Searching for Advanced Alien Engineering

 http://www.pbs.org/wgbh/nova/blogs/physics

Thought Experiments

28 May

By Kate Becker on Thu, 28 May 2015

Picture this: You’re the emperor of an advanced alien civilization. For millions of years, your planet’s engineers have been building bigger and better gadgets: supercomputers, spaceships, flying cars, that sort of thing. All this ultra-tech makes life pretty fantastic, but it takes a lot of energy. Where is all that energy going to come from?

Image by Flickr user longan drink, adapted under a Creative Commons license

 

In 1937, the science fiction writer Olaf Stapledon imagined one answer: an enormous, spherical solar collector, built to encircle an energy-hungry civilization’s home star like a giant mylar balloon. This hypothetical mega-structure would grab every last photon of sunlight, providing enough energy to run whatever future technologies engineers could dream up. In 1960, physicist Freeman Dyson fleshed out the scheme: instead of a giant balloon, he speculated, an advanced civilization might crumble up its solar system’s uninhabited planets to create a swarm of rocks that could gather solar energy more efficiently. Dyson also pointed out that, if such a sphere or swarm existed, it would look to us like an unusually dark star, radiating waste heat in the infrared.
“Dyson spheres,” as they’re called (to Dyson’s chagrin), have become sci-fi staples. But they have also gotten some (semi) serious attention from scientists searching for evidence of intelligent life beyond Earth. In two studies, published in 2004 and 2008, Richard Carrigan, a researcher at Fermilab, searched for lopsided, infrared-heavy spectra among some quarter-million infrared sources in a database amassed by the IRAS satellite. IRAS, launched in 1983, surveyed about 96% percent of the sky. The result: no Dyson spheres–or, at least, none that he could confidently distinguish from other potential lookalikes.
If a civilization is sophisticated enough to build a Dyson sphere around one star, though, why should it stop there? Why not outfit a whole galaxy with Dyson spheres? As Jason Wright, assistant professor of astronomy and astrophysics at Penn State, wrote:

Consider a space-faring civilization that can colonize nearby stars in ships that travel at “only” 0.1% the speed of light (our fastest spacecraft travel at about 1/10 this speed). Even if they stop for 1,000 years at each star before launching ships to colonize the next nearest stars, they will still spread to the entire galaxy in 100 million years, which is 1/100 of the age of the Milky Way.

That is, an advanced civilization can fan out across its home galaxy pretty quickly, cosmically speaking, and a galaxy overrun with Dyson spheres and other energy-collecting super-structures would have a global surplus of mid-infrared radiation. With that in mind, Wright and his colleagues have been searching for evidence of such supercivilizations by looking for galaxies whose spectra skew to the infrared. Their campaign, called Glimpsing Heat from Alien Technologies Survey (G-HAT), scoured some 100 million objects observed by NASA’s Wide Field Infrared Survey Explorer (WISE) satellite. In a paper published in April, lead author Roger Griffith reported that, from all those millions, they found 50 galaxies showing infrared excesses that could maybe, possibly be due to alien technology–but, far more likely, are due to natural astrophysical processes. (Incidentally, as Lee Billings reported in Scientific American, the G-HAT team wasn’t able to secure funding from the usual government sources; their work is supported by a grant from the private Templeton Foundation.)
Things may be looking a little bleak for Dyson spheres—and intelligent ET in general, if you’re guided by the Fermi paradox—but there’s some consolation from a pair of researchers in Turkey, who point out that alien engineers might not choose to put their Dyson spheres around sunlike stars in the first place. Instead, they argue, superintelligent engineers would build their Dyson spheres around dim stellar embers called white dwarfs. These mini-Dyson spheres would be all-but undetectable.
Why white dwarfs? First, they’re cooler than stars like the sun, so, assuming that you want to live on or near the Dyson sphere and that you don’t want to be burned to a crisp, a Dyson sphere should be placed much closer to a white dwarf than to a sun-like star. That means that the sphere itself could be a lot smaller and, potentially, easier to build.
Meanwhile, Zaza Osmanov, a researcher at the Free University of Tbilisi in Georgia, has proposed that super-advanced extraterrestrials might build Dyson spheres around pulsars, rapidly rotating neutron stars that emit focused beams of radiation from their poles. To capture this energy, you wouldn’t need an entire sphere: a smaller ring, coinciding with the path of the pulsar’s beam, would do the job.
It’s all extremely speculative, of course, and many would argue that searches for the signature of Dyson spheres, rings, and swarms are so unlikely to turn up any answers that they aren’t worth the computing time. But, as Wright puts it, there’s only one way to make a discovery: “You gotta look.”
Go Deeper
Editor’s picks for further reading

NOVA: Eavesdropping on ET
In this NOVA podcast, SETI astronomer Seth Shostak explains why he thinks it’s just a matter of time before we find evidence of other intelligent life in the universe.
Popular Mechanics: Cosmic Megastructures
Read up on the engineering challenges behind imagined cosmic megastructures, including Dyson spheres, space colonies, and more.
SETI Institute: SETI 101
A short history of the search for extraterrestrial intelligence, with links to more information on the Fermi paradox and the social implications of a confirmed detection.