There might be only one! Is our Universe all alone?

17 May 2018

A new study by Dr Luke Barnes and Prof. Geraint Lewis has cast doubt on the idea that our Universe is one of many in an immense multiverse.

Artistic Impression of multiverse. Credit:Jaime Salcido-EAGLE/Project
Artistic Impression of multiverse. Credit:Jaime Salcido-EAGLE/Project

The idea that we are living in one of many possible universes sounds like science fiction, but recently cosmology has called on this multiverse to solve some of the deepest cosmological parameters. But could this possibly be true? SIfA's Dr Luke Barnes (now Western Sydney University) and Prof. Geraint Lewis, and an international team of astronomers, have wondered the same.

Proposed back in the 80s, the concept of multiverse was introduced to explain why some fundamental properties of the universe appear to be fine-tuned, just the right values to allow complexity and life.

"The idea is there is a lot of things about our universe which seem 'fine-tuned'," says Dr Luke Barnes to the Sydney Morning Herald, "There are a whole lot of properties - like say how heavy an electron is - we don't know why they are that weight. And if you change them, even slightly, the universe becomes too simple to make life."

One of the strengths of the multiverse theory is that it can explain the amount of Dark Energy in the universe. This weird substance regulates the expansion of our universe, causing it to accelerate, but theoretical physicists predict there should be vastly more than it appears to be. However, the observed amount seems to be just right to let stars, planets, and ultimately, life to be. The multiverse idea solves this paradox by permitting each multiverse to have a different amount of dark energy, and we live in a very low dark energy one. While this is an attractive solution, the problem is that we cannot observe any of the multitude of other universe.

Dr Barnes and Prof. Lewis and the "Evolution and Assembly of GaLaxies and their Environments" (EAGLE) team use state-of-art simulations of the evolution possible alternative universes to investigate how varying the amount of the dark energy will affect the formation of stars and life. And the results are surprising:

"We asked ourselves how much dark energy can there be before life is impossible? Our simulations showed that the accelerated expansion driven by dark energy has hardly any impact on the birth of stars, and hence places for life to arise," said co-lead author Dr Pascal Elahi, a scientist at the University of Western Australia.

"The Multiverse was previously thought to explain the observed value of dark energy as a lottery — we have a lucky ticket and live in the Universe that forms beautiful galaxies which permit life as we know it," Dr. Luke Barnes "Our work shows that our ticket seems a

little too lucky, so to speak. It's more special than it needs to be for life. This is a problem for the Multiverse; a puzzle remains.

The two papers are published by Monthly Notices of the Royal Astronomical Society and available on arxiv ( here and here)

Contact: Prof. Geraint Lewis

Phone: 02 9351 5184

Email: 4c0424072d5f3a7d2851063b392a26372e01031a66072f3474073d