A cornerstone of modern cosmology is the realisation that not only is our universe
expanding, but it’s expanding at an accelerating rate. While much is still unknown about what’s
causing this, there are a few theories as to what it could mean for the fate of all things;
the end of the universe. And, according to one theory, the very fabric of time and space
could one day be destroyed because of it. This is Unveiled, and today we're answering
the extraordinary question; Is the universe tearing itself apart?
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For thousands of years, the universe was believed to be stagnant and unchanging. Sure, the planets
had their orbits around the stars, and moons had their orbits around their planets, but that was as
far as it went. It was believed that galaxies - and the distances between galaxies - never
changed. And that the wider universe had remained the same since the dawn of time.
It wasn't until Isaac Newton formulated his laws of gravity that this fundamental
belief was really called into question. In light of Newton’s new laws of nature,
a stagnant universe made no sense. If all objects had mass, which Newton showed they did,
then the gravity of that mass should have been causing the universe to collapse in on itself.
This obviously hasn’t happened, so what was it that was preventing gravity from doing its job?
The phenomenon went mostly unexplained until the year 1929 when, by studying the redshifts
of distant galaxies, the famed astronomer Edwin Hubble discovered that everything in
the universe was, in fact, moving away from us. For the first time in history, we had evidence
that the universe was expanding… which posed another new theory, that it must have been this
way since the beginning; since what came to be known as the Big Bang. However, at this stage,
we knew nothing about the expansion accelerating, and so it was assumed that the internal mass of
the universe would, still, eventually cause expansion to slow down and presumably even
hit reverse. This belief that the universe would one day contract back toward its ultimate demise
came to be known as the Big Crunch Theory. All known evidence indicated that this view
could well be the true view of the nature of the universe… up until the year 1998. Then,
two separate studies discovered one of the biggest surprises in all of modern physics. The Supernova
Cosmology Project and the High-Z Supernova Search Team were both charged with observing the light
from Type One-A supernovae, which are supernovae specifically occurring in binary star systems
where one of the stars is a white dwarf. Both projects had expected to observe that
the supernovae would be moving away from us at a decreasing rate, meaning that expansion was
slowing down. But what they actually discovered was that the pace was increasing, and we’ve known
since then that expansion is accelerating. It was a moment in time that completely changed
our understanding of how the universe works. And it prompted yet more questions… most notably,
why wasn't gravity slowing expansion? Physicists came to the conclusion that there must be some
unknown energy actively working against it. This inexplicable force is now known as dark energy.
While most of everything about dark energy is still unknown, scientists have calculated that
it must be responsible for sixty-eight percent of the universes' matter-energy composition.
For comparison, dark matter is thought to make up twenty-seven percent, and all visible matter - all
the stars, planets, and moons - only make up about five percent of the universe.
Besides the fact that it exists, the very little we can say about dark energy is almost entirely
theoretical. The problem is that it’s only indirectly observable, meaning we can only
examine the way it interacts with gravity and visible matter… and there’s not yet a physical
way for us to examine it directly. Nevertheless, most of the evidence we have indicates that,
unlike matter and radiation, for example, dark energy is uniform throughout the universe. It
doesn't dramatically shift or change in density as new space is created. Instead,
it’s an intrinsic property of space itself. And this base understanding has allowed physicists to
theorize three possible fates for our universe. If the energy density is, in fact, a constant,
then the universe will simply continue to expand at a steadily increasing rate,
culminating in what’s known as a Big Freeze. Eventually, cosmic distances would measure
towards infinity, and only objects that are gravitationally bound to each other would remain
linked in any way. New stars would no longer form, and all existing stars would begin to die out.
After trillions of years, only black holes would remain, before they too would disappear according
to Stephen Hawking's radiation theory. The Big Freeze gets its name because all that would be
left of the universe is a cold and empty void. But what happens if the density of dark energy
isn’t a constant? Scientists can’t rule out that there could be slight variations in how
dark energy works, and how much of the universe is comprised of it. And, in fact, early observations
do suggest that dark energy may be either slightly increasing or slightly decreasing in strength.
If it decreases enough then we’re back to a Big Crunch scenario, where things return inwards. But,
if it increases in strength, then it’s thought the force of dark energy could become so strong
that the fabric of space-time itself would be under threat and could even tear apart.
This is the Big Rip scenario. And it’s potentially terrible news for, well, everything.
In this scenario, dark energy overcomes all other forces of nature, including gravity.
Whole groups of galaxies are pulled and stretched across the universe.
In the Milky Way, we’d first see the star systems on the outer arms break off…
but nothing would be truly safe. Eventually, the Big Rip would reach as far as our solar system,
relatively central in the Milky Way, pulling it into the abyss to drift through the cosmos
all on its own. And then, even the solar system would shatter as dark energy becomes
too powerful. The planets would one by one be ripped from their orbits, and then they, too,
would be singularly destroyed. According to some models, the strength of dark energy could
continue to grow to an infinite degree, so that planets, creatures, plants would all be pulled
apart. And then the atoms themselves would split into their subatomic parts, which in turn would
eventually disintegrate. Besides dark energy, the universe would again be left as an empty void.
It’s just that, this time, it will have taken an incredibly violent path to get there.
Unfortunately, because there is a suggestion that dark energy may be either increasing or decreasing
in strength, scientists can’t yet rule out that the universe is ripping itself apart - and many
confidently claim that it’s beyond doubt, the Big Rip is happening. Fortunately, however, according
to most current predictions, if the Big Rip is to occur then it won't be at least for another eighty
billion years from now. That's almost twenty times as long as the Earth has existed for.
And what’s more good news is that it’s thought it would take around ten billion years before
the first even slightly noticeable effects of this incredible phenomenon would take hold.
So, rest assured that you’re not about to be torn apart today, tomorrow or next week. It’s a problem
for your very, very, very distant descendants to work out… but, for now, you’re safe!
Of course, the fate of the universe remains an ongoing question for science, regardless. And,
whatever happens to it, we’re increasingly confident that dark energy will play a large
part. Luckily, the coming years will see a number of next-generation telescopes put into action.
And these could trigger a new age of cosmological enlightenment,
as we begin to unravel the secrets of dark energy. The first of these telescopes, EUCLID, is set to
launch any time before December 2022… and will be able to measure the redshift of galaxies,
and therefore the density of dark energy, with all new levels of accuracy.
Still, if the universe really is ripping itself open then there will likely never
be anything we can do to stop it from happening. It would be nice to know what the future holds,
though, wouldn’t it? And that’s why the universe might be tearing itself apart.
What do you think? Is there anything we missed? Let us know in the comments, check out these other
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