As far as technological races go, humans are welterweights in comparison to hypothetical alien civilizations that could, conceivably, inhabit an entire galaxy. But if these vastly advanced extraterrestrials do exist, how could our current (and, frankly, meager) technology go about detecting them?
The answer could be in seeking out the galactic waste - heat waste to be precise - that such huge civilizations would generate. What's more, we may already have the observational data to begin a detailed search of the Cosmos.
Glimpsing Heat from Alien Technologies
In a new study accepted for publication in The Astrophysical Journal, a team of astronomers headed by Jason Wright of the Center for Exoplanets and Habitable Worlds, Penn State University, argue the case for using survey data from NASA's Wide-field Infrared Survey Explorer (WISE) and Spitzer space telescopes to identify advanced extraterrestrial intelligences that have fully utilized all the energy from a star or even spread throughout their host galaxies.
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The proposed "Glimpsing Heat from Alien Technologies" survey (called, simply, G-HAT) will seek out radiation in mid-infrared (MIR) wavelengths. The G-HAT astronomers' rationale is that publicly available WISE data could be used to find galaxies that generate excessive quantities of MIR radiation. This radiation could be associated with the heat waste of extraterrestrial civilizations converting stellar energy into an energy resource. Regardless of how advanced they are, this heat waste will be unavoidable.
"An (extraterrestrial intelligence's) energy collection and generation must be balanced by energy disposal in steady-state," write Wright and co. "This disposal most naturally occurs in mid-infrared wavelengths, potentially rendering large alien civilizations easily detectable and distinguishable from natural sources with new mid-infrared surveys such as that recently conducted by WISE."
The researchers focus on Kardashev Type III civilizations. First proposed in 1964 by Soviet astronomer Nikolai Kardashev, the Kardashev scale refers to the technological sophistication a civilization is capable of based on the amount of energy they are able to collect. The more energy you collect, the greater the scope and advancement of technology is feasible. Humanity isn't even a Type I civilization yet as we haven't fully harnessed the energy that is delivered to the surface of the Earth by our sun - some estimates suggest we may attain Type I in 100-200 years.
Type II alien civilizations will have expanded beyond their homeworld to become masters of their star system, utilizing all the available energy from their star, using it as a power station for their expanding technological prowess. One hypothetical technology that could achieve this feat is that of a Dyson Sphere - a huge shell, or system of rings - that would cocoon a star, feeding off all of its radiative energy and converting it into a useful power resource.
Slaves to Physics
Beyond the Type II is a civilization that would outshine our most extreme sci-fi notions. Type III civilizations would endeavor to harness the total energy from their galaxy, jumping from star system to star system, using their technologies to completely dominate interstellar space. The researchers argue that a Type III civilization would be a network of iterative steps through Type II star systems; the extraterrestrial civilization may set up a series of Dyson Spheres, feeding off the energy generated by each and every star they visit. This network of stellar energy collection platforms could be complemented with other, more exotic means of energy generation, such as black holes. What's more, galactic dominance could happen relatively quickly.
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"If spacefaring extraterrestrial intelligences (ETI's) capable of colonizing other stars in its galaxy exist in the Milky Way or in another galaxy, we find ... that its galaxy can be fully colonized on the timescale of a galactic rotation (i.e. significantly less than the age of the galaxy)."
But regardless of how advanced these civilizations become, they will still be a slave to physics.
Energy cannot be created or destroyed, it can only be converted into other forms of energy. For example, a solar cell converts radiative energy from the sun and converts it into electrical energy that can be used by our technology to function. But the system also converts the radiative and electrical energy into not-so-useful waste energy. The sunlight may heat up the solar cell's material that will then radiate infrared radiation, making the cell less efficient. Also, the electrical energy that goes on to do something useful, like powering a light bulb, will generate heat; waste heat that can be detected in infrared wavelengths.
Although this example uses rudimentary technology available to us today, it illustrates some basic points of energy loss through infrared radiation - MIR energy wastage that even efficient alien technologies will generate.
Exacerbating the Fermi Paradox?
Using WISE data, the researchers have performed a preliminary ("zeroth order") G-HAT survey of galaxies to see if they generate excessive quantities of MIR radiation. But they turned up empty handed, which may, at first, appear to only exacerbate the Fermi Paradox: "(W)e show, for the first time, that Kardashev Type III civilizations (as Kardashev originally defined them) are very rare in the local universe."
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This first null result doesn't prove that Type III civilizations don't exist, it just places a lower boundary on how many of these advanced civilizations populate nearby galaxies... or it illustrates a limitation of our instrumental capabilities.
To improve on this result, further analysis of survey data is needed. Also, the researchers identify possible sources of MIR radiation that could be misinterpreted as heat waste from a civilization, such as dusty stars generating excessive MIR radiation.
Although they point out that it would be easier to spot a galaxy-spanning Type III alien civilization in other galaxies than spotting MIR waste from single Type II star systems (i.e. Dyson Spheres), with the help of the recently-launched European Gaia space telescope that is tasked to map one billion Milky Way stars (and thousands of sub-stellar objects) in 3-D, complementary MIR data from WISE and Spitzer could make the Type II search within our own galaxy plausible.
Regardless of whether or not advanced alien civilizations exist, it's exciting to think that broad searches for extraterrestrial technologies and artifacts (searches known as "SETT" and "SETA," respectively) can be carried out today using survey data that is already available. Indeed, this work can be used to complement current SETI searches.
But one can't help but imagine that if G-HAT does turn up a galaxy that is glowing in excessive MIR emissions, which is confirmed by other observatories to be an artificial source, how will it change humanity and our myopic view on the Universe?
Publication: The G-HAT Infrared Search for Extraterrestrial Civilizations with Large Energy Supplies. II. Framework, Strategy, and First Result, Write et al., 2014. arXiv:1408.1134v1 [physics.pop-ph]