Astronomy as Sherlockian Drama

by Shane L. Larson

The world, and social media in particular, was riveted this past week by the announcement of a strange optical signal from a star 1480 lightyears away in the constellation Cygnus, called KIC 8462852. Part of the suite of targets observed by the Kepler mission, the data shows the brightness of the star going up and down in odd ways, unusual when compared to typical stellar brightness records (what astronomers call a “light curve”) that we’ve ever seen.

The location of KIC 8462852 in the sky, 1480 lightyears from Earth, in the constellation of Cygnus.

The location of KIC 8462852 in the sky, 1480 lightyears from Earth, in the constellation of Cygnus.

In an of itself, the changing of a star’s brightness would not normally garner news around the world. Many stars fluctuate in brightness, and dips in brightness caused by a planet passing in front of a star is a common tool to search for worlds elsewhere (this is, in fact, what Kepler’s primary observational goal was).

No, what caused the stir is the somewhat speculative notion that the weird light curve could be artificial in origin, caused by mega-structures, built by some unimaginably advanced alien civilization, orbiting this star.

For a species that longs to know if we are alone in the universe or not, and for a civilization that is well versed in speculating on the existence of life elsewhere for entertainment purposes, the idea of alien mega-structures immediately conjures well imagined pictures and ideas in our heads, and generates tremendous excitement. Hence, the response of the world-girdling infoweb.

Alien mega-structures might slowly be built up to girdle the parent star, occasionally blocking the light. [Image by Kevin M. Gill]

Alien mega-structures might slowly be built up to girdle the parent star, occasionally blocking the light. [Image by Kevin M. Gill]

The idea has been met with tempered and cautious response from scientists (here, here, here, many more!). There are many competing psychological and sociological forces at work. First: we don’t want to squelch people’s enthusiasm for our work (“OMG! The world cares about light curves!”). We also don’t want to give the impression that we put much stock in an (obviously crazy) idea like “alien mega-structures.” But we also want to impress upon people that we entertain any and all ideas.

I’m a practicing scientist myself, and I’d like to take a slightly different view on this matter. We shouldn’t be tempering our response at all! There is nothing wrong with assuming from the get-go that this signal IS alien mega-structures — the analysis and  evolution in our thinking that follows will be the same either way.  So how will it all shake out?

Annual World Energy Demand. Note the constant and steady growth over time. [Wikimedia Commons]

Annual World Energy Demand. Note the constant and steady growth over time. [Wikimedia Commons]

To begin the story, it is useful to go back to the beginning — where did the idea of alien mega-structures come from? It is part of a very old observation that as our civilization grows, and our dependence on technology grows, our need for energy grows as well. Since the Industrial Revolution this growth has, more-or-less, been unchecked. Looking at a graph of the growth in energy use by the human race, we see that there will come a time when we will outgrow our ability to produce the energy we need by “simple” means (such as burning fossil fuels).

This idea of predicting the future is a large part of what science and engineering are all about: take some observations of the world today (“data”), look at what the evolution up to today has been (“historical record”), and using the Laws of Nature calculate what should happen tomorrow (“prediction”). When tomorrow gets here, you make a new observation and ask, “did things turn out like I expected?” If not, you refine your prediction method and try again. Over time, you get very good at predicting the future.

Scientists do it all the time — we know where Mars is will be when we shoot rockets towards it; we know how much water and waste dialysis removes from a kidney patient’s blood and can tell how often they have to dialyze; we know how much friction the cylinders in your car experience, so know how much heat your cooling system has to dissipate; and so on. Science is about predicting the future, and using that power to improve our lives.

Freeman Dyson

Freeman Dyson

So in 1960, physicist Freeman Dyson was thinking about the escalating energy needs of our civilization, and proposed that some day we would reach a point where the best possible source of energy was the Sun, and in order to maximize the use of that energy, we should completely surround the Sun by a solid sphere (now known as a “Dyson sphere”), so that every bit of sunlight was captured and could potentially be used. The idea has originally been proposed in a science fiction novel by Olaf Stapleton (“Star Maker” in 1937), and Dyson suggested one way to look for alien civilizations was to look for such a mega-structure in the Universe.

Find a quiet corner of your couch, grab a bowl of popcorn, and start thinking about building such a structure. You can imagine what an enormous engineering endeavour it would be — the sphere would have a surface area 550 million times larger than the Earth! Obviously it would have to be built by a civilization far more advanced than ours. Perhaps more obviously, it could not be built all at once — it would take generations to design, construct, and maintain! So one might imagine that it could be built up piecemeal, not as an entire sphere, but as a swarm of parts that if connected, would form a Dyson sphere. One famous realization of this is Larry Niven’s “Ringworld”, where a star was girdled by a single continuous ring, with the inhabitants living on the starward side of the ring.

