Astroengineering

Abstract: Pulsars have at least two impressive applications. First, they can be used as highly accurate clocks, comparable in stability to atomic clocks; secondly, a small subset of pulsars, millisecond X-ray pulsars, provide all the necessary ingredients for a passive galactic positioning system. This is known in astronautics as X-ray pulsar-based navigation (XNAV). XNAV is comparable to GPS, except that it operates on a galactic scale. I propose a SETI-XNAV research program to test the hypothesis that this pulsar positioning system might be an instance of galactic-scale engineering by extraterrestrial beings. The paper starts by exposing the basics of pulsar navigation, continues with a critique of the rejection of the extraterrestrial hypothesis when pulsars were first discovered. The core section of the paper proposes lines of inquiry for SETI-XNAV, related to the pulsar distribution and power in the galaxy; their population; their evolution; possible pulse synchronizations; pulsar usability when navigating near the speed of light; decoding galactic coordinates; directed panspermia; and information content in pulses. Even if pulsars are natural, they are likely to be used as standards by ETIs in the galaxy. I discuss possible objections and potential benefits for humanity, whether the research program succeeds or not.

Abstract: Introduction: Since the Dyson sphere was first proposed almost 50 years ago, numerous schemes for detecting large astro-engineering projects have been proposed [1, 2]. However, while a highly advanced alien civilization may posess the technology to build Dyson spheres, there are numerous fundamental issues that make it an unfeasible endeavor for current human technology. In the spirit of the many Dyson sphere variants developed by others [3, 4], we propose the Dyson-Harrop satellite (DHS) as an alternative scenario to the traditional Dyson sphere. Initial numerical modeling suggests the DHS is advantageous for power production, is feasible using modern technology, and is therefore an astro-engineering project that alien civilizations may consider building. However, detection of such a system remains beyond the grasp of modern technology, unless the DHS is very large. Dyson Sphere Impracticalities: Athough the Dyson sphere can produce very high amounts of power (~4 x 10 W) [5], its design has a number of disadvantages. If all of the matter in a solar system roughly the mass of ours is used to construct a sphere with radius of just 1 AU, the sphere would only be 8 cm thick (with an average density equal to that of steel). Additionally, it has been calculated [6] that the minimal radius of a Dyson sphere must be at least 1.66 AU in order to successfully dissipate thermal energy absorbed by the Sun in a useful fashion—a smaller sphere could suffer a cataclysmic thermal event (e.g. explosion or melting). Currently, there exist no manmade materials that can stand up to the stress that would be felt at every point along the surface of such a gargantuan structure [7]. Aside from the lack of net gravitational force on the inside of the Dyson sphere, a spherical shell around the Sun would have no net gravitational force on it either (Divergence Theorem). Drift of the sphere from its concentric location would have to be actively corrected for. Unfortunately, a drift speed of just 2 m/s would require virtually all of the power the sphere collects for the correction. The Dyson-Harrop Satellite (DHS): Several Dyson variants have been proposed [4, 8], though all share a common theme of solar power collection. The DHS, however, draws energy from the solar wind’s electrons, using the Sun’s high energy photons only to eject the electrons once their useful electronic energy has been collected. Fig. 1: The Dyson-Harrop Satellite. See text below for design.

Abstract: According to Dyson (1960), Malthusian pressures may have led extra-terrestrial civilizations to utilize significant fractions of the energy output from their stars or the total amount of matter in their planetary systems in their search for living space This would have been achieved by constructing from a large number of independently orbiting colonies, an artificial biosphere surrounding their star Biospheres of this nature are known as Dyson spheres If enough matter is available to construct an optically thick Dyson sphere the result of such astroengineering activity, as far as observations from the earth are concerned, would be a point source of infra-red radiation which peaks in the 10 micron range If not enough matter is available to completely block the stars’ light the result would be anomalous infra-red emission accompanying the visible radiation (Dyson 1960)

Abstract: Huge space power plants (Dyson Spheres) utilizing most of a star’s energy should be detectable as infrared or microwave sources. A recent far infrared all-sky survey has revealed many sources with a spectrum peaking on this region which is characteristic of the thermal emission of the hypothetical Dyson spheres. The possibility of confusing them with thick circumstellar dust shells around evolved red giant stars is discussed. Microwave detection of cool extended Dyson Spheres by all-sky surveys searching for microwave background fluctuations is also considered.