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One day the universe will die.
But why? And how? And will the universe
be dead forever?
And how do we know that?
First of all, the universe is expanding.
And not only that, the rate of
its expansion is accelerating.
The reason: dark energy.
Dark energy is a strange phenomenon that
scientists believe permeates the universe.
Until 1998 we thought that the universe
must work a bit like
a ball that you throw into the sky.
The ball moves up, but at some point
it has to come down again.
But the expansion of the universe
is actually speeding up.
That’s like throwing a ball up
and watching it fly away
faster and faster and faster.
Where is this acceleration coming from?
Well, we don’t know, but
we call it “dark energy”.
Einstein thought of it first and
then decided it was stupid.
Now, astrophysicists have
decided it is plausible.
Trouble is, this is all very theoretical,
and we don’t actually know
what the properties of dark energy are.
But there are various theories and they
lead us to three scenarios
for the end of the universe.
One: the Big Rip.
Since its birth, the universe
has been expanding.
For unknown reasons new spaces
created everywhere equally.
The space between galaxies expands,
so they move apart.
The space inside galaxies also expands,
but here, gravity is strong enough
to keep them together.
In the Big Rip scenario, the expansion
accelerates up to a point where
space expands so fast that gravity
can’t compensate for this effect anymore.
The result is a Big Rip.
At first, only large structures like
galaxies are torn apart,
since space between the single objects
expands very fast.
Next, big bodies like black holes,
stars, and planets die.
Their gravity isn’t strong enough to keep
them together,
so they dissolve into their components.
In the end, space would expand
faster than the speed of light.
Atoms would now be affected,
and they would just disband.
Once space is expanding faster than light,
no particle in the universe can interact
with any other particle anymore.
The universe would dissolve into countless
lonely particles that won’t be able to
touch anything else in a strange,
timeless universe.
Hmm, and you thought you felt lonely!
Two: Heat death or a Big Freeze.
In a nutshell, the difference between
the Big Rip and heat death is that
in a heat death scenario matter stays
intact and is converted
over an incredibly long but finite period
of time into radiation,
while the universe expands forever.
But how does this work?
Let’s talk about entropy.
Every system tends towards the
state of highest entropy,
like when we have a latte macchiato.
Initially, it has different regions, but
over time, they will
cool down and disintegrate,
until it’s uniform.
And this also applies to the universe.
So, while the universe gets
bigger and bigger,
matters slowly decays and spreads out.
At some point, after lots of generations
of stars, all the gas clouds necessary
to form stars will be exhausted,
so the universe will turn dark.
The remaining suns will die;
black holes will slowly degenerate
and evaporate over trillions of years
due to what’s known as Hawking radiation.
When this process is complete, only a
dilute gas of photons and light particles
remains, until even this decays.
All activity in the universe ceases
at this point;
entropy is at its maximum and
the universe is dead forever.
Unless… theoretically, it might
be possible
that after an incredibly
long amount of time,
there might be a spontaneous entropy
decrease as a result of something called
“quantum tunneling”, leading to
a new Big Bang.
Three: Big Crunch and Big Bounce.
This is the most uplifting scenario.
If there is less dark energy than we think
or it decreases over time, gravity will be
the dominating force in the
universe one day.
In a few trillion years, the rate of
expansion of the universe
will slow down and stop.
After that, it reverses.
Galaxies will race at each other,
merging as the universe becomes
smaller and smaller.
Since a smaller universe also means
a hotter universe, temperatures rise
everywhere all at once.
One hundred thousand years before the Big
Crunch, background radiation would be
hotter than the surfaces of the
most stars, which means that
they would be cooked from the outside.
Minutes before the Big Crunch happens,
atom cores are ripped apart,
before supermassive black holes
devour everything.
Finally, all black holes would emerge into
a supermassive mega-black hole
that contains the entire
mass of the universe,
and in the last moment before
the Big Crunch
it would devour the universe,
including itself.
The Big Bounce theory states that this
has happened a lot of times
and that the universe goes through
an infinite cycle of
expansion and contraction.
Well, wouldn’t that be nice?
So what will actually happen to
the universe in the end?
At the moment, heat death seems the most
likely, but we at Kurzgesagt hope that
this “dead forever” stuff is wrong and the
universe will start over and over again.
We don't know for sure either way, so
let’s just assume
the most uplifting theory is true.
By the way, we have a Twitter account.
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