Alien megastructures

For the past five decades the search for extraterrestrial intelligence has been dominated by the search for radio signals. There are good reasons why this search strategy makes sense, but the available search space is so vast (our dishes have to be pointing in the right direction at the right time, and tuned to the right frequency) that the phrase “radio SETI” is an excellent synonym for the phrase “looking for a needle in a haystack”. Are there any other options for the search?

Personally, I believe that we need to adopt a Stapledonian approach to the problem.

Olaf Stapledon, a British philosopher and science fiction author, considered what might happen to intelligence in the distant future. For example in one of his novels, Star Maker, published in 1937, he described what we now call Dyson spheres: structures that orbit a star and enable a civilisation to utilise most of the energy output of its parent star. The creation of a Dyson sphere is far beyond our present technical capabilities, but who knows what we (or our mind-children) will be able to achieve a thousand years from now, or ten thousand years from now, or a hundred thousand years from now. And 100,000 years is an eye blink in cosmic terms; if there are extraterrestrial intelligences out there then they might be millions of years in advance of us. Thus in a Stapledonian approach to SETI we would look for examples of astroengineering, or megastructures that could only have been developed by technologically advanced intelligences. The detection of such a megastructure wouldn’t open up the possibility of communication, as a traditional radio SETI detection might do, but it would at least tell us that we were not alone. That in itself would be a terrifically important discovery.

The recent furore surrounding KIC 8462852 is an example of how a Stapledonian approach is starting to appear in the ongoing search for extraterrestrial intelligence. KIC 8462852 is an F-type main-sequence star about 1480 light years away from Earth in the constellation Cygnus. The Kepler space telescope recorded fluctuations in the light from the star – but a recent paper demonstrated that the fluctuations were so bizarre that they could not come from a transiting exoplanet. For one thing, the dimming of the starlight is not periodic; for another, the dimming is extreme (15% in one episode, 22% in another; for comparison, a Jupiter-sized planet blocks about 1% of its star’s light). So what is causing this weird behaviour? We don’t know. The authors of the paper suggest that the dimming might be caused by a series of comets, surrounded by clouds of gas, perturbed from their usual orbits by the gravitational influence of a nearby star; a small red dwarf close to KIC 8462852 might be the culprit. It’s possible. But it’s far from certain that this story can explain all the features that are seen. Any other explanations? Well … could it be that we have caught an advanced alien civilisation in the act of building a Dyson sphere? I doubt it. I REALLY doubt it. Just because we observe something we can’t immediately explain we shouldn’t immediately attribute it to alien intelligence (remember that, for a short while, the radio signals from pulsars were thought to be evidence for ETI; astronomers soon figured out the true explanation for the radio emissions). Nevertheless, it surely can’t harm to follow up these observations of KIC 8462852 with traditional radio-based SETI observations.

Several astronomers have already searched for the infrared emission that would accompany a Dyson sphere. But the search for Dyson spheres would form only a small part of a Stapledonian approach to SETI. We need to use our imagination and try to envisage the sorts of technology that a truly advanced civilisation might develop. In a previous post I looked at how John Smart’s transcension hypothesis argues that black holes are an attractor for intelligence. The philosopher Clément Vidal adopts a related approach. (Incidentally, in my book I wrote that is Belgian. He works in Belgium, but is in fact French. Apologies, Clément!)

Clément uses a two-dimensional metric, first proposed by John Barrow, to describe advanced civilisations. The Kardashev metric is well known: K1 civilisations control the energy output of their home planet, K2 civilisations control the energy output of their home star, K3 civilisations control the energy output of their home galaxy. But Barrow pointed out that there is a scale of inward manipulation that might be just as applicable to extraterrestrial civilisations: a B1 civilisation can manipulate the universe at the 1m level; a B2 civilisation can work at the 10–7m scale; a B3 civilisation manipulates at the nanoscale; and a BΩ civilisation can manipulate spacetime at the Planck level. In a 2011 paper Clément talks about the possibility of K2-BΩ civilisations; he has since switched to a more memorable appellation “stellivore”.

If we accept that stellivores could exist, an obvious question is: what might stellivores be doing that our telescopes and instruments might pick up?

Well, a stellivore might possess a technology involving black holes. (I won’t go here into the many reasons they might want to use black holes. Suffice it to say that a Stapledonian mindset would consider black holes to be a natural endpoint for many technologies.) And we know that in principle it is possible to detect activity around black holes; we know this because astronomers have already investigated X-ray binaries (XRBs). In an XRB a donor object (typically a star) loses material to a compact accretor (typically a black hole). The infalling matter releases huge amounts of gravitational potential energy. So could XRBs provide evidence for stellivores? In my book I write that we could “look for evidence for the regulation of energy flow within XRBs”. As Clément points out, there’s already evidence for such regulation; the key question – just as it is with KIC 8462852 – is whether the observations are best interpreted in terms of astrophysics or astrobiology?

Since Clément’s 2011 paper he has extended his vision to include a wider range of XRBs: the stellivore family could include cataclysmic variable X-ray pulsars, for example, with black holes being the end stage.

To my mind, the great thing about this Stapledonian sort of approach is that it broadens the range of techniques we can apply when searching for signs of extraterrestrial intelligence. Traditional radio-based SETI has its place. But the ideas of John Smart and Clément Vidal tell us that we could also profitably search at the highest energies.