Here lies the universe.
It lived a great life.
full of energy and excitement but, sadly, all things come to an end.
or do they?!
Hey Crazies.
I wanted to finish off our cosmology series properly.
with the death of the universe.
That death will happen sometime in the VERY distant future
but how that will go down, depends heavily on the past and present.
Let’s start with the present.
First, we need a number that can tell us how big the universe has grown.
and that can be tricky if the universe is infinite.
We know the observable universe is 93 billion light years across
but, since the cosmic horizon can grow at a different rate than the universe expands
that bubble doesn’t always contain the same amount of stuff.
We need something a little more useful.
The observable universe contains about 10 million super-clusters.
That means the average distance between super-clusters is currently about 400 million light years.
So anything we come up with for our universe, better at least match that.
Yes, but there weren’t always galaxies in the past and there might not always be galaxies
in the future.
Hmmmm, you’re right.
Average super-cluster distance is great as long as there are super-clusters
but we don’t know if there will be when the universe dies.
What we need is something that’s a little more generic.
Let’s do this the easy way and just label the present day: one.
When the universe is smaller, this scale will be less than one.
When the universe is bigger, this scale will be greater than one.
Wait a minute!!
That’s just the scale factor from the Flower Metric!
Huh, it’s neat how this all fits together.
The fact that we even get to use a metric that simple is because the universe is mind-blowingly
uniform on the large scale.
Our world isn’t uniform.
It’s part of what makes it interesting.
The same can be said for the scale of planets, stars, galaxies, or even clusters of galaxies.
But, on the grand scale, those are insignificant details.
The universe is simple.
OK, to make any predictions about the future, we need a predictable pattern for how that
scale factor is changing.
In other words, we want to know what the past looks like, so we can figure out what the
future looks like.
Here’s what we need: The Flower Metric, Einstein’s Equations,
Yes, more than one.
There are technically 10.
Matter Density, that’s both regular and dark matter,
Dark Energy Density, and Spatial Curvature.
If we take what we know from the metric and toss it into Einstein’s Equations, we get
something called the Friedmann Equations, named after Russian Physicist Alexander Friedmann.
As you can see, regular Energy adds to the curvature of space and slows down the expansion.
Dark Energy also adds to the curvature of space, but speeds up the expansion.
These two equations describe all possible futures for the universe.
So, the moment you’ve been waiting for… here are the options:
There’s the Big Crunch, where the universe eventually re-collapses.
That’s closely related to my personal favorite: The Cyclic Universe, where the universe expands
and collapses over and over again in a Big Bounce.
There’s the Big Freeze or the Heat Death, where the expansion could slow down or speed
up, but it never stops, so the universe expands forever.
Then there’s the Big Rip, the most extreme possible future, where the universe accelerates
so quickly that the scale factor becomes infinite in a finite amount of time.
The universe rips itself into infinitely small pieces.
Which one is our universe?
That’s a great question!
Thankfully, a lot of scientists have done the hard work of measuring these numbers.
Our universe appears to be this one.
It started accelerating in its expansion about 6 billion years ago, but it’s not accelerating
fast enough to rip itself to bits.
We have a heat death to look forward to.
At which point, you might be wondering:
What's a heat death?!
Exactly what it sounds like!
Right now, we live in a time of complexity.
There are trillions of galaxies each filled with 100’s of billions of stars.
Many of those stars have orbiting planets and at least one of those planets has a
living ecosystem.
What a time to be alive!
But it won’t always be this way.
Trillions of years from now, all the stars will burn out leaving behind cold corpses.
Eventually, all black holes will evaporate through Hawking Radiation.
After that, matter and photons just continue spreading out as the universe expands.
One day, every particle will be so far apart that nothing happens anymore.
That’s a heat death.
Maximum entropy!
The upside is it’s not supposed to happen for at least another googol years, so you’ll
all be long gone by then.
That is, if the false vacuum collapse doesn’t consume us first.
Nightmare Fuel!!
So, which ending do you like the best?
I’ll include some of your answers in the next comment response video, where we’ll
go over a bunch of comments from this whole series.
Thanks for liking and sharing this video.
Don’t forget to subscribe if you’d like to keep up with us.
And until next time, remember, it’s OK to be a little crazy.