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A Big Waste of Mass
by Nicholas J. Szabo

According to an article in New Scientist this past October, light pollution from cities and the presence of CFCs and other artificial compounds in the atmosphere (indicated by absorption at characteristic wavelengths) could be signs of intelligent life on alien planets. It has been suggested that we could construct orbiting observatories to detect just such biosignatures. I think otherwise.

Humans building large space structures to detect aliens emitting CFCs, which humans have already rendered obsolete after extremely brief use, strikes me as oddly backwards. It is the aliens, most likely hundreds of millions of years more advanced than us, who will have the astronomically sized structures, not ourselves in the near future.

Still, looking for CFCs does hint at the strategy which I have proposed -- look for artificial surfaces with very optically improbable properties, including chemicals that are highly unlikely or rare in natural dust clouds. For example, the surfaces of human satellites and many skyscraper windows have improbably very high concentrations of gold due to its good optical and thermal properties.

Paint contains many artificial molecules. The result is that artificial surfaces have very artificial-looking optical properties and spectra. Given that ETI of the most probable ages (i.e. hundreds of millions of years older than us) could have already spread across its galaxy and converted most of its visible surfaces into artificial surfaces, this search strategy should work for ETI in other galaxies, and indeed given the statistics is more likely to work than looking at star systems within our own galaxy. And, it can be done with normal-sized telescopes and standard spectroscopy. ETI will be far more advanced than we, and should be as easy or easier to detect than planets.

Looking for artificial radiation sources is also a good strategy. They will be too small or too faint or too relatively bright or faint in certain spectra to be stars; indeed they will probably have very artificial-looking spectra. These artificial lights will be parts of astrostructures, rather than strung out on the surface of a planet as in our current brief stage of human development.

The very existence of a planet around a star is strong evidence against the existence of ETI there. Dandridge Cole and Gerard O'Neill long ago showed that planets are a very poor way to house a technologically advanced civilization -- they are a big waste of mass.

Disclaimer: The opinions expressed in editorials are those of the individual authors, and do not necessarily reflect the position of The SETI League, Inc., its Trustees, officers, Advisory Board, members, donors, or commercial sponsors.

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