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Imagine a distant future when humans
reach beyond our pale blue dot,

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forge cities on planets 
thousands of light-years away,

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and maintain a galactic web 
of trade and transport.

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

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

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What might a galactic government
look like?

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And one of the most fundamental 
of all:

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where would we get enough energy
to power that civilization—

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its industry, its terraforming operations,
and its starships?

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An astronomer named Nikolai Kardashev
proposed a scale

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to quantify an evolving civilization’s 
increasing energy needs.

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

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planet-based fuel sources 
like fossil fuels,

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solar panels and nuclear power plants

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are probably enough to settle other 
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 
and final stage,

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expansion on a galactic scale 
would require about 100 billion times

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more energy than the full 385 yotta joules
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 
that could suffice:

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a supermassive black hole.

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

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

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

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Because of conservation 
of angular momentum,

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

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Instead, they slowly spiral.

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Due to the intense gravitational field 
of the black hole,

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these particles convert their potential
energy to kinetic energy

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as they inch closer to the event horizon.

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Particle interactions allow
for this kinetic energy

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to be radiated out into space

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at an astonishing matter-to-energy 
efficiency:

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

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This drastically outshines
nuclear fission,

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currently the most efficient 
widely available mechanism

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to extract energy from mass.

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

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The key to harnessing this power 
may lie in a structure

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devised by physicist Freeman Dyson,
known as the Dyson sphere.

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

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could engineer an artificial sphere 
around their main star,

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capturing all of its radiated energy 
to satisfy their needs.

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A similar, though vastly 
more complicated design

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could theoretically be applied 
to black holes.

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

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

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

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of many supermassive black holes

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would blow any structure 
in their way to smithereens.

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So instead, we might design 
a sort of Dyson ring,

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made of massive, 
remotely controlled collectors.

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

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

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These devices could use 
mirror-like panels

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to transmit the collected energy
to a powerplant,

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or a battery for storage.

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

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

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

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and might be disrupted by stars orbiting
the black hole.

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We would likely need several Earths
worth of highly reflective material

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like hematite to construct
the full system—

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

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Once built, the Dyson ring 
would be a technological masterpiece,

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powering a civilization spread
across every arm of a galaxy.

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This all may seem like wild speculation.

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But even now, 
in our current energy crisis,

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

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New ways of sustainable energy
production will always be needed,

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especially as humanity works 
towards the survival

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and technological progress of our species.

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Perhaps there’s already a civilization
out there

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that has conquered 
these astronomical giants.

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We may even be able to tell

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by seeing the light 
from their black hole periodically dim

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

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

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Only time— and our scientific ingenuity— 
will tell.