In the search for extraterrestrial intelligence (SETI), of life beyond this world, astronomers look for tell-tale radio (and other broadcast) signals in the vicinity of sun-like stars, or detectable exoplanets. More recently, some have begun to hunt for ‘ultra-short’ laser pulses — indicating a more advanced communication system.
But the problem with searching for these signals is that, as a civilization advances, it may shift to other forms of communication (as in our shift to cable and fibre-optics from radio and broadcast signals), making them less detectable from afar.
But there’s a new, and rather simple, idea floating about the SETI community that was inspired by our own Earth-monitoring, space technology: city lights.
Bright Lights, Big City, Intelligent Life
The idea was presented in a recent paper by astrophysicists Avi Loeb (Harvard-Smithsonian Center for Astrophysics) and Edwin Turner (Princeton University) and was based upon a “reasonable assumption” that an E.T. civilization would be using similar forms of technology used here on Earth, as well as be living in large, population concentrations akin to our urban environments.
The argument for this assumption is that any intelligent life that evolved on a rotating planet in orbit about its parent star would have a period of darkness for which the civilization would have developed some means of artificial lighting to illuminate that darkness.
But detecting these lights would be quite tricky with distant planets orbiting relatively close to their parent stars; glare from the parent star would interfere with any light emanating from the surface of an alien planet. In the paper, Loeb and Turner suggest a method for distinguishing alien urban lighting from solar glare: measure the change in light from an exoplanet as it moves around its star.
Viewed from Earth or a space-based telescope, the putative alien-inhabited world would go through phases similar to our Moon’s as it orbits about its star. As the planet enters its darkest phase, more artificial light would be visible from its surface than reflected light from its day side.
How the detection technique would work
According to the two researchers, the “total flux” from any planet with urban lights will vary in measurable ways from a planet without said lights. Quoting the paper abstract: “…we propose to measure the variation of the observed flux (denoted as F) from such objects as a function of their changing orbital distances (denoted as D).”
Artificial lighting would exhibit a different “logarithmic slope”. If such a slope were found, then follow-up observations (using large telescopes) of the planet’s spectra would help determine if it was illuminated by artificial lighting.
“This method opens a new window in the search for extraterrestrial civilizations,” state the authors.
Testing the method and building new telescopes
Still, this flux differential would be quite small, and would require a new generation of telescopes to detect. The paper’s authors suggest that the technique could be tested closer to home, that is, at the outer edges of our own solar system.
The researchers assert that our best optical telescopes would be able to detect the light from a Tokyo-sized metropolis at the distance of the Kuiper Belt (i.e., about 100 trillion miles), which is the outer-most region of our solar system occupied by (the former planet) Pluto and other smaller, icy bodies. If there was some alien civilization out there now, we should be able to detect it.
“It’s very unlikely that there are alien cities on the edge of our solar system, but the principle of science is to find a method to check,” Turner said. “Before Galileo, it was conventional wisdom that heavier objects fall faster than light objects, but he tested the belief and found they actually fall at the same rate.”
The technique, once perfected, would then be trained on Earth-sized worlds orbiting stars (like red dwarf stars) in our Milky Way galaxy.
The paper, ‘Detection Technique for Artificially-Illuminated Objects in the Outer Solar System and Beyond‘ was published in the journal Astrobiology
Headquartered in Cambridge, Mass., the Harvard-Smithsonian Center for Astrophysics (CfA) is a joint collaboration between the Smithsonian Astrophysical Observatory and the Harvard College Observatory. CfA scientists, organized into six research divisions, study the origin, evolution and ultimate fate of the universe.
Top image: David A. Aguilar (CfA)
This idea has been suggested by others. But this paper lays out exactly how to do it, measurement wise.
Given the future development of ‘next gen’ telescopes, this theory also assumes that alien populations would concentrate themselves into dense, urban-like locales where sufficient artificial lighting would also be concentrated, and thus detectable. It also assumes that any putative civilization is not living completely underground (for energy source or protection reasons).
The E.T.’s may also have gone completely ‘green’ (in the eco sense, not the alien life form sense) and decided to turn off their unnecessary lights at night, making them less detectable. Thus, we may end up detecting only civilizations comparable to our own, while the really advanced ones go unnoticed (smart move).
I welcome readers’ comments and thoughts on this theory.