark energy’’
Our work provides a simpler, better motivated model for dark energy set within the well-known dynamical triangulations (DT) approach to quantum gravity
Notice that since action values are global observables, this effect is independent of the local details of the ‘‘metric’’, i.e. the local structure of the triangulation
Summary
Multiple independent sets of empirical data [1,2,3,4] indicate that about 70% of the matter and energy in our universe comes from a mysterious repulsive gravitational effect known as ‘‘dark energy’’. Our work provides a simpler, better motivated model for dark energy set within the well-known dynamical triangulations (DT) approach to quantum gravity. This model assumes no holographic principle, uses no additional matter fields or finely tuned parameters, and does not modify general relativity beyond the geometric discretization inherent in dynamical-triangulations spacetimes. The progenitor of the DT theory, called the Regge calculus, has been used successfully in numerical general-relativity and quantum gravity for nearly five decades [25,26,27,28,29,30,31]. We suspect that the effect described in this paper is a generic feature of any quantum-gravity theory which predicts a discrete spacetime geometry and which has general relativity as its large-distance limit
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