We proudly present to you: The
kurzgesagt Guide to Curiosity. Join us on an interactive adventure across
160 thrilling pages that will change your perspective on the world forever.
Available now on the kurzgesagt shop. You might be inside a black hole that's
inside a black hole that is inside a black hole. Everything in existence could
be black holes all the way down. It turns out black holes are much weirder than
you think and they break the universe much more than is usually explained, destroying time and
space – and they may actually create infinite universes in the process. But before we can
get to that, let’s first build a black hole out of air. Everything can become a black hole if you
squeeze it to a critical limit. You'd need to squeeze Earth down to the
size of a coin for it to turn into a black hole. The Sun needs to be squeezed down to the
size of a small city to become a black hole. And if a lot of mass is concentrated in a really
tiny space, you get something super dense. This is usually how black holes are explained.
Stuff becomes super dense and collapses into a black hole. But actually you don’t
need any ultra dense stuff to make them! We're ignoring some math here, but all
you really need to know is one thing: The larger black holes get, the less dense they
are. So really large black holes are kind of thin. A sun-mass black hole is only about 6 km wide
and has a density of about one Himalayan range per cubic meter. The supermassive black hole
at the center of the Milky Way has a mass of 4 million suns, a diameter of 24 million kilometers,
and a density of 6 blue whales per cubic meter. The ultramassive black hole IRAS 20100−4156
has a mass of 3.8 billion suns and is as wide as a solar system. But because it's
so large, it is only as dense as air! This means, at least in theory, that if you take
a gigantic balloon and fill it with undecillions of tons of air, the moment it gets to the size
of a solar system, an event horizon suddenly forms and it turns into a supermassive
black hole. Without violence or squeezing. So now let’s think big. What do we need to
make a black hole the size of the universe? A Universe-Sized Black Hole The chunk of the universe that we can see
from Earth is a sphere with a radius of 45 billion light-years, filled with hundreds of
billions of galaxies, lots of gas and a bunch of other things. If you add them up, it has the
mass of about a million billion billion suns. Which sounds a lot – but on average, the
universe is not very dense. If we break up all the galaxies, stars, gas and energy, and spread
them equally inside the volume of the universe, we get an average density of about 5
hydrogen atoms per cubic meter. You can imagine this as the sort of ultra thin
“cosmic air” that makes up the universe. What would happen if we take a balloon as big as the observable universe and
fill it with “cosmic air”? Well, it turns out that all the mass in the
observable universe is more than enough to create a black hole. Actually, it's
enough to make a black hole 10 times larger than the observable universe.
But that can only mean one thing – we should be living deep inside a truly
gargantuan, cosmic-sized black hole! There is one catch though. We know that our
universe is expanding – and an expanding universe is not what you'd expect to
see if you were inside a black hole. So our universe can’t be a black hole – at least
not in the naive way we’ve just described. Except there is a wild and mind-bending
trick the universe could play on us. To find out how, let's jump
into a black hole and die! A Whole Universe Born Inside a Black Hole We usually imagine black holes as spheres
with a singularity at their center, a point where all their mass
is concentrated so much that our math breaks down. But this is
a lie – they are SO much weirder. From the outside a black hole looks like
a normal black sphere. But the inside is where things stop making sense. Black holes warp the universe so
much that, at the event horizon, space and time switch their roles. Inside a normal
sphere, space is finite but time goes on forever. But inside a black hole it's the other way around
– space goes on forever but time is finite. So once inside, you see an infinite universe
with no center. The geometry is too complicated, so we're simplifying. But basically
you could walk forever in one direction or walk in another direction and
arrive at the same place again. But not only that. Inside a black hole time
is finite, and it's now running out. So after a while you start to notice that
space itself is slowly changing. In one direction space is being stretched, while in
all other directions space is shrinking – the whole universe is being squeezed, kind
of turning into a collapsing spaghetti. Sooner or later, the whole black hole
universe collapses into itself. All of space, every single part of it, is turning into a
singularity. So the singularity of a black hole is not at its center or in any
direction at all. It's in the future of whatever falls inside. We made a whole
video about this if you want to learn more. So the singularity is not a place where you
can go – it's an event in time that happens. Once it happens, you and everything else that
fell inside the black hole will be mercilessly crushed into an infinitely small region with
