The Black Hole Bomb and Black Hole Civilizations

In a Nutshell Animations

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00:00Black holes are the largest collections of pure, violent energy in the universe.

00:06If you come too close, they'll devour you and add your energy to their collection.

00:11And so, the energy is lost to us forever.

00:14Or is it?

00:16It turns out there's a universe cheat code, a way of powering civilizations until the

00:21very death of everything, or of constructing the largest bomb in the universe.

00:27But how?

00:28Didn't we learn that all energy is trapped forever in black holes, even light?

00:33This is true.

00:34Everything you think you know about the weirdest thing in the universe is about to get weirder

00:38for one simple reason.

00:40Black holes are spinning.

00:43Why black holes spin?

00:48When really, really massive stars die, their cores collapse under their own gravity into

00:53black holes.

00:54This means something very big becomes very, very tiny.

00:58Like the tiniest anything can be in this universe.

01:02But stars are rotating, and a fundamental property of our universe is that things that

01:07are spinning don't want to stop spinning.

01:09We call this angular momentum.

01:12And this angular momentum can't go away.

01:15A big thing that spins and becomes smaller spins faster.

01:20So, as the core of a star collapses, its momentum makes it spin faster and faster and faster

01:26until it collapses into a black hole.

01:29And the black hole keeps on spinning, inconceivably fast.

01:34Some of them spin millions of times a second.

01:37Why spinning black holes are special?

01:41Just like non-spinning black holes, spinning black holes have an event horizon and a singularity

01:46at their core, where all of their mass is concentrated.

01:50The singularity is usually described as a single, infinitely small point with no surface

01:55area.

01:56But points can't rotate, so a rotating singularity can't be a point.

02:02Instead, it's a ringularity.

02:05A ringularity is a ring with a thickness of zero and no surface, spinning extremely fast,

02:11containing all the mass of the black hole.

02:14The black hole is spinning so fast that it morphs space and time itself.

02:18It literally drags space with it, such is its power.

02:22This creates a new and super weird region of space-time, the ergosphere, which envelops

02:29the black hole.

02:30If space and time are completely broken inside the event horizon, then they're only half

02:36broken inside the ergosphere.

02:39Inside the ergosphere, nothing makes sense.

02:41It's possible to enter it and then leave it again, but it's probably not a great experience.

02:47You can imagine it like this.

02:49Falling into a static black hole is like sliding down a hole.

02:54Being inside the ergosphere of a spinning black hole is like spiraling down a deadly

02:58drain.

03:00The black hole transfers its own kinetic energy in the form of rotation to everything that

03:05enters the ergosphere.

03:07The ringularity makes you dance, whether you want to or not.

03:11You need to move faster than the speed of light just to stand still here, which is impossible.

03:16But here's our cheat code.

03:18We can steal this energy.

03:20And there's a lot of energy to steal.

03:23How to steal energy from a monster?

03:27Take the supermassive black hole at the center of the Milky Way.

03:31We could steal as much energy from it as every single star in the Milky Way emits in a billion

03:36years combined.

03:38The easiest way to steal this energy is, oddly enough, to drop something into the black hole.

03:44We've seen that the ringularity forces energy on us when we enter the ergosphere, which

03:49is a lot like being in a whirlpool with space-time rushing around and around.

03:54If you're clever, you can use the water to your advantage and swim faster than before.

04:00In practice, this means sending a rocket into the ergosphere and making a trade with the

04:05black hole.

04:06We give it some mass energy, and it gives us some of its rotational energy.

04:11But it's not a fair trade.

04:13We get the better deal.

04:15Normally, if you fire a rocket, you exchange chemical energy for kinetic energy.

04:22This is like pushing yourself forward in a swimming pool.

04:25But if you fire a rocket inside the ergosphere, it's like pushing yourself forward in a wavepool.

04:31The rotational energy of the waves gives you a much stronger boost than you could get just

04:36by pushing yourself.

04:38The boost from the rotation of the black hole is so big that you leave the ergosphere with

04:43much more energy than you entered it.

04:46The black hole gives a tiny amount of its rotational energy to you and slows down a

04:50little.

04:51Obviously, this requires a lot of food.

04:54Fortunately, black holes aren't picky eaters.

04:57An advanced future civilization would probably harvest asteroids to drop them into the black

05:02hole when they needed an energy boost.

05:05But there's an even better way to get energy from a black hole, and oddly enough, it builds

05:09the biggest bomb any living thing could ever hope to build.

05:13The black hole bomb.

05:17We only need two things to build a black hole bomb, a fast spinning black hole, and a big

05:22mirror.

05:23The mirror has to completely envelop the black hole, which is similar to a Dyson sphere,

05:28a megastructure that harvests the energy of an entire star.

05:32Although our mirror would be easier to build.

05:35Mirrors are simpler, and black holes are much, much more compact than stars.

05:41If we made the mirror 10 centimeters thick, the metal of a big asteroid would probably

05:45be enough material for a black hole with the mass of our sun.

05:49Once our mirror is in place, we only need to open a window and shoot electromagnetic

05:55waves at the black hole.

05:57You can imagine what happens next by imagining tossing a ball at a wall and it coming back

06:01faster than a bullet.

06:03The waves hit the black hole at light speed.

06:06A small proportion of the waves falls past the event horizon to disappear forever.

06:11But a much larger amount sloshes through the ergosphere, where the black hole forces some

06:16of its rotational energy on them and amplifies them.

06:20They now begin superradiant scattering, which are fancy science words meaning bouncing around

06:26between mirror and black hole and getting stronger.

06:29Every time they go around, they are getting exponentially stronger.

06:33By opening some windows in the mirror, we can extract the energy from the waves as fast

06:38as they grow, which we could use in theory to create what would be for all practical

06:43purposes an endless source of energy for trillions of years.

06:47Or we could blow it up.

06:50If the waves are not released, they will continue to get stronger and stronger and take more

06:55and more energy from the black hole until the mirror shatters.

06:59A supermassive black hole would release as much energy as a supernova, making the bomb

07:04the largest explosion any living being could ever create.

07:09The last home in a dying universe.

07:12The beauty of the black hole bomb, the Penrose process and the superradiant scattering is

07:17that they are not science fiction.

07:19In the far, far future, this might be the only way to survive in our dying universe.

07:25After all the red dwarfs have cooled down and all the white dwarfs transformed into

07:30black dwarfs, the universe will turn dark forever.

07:34Rotating black holes might be the only sources of energy in the entire universe that life

07:39could harvest.

07:40If so, the last living being in existence might one day end its life around a black

07:47hole, which is equally chilling and uplifting.

07:52It turns out that even without any light, there are places we can go.

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