The universe today is happy and healthy, with exciting things going on
But at some point the night will turn dark. Everything that once was will peacefully sleep forever
But what is the last thing that will ever happen, and when will it be
It turns out there is such a thing, and you probably haven't heard about it
Let's travel to the end of the universe and look at the last thing
the last thing. After a messy birth, our universe was a sleepy baby, warm and dark, filled with
swirling clouds of hot hydrogen and helium. The story of creation is a story of this gas and where
it will end up. Shortly after, the universe got busy making the first generation of stars
They were massive and lived violent lives, forging new elements, only to release most of them
when they blew up. Countless stars were born and refined the gas available in the universe
universe, cycling matter around, each generation giving most of its gas and fresh elements to the next
But not all gas is returned. Every time a new generation of stars forms, they also make more and more red dwarfs that burn slowly and live for trillions of years
When they die, they don't give their gas back to the universe, but turn it into white dwarfs
So red dwarfs lock up more gas forever. Some more gas is locked forever in other remains of dead stars
neutron stars and black holes, which is bad as it reduces the material available for new stars
Today, the universe is a great home for us and will remain so for billions of years
But most of the gas has been used up or trapped. Over 90% of the stars that will ever be born have been born already
To get to the last thing to ever happen, all other things need to happen first
The next few hundred billion years will be fun and a great time for galactic exploration
But, step by step, large stars and stars like our sun will die out
Eventually, almost all the stars will be red dwarfs slowly dying. The end of everything, but not quite
In a few trillion years, the cosmic gas will finally have run out. About 88% of the mass of every galaxy will be white dwarfs, 2% neutron stars and black holes
and about 10% gas giants, and sad brown dwarf losers. White dwarfs are the corpses of old stars, not much bigger than Earth, but on average, as massive as half our sun, some even much more
This makes them the third densest objects in the universe, after neutron stars and black holes
About a million times denser than the sun today Since they used to be active stars their surface can be as hot as 150 degrees White dwarfs are dim hot dense spheres that don do anything anymore
But eventually, even white dwarfs will die because they're slowly losing their heat
It takes at least 10 trillion years, more than 700 times longer than the current age of the universe
As they do their cooling down, the universe around them will irreversely
grow dark as more and more white dwarfs burn out and turn into dead husks, black dwarfs
Spheres of death, as cold as space itself, invisible against the dark backdrop
Over trillions and trillions of years, every object in every galaxy is eventually either
ejected into the void or its orbit decays and it will fall into the central black hole
and be destroyed. In about a quintillion years, all galaxies have evaporated and every object is
On its own, in the center of its own observable universe, emptiness as far as can be seen in any
direction, travelling through black nothingness. Still, there are things that will happen
Black holes are dying, slowly. They'll fizzle away by emitting hawking radiation until they're so small that they die
in a final flash of light. This will take about a gougol year, 10 to the power of 100 years, until the last supermassive black hole dies
A number so absurd, there's nothing to compare it to. Maybe some living beings could have survived around black holes
but even this science fiction option ends now. After this unsettling amount of time, we're not even close to the end
Now is the time of the black dwarfs. It turns out there's some weird physics going on inside the dead husk of stars
The weird physics of black dwarfs. A black dwarf is a sphere of the size of Earth
as massive as a star, but almost as kind. as absolute zero. Stars stay alive because of their intense heat in their course, so why
do black dwarfs not collapse into a black hole? What keeps them together? Deep inside
a black dwarf, matter is squeezed to densities millions of times greater than anything
we see on Earth. The pressure is so great that electrons can't combine with nuclei to form atoms
Instead, matter is weird, degenerate. The nuclei are compressed by the weight of the star, locked
into a rigid lattice, while the electrons form a plasma between them
And these electrons hold the star together. We're simplifying, but imagine matter as a subway train and electrons as passengers
If there are empty seats that passengers spread out because they care a lot about their personal space
But as a black dwarf is so incredibly dense this is like squishing more and more passengers into our train Gravity is pushing in trying to collapse it The passengers are forced to sit and stand close together which they hate And so the passengers our electrons try to push out against gravity as hard as they can
This way, the electrons that are having a horrible time in the crowded train that's the black dwarf
hold up the star. Everything else in the universe may have trumbled already
but these tiny particles push against each other until the end of time
or they would if quantum mechanics didn't ruin everything. Simplifying a lot, when particles get close enough
sometimes they can jump at each other and fuse together, a process called quantum tunneling
This happens constantly in stars because of their intense heat. It's one of the key reasons stars can fuse elements into new ones
but it also happens at a temperature near absolute zero, just, well, mind-numbingly slowly
This is the final step to create. the last interesting thing to ever happen in our universe
Here, in this lone black dwarf, something fantastic occurs. Nothing happens for a trillion years, nothing at all
Can you imagine that? But then, a single fusion reaction. Two carbon nuclei combined by quantum tunneling to become magnesium
Another 100 trillion years pass. It happens again. Then nothing for another bazillion years
Oh, two or two or four years. Two oxygen nuclei combine into silicon
As eons pass, the nuclei in the frozen black dwarf slowly combine
making new heavier nuclei. And these take even longer to fuse, but given enough time, they eventually will
Remember the breathtaking amount of time it took for a supermassive black hole to evaporate
That's a brief moment in comparison to what's going on here. The difference between a second and trillions of years has lost all meaning
Over a time so absurd that it has no name, nuclei keep fusing into heavier elements
Until, when silicon nuclei fuse, they form nickel 56. Nickel 56 is radioactive, which means it's unstable
And when it eventually decays and turns into iron, it emits two positrons, antimatter electrons
And these two positrons find two electrons and annihilate them and themselves
Which is a problem? Remember how the uncomfortable electrons produce the problem
pressure to hold the star together. Destroying the electron means fewer friends to help them hold up the star
Losing an electron does not give them more space to scratch their butts, it just makes gravity squeeze harder the walls closing in on those that remain
In the case of the most massive black dwarfs, this is catastrophic. Bit by bit the black dwarf turns into a sphere of iron and more electrons are annihilated For at least 10 to the power of 1 years almost but not quite forever there no visible change in the entire universe
And then, finally, the last thing to ever happen happens. The Black Dwarf has lost one too many electrons
It can no longer support its immense mass and goes into an uncontrolled collapse, a supernova
It first implodes and then explodes as bright as a galaxy and fills
the empty universe with light again. A beautiful moment, nobody will get to enjoy. And then as quickly
as it began, it's all over. Darkness again. Emptiness. That was the last thing that will ever happen
The universe may now be truly dead. But don't be bummed out about it. This is so far away in the future
that forever hardly describes it. Today, the universe is the best place it could be
for us. And you can sleep tight tonight, knowing the last interesting thing that will ever happen
is forever long away. For now, there are still plenty of interesting things to discover
and the younger you start discovering, the more you'll understand about the world we live in
Our sponsor Keebiko helps kids get a head start there, with a range of unique crates on a
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At Kuzat, we love to spark curiosity, and we love to work with companies that share this goal