Should the search for alien
life in our universe come up empty-handed, it might be worth checking in on a
neighboring universe instead. According to a new pair of studies in the journal
Monthly Notices of the Royal Astronomical Society, there’s a decent chance that
life-fostering planets could exist in a parallel universe — even if that
universe were being torn apart by dark energy.
The idea that our universe
is just one of many, perhaps infinite, other universes is known as the
multiverse theory. Scientists have previously thought that such parallel
universes, if they exist, would have to meet an extremely strict set of
criteria to allow for the formation of stars, galaxies and life-fostering
planets like those seen in our own universe.
In the new study,
researchers ran a massive computer simulation to build new universes under
various starting conditions. They found that the conditions for life might be a
little broader than previously thought — especially when it comes to the
mysterious pull of dark energy.
Dark energy is a mysterious,
invisible force thought to exist in the empty spaces of our universe. You could
think about it as the archnemesis of gravity; while gravity pulls matter closer
together, dark energy flings it apart — and dark energy is winning this cosmic
tug-of-war handily.
Not only is our universe
expanding, thanks to the constant, invisible push of dark energy, but the rate
of that expansion is also getting faster and faster every day. It's thought
that, as more empty space appears in the universe, even more dark energy appears
to fill it. (Dark energy is not the same as dark matter, which is an abundant,
invisible form of matter thought to be responsible for some very weird
gravitational phenomena around space.)
Scientists don't know
exactly what dark energy is or how it works; some think it's an intrinsic
property of space — what Einstein called the cosmological constant — while
others attribute it to a fundamental force called quintessence, with dynamic
rules all its own. Others don't even agree that it exists. But whatever it is,
everyone can agree that there's a whole lot of it: According to the best
current estimates, nearly 70 percent of the mass-energy of our universe may be
made of dark energy.
This quantity, for whatever
reason, is in the right range to allow galaxies to grow and foster life. It is
thought that if we lived in a universe with too much dark energy, space might
expand faster than galaxies could possibly form. Too little dark energy, and
runaway gravity could cause every galaxy to collapse in on itself before life
ever had a chance to appear.
But the question of how much
dark energy is "too much" or "too little" is a topic for
debate — and it's this issue of quantity that the authors of the new studies
hoped to narrow down.
In each simulation, the
researchers adjusted the amount of dark energy present in that universe,
ranging from none to several hundred times the amount in our own universe. The
good news: Even in universes with 300 times as much dark energy as ours, life
found a way.
"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," study co-author
Pascal Elahi, a research fellow at the University of Western Australia, said in
a statement. "Even increasing dark energy many hundreds of times might not
be enough to make a dead universe."
That's good news for fans of
extraterrestrial life and the multiverse theory. But a bigger question remains:
If galaxies could still thrive on so much dark energy, why did our universe get
handed such a seemingly small amount?
"I think we should be
looking for a new law of physics to explain this strange property of our
Universe," co-author Richard Bower, a professor at Durham University's
Institute for Computational Cosmology, said in the statement.
Of course, finding new laws
of physics is easier said than done. Scientists won't give up easily — but
perhaps, to hedge their bets, they should also look for a parallel universe
where some intelligent life has already done it for them.
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