A ringworld is one option for a civilization that does not want to invest in building an entire Dyson Sphere. Perhaps it is just an intermediate stage that will ultimately lead to a full sphere. [Wikimedia Commons]

A ringworld is one option for a civilization that does not want to invest in building an entire Dyson Sphere. Perhaps it is just an intermediate stage that will ultimately lead to a full sphere. [Wikimedia Commons]

This all sounds perfectly reasonable, provided you can imagine the construction endeavour needed to construct such an artifact.  So why all the skepticism toward the idea of the signal in KIC 8462852 being alien mega-structures? The simple fact of the matter is we can’t imagine humans building a mega-structure, so we find it hard to imagine any civilization building a mega-structure.

The cautious skepticism of the scientific community can be summarized by Marcello Truzzi’s observation that was popularized by Carl Sagan in Cosmos:Extraordinary claims require extraordinary evidence.” This is often regarded as a modern restatement of the Principle of Laplace: “The weight of the evidence should be proportioned to the strangeness of the facts.”

[L] Carl Sagan, [M] Marcelo Truzzi, [R] Pierre-Simon Laplace

[L] Carl Sagan, [M] Marcelo Truzzi, [R] Pierre-Simon Laplace

Laplace was highly cognizant of the fact that our knowledge of the world, and hence our understanding of the world, evolves over time. New discoveries and new observations necessarily make way for new ways of thinking. So what to do when you encounter something strange and unusual?  Laplace wrote in 1814 in his essay Essai philosophique sur les probabilités, “We are so far from knowing all the agents of nature and their diverse modes of action that it would not be philosophical to deny phenomena solely because they are inexplicable in the actual state of our knowledge. But we ought to examine them with an attention all the more scrupulous as it appears more difficult to admit them.”

So, at the outset, intellectual honesty insists that we cannot deny the weird signal from this star may be due to alien mega-structures. But we must examine such claims with extreme skepticism. Because it appears difficult to explain how it might be alien mega-structures.

Or is it? Why is it difficult to explain these as alien mega-structures? Any more-so than some other plausible explanation (many of which astronomers have already discounted)?

Astronomy is a Sherlockian drama, and as the famous detective observed to Watson (in “The Sign of the Four” [1890]), “When you have eliminated the impossible, whatever remains, however improbable, must be the truth.” Astronomers are starting at the top of their list of possible “natural” causes, and eliminating them one by one.  The data at hand is that we see the brightness of the star changing with time, and the pattern of brightness changes looks… weird.  What could it be?

Light curves for KIC 8462852. The top panel shows the full light curve. [C] Enlarged view of the dip around day 793; very typical shape for

Light curves for KIC 8462852 — the lines plot the brightness of the star, with time across the horizontal direction. If the line is high, the star is bright, and if the line dips, the star gets dimmer by some amount. The deeper the dip, the bigger the change in brightness. The top panel shows the full light curve. [C] Enlarged view of the dip around day 793; very typical shape for “common” dips used to detect planets, but BIG. [d-f] These enlargements of other dips are the mystery — they are BIG, but also show remarkably complex structure. What is causing this? [Figure adapted from Boyajian et al (2015)]

Perhaps it is just a variable star. We know of many different kinds of variable stars in the Cosmos. These stars, due to some process in their innards or due to some interaction with their environment, change in brightness in a steady and regular way. These variations seen in KIC 8462852 are not apparently regular in immediately obvious ways. More to the point, astronomers would not normally expect there to be intrinsic variations in the brightness of this star. Why? We know how big and how old it is, its temperature and composition — all of these bits of information define what astronomers call the “spectral type.” It’s a bit like classifying different breeds of cats — you know one cat is a different type than another based on gross, observational characteristics like fur color and length, tail and ear structure, and so on.

KIC 8462852 is a spectral type F3 V/IV (just in case you ever get that question in a round of Trivial Pursuit) — this means it is about 1.0-1.4 times the mass of our Sun, and has a surface temperature between 5700 and 6700 degrees Celsius. There are lots of F-type stars known to astronomers — they are yellow dwarf stars, in the middle of their lives, stably burning hydrogen on the main-sequence. To see an F-type star show tremendous strange variability would be a serious challenge to our understanding of stellar astrophysics, and the overwhelming data supporting the stable brightness of F-type stars in the galaxy. Astronomers think this is not what is causing the light curves.

Perhaps it is a debris disk of some sort. The Oort Cloud is a bubble of debris that surrounds the outermost fringes of stars like the Sun, the left-over icy detritus from the formation of the Sun and its attendant planets. We know of the Oort Cloud because periodically, it drops an icy rock into the inner solar system, which you and I call a comet. Maybe another star in the galaxy passed very close to KIC  8462852 (a rare, but not impossible occurrence) and disturbed its Oort Cloud. The gravitational tug of this passing star would have churned up the Cloud, and destabilized it so lots of comets dropped in toward the star. That doesn’t sound far fetched until you look at the light curve — fully 22% of the light from the star is blocked during some of the light curve dips. Comets are tiny, only 1/10,000th the diameter of a star. It would take an absurdly large number of comets to make the data look the way it looks.

