0:00:07.814,0:00:12.887
Imagine a distant future when humans[br]reach beyond our pale blue dot,

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forge cities on planets [br]thousands of light-years away,

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and maintain a galactic web [br]of trade and transport.

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What would it take for our civilization[br]to make that leap?

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There are many things to consider—[br]how would we communicate?

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What might a galactic government[br]look like?

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And one of the most fundamental [br]of all:

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where would we get enough energy[br]to power that civilization—

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its industry, its terraforming operations,[br]and its starships?

0:00:43.582,0:00:47.582
An astronomer named Nikolai Kardashev[br]proposed a scale

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to quantify an evolving civilization’s [br]increasing energy needs.

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In the first evolutionary stage, [br]which we’re currently in,

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planet-based fuel sources [br]like fossil fuels,

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solar panels and nuclear power plants

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are probably enough to settle other [br]planets inside our own solar system,

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but not much beyond that.

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For a civilization on the third [br]and final stage,

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expansion on a galactic scale [br]would require about 100 billion times

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more energy than the full 385 yotta joules[br]our sun releases every second.

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Barring a breakthrough in exotic physics,

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there’s only one energy source [br]that could suffice:

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a supermassive black hole.

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It’s counterintuitive to think [br]of black holes as energy sources,

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but that’s exactly what they are, [br]thanks to their accretion disks:

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circular, flat structures formed [br]by matter falling into the event horizon.

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Because of conservation [br]of angular momentum,

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particles there don’t just plummet [br]straight into the black hole.

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Instead, they slowly spiral.

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Due to the intense gravitational field [br]of the black hole,

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these particles convert their potential[br]energy to kinetic energy

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as they inch closer to the event horizon.

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Particle interactions allow[br]for this kinetic energy

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to be radiated out into space

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at an astonishing matter-to-energy [br]efficiency:

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6% for non-rotating black holes, [br]and up to 32% for rotating ones.

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This drastically outshines[br]nuclear fission,

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currently the most efficient [br]widely available mechanism

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to extract energy from mass.

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Fission converts just 0.08% [br]of a Uranium atom into energy.

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The key to harnessing this power [br]may lie in a structure

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devised by physicist Freeman Dyson,[br]known as the Dyson sphere.

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In the 1960s, Dyson proposed [br]that an advanced planetary civilization

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could engineer an artificial sphere [br]around their main star,

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capturing all of its radiated energy [br]to satisfy their needs.

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A similar, though vastly [br]more complicated design

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could theoretically be applied [br]to black holes.

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In order to produce energy, [br]black holes need to be continuously fed—

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so we wouldn’t want to fully cover [br]it with a sphere.

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Even if we did, the plasma jets [br]that shoot from the poles

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of many supermassive black holes

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would blow any structure [br]in their way to smithereens.

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So instead, we might design [br]a sort of Dyson ring,

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made of massive, [br]remotely controlled collectors.

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They’d swarm in an orbit [br]around a black hole,

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perhaps on the plane [br]of its accretion disk, but farther out.

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These devices could use [br]mirror-like panels

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to transmit the collected energy[br]to a powerplant,

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or a battery for storage.

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We’d need to ensure that these collectors[br]are built at just the right radius:

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too close and they’d melt [br]from the radiated energy.

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Too far, and they’d only collect [br]a tiny fraction of the available energy

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and might be disrupted by stars orbiting[br]the black hole.

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We would likely need several Earths[br]worth of highly reflective material

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like hematite to construct[br]the full system—

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plus a few more dismantled planets[br]to make a legion of construction robots.

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Once built, the Dyson ring [br]would be a technological masterpiece,

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powering a civilization spread[br]across every arm of a galaxy.

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This all may seem like wild speculation.

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But even now, [br]in our current energy crisis,

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we’re confronted [br]by the limited resources of our planet.

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New ways of sustainable energy[br]production will always be needed,

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especially as humanity works [br]towards the survival

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and technological progress of our species.

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Perhaps there’s already a civilization[br]out there

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that has conquered [br]these astronomical giants.

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We may even be able to tell

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by seeing the light [br]from their black hole periodically dim

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as pieces of the Dyson ring pass [br]between us and them.

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Or maybe these superstructures are fated [br]to remain in the realm of theory.

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Only time— and our scientific ingenuity— [br]will tell.