Dyson Sphere

The Dyson sphere is a huge, artificial biosphere that is created around a star by an intelligent species as part of its technological growth and expansion within an alien solar system. This hypothesized giant structure would probably be formed by a swarm of artificial habitats and miniplanets that are capable of intercepting essentially all the radiant energy from the parent star. The captured radiant energy would be converted for use through a variety of techniques such as living plants, direct thermal-to-electric conversion devices, photovoltaic cells, and perhaps other exotic (as yet undiscovered) energy conversion techniques.

In response to the second law of thermodynamics, waste heat and unusable radiant energy would be rejected from the "cold" side of the Dyson sphere to outer space. From contemporary knowledge of engineering heat transfer, the heat rejection surfaces of the Dyson sphere might have a temperature that ranges from a lower limit of about -100°F (-73°C) to an upper limit of about 80°F (27°C). When observed at interstellar distances, this enormous collection of millions of artificial structures would offer a distinct thermal infrared signature. An unidentified celestial object that is one to two astronomical units in diameter and lies within the previously mentioned temperature range could be an alien civilization's Dyson sphere.

This hypothesized astroengineering project is an idea of the British-American theoretical physicist Freeman John Dyson (1923- ). In essence, what Dyson has proposed is that advanced extraterrestrial societies, responding to Malthusian pressures, would eventually expand into their local solar system, ultimately harnessing the full extent of its energy and materials resources. Just how much growth does this type of expansion represent?

To explore this interesting concept further, scientists usually invoke the principle of mediocrity (that is, that conditions are pretty much the same throughout the universe) and then use humans' solar system as the model. The energy output from the Sun—a G2V-spectral class star—is approximately 4 x 1026 watts (joules per second [ J/s]). For all practical purposes, scientists and engineers treat the Sun as a blackbody radiator at a temperature of approximately 9,980°F (5,800 K). The vast majority of the Sun's energy output occurs as electromagnetic radiation, predominantly in the wavelength range 0.3 to 0.7 micrometers (pm), which corresponds to visible light.

As an upper limit, the available mass in the solar system for very large-scale (astroengineering) construction projects may be taken as the mass of the planet Jupiter, some 4.4 X 1027 pounds (2 X 1027 kg). Contemporary energy consumption by human beings on Earth is about 10 terawatts (TW). The next step is to postulate just a 1 percent growth in terrestrial energy consumption per year. At this growth rate, within a mere three millennia, humans' energy consumption would reach the energy output of the Sun itself. Today, several billion human beings live in a single biosphere, planet Earth—with a total mass of some 11 X 1024 pounds (5 X 1024 kg). A few thousand years from now, the Sun could be surrounded by a swarm of habitats, containing trillions of human beings.

The Dyson sphere may be regarded as representing an upper limit for physical growth within the solar system. It is simply "the best human beings can do" from an energy and materials point of view in this particular corner of the galaxy. The vast majority of these hypothesized humanmade habitats will most likely be located in the ecosphere, or continuously habitable zone (CHZ), around the Sun—that is, at a distance of about a one astronomical unit (AU) from our parent star. However, this does not preclude the possibility that other habitats, powered by nuclear fusion energy, might also be found scattered throughout the outer regions of a somewhat dismantled solar system. Such fusion-powered habitats could also represent the technical precursors to the first interstellar space arks— enormously large starships that carry significant numbers of human beings on one-way journeys to explore and then settle other star systems.

By using humankind's solar system and planetary civilization as a model, some exobiologists project that within a few millennia after the start of industrial development, an intelligent species could rise from the level of a planetary civilization (that is, a Kardashev Type I civilization) and eventually occupy a swarm of artificial habitats that completely surround their parent star, creating a fully matured Kardashev Type II civilization. Of course, these intelligent creatures might also elect to pursue interstellar travel and galactic migration, as opposed to completing the Dyson sphere within their home star system. This decision would represent the start of a Kardashev Type III civilization. (See chapter 8 for a discussion of extraterrestrial civilizations.)

It was further postulated by Dyson that the existence of such advanced extraterrestrial civilizations might be detected by the presence of a characteristic thermal infrared signature from very large objects in space that had dimensions of one to two astronomical units in diameter. Thus far, sophisticated, space-based infrared telescopes, like NASA's Spitzer Space Telescope, have not detected such unusual objects.

The Dyson sphere is certainly a grand, far-reaching concept. It is also quite appropriate for each reader to realize that the International Space

Station (ISS), currently being assembled in low Earth orbit, can be viewed as the very first habitat in the potential swarm of artificial structures that humans might eventually construct as part of their solar-system-level civilization.

Getting Started With Solar

Getting Started With Solar

Do we really want the one thing that gives us its resources unconditionally to suffer even more than it is suffering now? Nature, is a part of our being from the earliest human days. We respect Nature and it gives us its bounty, but in the recent past greedy money hungry corporations have made us all so destructive, so wasteful.

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