logologo

Popular Boards

1 Mentions
Jean-Luc Lehners | Physical review. D. Particles, fields, gravitation, and cosmology/Physical review. D, Particles, fields, gravitation, and cosmology | (2012)
Primary Link DOI Openalex Full text (OA)

Abstract

Eternal inflation produces pocket universes with all physically allowed vacua and histories. Some of these pocket universes might contain a phase of slow-roll inflation, some might undergo cycles of cosmological evolution and some might look like the galilean genesis or other "emergent" universe scenarios. Which one of these types of universe we are most likely to inhabit depends on the measure we choose in order to regulate the infinities inherent in eternal inflation. We show that the currently leading measure proposals, namely the global light-cone cut-off and its local counterpart, the causal diamond measure, as well as closely related proposals, all predict that we should live in a pocket universe that starts out with a small Hubble rate, thus favoring emergent and cyclic models. Pocket universes which undergo cycles are further preferred, because they produce habitable conditions repeatedly inside each pocket.

Tags

Sample Definition And Size

The paper is theoretical and does not involve empirical sampling; it analyzes pocket universes produced by eternal inflation using measure proposals. No sample size is applicable.

Study Type

Theoretical cosmology study; analytical investigation of measure proposals in eternal inflation (global light-cone cutoff, causal diamond measure) and their implications for pocket universe types.

Conflicts Of Interest

No conflicts of interest are declared in the paper (no statement found in available metadata).

Results Summary

The analysis shows that leading measure proposals (global light-cone cutoff and causal diamond measure) predict that we are most likely to inhabit a pocket universe that begins with a small Hubble rate, favoring emergent and cyclic universe models. Among these, cyclic pocket universes are further preferred because they repeatedly produce habitable conditions within each pocket. ([journals.aps.org](https://journals.aps.org/prd/abstract/10.1103/PhysRevD.86.043518?utm_source=openai))

Referenced In

StarTalk

Season 17, Episode 3: Bubble Universes Explained

Hey StarTalkers! Season 17, Episode 3 saw Neil and Chuck tackle a selection of “Cosmic Queries,” including lots of black hole questions and one intriguing inquiry about “bubble universes.”

Alcubierre Drives, Antimatter Multiverses & More! | Cosmic Queries #103This “bubble universe” discussion covered some interesting ground – such as the possible relationship with dark energy and dark matter – but it was quite short for a topic so complex.

So if you’re feeling lost about what a bubble universe even is, this is the crash course you’ve been looking for. While there are many interesting papers touching on the original question, here the focus is on Alan Guth’s influential 2007 paper.

The “False” Vacuum and the Creation of the Universe

The crucial idea underpinning “bubble” universes is the idea of a false vacuum. Check the first attached figure (taken from the paper) for a useful visual.

The core idea is that the “inflaton field” – a field hypothesized to drive cosmic inflation – was originally resting at a “false vacuum.”

The figure shows it perfectly: imagine you lived your life on a raised plateau – like the ball in the diagram – and never knew anything beyond this surface. You’d think this was as low as things got, but in fact, what you see as the “lowest point” is much higher than the true lowest point.

You don’t know it, but you can still fall.

But for the inflaton field, “falling” means generating a new universe. Just like you’d lose gravitational potential falling from the plateau, the inflaton field loses potential energy, creating a bubble-burst of inflation, a.k.a. a universe.

The Cosmic Foam Multiverse

But it doesn’t stop there. Take a look at the next figure.

The false vacuum at the top splits into three: the new universe and two false vacuums. Crucially, this figure doesn’t show expansion: each new false vacuum is actually the same size as the original one.

As the graph continues downwards, you see what happens. Just like the original false vacuum state collapsed, so do the next two, and the next two, and so on.

A single bubble becomes a frothing mess of bubble universes: the bubble multiverse.

So the universe we know could be just a single bubble in a vast cosmic foam.  

Read Full Post
5