This is the Universe.
And this little dot here is the Earth.
And this is a Big Bounce coming up,
and it's about to squash our planet.
Yikes.
It's generally accepted that the Universe
emerged from one single point
of infinite density, and then rapidly expanded
in what we call the Big Bang.
But when it happened,
nobody was around to see it for themselves.
So here comes a new theory.
What if it all didn't start with the Big Bang
13.8 billion years ago?
What if, instead, the Universe
had no beginning and no end,
but was expanding and contracting back,
over and over again?
The cyclic Universe involves
a series of Big Bounces,
where the Universe acts like an enormous
cosmic lung, inhaling and exhaling
a giant breath with every bounce.
Basically, you've got nothing to worry about.
Because the cyclic Universe
expands for several billion years,
and then contracts for billions of years.
On a scale of a human lifespan,
this timeline is just not developing fast enough
to affect you in any way.
But we here at WHAT IF like to
add some spice to our stories.
In this case, we'll speed things up,
and have the Universe go
through its bouncing cycle
almost every day. 
And the next bouncing event
is scheduled for tomorrow.
You'd start the day with some
worrisome news from astrophysicists.
The stars and galaxies that normally move
slowly away from each other,
would now be moving toward one another.
And fast.
Every planet, star, and every galaxy
on the edge of the Universe would be
rushing towards its center,
breaking the cosmic light speed limit.
Black holes would be
colliding with other black holes.
They'd be sending huge amounts
of cosmic radiation in all directions,
and growing into even bigger black holes.
No planet in the Universe would
have a stable orbit anymore.
They'd go flying across the galaxy
to meet up at the cosmic "downtown."
At this point, things would get
quite messy on our planet.
And you wouldn't be able
to do a thing to stop it.
So just sit back, and watch the world end.
As the Universe continued
to collapse in on itself,
its temperature would rapidly become hotter.
The superheated temperatures
would evaporate our oceans,
our planet, and even our atoms.
Everything that ever existed
would be wiped out.
Finally, when the Universe contracted
to its densest point,
it would become a superhot,
dense mix of matter.
It would slow down for a moment,
and then suddenly start expanding again.
A new bouncing cycle would begin.
A totally new Universe would emerge.
New Universe, old rules.
From hot cosmic dust, gravity
would form new planets,
new stars and new galaxies.
And then new lifeforms would emerge
on these new worlds.
This new Universe would
expand until it reaches its limit.
And then it would go back
to becoming a dense, hot ball of matter.
The cycle would repeat.
And again.
And again.
But we would be too long
gone to know about it.
That turned out a bit dark.
But hey, the Universe is only
13.8 billion years old.
We've got a few billion more
until the contraction will begin.
And honestly, it's quite a
deep topic to dive into.
We've got more questions.
And there's no one better to ask them to
than the very person who developed
this cyclic model of the Universe.
On What If Discussed,
we talked to Dr. Anna Ijjas,
a theoretical physicist
at the Max Planck Institute
for Gravitational Physics.
Check it out to learn more
about the Big Bounce
and how dark matter fits into it.
