Humankind is energy-hungry. As our civilization has industrialized over the last couple centuries, global energy consumption has spiked more than twentyfold with no end in sight. When demand outstrips what we can reap from Earth and its vicinity, what will our power-craving descendants do?

A bold solution: the Dyson Sphere. This megastructure—usually conceived of as a gigantic shell enclosing the sun, lined with mirrors or solar panels—is designed to collect every iota of a star's energetic output. In the case of our sun, that colossal figure is 400 septillion watts per second, which is on the order of a trillion times our current worldwide energy usage. What's more, the interior of the Dyson Sphere could, in theory, provide far more habitable real estate than a measly planet.

Physicist Freeman Dyson speculated that a technologically advanced race, reaching the limit of its civilization's expansion because of dwindling matter and energy supplies, would seek to exploit their sun for all it is worth.

"One should expect that, within a few thousand years of its entering the stage of industrial development, any intelligent species should be found occupying an artificial biosphere which completely surrounds its parent star," Dyson wrote in the 1960 Science paper that led to his becoming the namesake of this megastructure.

A Dubious Sphere

From an engineering perspective, a Dyson Sphere sounds pretty wild. And it is: As an immense, hollow ball, the structure is impossible. "An actual sphere around the sun is completely impractical," says Stuart Armstrong, a research fellow at Oxford University's Future of Humanity Institute who has studied megastructure concepts.

Armstrong says the tensile strength needed to prevent the Sphere from tearing itself apart vastly exceeds that of any known material. Another problem: The Sphere would not gravitationally bind to its star in a stable fashion. This is perhaps counterintuitive; you might think that a perfect sphere around a

star would be stable. But if any part of the sphere were nudged closer to the star—say, by a meteor strike—then that part would be pulled preferentially toward the star, creating instability.

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