Olaf Stapledon’s 1937 science-fiction novel, Star Maker, pushed the imagination by featuring an advanced civilization that built a spherical shell around its host star to capture the radiation and meet its energy requirements. This spherical shell would later become known as a Dyson sphere (see Figure 1), after the astrophysicist who contemplated the mid-IR excess such an object would release. While the concept originated in fiction, it has since gained a niche as a potential alien mega-structure that could be observed. It also emphasizes that the search for extraterrestrial intelligence (SETI) is difficult due to the limitations of our imagination. While SETI is fundamentally a search for a society capable and willing to communicate, there exist other approaches that make the SETI more feasible and draw on the concept of waste-heat from alien activities, such as the Dyson sphere. Jason Wright and fellow scientists recently published a four-part series to motivate and present the Glimpsing Heat from Alien Technologies (G-HAT or Ĝ) survey. Wright et. al. argue the sensitivity of a waste-heat search would be greatest for a civilization which satisfies a physicist’s definition of intelligent life. This defined ETI as a species that (i) “processes resources and energy to produce more of itself” and (ii) “overcome[s] local resource limitations through the application of energy”. They surmise that “if a species is spacefaring, then its level of intelligence is such that there is no practical resource limitation that it cannot overcome, except that of energy”. The authors note there may be other intelligent life excluded by this definition of intelligent life, but argue such a society would not be easily detected through the Ĝ survey.
The first paper introduces the philosophies of SETI, with particular emphasis on the Hart argument that the dearth of ETI encounters implies we must be the first intelligent species in our galaxy. Hart stated there were four categories of solutions to this problem: (i) physical, (ii) sociological, (iii) temporal, and (iv) ETI has visited, but he denounced each solution and conclude we were alone in our galaxy. Wright et. al. review each of the categories with insights from our current understanding of astrophysics and reinforce the temporal and sociological reasons presented by Hart. An order-of-magnitude calculation show a colony of ships traveling at 10-4 c (comparable to the velocity of Voyager 2 or Pioneer) in a rotating disk (i.e. our galaxy) should populate the Milky Way in at most a billion years. With regards to the extinction theories, the authors aptly note this must hold for all colonies of a civilization that has spread throughout its galaxy. A species confined to one planet can go extinct but as long as there is a self-sufficient colony somewhere away from a gamma ray burst or interstellar war (anything lethal), the species can always repopulate the galaxy. The authors state that sustainability arguments do not hold because, before all stars are colonized, there is no limit in the relevant resource (stars) and there is no reason galactic hegemony must be explicitly driven by a lack of resources.
While Hart’s argument was pessimistic, it only considered one galaxy. Therefore, if each galaxy is considered to be an “independent realization” of his experiment, there could exist galaxy-spanning ETIs. Wright et. al. then describe the previous searches for Dyson spheres and discuss the promise of NASA’s Wide-Field Infrared Explorer (WISE). Wright has stated that “WISE was launched by NASA for pure, natural astrophysics; it just happened to be perfect Dyson sphere finder.” In the case of a Dyson sphere, if a star were perfectly encased by a shell at roughly 1 AU, the resulting spectrum could be approximated with a few-hundred-Kelvin blackbody. The results of searching for this heat-waste, this artifact of ETI activity, would at worst put an upper limit on alien activity.
The Ĝ survey strives to address some of the issues inherent in typical SETI, namely the assumption that ETI is emitting a signal amenable to radio detection. Instead of forcing ETI to behave this way, artifact SETI seeks to detect the thermodynamic consequences of galactic-scale colonization. In this first paper, the Wright et. al. briefly note something like the Ĝ survey will be “hard pressed to prove that an unusual source is artificial”. IR observations are prone to contamination from dust and must be disentangled form other, astrophysical processes. The survey analyzed roughly 100,000 galaxies to determine the reddest sources and concluded “no galaxies resolved by WISE contain galaxy-spanning supercivilizations with energy supplies greater than 85% of the starlight in the galaxy”. Others have introduced possible corrections to the treatment of data, but nothing so far suggests galaxy-spanning civilizations exist.
Movie 1: Above is a video showing KIC 8462852 and a possible alien mega-structure (around the 1:00 mark) explaining the decrease in flux. Source: The Washington Post
While the Ĝ survey is more scientific and data driven than conventional SETI, it is important to carefully vet candidates and, at the very least, apply the law of parsimony. One such example of artifact SETI gone awry is KIC 8462852 (see Movie 1). Perhaps to Wright’s chagrin, he has been “credited” with fomenting the idea that an alien mega-structure is to blame for the dips in KIC 8462852 (see here and especially here). Additional observations suggest optically thin dust may cause the dips. The biggest damage is to the credibility of SETI, as it degrades the science behind these papers to nothing more than a form of sensational pseudoscience. The support from the Templeton Foundation, often criticized as having a history of supporting controversial and speculative research (see here for physicist’s opinion), is another issue that may affect the credibility of the Ĝ survey. Regardless of one’s prior on SETI, Dyson provides some keen insight:
“If there are any real aliens, they are likely to behave in ways that we never imagined. The WISE result shows that the aliens did not follow one particular path. That is good to know. But it still leaves a huge variety of other paths open. The failure of one guess does not mean that we should stop looking for aliens.”
This blogger, while having concerns with SETI as a whole, firmly believes more research should be done with both conventional SETI and artifact SETI. Until there is more data, it is unscientific to completely reject the premise of SETI, however flawed its premise may be.