In which we win an award from the New Frontiers in Astronomy Program.
The last, but not least of the Big Questions solicited in the Call for Proposals, was:
Are we alone in the universe? Or, are there other life and intelligence beyond the solar system?
There were four awards in this "Astrobiology and SETI" category, focusing on different approaches in the search for life elsewhere in the Universe.
We got one:
"Constraining the Abundance of Kardashev Type II and III Civilizations From Large Area Infrared Surveys"
with PI Prof. Jason Wright (Penn State), yours truly, and Prof. Matthew Povich, formerly at Penn State, now at Cal Poly.
This is one of the most fun projects I've been involved with, and I am really looking forward to working on this over the next couple of years, and hopefully beyond, if we find something...
The proposal came together serendipitously when I bumped into Jason in a stairwell at the office. Jason had just been to a seminar on infrared surveys, and I had been thinking about the New Frontiers call for proposals (I was working on another proposal on complexity, which, sadly, did not get selected).
Within hours we had put together a pre-proposal and sent it in to New Frontiers.
The proposal then made the cut to be invited for a submission of a full proposal.
The full proposal was actually really good, in my humble and impartial opinion, and, we got one of the awards.
So... now what?
Well, the basic idea (see links below for a nice series of explanations by Prof. Wright), is that IF there are Arbitrarily Advanced Civilizations (AACs) out there, in some abundance, then some will both use Standard Model physics, and will be power hungry.
There are interesting things that can be done with large amounts of free energy, and it is physically possible to get off planets and do engineering.
Hence we get the Kardashev Scale - a metric for power hungry alien civilizations.
We implicitly assume that the AACs are bound by thermodynamics, and that the power consumption, the rate of use of free energy, has to be dumped out as high entropy electromagnetic radiation at some low (range in) effective temperature. Yeah, we do factor in possible neutrino losses...
The obvious approximate Teff to look for is about 300K, but there is still a lot of free energy left in radiation that warm, so ecoconscious AACs ought to try to capture that and radiate at somewhat lower Teff, however as Teff approaches the cosmic microwave background temperature, diminishing returns really kick in.
We ignore, for the moment, any alien use of non-Standard Model physics, such as dark matter and dark energy, and we assume that there are, in at least some cases, no overriding imperatives for the aliens to stealth their presence to avoid berserkers or other hostiles...
We also do not, for now, consider the trade-off between utilizing free energy from natural sources and artificial conservation of energy sources on extremely long time scales. ie. we assume ET lets the stars burn, for now.
So, AACs using their host star's output (type IIs) ought to be seen as bright mid-IR sources, and these are detectable with infrared observations, in particular those from space.
Carrigan at Fermilab did a search for nearby KIIs in IRAS data but since then we have flown more sensitive observatories, and it is worth looking again. Nearby KII civilizations are detectable, though there is always the concern of if they are there, why aren't they here?
For real fun though, consider Kardashev type III civilizations.
These have taken over their host galaxy - a diffusive spread of an AAC hopping star-by-star across a normal galaxy would take a few hundred million years, assuming no new physics, that is just by hopping slowly between adjacent stars going not much faster than Voyager is doing already.
This is a short time compared to the lifetime of the universe, which suggests that if some alien civilizations get off planet, expand, and are driven to utilize efficiently the available free energy from natural sources, then some galaxies might be broadly colonized by AACs and their entire energy output harvested.
Including any accretion at the central supermassive black hole.
KIII sources are also detectable in principle with current technology, and we argued that it is also worth surveying for their presence in the local universe, basically looking at classes of extreme extended sources, with the expectation that we will be able to either detect nearby KIIIs, or quantitatively constrain the abundance of KIIIs in the local universe.
We should be able to count what fraction of nearby galaxies host very powerful pervasive technological civilizations.
Anything that mimics a KIII but is not, is also potentially very, very interesting, and actually worth looking for per se.
Free Energy Limited Species - Prof. Wright explains the Kardashevs Part I
Kardashev for the Byrds - Prof. Wright discusses Dyson Spheres. Kardashevs Part II
Climbing Kardashev's Scale - Prof. Wright on Kardashevs Part III
CTA-102 the Byrds immortalise Kardashev...
"...it's strange to write a serious research proposal and have half of your bibliography be science fiction."
Wouldn't a Dyson sphere be very vulnerable to Kessler syndrome? I never was quite convinced it would be actually worth building one even if you managed to acquire the ability to do it...
At this level of technology Kessler Syndrome is a nuisance effect... it is in fact a temporary way to complete the absorption fraction for near full Dyson scale (K2) occupancy.
The argument is that as long as there is significant (fraction of stellar power) free energy flow escaping to infinity, it will be worth it to some part of the civilization to intercept it and use it - whether it is managed centrally, emerges spontaneously or happens chaotically.
All we care is whether time averaged there are artificial structures capturing most or all of the stellar flux over interestingly long time scales (100++ Myrs).
There are many ways to for K2 and K3s to go wrong, but if the technology is achievable and there is life out there, some fraction ought to get to that point and some fraction of those ought to persist.
It looks like we can already get surprisingly tight quantitative constraints on the abundance - technology really has improved drastically in the last decade.
It's much more productive to search for K3 type civilizations than type I or II. The lifetimes of K1 and K2, before they evolve into K3, are probably quite short on astronomical time scales. Due to the Malthusian imperative, a type III will make much more complete use of the matter and energy in their environment, resulting in their environment looking much more artificial and radiating at far higher power. So type IIIs can be expected to (1) greatly outnumber type Is and type IIs combined, (2) outshine them by many orders of magnitude, and (3) have more artificial looking spectra even with the same power output. Since we haven't already discovered such blatant type IIIs, we can expect type Is and IIs to be far too uncommon to be detectable against the natural background.
We must necessarily speculate about their technology, but the scientific way to do this is to hypothesize about what we could actually directly observe -- namely the chemical composition and optical/thermal properties of their surfaces, and the emissions of their illumination devices (including communications and weaponry using electromagnetic radiation or similar). We shouldn't worry so much about what we can't observe, such as whether certain kinds of structures are possible or desirable or not. And it doesn't much matter whether e.g. it's a 10^20 watt laser or 10^20 1-watt lasers as long as it the net result is of sufficient power and spectral precision to produce a distinct spectral spike. And what they use as a source of energy is largely beside the point -- we should focus our hypotheses on how they may radiate waste energy, and otherwise how they may use their energy in observable ways (e.g. illumination), since that is what we would most directly observe.
Generally speaking, illumination and surface engineering tends to optimize desired optical or thermal properties resulting in distinctly artificial looking spectra. For example:
* The extreme narrow spikes produced by quantum illumination devices such as LEDs and lasers
* Spectra produced by many of the artificial molecules in paints. (Similar to how evolution produces molecules like chlorophyl that are extremely rare, to say the least, without life, with a resulting spectral signature).
* The extremely unnatural proportions of gold on the surfaces of most satellites and many building windows, due to gold's excellent optical and thermal properties.
Their surface and illumination technologies are likely to be far in advance of ours, but if anything superior optical and thermal properties in such technology should produce even more artificial looking spectra.
I comment more on this here :
(Although I do realize now that "archaeology" is a poor term to use in this context -- we should be looking for maintained surfaces and working illumination devices. Unmaintained surfaces quickly degrade to a more natural looking state).