1 00:00:00,940 --> 00:00:06,240 Black holes are the largest collections of pure violent energy in the universe. 2 00:00:06,240 --> 00:00:10,880 If you come too close, they'll devour you and add your energy to their collection. 3 00:00:11,300 --> 00:00:13,940 And so, the energy is lost to us forever. 4 00:00:14,040 --> 00:00:18,540 Or is it? It turns out there's a universe cheat code. 5 00:00:18,640 --> 00:00:26,560 A way of powering civilizations until the very death of everything, or of constructing the largest bomb in the universe. 6 00:00:26,640 --> 00:00:27,520 But how? 7 00:00:27,720 --> 00:00:32,220 Didn't we learn that all energy is trapped forever in black holes, even light? 8 00:00:32,500 --> 00:00:33,840 This is true. 9 00:00:33,840 --> 00:00:39,820 Everything you think you know about the weirdest thing in the universe is about to get weirder, for one simple reason: 10 00:00:40,080 --> 00:00:42,080 Black holes are spinning. 11 00:00:57,100 --> 00:01:03,240 When really really massive stars die, their cores collapse under their own gravity into black holes. 12 00:01:03,340 --> 00:01:10,840 This means something very big becomes very, very tiny. Like the tiniest anything can be in this universe. 13 00:01:11,000 --> 00:01:18,460 But stars are rotating and a fundamental property of our universe is that things that are spinning don't want to stop spinning. 14 00:01:18,660 --> 00:01:21,160 We call this: angular momentum. 15 00:01:21,160 --> 00:01:29,000 And this angular momentum can't go away. A big thing that spins and becomes smaller, spins faster. 16 00:01:29,100 --> 00:01:38,140 So, as the core of a star collapses, its momentum makes it spin faster and faster and faster, until it collapses into a black hole . 17 00:01:38,340 --> 00:01:42,660 And the black hole keeps on spinning, inconceivably fast. 18 00:01:42,660 --> 00:01:45,720 Some of them spin millions of times a second. 19 00:01:50,160 --> 00:01:52,200 Just like non spinning black holes, 20 00:01:52,200 --> 00:01:58,920 ...spinning black holes have an event horizon and a singularity at their core, where all of their mass is concentrated. 21 00:01:59,200 --> 00:02:05,200 The singularity is usually described as a single infinitely small point with no surface area. 22 00:02:05,400 --> 00:02:10,680 But points can't rotate, so a rotating singularity can't be a point. 23 00:02:11,140 --> 00:02:13,560 Instead, it's a RINGularity. 24 00:02:13,800 --> 00:02:22,460 A ringularity is a ring with a thickness of zero and no surface, spinning extremely fast, containing all the mass of the black hole. 25 00:02:22,660 --> 00:02:27,760 The black hole is spinning so fast, that it morphs space and time itself. 26 00:02:27,760 --> 00:02:31,180 It literally drags space with it, such is its power. 27 00:02:31,500 --> 00:02:39,400 This creates a new and super weird region of space-time: the Ergosphere, which envelops the black hole. 28 00:02:39,840 --> 00:02:47,300 If space and time are completely broken inside the event horizon, then they're only half broken inside the ergosphere. 29 00:02:47,700 --> 00:02:50,480 Inside the ergosphere, nothing makes sense. 30 00:02:50,480 --> 00:02:55,700 It's possible to enter it and then leave it again, but it's probably not a great experience. 31 00:02:56,460 --> 00:03:02,240 You can imagine it like this: Falling into a static black hole is like sliding down a hole. 32 00:03:02,640 --> 00:03:08,240 Being inside the ergosphere of a spinning black hole is like spiraling down a deadly drain. 33 00:03:08,680 --> 00:03:15,660 The black hole transfers its own kinetic energy in the form of rotation, to everything that enters the ergosphere. 34 00:03:15,900 --> 00:03:19,760 The ringularity makes you dance whether you want to or not. 35 00:03:19,840 --> 00:03:24,860 You need to move faster than the speed of light just to stand still here, which is impossible. 36 00:03:25,020 --> 00:03:31,520 But here's our cheat code: We can steal this energy, and there's a lot of energy to steal. 37 00:03:36,180 --> 00:03:39,940 Take the supermassive black hole at the center of the Milky Way. 38 00:03:40,120 --> 00:03:47,100 We could steal as much energy from it as every single star in the Milky Way emits in a billion years combined. 39 00:03:47,220 --> 00:03:53,240 The easiest way to steal this energy is, oddly enough, to drop something into the black hole. 40 00:03:53,500 --> 00:03:58,000 We've seen that the ringularity forces energy on us when we enter the ergosphere, 41 00:03:58,000 --> 00:04:02,900 ...which is a lot like being in a whirlpool, with space-time rushing around and around. 42 00:04:02,960 --> 00:04:08,820 If you're clever you can use the water to your advantage, and swim faster than before. 43 00:04:09,480 --> 00:04:15,180 In practice, this means sending a rocket into the ergosphere, and making a trade with the black hole: 44 00:04:15,180 --> 00:04:20,120 We give it some mass-energy, and it gives us some of its rotational energy. 45 00:04:20,200 --> 00:04:24,080 But it's not a fair trade, we get the better deal. 46 00:04:24,300 --> 00:04:30,440 Normally, if you fire a rocket, you exchange chemical energy for kinetic energy. 47 00:04:30,760 --> 00:04:34,280 This is like pushing yourself forward in a swimming pool. 48 00:04:34,600 --> 00:04:39,940 But if you fire a rocket inside the ergosphere, it's like pushing yourself forward in a wave pool. 49 00:04:40,180 --> 00:04:46,700 The rotational energy of the waves gives you a much stronger boost than you could get just by pushing yourself. 