This is not some DVD floating in space.
It's a megastructure that might one day
become humanity's home.
The Earth might not remain habitable forever.
It could get engulfed by a massive solar flare,
or become too hot due to climate change,
or have all its life wiped out
by one enormous asteroid.
What if I told you we could
outlive all these disasters?
And that we could do that
by building a space megastructure
bigger than the Sun itself?
Why would we colonize other,
currently uninhabitable planets,
if we could, hypothetically,
build a habitat of our own?
Something that would host many billions of future humans
without ever running out of space.
It does look like a DVD, doesn't it?
Only it has the mass of 3,000 suns.
The reason why we'd need our Alderson Disk
to have such a huge mass is gravity.
All objects with mass are gravitationally drawn to each other.
And objects with a greater mass
have a greater gravitational pull.
For the Alderson Disk to be stable enough to host life,
we'd need it to have a stronger
pull than the Sun does.
That's where it gets tricky,
because the Sun is the most massive
object in our Solar System,
accounting for 99.8% of its total mass.
To have enough material to outweigh the Sun,
we'd have to get it by breaking down every planet,
moon and asteroid in a radius
of hundreds of light-years around us.
Or, we could give our Alderson Disk artificial gravity.
This type of gravity isn't caused by attraction,
but by acceleration or centrifugal force.
In other words, we'd have to spin our disk
fast enough that it doesn't collapse into a donut,
or get swallowed by the Sun.
But since we haven't really figured out artificial gravity yet,
let's stick with the first option,
and make our Alderson Disk very, very massive –
241 million km (150 million mi) wide.
That would make it stretch past the orbit of Mars.
It would also be several thousand kilometers (or miles) thick,
and would have a surface area equivalent to over one billion Earths.
Just imagine how many
billions of humans could live on it.
But not so fast.
Our Alderson Disk wouldn't be habitable everywhere.
And before I explain that,
let me talk about the Sun for a moment.
Our Sun would be sitting stationary
in the hole at the center of the disk.
And because of this, our disk
would have no day and night cycle.
Only a never-ending twilight.
But since our disk would have a bigger mass
and a stronger gravitational pull,
there is a chance that the Sun would wobble up and down.
That would somewhat solve our day and night problem, but
it could also increase the possibility
of colliding with our star.
We might need to install gamma-ray lasers
to have more control over the Sun's wobbling.
And still, our disk-shaped world
would need way more things to become
suitable for us to live on it.
One of the most important things
is an atmosphere.
On Earth, the atmosphere protects us
from harmful ultraviolet radiation.
It reduces the temperature extremes,
and it creates pressure that allows liquid water to exist.
We'd need an atmosphere to do
all the same things for our Alderson Disk.
And to keep the Sun from stealing it,
we'd need to build a wall around the disk's inner edge.
Unlike Earth, the Alderson Disk
wouldn't have liquid metal in its core
to give it a magnetosphere.
A magnetic field is important because
it keeps the solar wind from stripping off the atmosphere.
Without it, the solar wind would erode
the part of the Alderson Disk closer to the Sun.
This could make the entire structure unstable,
and possibly destroy it altogether.
Once we figure out how to make
the atmosphere and magnetic field,
we could bring in water.
We'd make holes in the disk that would allow for oceans.
Because of the way gravity would work on our Alderson Disk,
the water could be suspended.
The oceans on the disk-shaped structure
would literally be bottomless.
For the same gravitational reasons,
humans would be able to live on both the top
and the bottom side of the disk.
And for those living on the bottom side,
it wouldn't feel as if they were walking upside down.
It would be just normal on each side.
But of course, this space megastructure
could have some flaws.
Because of the disk's enormous mass,
its gravity might make it collapse into a gigantic torus,
or even worse – a black hole.
Then, there are asteroids.
Even though we used up all the nearby asteroids
to form our Alderson Disk in the first place,
there's no guarantee new interstellar space rocks
wouldn't come and bombard our disk world.
And not just asteroids, but rogue planets as well.
Even the slightest hit could destabilize the disk
and plunge it right into the Sun.
Speaking of the Sun, remember I said that
not all of the Alderson Disk would be habitable?
That's because the Sun wouldn't be heating it evenly.
The inner side of the disk would be very hot.
To withstand the tremendous heat,
we'd have to give our disk a heat shield,
just like the one we developed for the Parker Solar Probe.
The outer edges of the disk would be freezing cold.
But the middle band of the structure would be just perfect for life.
Although there would be a lot of unused space,
the habitable area would still be
50 million times larger than the entire surface of Earth.
A giant platter with the thickness of several thousand kilometers.
It might not survive in space.
Luckily, I have another idea in mind.
But that's a story for another WHAT IF.