What would happend if could build this massif construction?
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00:00 This is not some DVD floating in space.
00:05 It's a megastructure
00:07 that might one day become humanity's home.
00:11 The Earth might not remain habitable forever.
00:16 It could get engulfed by a massive solar flare,
00:20 or become too hot due to climate change,
00:23 or have all its life wiped out
00:26 by one enormous asteroid.
00:29 What if I told you we could outlive all these disasters?
00:34 And that we could do that
00:36 by building a space megastructure
00:38 bigger than the Sun itself?
00:41 Just how big would we have to make it?
00:45 And what would life be like on a structure like that?
00:51 This is WHAT IF,
00:53 and here's what would happen
00:55 if we could build an Alderson disk.
01:00 Why would we colonize other,
01:01 currently uninhabitable planets,
01:04 if we could hypothetically build a habitat of our own?
01:08 Something that would host many billions of future humans
01:13 without ever running out of space.
01:16 It does look like a DVD, doesn't it?
01:19 Only it has the mass of 3,000 Suns.
01:24 The reason why we'd need our Alderson disk
01:27 to have such a huge mass is gravity.
01:31 All objects with mass
01:33 are gravitationally drawn to each other.
01:36 And objects with a greater mass
01:39 have a greater gravitational pull.
01:42 For the Alderson disk to be stable enough to host life,
01:46 we'd need it to have a stronger pull than the Sun does.
01:51 That's where it gets tricky.
01:53 Because the Sun is the most massive object in our Solar System,
01:58 accounting for 99.8% of its total mass.
02:02 To have enough material to outweigh the Sun,
02:05 we'd have to get it by breaking down every planet,
02:09 Moon and asteroid in a radius of hundreds of light-years around us.
02:15 Or we could give our Alderson disk artificial gravity.
02:20 This type of gravity isn't caused by attraction,
02:23 but by acceleration or centrifugal force.
02:27 In other words, we'd have to spin our disk
02:30 fast enough that it doesn't collapse into a donut,
02:33 or get swallowed by the Sun.
02:36 But since we haven't really figured out artificial gravity yet,
02:40 let's stick with the first option
02:42 and make our Alderson disk very, very massive.
02:46 241 million km (1.2 billion mi) wide.
02:51 That would make it stretch past the orbit of Mars.
02:55 It would also be several thousand km (1,000 mi) thick,
03:00 and would have a surface area equivalent to over one billion Earths.
03:06 Just imagine how many billions of humans could live on it.
03:12 But not so fast.
03:14 Our Alderson disk wouldn't be habitable everywhere.
03:19 And before I explain that,
03:21 let me talk about the Sun for a moment.
03:24 Our Sun would be sitting stationary in the hole at the center of the disk.
03:29 And because of this,
03:31 our disk would have no day and night cycle,
03:35 only a never-ending twilight.
03:38 But since our disk would have a bigger mass
03:42 and a stronger gravitational pull,
03:45 there's a chance that the Sun would wobble up and down.
03:49 That would somewhat solve our day and night problem,
03:51 but it could also increase the possibility of colliding with our star.
03:59 We might need to install gamma-ray lasers
04:01 to have more control over the Sun's wobbling.
04:04 And still, our disk-shaped world would need way more things
04:08 to become suitable for us to live on it.
04:12 One of the most important things is an atmosphere.
04:16 On Earth, the atmosphere protects us from harmful ultraviolet radiation.
04:21 It reduces temperature extremes,
04:24 and it creates pressure that allows liquid water to exist.
04:29 We'd need an atmosphere to do all the same things for our Alderson disk.
04:34 And to keep the Sun from stealing it,
04:37 we'd need to build a wall around the disk's inner edge.
04:42 Unlike Earth, the Alderson disk wouldn't have liquid metal in its core
04:46 to give it a magnetosphere.
04:49 A magnetic field is important because
04:51 it keeps the solar wind from stripping off the atmosphere.
04:55 Without it, the solar wind would erode the part of the Alderson disk closer to the Sun.
05:02 This could make the entire structure unstable,
05:05 and possibly destroy it altogether.
05:09 Once we figure out how to make the atmosphere and magnetic field,
05:13 we could bring in water.
05:15 We'd make holes in the disk that would allow for oceans.
05:20 Because of the way gravity would work on our Alderson disk,
05:24 the water could be suspended.
05:27 The oceans on the disk-shaped structure would literally be bottomless.
05:33 For the same gravitational reasons,
05:36 humans would be able to live on both the top and the bottom side of the disk.
05:41 For those living on the bottom side,
05:43 it wouldn't feel as if they were walking upside down.
05:47 It would be just normal on each side.
05:50 But of course, this space megastructure could have some flaws.
05:55 Because of the disk's enormous mass,
05:58 its gravity might make it collapse into a gigantic torus,
06:02 or even worse, a black hole.
06:06 Then there are asteroids.
06:09 Even though we used up all the nearby asteroids
06:12 to form our Alderson disk in the first place,
06:15 there's no guarantee new interstellar space rocks
06:19 wouldn't come and bombard our disk world.
06:21 And not just asteroids, but rogue planets as well.
06:27 Even the slightest hit could destabilize the disk
06:30 and plunge it right into the Sun.
06:34 Speaking of the Sun, remember I said that
06:36 not all of the Alderson disk would be habitable?
06:40 That's because the Sun wouldn't be heating it evenly.
06:44 The inner side of the disk would be very hot.
06:48 To withstand the tremendous heat,
06:50 we'd have to give our disk a heat shield,
06:53 just like the one we developed for the Parker Solar Probe.
06:58 The outer edges of the disk would be freezing cold.
07:02 But the middle band of the structure
07:04 would be just perfect for life.
07:06 Although there would be a lot of unused space,
07:10 the habitable area would still be 50 million times larger
07:14 than the entire surface of Earth.
07:18 So a giant platter with the thickness
07:21 of several thousand kilometers,
07:24 it might not survive in space.
07:27 Luckily, I have another idea in mind.
07:32 But that's a story for another WHAT IF.
07:36 [music]
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