# Arrows of time and the beginning of the universe

@article{Vilenkin2013ArrowsOT, title={Arrows of time and the beginning of the universe}, author={Alexander Vilenkin}, journal={Physical Review D}, year={2013}, volume={88}, pages={043516} }

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, assumes that the two asymptotic regions are separated by a de Sitter-like bounce, with low-entropy boundary conditions imposed at the bounce. Such boundary conditions naturally arise from quantum cosmology with Hartle-Hawking wave function of the universe. The bounce hypersurface breaks de Sitter…

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## References

SHOWING 1-10 OF 69 REFERENCES

### Arrows of Time in the Bouncing Universes of the No-boundary Quantum State

- Physics
- 2012

We derive the arrows of time of our universe that follow from the no-boundary theory of its quantum state (NBWF) in a minisuperspace model. Arrows of time are viewed four-dimensionally as properties…

### Inflation without a beginning: A Null boundary proposal

- Physics
- 2003

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…

### Origin of structure in the Universe.

- PhysicsPhysical review. D, Particles and fields
- 1985

A scale-free spectrum of density perturbations which could account for the origin of galaxies and all other structure in the Universe is obtained.

### Open and closed universes, initial singularities, and inflation.

- MathematicsPhysical review. D, Particles and fields
- 1994

The existence of initial singularities in expanding universes is proved without assuming the timelike convergence condition, which means that a recent result on initial singularity in open, future-eternal, inflating spacetimes may not be extended to include many closed universes.

### 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…

### Dynamics of false-vacuum bubbles.

- PhysicsPhysical review. D, Particles and fields
- 1987

The possibility of localized inflation is investigated by calculating the dynamics of a spherically symmetric region of false vacuum which is separated by a domain wall from an infinite region of true vacuum, and it is suggested that this mechanism is likely to lead to an instability of Minkowski space.

### Bounce behaviour in Kantowski–Sachs and Bianchi cosmologies

- Physics
- 2006

Many cosmological scenarios envisage either a bounce of the universe at early times, or collapse of matter locally to form a black hole which re-expands into a new expanding universe region. Energy…

### Boundary conditions in quantum cosmology.

- PhysicsPhysical review. D, Particles and fields
- 1986

A boundary condition in superspace is proposed which selects the tunneling solution for \ensuremath{\psi}.

### Symmetric-bounce quantum state of the universe

- Physics
- 2009

A proposal is made for the quantum state of the universe that has an initial state that is macroscopically time symmetric about a homogeneous, isotropic bounce of extremal volume and that at that…