A Type II civilization would be capable of tapping its entire stellar energy, using about 4 × 1026 watts. It could restructure an entire solar system; but such a level of technology, argued Kardaschev, would have reached beyond our technological horizons. Their civilization would also have passed through the critical self-destruct phase. If they thought that communication with Earth was desirable, they could communicate from their nearest galactic neighbours.
A Type III civilization would be capable of controlling and reconstructing whole galaxies, with an energy output of4 × 1037 watts, and could communicate across the entire universe. If Type II and III civilizations exist, their energy consumption would make them detectable and proposals were made by Sagan and Kardaschev for a search for Types II and III among the nearest galaxies.
Whereas communication with a Type I civilization might be within our communicative horizon, it may be too far away for us to receive their signal. Kardaschev therefore assumed that we are less likely to detect a Type I civilization than a Type II or a Type III which means that contact is likely to be with those who are considerably more advanced than us. Types II and III could reach us with their signal but Type III are well beyond our communicative horizon and it is unlikely that they would be interested in talking to us, although a few might wish to engage in some form of antiquarian dialogue.
A similar hypothesis was developed during the 1960s by Freeman J. Dyson (1960) who claimed that an advanced civilization might be driven by pressures of population growth forcing it to seek more living space and thus reassemble planetary matter to construct a huge sphere around its home star in order to intercept and utilize radiation from the parent star or build a habitable swarm of smaller spheres around the parent star. According to Dyson, Malthusian pressures would drive a civilization to an efficient exploitation of all their resources within a few thousand years of entering the stage of industrial development. Thus they might re-arrange the total mass of a planet the size of Jupiter to construct a spherical shell around the Sun at twice the Earth’s distance from it. It would be about 2–3 metres thick and would contain all the energy from the Sun and provide a habitable biosphere for an expanding population and all the machinery for exploiting solar radiation on the inside. Such feats of engineering, he claimed, would leave indications of waste heat that we could observe in the form of infrared emissions across the galaxy.
These spheres, known as ‘Dyson spheres’, have actually been sought by radio astronomers. Dyson (1960) suggested searches for dark objects with a size similar to the Earth’s orbit, having a surface temperature of 200ºK to 300ºK, and radiation in the infrared, around 10 microns wavelength. This search for ‘infrared’ stars could be conducted independently or in connection with radio searches.
Dyson’s hypothesis, although strikingly bold, has the merit of being related to possible observations and is suggestive of possible places to look for intelligent ET life. It also has the advantage of not employing the assumption that advanced extraterrestrials are actually trying to communicate with us or colonize
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us. His suggestion involves an alternative to radio searches: that attention should focus upon the amount of infrared emission coming from the extended habitable zone, thus eliminating the need for an expensive array of antennae as indicated in Project Cyclops; and he therefore argues that a rational approach to SETI would be based on an extension of infrared astronomy.
Dyson actually suggests that a failure to detect these spheres should be considered as evidence of the non-existence of ETI. This may be in conformity with the falsifiability criterion of Popperian methodology but it is restrictive and could prematurely prohibit many fruitful hypotheses concerning ET life. First, ETs may not develop in directions which would lend themselves to the construction of spheres; second, there are insufficient probabilistic reasons for inferring the existence of Dyson spheres. If they do exist, however, a civilization that could construct a Dyson sphere would find the construction of a powerful communicative beacon mere child’s play. Yet no beacon has been detected. While it is intriguing to admit the plausibility of Dyson spheres, the case for their existence is not probable enough to base an entire search strategy on them. There are no fine details concerning the assembly of the orbiting structures or how they are to be made habitable. In this respect Dyson’s account of possible advanced civilizations suffers from the inadequacies of so many appeals to the future and faraway. We are not told in any great detail as to how their technology could solve problems which are beyond the range of our knowledge. Appeals to the current infancy of science can never be trusted. There are limits to what is technologically possible and it is the scientists’ job to point them out and to show how, if it is possible, they can be surpassed.
Dyson would also have to resolve the problem of whether civilizations would be destroyed through the effects of over-population before they developed the technology for successful stellar manipulation or migration. Then there are problems concerning the observation of Dyson spheres. The main problem here is that of separating data indicative of Dyson spheres from other naturally occurring infrared astronomical objects. Detection would not be easy, as the excess infrared radiation from the spheres would be indistinguishable from that produced by a lot of dust around a star. Many infrared sources were picked up by NASA’s Infrared Astronomical Satellite (IRAS) in 1983, but they could have been of natural origin, such as stars with disks of dust. The IRAS data include 50,000 sources of infrared radiation which could be Dyson spheres, although they could be baryonic matter, and as Learned et al. (1994: 327–8) point out, ‘There is no reason to believe that we would have as yet identified a Dyson shell even if very large numbers are nearby in the Galaxy.’
IRAS surveyed 130,375 infrared sources that corresponded to stars. From this Professor Jun Jugaku of Tokai University selected 594 stars which resemble our Sun and searched for additional infrared radiation. Only three had an infrared excess and after further examination this was explained by natural causes (Heidmann, 1995: xviii–xix). While many objects have turned out to have the expected spectrum of Dyson spheres, there has been no positive proof, as they
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