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Wormhole Nucleation from Anti-de Sitter vs Hartle-Hawking No-Boundary

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	Wormhole Nucleation from Anti-de Sitter Speculative	Hartle-Hawking No-Boundary Speculative
Proposed	2024 / 2026	1983
Key figures	Panos Betzios, Olga Papadoulaki, George Lavrelashvili, Jean-Luc Lehners	James Hartle, Stephen Hawking
In one sentence	A wave function for the universe in which a Euclidean wormhole, anchored in an anti-de Sitter region, gives birth to an expanding universe that begins with inflation.	The universe has no temporal boundary at the beginning. In Euclidean time, the universe is a smooth four-dimensional surface with no edge, like asking what is south of the South Pole.
Predictions	A small shift and faint oscillations in the [[cosmic microwave background]] on the largest angular scales, with a size set by the wormhole's charge Short-wavelength fluctuations identical to those of standard inflation, so the signature appears only on the largest scales Wormholes with small charge give a longer phase of inflation than wormholes with large charge	No initial [[singularity]] Universe wavefunction smooth at a = 0 Predicts a specific spectrum of cosmological perturbations
Where it breaks	Lavrelashvili and Lehners find that no-boundary instantons still dominate the overall probability, which weakens the case that wormholes are the preferred beginning. The universe needs a parent anti-de Sitter or flat region to emerge from, which moves the question of origins back one step. The predicted signal sits on the largest scales of the sky, where there are too few independent patches to measure it precisely.	Feldbrugge, Lehners, Turok (2017) argue the proposal predicts an unstable universe Direction of "outgoing" vs "incoming" mode is contested A more careful mathematical analysis of the path integral suggests deeper problems, hinting the proposal may predict unstable outcomes (see Go Deeper) Maldacena (2024) re-examines the no-boundary proposal and finds it predicts spatial curvature in conflict with observations, and is non-normalizable for landscape-like potentials. Ivo, Li & Maldacena (2024) show that once you account for the regions of space we cannot observe, the mathematics of the no-boundary state leads to physically unrealistic predictions, sharpening the case against the original proposal.
Key unresolved problem	Which beginning wins: the wormhole, or the no-boundary instanton it turns into at zero charge. Current calculations still favour no-boundary overall, so the wormhole route needs a reason to be selected.	The instability problem: a careful redo of the math by Feldbrugge, Lehners, and Turok suggests the no-boundary proposal predicts runaway, ever-growing fluctuations, which would mean an unstable universe rather than the smooth one we see.
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Wormhole Nucleation from Anti-de Sitter

2024 / 2026 · Speculative

Hartle-Hawking No-Boundary

1983 · Speculative

Proposed

2024 / 2026

1983

Key figures

Panos Betzios, Olga Papadoulaki, George Lavrelashvili, Jean-Luc Lehners

James Hartle, Stephen Hawking

In one sentence

A wave function for the universe in which a Euclidean wormhole, anchored in an anti-de Sitter region, gives birth to an expanding universe that begins with inflation.

The universe has no temporal boundary at the beginning. In Euclidean time, the universe is a smooth four-dimensional surface with no edge, like asking what is south of the South Pole.

Predictions

A small shift and faint oscillations in the [[cosmic microwave background]] on the largest angular scales, with a size set by the wormhole's charge
Short-wavelength fluctuations identical to those of standard inflation, so the signature appears only on the largest scales
Wormholes with small charge give a longer phase of inflation than wormholes with large charge

No initial [[singularity]]
Universe wavefunction smooth at a = 0
Predicts a specific spectrum of cosmological perturbations

Where it breaks

Lavrelashvili and Lehners find that no-boundary instantons still dominate the overall probability, which weakens the case that wormholes are the preferred beginning.
The universe needs a parent anti-de Sitter or flat region to emerge from, which moves the question of origins back one step.
The predicted signal sits on the largest scales of the sky, where there are too few independent patches to measure it precisely.

Feldbrugge, Lehners, Turok (2017) argue the proposal predicts an unstable universe
Direction of "outgoing" vs "incoming" mode is contested
A more careful mathematical analysis of the path integral suggests deeper problems, hinting the proposal may predict unstable outcomes (see Go Deeper)
Maldacena (2024) re-examines the no-boundary proposal and finds it predicts spatial curvature in conflict with observations, and is non-normalizable for landscape-like potentials.
Ivo, Li & Maldacena (2024) show that once you account for the regions of space we cannot observe, the mathematics of the no-boundary state leads to physically unrealistic predictions, sharpening the case against the original proposal.

Key unresolved problem

Which beginning wins: the wormhole, or the no-boundary instanton it turns into at zero charge. Current calculations still favour no-boundary overall, so the wormhole route needs a reason to be selected.

The instability problem: a careful redo of the math by Feldbrugge, Lehners, and Turok suggests the no-boundary proposal predicts runaway, ever-growing fluctuations, which would mean an unstable universe rather than the smooth one we see.

Reader vote

No votes yet