Three ways the universe could end Venus Keus
We know about our universe’s past:
the Big Bang theory predicts that all
matter, time, and space
began in an incredibly tiny, compact
state about 14 billion years ago.
And we know about the present:
scientists’ observations of the movement
of galaxies
tell us that the universe is expanding
at an accelerated rate.
But what about the future?
Do we know how our universe
is going to end?
Cosmologists have three
possible answers for this question,
called the Big Freeze,
the Big Rip and the Big Crunch.
To understand these three scenarios,
imagine two objects representing galaxies.
A short, tight rubber band is
holding them together—
that’s the attractive force of gravity.
Meanwhile, two hooks are
pulling them apart—
that’s the repulsive force
expanding the universe.
Copy this system over and over again,
and you have something
approximating the real universe.
The outcome of the battle between
these two opposing forces
determines how the end of the
universe will play out.
The Big Freeze scenario is what happens
if the force pulling the objects apart
is just strong enough to stretch the
rubber band until it loses its elasticity.
The expansion wouldn’t be able to
accelerate anymore,
but the universe would keep
getting bigger.
Clusters of galaxies would separate.
The objects within the galaxies–
suns, planets, and solar systems
would move away from each other,
until galaxies dissolved into
lonely objects
floating separately in the vast space.
The light they emit would be redshifted
to long wavelengths
with very low, faint energies,
and the gas emanating from them
would be too thin to create new stars.
The universe would become
darker and colder,
approaching a frozen state
also known as the Big Chill,
or the Heat Death of the Universe.
But what if the repulsive force
is so strong
that it stretches the rubber band
past its elastic limit,
and actually tears it?
If the expansion of the universe
continues to accelerate,
it will eventually overcome not only
the gravitational force –
tearing apart galaxies and solar systems–
but also the electromagnetic, weak,
and strong nuclear forces
which hold atoms and nuclei together.
As a result,
the matter that makes up stars
breaks into tiny pieces.
Even atoms and subatomic particles
will be destroyed.
That’s the Big Rip.
What about the third scenario,
where the rubber band wins out?
That corresponds to a possible future
in which the force of gravity brings the
universe’s expansion to a halt—
and then reverses it.
Galaxies would start rushing
towards each other,
and as they clumped together
their gravitational pull would
get even stronger.
Stars too would hurtle
together and collide.
Temperatures would rise as space
would get tighter and tighter.
The size of the universe would plummet
until everything compressed into such
a small space
that even atoms and subatomic particles
would have to crunch together.
The result would be an incredibly dense,
hot, compact universe —
a lot like the state that
preceded the Big Bang.
This is the Big Crunch.
Could this tiny point of matter explode
in another Big Bang?
Could the universe expand and contract
over and over again,
repeating its entire history?
The theory describing such a universe
is known as the Big Bounce.
In fact, there’s no way to tell how many
bounces could’ve already happened—
or how many might happen in the future.
Each bounce would wipe away any record
of the universe’s previous history.
Which one of those scenarios
will be the real one?
The answer depends on the exact shape
of the universe,
the amount of dark energy it holds,
and changes in its expansion rate.
As of now, our observations suggest
that we’re heading for a Big Freeze.
But the good news is that we’ve probably
got about 10 to the 100th power years
before the chill sets in —
so don’t start stocking up
on mittens just yet.