WEBVTT 99:59:59.999 --> 99:59:59.999 Imagine a distant future when humans reach beyond our pale blue dot, 99:59:59.999 --> 99:59:59.999 forge cities on planets thousands of light-years away, 99:59:59.999 --> 99:59:59.999 and maintain a galactic web of trade and transport. 99:59:59.999 --> 99:59:59.999 What would it take for our civilization to make that leap? 99:59:59.999 --> 99:59:59.999 There are many things to consider— how would we communicate? 99:59:59.999 --> 99:59:59.999 What might a galactic government look like? 99:59:59.999 --> 99:59:59.999 And one of the most fundamental of all: 99:59:59.999 --> 99:59:59.999 where would we get enough energy to power that civilization— 99:59:59.999 --> 99:59:59.999 its industry, its terraforming operations, and its starships? 99:59:59.999 --> 99:59:59.999 An astronomer named Nikolai Kardashev proposed a scale 99:59:59.999 --> 99:59:59.999 to quantify an evolving civilization’s increasing energy needs. 99:59:59.999 --> 99:59:59.999 In the first evolutionary stage, which we’re currently in, 99:59:59.999 --> 99:59:59.999 planet-based fuel sources like fossil fuels, 99:59:59.999 --> 99:59:59.999 solar panels and nuclear power plants 99:59:59.999 --> 99:59:59.999 are probably enough to settle other planets inside our own solar system, 99:59:59.999 --> 99:59:59.999 but not much beyond that. 99:59:59.999 --> 99:59:59.999 For a civilization on the third and final stage, expansion on a galactic scale 99:59:59.999 --> 99:59:59.999 would require about 100 billion times more energy 99:59:59.999 --> 99:59:59.999 than the full 385 yotta joules our sun releases every second. 99:59:59.999 --> 99:59:59.999 Barring a breakthrough in exotic physics, 99:59:59.999 --> 99:59:59.999 there’s only one energy source that could suffice: a supermassive black hole. 99:59:59.999 --> 99:59:59.999 It’s counterintuitive to think of black holes as energy sources, 99:59:59.999 --> 99:59:59.999 but that’s exactly what they are, thanks to their accretion disks: 99:59:59.999 --> 99:59:59.999 circular, flat structures formed by matter falling into the event horizon. 99:59:59.999 --> 99:59:59.999 Because of conservation of angular momentum, 99:59:59.999 --> 99:59:59.999 particles there don’t just plummet straight into the black hole. 99:59:59.999 --> 99:59:59.999 Instead, they slowly spiral. 99:59:59.999 --> 99:59:59.999 Due to the intense gravitational field of the black hole, 99:59:59.999 --> 99:59:59.999 these particles convert their potential energy to kinetic energy 99:59:59.999 --> 99:59:59.999 as they inch closer to the event horizon. 99:59:59.999 --> 99:59:59.999 Particle interactions allow for this kinetic energy 99:59:59.999 --> 99:59:59.999 to be radiated out into space at an astonishing matter-to-energy efficiency: 99:59:59.999 --> 99:59:59.999 6% for non-rotating black holes, and up to 32% for rotating ones. 99:59:59.999 --> 99:59:59.999 This drastically outshines nuclear fission, 99:59:59.999 --> 99:59:59.999 currently the most efficient widely available mechanism 99:59:59.999 --> 99:59:59.999 to extract energy from mass. 99:59:59.999 --> 99:59:59.999 Fission converts just 0.08% of a Uranium atom into energy. 99:59:59.999 --> 99:59:59.999 The key to harnessing this power may lie in a structure 99:59:59.999 --> 99:59:59.999 devised by physicist Freeman Dyson, known as the Dyson sphere. 99:59:59.999 --> 99:59:59.999 In the 1960s, Dyson proposed that an advanced planetary civilization 99:59:59.999 --> 99:59:59.999 could engineer an artificial sphere around their main star, 99:59:59.999 --> 99:59:59.999 capturing all of its radiated energy to satisfy their needs. 99:59:59.999 --> 99:59:59.999 A similar, though vastly more complicated design 99:59:59.999 --> 99:59:59.999 could theoretically be applied to black holes. 99:59:59.999 --> 99:59:59.999 In order to produce energy, black holes need to be continuously fed – 99:59:59.999 --> 99:59:59.999 so we wouldn’t want to fully cover it with a sphere. 99:59:59.999 --> 99:59:59.999 Even if we did, the plasma jets that shoot from the poles 99:59:59.999 --> 99:59:59.999 of many supermassive black holes 99:59:59.999 --> 99:59:59.999 would blow any structure in their way to smithereens. 99:59:59.999 --> 99:59:59.999 So instead, we might design a sort of Dyson ring, 99:59:59.999 --> 99:59:59.999 made of massive, remotely controlled collectors. 99:59:59.999 --> 99:59:59.999 They’d swarm in an orbit around a black hole, 99:59:59.999 --> 99:59:59.999 perhaps on the plane of its accretion disk, but farther out. 99:59:59.999 --> 99:59:59.999 These devices could use mirror-like panels 99:59:59.999 --> 99:59:59.999 to transmit the collected energy to a powerplant, 99:59:59.999 --> 99:59:59.999 or a battery for storage. 99:59:59.999 --> 99:59:59.999 We’d need to ensure that these collectors are built at just the right radius: 99:59:59.999 --> 99:59:59.999 too close and they’d melt from the radiated energy. 99:59:59.999 --> 99:59:59.999 Too far, and they’d only collect a tiny fraction of the available energy 99:59:59.999 --> 99:59:59.999 and might be disrupted by stars orbiting the black hole. 99:59:59.999 --> 99:59:59.999 We would likely need several Earths worth of highly reflective material 99:59:59.999 --> 99:59:59.999 like hematite to construct the full system–– 99:59:59.999 --> 99:59:59.999 plus a few more dismantled planets to make a legion of construction robots. 99:59:59.999 --> 99:59:59.999 Once built, the Dyson ring would be a technological masterpiece, 99:59:59.999 --> 99:59:59.999 powering a civilization spread across every arm of a galaxy. 99:59:59.999 --> 99:59:59.999 This all may seem like wild speculation. 99:59:59.999 --> 99:59:59.999 But even now, in our current energy crisis, 99:59:59.999 --> 99:59:59.999 we’re confronted by the limited resources of our planet. 99:59:59.999 --> 99:59:59.999 New ways of sustainable energy production will always be needed, 99:59:59.999 --> 99:59:59.999 especially as humanity works towards he survival 99:59:59.999 --> 99:59:59.999 and technological progress of our species. 99:59:59.999 --> 99:59:59.999 Perhaps there’s already a civilization out there 99:59:59.999 --> 99:59:59.999 that has conquered these astronomical giants. 99:59:59.999 --> 99:59:59.999 We may even be able to tell by seeing the light from their black hole periodically dim 99:59:59.999 --> 99:59:59.999 as pieces of the Dyson ring pass between us and them. 99:59:59.999 --> 99:59:59.999 Or maybe these superstructures are fated to remain in the realm of theory. 99:59:59.999 --> 99:59:59.999 Only time––and our scientific ingenuity––will tell.