infinite gravity and infinite energy. Time, space, none of it matters anymore, both kind of
stop existing in ways that we would recognize. And then? Is this the end? Well, maybe not. This collapse of the black hole universe
into a singularity looks like one of the scenarios for the end of our universe: The Big
Crunch, where long after the Big Bang the whole universe collapses into a singularity again. But if there is a Big Crunch,
there might be a Big Bounce – like a rubber ball that you’ve
squeezed too much and that suddenly rebounds, space might expand again. So a new
universe could be born inside a black hole. The funny thing about this
scenario is that nothing has changed in the slightest outside the
black hole. Watching from the outside, it's still a black sphere of nothingness. And
yet, on the inside a new universe has been born. So maybe our universe was born like
this and we are all actually inside a black hole. But if our universe can also
create black holes, they might give birth to new universes. Is our black hole universe
also just part of a universe “further up”, that's also a black hole inside another
universe? Is there an end to it? Is there one original universe? Is the cosmos black
holes inside black holes inside black holes? Infinite Black Hole Universes If the universe creates black
holes that create universes, that then create new black holes that create
new universes, this cosmic self-reproduction would be subject to natural selection.
A Big Bang is a chaotic and messy event, so it’s possible that the new daughter universes
would not always be fully identical to their mums. Sometimes physics may be slightly different,
with some fundamental values higher or lower. And so some universes might be able to create
loads of stars, planets and black holes. Others might not, maybe creating a uniform cosmic soup
where no stars, planets and black holes form. But if all universes are born inside black
holes, in the long run all universe lines that don’t create loads of black holes
would die out. The universes with the conditions for loads of black holes would
become the most common and spawn the most daughter universes. Survival of the fittest,
but with universes instead of organisms. Our observable universe alone has created at
least 1017 black holes so far. So maybe our universe has the physics and laws it has,
because it was born after a long process of cosmological selection that favored
the production of tons of black holes. And that would have a lovely side effect. If universes are optimized to create as
many new black hole universes as possible, they're optimized to create loads of galaxies
and stars. And thereby also, by accident, the conditions for life to emerge. So universes
that are the best at creating new universes are also the best at creating life. If this scenario
is true, who knows how many bazillions of black hole universes might be out there. All with stars
and planets, potentially home to others like us. So. Is our universe like this? The
truth is we don’t know. While these ideas are based on real science and work on paper, they're speculative and not testable. Also
cyclic universes don’t actually explain why the universe exists in the first place or why it
is the way it is. Instead of providing answers, these are really just new questions in disguise,
so keep that in mind before getting too excited. But isn’t it just wonderful and
heartwarming that we're living in a universe where ideas as big as this
one are even thinkable? There might be so much life. And if new universes are created
constantly, maybe life will go on forever. We’ve heard rumors of a chosen one.
A special birb who has the power to illuminate the vast darkness of the universe,
uncovering the great mysteries of the world. We are all born with this power.
But only few are able to master it. We use the same power here at kurzgesagt to find the latest science and come up
with the most exciting videos. This special power is called: curiosity.
And the special birb… could be you! Our Guide to Curiosity is now available on
our shop. It’s an adventure that will help you to think like a kurzgesagt birb
and unlock your curiosity potential. Join us across 160 thrilling, interactive
pages designed to awaken your curiosity, changing your perspective on the world forever. But be prepared! We will send you on
epic quests to find incredible creatures, challenge you to build unprecedented structures, ask you to cook up something surprising, and solve
riddles to unveil hidden truths about the world. But don’t worry, the birbs will be with you every
step of the way. And you can also bring a friend! The 18 curiosity quests were developed
right here at the kurzgesagt headquarters. After hundreds and hundreds of hours of
research and lots of trial and error, we created the ultimate curiosity adventure.
It was the most fun we ever had making a product – and we are so excited to
finally share this experience with you. So head over to the kurzgesagt shop and
find out if you are the chosen birb. Every kurzgesagt product you buy
directly funds another moment we get to spend working on our videos – and you
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story and making this channel possible.