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Thread: Finding Alien civilizations - the way it will happen

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    Veteran Member Yaglakar's Avatar
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    Default Finding Alien civilizations - the way it will happen

    Earth-like civilizations generate heat from the energy that they utilize. The thermal radiation from this heat can be a thermodynamic marker for civilizations. Here we model such planetary radiation on Earth-like planets and propose a strategy for detecting such an alien unintentional thermodynamic electromagnetic biomarker. We show that astronomical infrared (IR) civilization biomarkers may be detected within an interestingly large cosmic volume using a 70 m-class or larger telescope. In particular, the Colossus telescope with achievable coronagraphic and adaptive optics performance may reveal Earth-like civilizations from visible and IR photometry timeseries’ taken during an exoplanetary orbit period. The detection of an alien heat signature will have far-ranging implications, but even a null result, given 70 m aperture sensitivity, could also have broad social implications.

    The detection of extraterrestrial life will be an important scientific achievement. Searches for intentional or beaconed alien signals have made great advances in sensitivity (Backus & The Project Phoenix Team 2002; Phoenix Project 2002) but, until we detect a signal, these results are difficult to interpret. Unambiguous conclusions from such null results require tenuous assumptions about alien sociology and ‘cosmological principles.’ Furthermore, our imaginations simply may not encompass the alien communication modes we could encounter. Gaining a better understanding of our evolution, either as one of many realizations of some biological ‘Copernican Universalism,’ or as a unique ‘Anthropic requirement’ (cf. Michaud 2007) of physical and biological laws, needs more than just a binary answer to the question ‘are we alone in the universe?’ The last decade of exoplanet studies have taught us that the Earth probably ‘is not special’ on a cosmic scale (e.g., Pepe et al. 2011; Kopparapu et al. 2014). Could it be that advanced life also ‘is not special’? We seek biomarkers whose completeness can be quantified with respect to the cosmic volume probed versus civilization type or advancement. With this aim, we propose here a strategy to find unavoidable thermodynamic alien biomarkers that would be difficult to hide from our remote sensing technologies.

    The radio or optical signalling power that ‘leaks’ from an advanced civilization is difficult to predict (e.g., Loeb & Zaldarriaga 2007; Forgan & Nichol 2011), but such power estimates are a useful classification scheme. Kardashev (1964) argued that advanced civilizations could be distinguished by the radio power they can generate. He called the Earth early Type I, Type II civilizations harness the full power of their host star, and a Type III can harness the power of its Galaxy. The idea of classifying a planetary civilization by its power generation was further refined by defining an index K = log10(P)/10–0.6, where P is the average power (in Watts) consumed by the planetary civilization (Shklovskii & Sagan 1966). On this scale Earth has K = 0.7, since P was about 15 TW in the year 2010.

    Dyson (1960) suggested searching for the thermodynamic signature of aliens capable of building a star-enclosing ‘biosphere’ at roughly their planet's orbit radius. He argued that they could capture their star's luminosity for their uses while unavoidably (due to the First Law of Thermodynamics) radiating the thermal waste into space with a black-body temperature near the planet's equilibrium temperature. While astronomical infrared (IR) surveys have not turned up any such Type II or III candidates (Carrigan 2009), the concept of using alien thermal waste is a powerful unintentional ET biomarker.

    Waste heat is a nearly unavoidable indicator of biological activity, just as the energy that civilization consumes is eventually reintroduced into the planetary environment as heat. On planetary scales, biologically produced heat tends to be spatially clustered, just as an ET civilizations’ technological heat is difficult to distribute uniformly. Planetary surface topography and the efficient tendency for population to cluster in agrarian and urban domains leads to heat ‘islands’ (cf. Rizwan et al. 2008).The temporal and spatial distribution of this heat can be an observable ‘fingerprint’ for remote sensing of civilizations. Here we argue that we may soon be in a position to detect this thermodynamic signal from Type I, nearly Earth-like civilizations.

    We believe that thriving Type I civilizations evolve towards greater power consumption. Notably, there is a strong correlation between our power consumption and society's accumulated information content. Humanity collects information with a doubling time of about 3 years (Gantz et al. 2008), and our power consumption is increasing faster than the population (IEA 2013). Even an advanced efficient civilization will have vast power requirements because of the fundamental information-theoretic energy cost to acquire and manipulate its knowledge base (cf. Maruyama et al. 2009).

    Planetary temperatures are determined by balancing the energy inputs (stellar, planetary heat sources, etc.) with the thermal energy radiated from the planet. Since most of the consumed power is eventually returned to the planet environment as heat, a civilization with growing power needs will eventually reach a point where they become uncomfortably warm. Perhaps a sufficiently advanced civilization can engineer the planet's albedo and radiative efficiency to moderate such global warming or they might find an energetically favourable way to radiate this heat away from the planet above the atmosphere, but this must also be detectable remotely. However, it is likely that such measures can help only temporarily if P continues to grow. Finding a planet that is ‘too hot’ compared to its stellar heat budget with a geographic temperature excess that is not geothermal might also be a sign of advanced life. We assume that eventually mass-migration to another planet can become energetically advantageous. Thus, for somewhat general reasons we may expect planetary civilizations to evolve towards a maximum Ω(t) = Ω0 ≤ 1 and then either moderate their power consumption or undergo planetary migration. The value of Ω0 is uncertain.

    Seeking the heat

    To date, there are few images obtained of exoplanets — they're faint and their parent stars tend to overwhelm their radiated light. That's why such a large mirror is needed to peer at them, Kuhn said.
    "The biggest telescopes that we're likely to see in the next 100 years or so will not be able to directly image cities or organized structures on the planet," he said. Still, he added, local heat sources could be visible.
    "We do that by using the fact that the planet has to rotate, and that civilization is clustered either by the formation of continents or the use of land, which is agrarian versus organized into population centers. The assumption we make is that civilizations will cluster their heat use. It won't be uniform; they distribute it."
    Volcanoes and other natural features also produce heat, Kuhn said, but astronomers would probe heat sources in at least two different wavelengths to obtain the temperature. Natural features are likely to be far above the background heat of the planet. Those heat sources that are slightly above the planet's natural radiation are more likely to be signs of civilization, he said.

    https://www.ncbi.nlm.nih.gov/pubmed/26321880
    https://www.space.com/21480-extrater...telescope.html


    IMO much better than the SETI assumption of intercepting alien communications. A type 1 civilization (or beyond), if one is out there, will not be able to hide those heat signatures. However, if civilizations are stuck somewhere in the iron age, we won’t see it because difference in the produced energy compared to the background energy will be too low to detect, at least with current technology.
    It will be more like you can look, but you can’t touch rather than War of the Worlds.


    The Colossus Telescope:





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