50 00:04:47,080 --> 00:04:54,600 The boost from the rotation of the back hole is so big, that you leave the ergosphere with much more energy than you entered it. 51 00:04:54,820 --> 00:05:00,140 The black hole gives a tiny amount of its rotational energy to you, and slows down a little. 52 00:05:00,880 --> 00:05:03,280 Obviously, this requires a lot of food. 53 00:05:03,500 --> 00:05:06,340 Fortunately, black holes aren't picky eaters. 54 00:05:06,680 --> 00:05:13,580 An advanced future civilization would probably harvest asteroids to drop them into the black hole when they needed an energy boost. 55 00:05:13,940 --> 00:05:22,200 But there's an even better way to get energy from a black hole, and oddly enough, it builds the biggest bomb any living thing could ever hope to build: 56 00:05:26,540 --> 00:05:32,320 We only need two things to build a black hole bomb: a fast-spinning black hole, and a big mirror. 57 00:05:32,540 --> 00:05:35,620 The mirror has to completely envelop the black hole, 58 00:05:35,620 --> 00:05:40,740 ...which is similar to a Dyson Sphere, a mega structure that harvests the energy of an entire star. 59 00:05:41,000 --> 00:05:43,580 Although, our mirror would be easier to build. 60 00:05:43,900 --> 00:05:48,820 Mirrors are simpler, and black holes are much, much more compact than stars. 61 00:05:50,200 --> 00:05:58,360 If we made the mirror 10 centimeters thick, the metal of a big asteroid would probably be enough material for a black hole with the mass of our Sun. 62 00:05:58,520 --> 00:06:05,620 Once our mirror is in place, we only need to open a window, and shoot electromagnetic waves at the black hole. 63 00:06:05,740 --> 00:06:12,280 You can imagine what happens next, by imagining tossing a ball at a wall, and it coming back faster than a bullet. 64 00:06:12,400 --> 00:06:15,440 The waves hit the black hole at light speed. 65 00:06:15,440 --> 00:06:19,980 A small proportion of the waves falls past the event horizon to disappear forever. 66 00:06:19,980 --> 00:06:23,545 But a much larger amount sloshes through the ergosphere, 67 00:06:23,545 --> 00:06:29,020 ...where the black hole forces some of its rotational energy on them, and amplifies them. 68 00:06:29,020 --> 00:06:34,360 They now begin superradiant scattering, which are fancy science words meaning: 69 00:06:34,360 --> 00:06:37,900 "Bouncing around between mirror and black hole and getting stronger." 70 00:06:38,200 --> 00:06:41,780 Every time they go around, they are getting exponentially stronger. 71 00:06:42,300 --> 00:06:48,260 By opening some windows in the mirror, we can extract the energy from the waves as fast as they grow. 72 00:06:48,260 --> 00:06:56,780 Which we could use, in theory, to create what would be for all practical purposes, an endless source of energy for trillions of years. 73 00:06:56,800 --> 00:06:59,000 Or, we could blow it up. 74 00:06:59,200 --> 00:07:03,829 If the waves are not released, they will continue to get stronger and stronger, 75 00:07:03,829 --> 00:07:08,340 ...and take more and more energy from the black hole, until the mirror shatters. 76 00:07:08,340 --> 00:07:12,540 A supermassive black hole would release as much energy as a supernova, 77 00:07:12,540 --> 00:07:17,140 ...making the bomb the largest explosion any living being could ever create. 78 00:07:21,360 --> 00:07:28,640 The beauty of the black hole bomb, the Penrose process, and the super radiant scattering, is that they are not science-fiction. 79 00:07:28,680 --> 00:07:34,240 In the far far future, this might be the only way to survive in our dying universe. 80 00:07:34,240 --> 00:07:42,760 After all the red dwarfs have cooled down, and all the white dwarfs transformed into black dwarfs, the universe will turn dark forever. 81 00:07:43,320 --> 00:07:49,500 Rotating black holes might be the only sources of energy in the entire universe that life could harvest. 82 00:07:49,780 --> 00:07:57,240 If so, the last living being in existence might one day end its life around a black hole. 83 00:07:57,240 --> 00:08:00,660 Which is equally chilling and uplifting. 84 00:08:01,060 --> 00:08:06,940 It turns out that even without any light, there are places we can go. 85 00:08:07,860 --> 00:08:13,160 Black holes are as interesting as they are mysterious, but there's actually a surprising amount we do know. 86 00:08:13,480 --> 00:08:19,120 Using math we can calculate things and come up with theories about how we die if we fall into them. 87 00:08:19,160 --> 00:08:23,945 If you're the sort of person who gets excited about maths and calculating these things for yourself, 88 00:08:23,945 --> 00:08:29,660 ...our friends at Brilliant have put together a fantastic black hole quiz to help you get your head around them. 89 00:08:29,880 --> 00:08:35,500 Brilliant is a problem-solving website that teaches you to think like a scientist, by guiding you through the problems. 90 00:08:35,580 --> 00:08:43,520 They take concepts like these, break them up into bite-sized pieces, present clear thinking in each part, and then build back up to an interesting conclusion. 91 00:08:43,780 --> 00:08:53,060 If you visit Brilliant.org/nutshell or click the link in the description, you can sign up for free and learn all kinds of cool stuff. 92 00:08:53,060 --> 00:09:00,320 And as a bonus for Kurzgesagt viewers, the first 688 people will also get 20% off their annual membership. 93 00:09:00,900 --> 00:09:07,440 If you want to truly learn about black holes and support Kurzgesagt, this is one of the best ways to do it.