Alan

Nov 10, 2015

3 min read

The problem with Dyson Spheres

Claiming that (eventually) an advanced space-faring civilization would run out of space/energy in the solar system where they live sounds like a reasonable claim. It probably is. As such, it’s tempting to think that this civilization would obscure all of the light from its star in its frenzy to gobble up as much energy as it can before having to undertake an absurdly costly interstellar voyage. So the vision of a sphere with a radius of 1 Astronomical Unit (AU) sounds justified… except for the 1 AU number, which is willfully arbitrary. But keep diving, and you’ll find surprising things.

Consulting the real physics, you’ll also find that a Dyson sphere doesn’t maximize energy use either — at least not useful energy. See, to quantify what you can get out of any engine, you have to consider the temperatures of the reservoirs over which energy flows. This applies to solar panels just as it applies to steam engines. We just don’t typically care because the temperature of the sun’s photons are fixed, and ambient temperature on Earth is fixed. But in space, seeking absurdly lower temperatures can increase the efficacy of an engine several times over.

This argument turns out to favor extremely large Dyson spheres with extremely cool temperatures on the outside facing space. But does this agree with the principle of a Dyson sphere? Sure, it’s more energy, but it demands that civilization is even further spaced out. That decreases the vibrancy (and the computational power) of the civilization.

But consider the following alternative.

Orbital Station with low T reservoir

Excuse the jargon in the image, the point is simply that the penumbra of a space station is used to shield the radiating portion of the station from sunlight. This very sharply divides the station into hot and cold portions.

As biological beings, we have a clear temperature preference. Thankfully, this is not compatible with this scheme. Computers might prefer to operate at super-low temperature at the future, but humans could operate at their normal temperature while using a thermal cycle between themselves and space (with their body heat basically acting as the boiler heat source) to recoup extra heat.

Speculation? Everything remotely related to this subject matter is speculation. In fact, the only thing we can hope to claim for sure about hypothetical mega-structure designs is comparative in nature. Compare this design to a Dyson Swarm at 1 AU. These could still be located at 1 AU, but use less of the sun’s light in the process (by using what it gets more efficiently). The degree of centralization also favors this design over a Dyson swarm. You can state this two different ways. One, by getting higher power per unit of solar ray collection, you necessarily allow greater concentration of energy-consuming entities with less transportation of energy. Two, by noting that a perfect 1 AU Dyson Swarm has the obligation to spread out collectors over a very large area, limiting communication bandwidth between the different orbital stations. In this scheme, the orbital stations are inherently larger and fewer in number. Keeping the use of useful energy constant, this has fewer communication bottlenecks.

The rabbit hole goes further, and there is surprisingly little empirical consideration of the space mega-structure design space. If you want to dig further, I think you might find that most of everything we’ve ever presumed about the nature of a space-faring industrial society is wrong. Not even necessarily because of its inherent incomprehensibility, but simply due to a lack of trying.

Obligatory analytical writing, online participation account for Medium. Engineering, software, books, space, constant daydreaming.

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