There are many scenarios we can imagine that will generate vast debris fields around stars [NASA Image, PIA11375].

There are many scenarios we can imagine that will generate vast debris fields around stars [NASA Image, PIA11375].

Maybe there was an enormous collision between planetary sized objects, creating a debris disk or some kind of large asteroid field. This is not unheard of — the Earth’s Moon is thought to have formed by such an impact, early in the history of the solar system.  If there was such an event, there should be a lot of residual dust, which would glow brightly in infrared light. So far, astronomers have not noticed any extra infrared light from KIC  8462852, casting doubt on this idea.

And so on. We just keep working our way down the list of clever and plausible explanations.  But when we get to the bottom of the list, what if the one idea we have left is alien mega-structures? What will we do then?

I maintain that this should not bother us at all. The reason is simple: we have not looked for alien life long enough, nor the signatures of alien civilizations carefully enough, to know what their signatures are! When you’ve been doing zillions of experiments and making zillions of observations, it is easy to discount ideas in the face of overwhelming data, but in the case of alien civilizations, our experience in the search is so profoundly limited that scientific integrity demands we consider the possibility.  We haven’t searched for aliens enough to know whether they are improbable or not.

But science is not a game where you rest on your laurels either.  Everything we believe is subject to constant scrutiny no matter how confident we are in the results. That’s what science is about — not fooling yourself. As Feynman quipped, “The principle is that you must not fool yourself, and you are the easiest person to fool.” (Caltech Commencement Address [1974]).

So over the next many weeks, possibly months, maybe even years, we will observe and scrutinize and ponder KIC  8462852. Eventually someone will have a clever idea that suggests it is not alien mega-structures. When they do, astronomers will look at the idea and say, “if this is true, then this other thing should also be true” and they’ll go check.

If they are right, the idea of alien mega-structures will fade, and we will be no worse for wear. But if they are wrong, we won’t be able to discard the idea, and we’ll live with the notion of alien mega-structures a bit longer. And perhaps longer, and perhaps longer still.

My standard bet: a Dr. Pepper and a Boston Cream Donut. What have you got to lose?

My standard bet: a Dr. Pepper and a Boston Cream Donut. What have you got to lose?

But in the end, the Sherlockian drama will play itself out: whatever remains in the end, must be the truth. Alien mega-structures or not.

PS: In case you haven’t guessed: I don’t see any reason to favor or disfavor alien mega-structures. So I’ll bet you a Dr. Pepper and a Boston Cream donut it’s alien mega-structures… 😉


6 responses to “Astronomy as Sherlockian Drama

  1. Ha, ha…the way you end it is nice! A query, though, if you do not mind: the last sentence may perhaps read better as “So I’ll bet you….”?

  2. Shane
    To assume an alien mega-structure, one needs to remove oneself from the constraints of earthly processes. Our normal pattern of building such a big structure would be to ; budget, seek raw materials, process real materials, manufacture parts, install said parts, ensure a constant power source, and monitor on-going workability. All a bit hard to take on board.
    We are now only just embracing 3D printing so imagination being what it is suggests aliens could well have constructed this Dyson through pure thought transmission. Now that’s worth a Boston bun and a Dr.Pepper.
    Thanks Shane, I will lie awake tonight contemplating such radical ideas and explanations for star – light bending. Should be fun.B

    • Shane L. Larson

      Part of the Fermi Paradox argument is that to do something big — like explore the entire galaxy, or construct a Dyson sphere — aliens would not be doing things live and in person, they would certainly have robots do it. If I wanted to build a Ringworld or a Dyson sphere, I would have robotic factories capture asteroids, chew them up, and “3d print” the mega-structures. If I wanted to explore the whole galaxy, I’d build a robot to go to another star, dig up raw materials to build 10 copies of itself, then send those 10 out to do the same thing. The fact that we dont’ see the unbridled harnessing of technology, and hence don’t see evidence of aliens, is the heart of the Fermi Paradox — of course someone will do this EVENTUALLY, so where are they?

      As you note, we are just starting down the road to 3D printing, self-driving cars, etc. Maybe we are heading down the path to automating the construction of a Ringworld or Dyson mega-structures around Sol… 🙂

      — s

  3. Pingback: Astronomy as Sherlockian Drama | oshriradhekrishnabole

  4. I enjoyed the article … thanks.

    IMHO, As the Sun is moving through space, towards Orion, rather than a Dyson sphere, seeking to encompass the Sun, we could build Solar array surfaced spheres … a tenth or a quarter the size of the Earth’s moon, orbiting the Sun, but with orbits that traverse above and below the plane of the Sun’s trajectory, as well as the planetary plane. The spheres would not interfere with the Sun’s energy distribution along Sol’s planetary plane, and would provide an angle of attack to direct focused energy from the spheres to any planet or moon.


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