# Inflation without a beginning: A Null boundary proposal

@article{Aguirre2003InflationWA, title={Inflation without a beginning: A Null boundary proposal}, author={A. Aguirre and S. Gratton}, journal={Physical Review D}, year={2003}, volume={67}, pages={083515} }

We develop our recent suggestion that inflation may be made past eternal, so that there is no initial cosmological singularity or "beginning of time". Inflation with multiple vacua generically approaches a steady-state statistical distribution of regions at these vacua, and our model follows directly from making this distribution hold at all times. We find that this corresponds (at the semi-classical level) to particularly simple cosmological boundary conditions on an infinite null surface near… Expand

#### 56 Citations

Arrows of time and the beginning of the universe

- Physics
- 2013

I examine two cosmological scenarios in which the thermodynamic arrow of time points in opposite directions in the asymptotic past and future. The first scenario, suggested by Aguirre and Gratton,… Expand

The most probable size of the Universe

- Physics
- 2005

Abstract It has recently been suggested, by Firouzjahi, Sarangi, and Tye, that string-motivated modifications of the Hartle–Hawking wave function predict that our Universe came into existence from… Expand

Unitary Evolution and Cosmological Fine-Tuning

- Physics
- 2010

Inflationary cosmology attempts to provide a natural explanation for the flatness and homogeneity of the observable universe. In the context of reversible (unitary) evolution, this goal is difficult… Expand

Spontaneous inflation and the origin of the arrow of time

- Physics
- 2004

We suggest that spontaneous eternal inflation can provide a natural explanation for the thermodynamic arrow of time, and discuss the underlying assumptions and consequences of this view. In the… Expand

Initial conditions for bubble universes

- Physics
- 2008

The ''bubble universes'' of Coleman and De Luccia play a crucial role in string cosmology. Since our own Universe is supposed to be of this kind, bubble cosmology should supply definite answers to… Expand

The emergent universe: inflationary cosmology with no singularity

- Physics
- 2002

Observations indicate that the universe is effectively flat, but they do not rule out a closed universe. The role of positive curvature is negligible at late times, but can be crucial in the early… Expand

The eternal sunshine of the spotless mind

- Physics
- 2008

We extend the worldline measure for pocket formation in eternal inflation to allow for time-ordered bubble formation. Such a time-ordering is equivalent to imposing a preferred time-slicing on the… Expand

Does Inflation Provide Natural Initial Conditions for the Universe

- Physics
- 2005

If our universe underwent inflation, its entropy during the inflationary phase was substantially lower than it is today. Because a low-entropy state is less likely to be chosen randomly than a… Expand

Does inflation provide natural initial conditions for the universe

- Physics
- 2005

If our universe underwent inflation, its entropy during the inflationary phase was substantially lower than it is today. Because a low-entropy state is less likely to be chosen randomly than a… Expand

Eternal inflation and its implications

- Physics, Economics
- 2007

I summarize the arguments that strongly suggest that our universe is the product of inflation. The mechanisms that lead to eternal inflation in both new and chaotic models are described. Although the… Expand

#### References

SHOWING 1-10 OF 47 REFERENCES

Essay: An Alternative to Inflation

- Physics
- 2002

Inflationary models are generally credited with explaining the large scale homogeneity, isotropy, and flatness of our universe as well as accounting for the origin of structure (i.e., the deviations… Expand

Why does inflation start at the top of the hill

- Physics
- 2002

We show why the universe started in an unstable de Sitter state. The quantum origin of our universe implies one must take a ``top down'' approach to the problem of initial conditions in cosmology, in… Expand

Could the Universe Have Recovered from a Slow First Order Phase Transition

- Physics
- 1983

We investigate the cosmological consequences of a phase transition which is driven primarily by slow nucleation of bubbles of the new phase via the effectively zero temperature quantum tunneling… Expand

Steady state eternal inflation

- Physics
- 2002

Since the advent of inflation, several theorems have been proven suggesting that although inflation can (and generically does) continue eternally into the future, it cannot be extended eternally into… Expand

Inflationary universe: A possible solution to the horizon and flatness problems

- Physics
- 1981

The standard model of hot big-bang cosmology requires initial conditions which are problematic in two ways: (1) The early universe is assumed to be highly homogeneous, in spite of the fact that… Expand

Tall tales from de Sitter space I: Renormalization group flows

- Physics
- 2002

We study solutions of Einstein gravity coupled to a positive cosmological constant and matter which are asymptotically de Sitter and homogeneous. Regarded as perturbations of de Sitter space, a… Expand

Nonperturbative amplification of inhomogeneities in a self-reproducing universe.

- Physics, Medicine
- Physical review. D, Particles and fields
- 1996

The distribution of energy density in a stationary self-reproducing inflationary universe is investigated to demonstrate that nonperturbative effects in quantum cosmology, at least in principle, may have significant observational consequences, including an apparent violation of the Copernican principle. Expand

Creation of open universes from de Sitter space

- Physics
- Nature
- 1982

Hawking1,2 has shown that event horizons produce thermal radiation. I propose here a new cosmological model which has an early event horizon and in which the observed3 cosmic microwave background… Expand

Inflationary spacetimes are not past-complete

- Physics
- 2001

Many inflating spacetimes are likely to violate the weak energy condition, a key assumption of singularity theorems. Here we offer a simple kinematical argument, requiring no energy condition, that a… Expand

Causality and cosmic inflation

- Physics
- 1999

In the context of inflationary models with a pre-inflationary stage, in which the Einstein equations are obeyed, the null energy condition is satisfied, and spacetime topology is trivial, we argue… Expand