Could a multiverse be hospitable to life?

Artistic impression of a Multiverse — where our Universe
is only one of many. According to the research varying
amounts of dark energy have little effect on star
formation. This raises the prospect of life in other
universes — if the Multiverse exists. Credit: Jaime
Salcido/simulations by the EAGLE Collaboration

A Multiverse—where our Universe is only one of many—might not
be as inhospitable to life as previously thought, according
to new research.


Questions about whether other universes might exist as part of
a larger Multiverse, and if they could harbour life, are
burning issues in modern cosmology.

Now new research led by Durham University, UK, and Australia’s
University of Sydney, Western Sydney University and the
University of Western Australia, has shown that life could
potentially be common throughout the Multiverse, if it exists.

The key to this, the researchers say, is , a mysterious “force” that is
accelerating the expansion of the Universe.

Scientists say that current theories of the origin of the
Universe predict much more dark energy in our Universe than is
observed. Adding larger amounts would cause such a rapid
expansion that it would dilute matter before any stars, planets
or life could form.

The Multiverse theory, introduced in the 1980s, can explain the
“luckily small” amount of dark energy in our Universe that
enabled it to host life, among many universes that could not.

Using huge computer simulations of the cosmos, the new research
has found that adding dark energy, up to a few hundred times
the amount observed in our Universe, would actually have a
modest impact upon star and planet formation.




Simulations of the formation of structure in an expanding
universe, featuring a universe with no cosmological
constant/dark energy (left), a universe with 10 times more
dark energy than in our universe (center), and a universe
with a very large cosmological constant/dark energy, 100
times more than in our universe (right). In the color scheme,
blue colors represent high density regions of the universe
where stars are forming, and red, low density. The
simulations run for approximately 14 billion years. All
models use the same initial conditions after the big bang. At
early times, the Universe was very hot and dense. Gravity
pulls matter together to form structure, while the rapid
expansion caused by dark energy dilutes all matter as the
Universe ages, halting star formation. Credit: Jaime
Salcido/EAGLE

This opens up the prospect that life could be possible
throughout a wider range of other universes, if they exist, the
researchers said.

The findings are to be published in two related papers in the
journal Monthly Notices of the Royal Astronomical
Society
.

The simulations were produced under the EAGLE (Evolution and
Assembly of GaLaxies and their Environments) project—one of the
most realistic simulations of the observed Universe.

Jaime Salcido, a postgraduate student in Durham University’s
Institute for Computational Cosmology, said: “For many
physicists, the unexplained but seemingly special amount of
dark energy in our Universe is a frustrating puzzle.

“Our simulations show that even if there was much more dark
energy or even very little in the Universe then it would only
have a minimal effect on star and planet formation, raising the
prospect that life could exist throughout the Multiverse.”

Dr. Luke Barnes, a John Templeton Research Fellow at Western
Sydney University, said: “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.

“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.”




Simulations of the formation of a group of galaxies in an
expanding universe, featuring no cosmological constant (left)
and a very large cosmological constant (right). In the color
scheme, lighter colors represent denser parts of the
universe, when gravity is drawing matter together into
galaxies. The simulation runs for 15 billion years. Without a
cosmological constant (left), matter comes together under the
attractive force of gravity into smaller galaxies, which
combine into a large galaxy. With a large cosmological
constant (right), the faster expansion of the universe stops
matter from grouping together, and galaxies fail to form.
Credit: Luke A. Barnes, Pascal J. Elahi, Jaime Salcido,
Richard G. Bower, Geraint F. Lewis/EAGLE

Dr. Pascal Elahi, Research Fellow at the University of Western
Australia, said: “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 to arise. Even increasing dark energy many
hundreds of times might not be enough to make a dead universe.”

The researchers said their results were unexpected and could be
problematic as they cast doubt on the ability of the theory of
a Multiverse to explain the observed value of dark energy.

According to the research, if we live in a Multiverse, we’d
expect to observe much more dark energy than we do—perhaps 50
times more than we see in our Universe.

Although the results do not rule out the Multiverse, it seems
that the tiny amount of dark energy in our Universe would be
better explained by an, as yet, undiscovered law of nature.

Professor Richard Bower, in Durham University’s Institute for
Computational Cosmology, said: “The formation of stars in a
is a battle between the attraction of
gravity, and the repulsion of dark energy.

“We have found in our simulations that universes with much more
dark energy than ours can happily form stars. So why such a
paltry amount of dark in our Universe?

“I think we should be looking for a new law of physics to
explain this strange property of our Universe, and the
Multiverse theory does little to rescue physicists’
discomfort.”

Explore further:

After death, Hawking cuts ‘multiverse’ theory down to size

More information: Jaime Salcido et al, The impact of
dark energy on galaxy formation. What does the future of our
Universe hold?, Monthly Notices of the Royal Astronomical
Society
(2018). DOI:
10.1093/mnras/sty879

Luke A Barnes et al. Galaxy Formation Efficiency and the
Multiverse Explanation of the Cosmological Constant with EAGLE
Simulations, Monthly Notices of the Royal Astronomical
Society
(2018). DOI:
10.1093/mnras/sty846

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