The Absolute, Definitive Truth About Alien Megastructures

The title of this post is a joke, or taken literally, an outright lie. The only definitive truth is that no one knows if anyone has ever built a megastructure, or even if they would if they could. I have persistent doubts if such things exist anywhere in the universe, but I can't yet tell you if such doubts are reasonable.

Update 8 December 2016: I left out one type of motivation for building a megastructure - planetary climate control. Although these "Dyson Dots" would be relatively small, they might be detectable for transiting planets. I need to run the numbers...

The Usual Disclaimer

So, we're going to be speculative here yet again, and very probably wrong. I won't be able to cite many facts, so if that is the sort of thing you like to read, perhaps now would be a good time to hit the back button.

But I'm Completely Serious

We are interested in the conjectured alien megastructures because we might have a chance to observe them with technology we have or could well have in the near future. These structures would be bigger than planets (my definition), and since we can observe planets about other stars, we might well be able to observe these things, and so looking for them is a kind of SETI. I've written before about why I think SETI is worthwhile.

Almost certainly wrong: an alien megastructure speculation about KIC 8462852

Update: 20 September 2016 - with the Gaia DR1, we didn't really know which way the 300 micro arcsecond systematics would push, us, but now there is some evidence that the parallax measurements are systematically underestimated. Another nail in the coffin.

Update: 14 September 2016 - it would seem that today's Gaia data release invalidates this, as the the star is no further from us than what Boyajian, et. al., estimated from its brightness, and possibly a fair bit closer.  So what we are seeing is a real dimming.

OK, what follows is highly speculative, but as far as I can tell, is at least internally consistent and doesn't require any exotic new physics. I've got some facts in here, but if all you care about is the facts, this isn't for you.

As I pointed out recently, to find ET technological civilizations, we're going to have to be wrong a lot - unless they are trying to make it easy for us, which they very well may not be. So, I am a long term optimist but short term pessimist. Unfortunately, being persistently wrong is very painful for some people, many of which might be the most qualified to try and set out the theoretical parameters for ET technology.

So, let me have a crack at it for the case of the star KIC 8462852, commonly referred to on this blog as "Tabby's Star," and I could well be proven wrong in a few days with the first Gaia data release. I will stick to known physics exploited with unknown technology, and perhaps it may take a bit longer to prove me wrong.

The conjectured megastructure is actually a swarm (conceivably millions) of light sails flying close to the star, using light pressure in clever ways to maintain their positions (I won't detail this yet, because my model of "near field" stellar sailing isn't very good). The megastructure is a shell of reflectors, perhaps within one or two stellar radii (a few million kilometers) of the star's atmosphere. These sails are steered in a coordinated way such that they concentrate the star's light in a particular direction by a high magnification, for the purpose of accelerating (or possibly deaccelerating) a very large light sail and its payload up to interstellar speeds - perhaps a few percent of the speed of light. It would concentrate the star's light by several orders of magnitude.

Speculation - Hot Jupiters as Expended Batteries

Hot Jupiters are large planets – about the size of Jupiter or larger - that orbit very close to their star.  They comprise the upper left corner of this plot.   A year on one of these planets is only a few days, or even less. These planets are relatively easy to discover because of their large and short-period effect on their star's motion and a much higher probability of transit, so the statistics we have on extrasolar planets are skewed a bit toward this type of planet.  Nevertheless, they appear to be fairly common, though are no longer in the majority of the 843 2030 exoplanets catalogued to date.

Exoplanet Orbital period vs. age of host star

Hot Jupiters were a surprise to astronomers when first discovered, although Otto Struve had speculated on their existence in 1952, arguing that they were the only planets detectable by ground based telescopes. Hot Jupiters were not a real paradigm-buster, but were unexpected, because they can't form that close to the star -  it's like trying to get steam to condense on a hot soldering iron. Hot Jupiters have to form much further out from their star, and then migrate inward. There are plausible models for how this could happen fairly quickly as a result of complex tidal interaction with a disk of dust still surrounding the star shortly after it forms.  Such a natural migration may take only a few million years, but it has to happen early or there won't be enough of a disk to interact with.  What astronomers would really like to do is catch one of these planets in the act of migrating, but that will require a bit of luck and probably better telescopes.

The Natural Philosophy of Queerer and Queerer

A man's got to know his limitations.

--- Harry Callahan in Magnum Force 

A bit about Haldane's Law, and what it means about the search for other minds in the cosmos.

Haldane

You might recall that in our first post, there was a quote from the great Enlightenment thinker David Hume.  To paraphrase, all we can understand is what we have felt - either internally or externally.  The essential point is that when faced with something unfamiliar we interpret it in terms of the familiar.  We discover the universe in small steps.  Big conceptual leaps are rare, and even they depend strongly on what the "internal sense" has long known.

J.B.S. Haldane (1892-1964) was a distinguished evolutionary biologist and geneticist.  His Law is most often stated as:

I have no doubt that in reality the future will be vastly more surprising than anything I can imagine. The universe is not only queerer than we suppose, it is queerer than we can suppose.

A lifelong study of the evolution and diversity of life on Earth alone could easily have guided Haldane to that conclusion. We are still making sense of the biosphere that is right here in front of us, with the textbooks scrapped and rewritten on a regular basis.

Let's say Haldane was right. We believe we anticipate strangeness, but even the strangeness is strange. What could be stranger than a non-human intelligence, particularly a sophisticated one? Haldane says we can't meaningfully speculate about how strange they could become, and in ways we can't imagine. An alien being isn't just going to offer you a cup of coffee and then tell you about Seven Habits of Highly Effective Cosmic Guardians. Or it might, and then eat you.
Now that's discouraging. If Haldane was right, how can we know what to look for if we are in search of other minds in the universe? We might be looking straight at them and seeing nothing.

In fact, I would bet that we are doing just that. In his excellent book, The Eerie Silence, Paul Davies offers a different slant on the critique of UFO reality - that the UFO mythos taken as a whole isn't strange enough. Davies would fully expect something much weirder, not a phenomenon that falls right in line with millennia of folklore. There are those who would argue that UFOs are in fact plenty strange, but I think Davies has a point. If what is going on is something we can understand or even clearly define, then it's probably not aliens.
And yet when we talk about our first encounter with a non-human intelligences, we often think in terms of Hollywood fantasies like The Day the Earth Stood Still. Klaatu is a mythical man very much of Earthly making, and his landing on the Washington Mall only makes far too much sense to us. Why haven't they landed on the White House lawn? They already did - in our imaginations, which is likely as close as "they" will get. We are going to have to get way beyond that sort of scenario

So, if we are to form any hypotheses, or even conjectures, so we know what to look for when go in search of Other Minds, what hope do we have in light of Haldane's law? I don't have a clear answer, but perhaps we can formulate it in terms of our own limitations, and look for the silence behind our blind spots. What can't we see, and why?  

I am hopeful. Experience shows that we humans can eventually, over generations, get our arms around some pretty strange ideas, primarily using our talent for abstraction. For example, the very odd idea of a black hole was fished out of the mathematics of Einstein's equations decades before the first solid observational evidence that such things existed. By the time astronomers were ready to go looking for black holes, the theorists already had a fair idea of what to search for. Now there is evidence for many billions of black holes all over the universe and they are well incorporated into the astronomical paradigm.

The other bit of hope is that maybe Haldane's law is limited, and doesn't really hold for alien intelligences. Perhaps the constraints on the evolution of sentient life are so tight that we all end up resembling each other in important ways. Perhaps. But don't bet on it.

Dream of the Open Channel by Paul Carr is licensed under a Creative Commons Attribution-ShareAlike 3.0 Unported License.