Day 098 - Harnessing the sun

Submitted by Sam on 27 August, 2011 - 01:42

The laws of physics impose very definite constraints on the information processing capabilities of intelligent civilizations, placing limitations on how much heat can be dissipated away from information processing systems, how fast computers can run, how much information can be stored, and what size and density storage and computational devices can be. Barring technological regression caused by anti-technological movements, laws or accident, the information processing needs of a civilization will grow exponentially until limits set by physical law are met. In order to service this expansion to the very limits of possibility, a technologically advancing civilization will need to harvest ever more and more energy with ever greater efficiency in a logical escalation which will eventually lead to a Type II Kardashev civilization, where most or all of the energy output of their local star is captured.

If a civilization survives long enough to demand the total energy output of its star, it will have to embark on a megastructural engineering project to create a network of orbiting solar collectors around the star to maximally intercept its energy output. These hypothetical structures are referred to as Dyson spheres, after the physicist Freeman Dyson who first formalized the concept of a shell-like system of orbital solar collectors as a means of achieving maximal solar energy efficiency. In its most feasible form, a Dyson sphere is more strictly a series of Dyson rings, which are huge energy-gathering satellites deployed in rings that orbit around the sun, sharing a common axis of rotation with an orbital radius approximately equal to the earth-sun distance. A similar variant is the Dyson swarm, where solar collecting satellites and space habitats are arranged in a denser and more complex patterns to intercept more of the star's output, at the risk of orbital perturbations and instability as the independent orbits of the cloud of collectors interact with each other. Additional variants of the Dyson sphere include non-orbital collectors, anchored by light sails to remain stationary in relation to the star.

The idealized Dyson sphere is the Dyson shell, which would be a shell of solid matter that would completely enclose a star and thus intercept all of its emissions, but it would be likely to require more matter to construct than is available in our entire solar system, even if all the planets and gas giants were broken down into building materials. Furthermore, no existing or theoretical material would be able to stand the compressive pressure a static, rigid sphere large enough to encompass the sun would exert on itself.

Practical Dyson spheres will therefore never be 100% efficient, with gaps between collectors allowing energy to escape and the collectors themselves absorbing and then reradiating more of the total available energy. Theoretically, the wavelengths of the reradiated energy from the collectors would be sufficiently different from the expected wavelengths of light for the star's spectral type that they could be detected at interstellar distances. If an alien civilization has constructed a Dyson sphere using the kind of materials that are available in our solar system, then the infrared radiation re-emitted by the solar collectors should be detectable from earth. If there are Kardashev Type II civilizations out there, we should be able to see them through the altered light of their star system.

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