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“As Big as Space Itself:
Building Our Own Space Megastructures—and Searching for Them as Galactic Signatures of Alien Civilizations
by Les Johnson

In the context of deep space and deep time, humans are newcomers. Astronomers estimate that the universe is about 13.7 billion years old with humans arriving on the scene in only that last 200,000 years. For perspective, as a species, we've only been around for about 0.001% of the time since the universe began. If the age of the universe were one 24-hour Earth day, then humans would have only been around in the last second. We are a blip. To add another layer of humility, consider the diameter of the known universe: about 93 billion light years. To consider this vastness, we again need to put in context with distances we somewhat understand. The Earth is 93 million miles from the Sun and astronomers call this distance 1 Astronomical Unit (AU). The number of AU's in one light year and the number of inches in one mile are almost the same: 1 light year is ~63,000 AU's and 1 mile contains ~63,000 inches. If we scale 1 AU to be 1 inch, then 1 light year equals 1 mile. This means that Alpha Centauri is "only" about four miles away and the diameter of the universe is then "only" 93 billion miles, each "inch" of which is really 93 million miles! We are again only a blip.

We are only now beginning our first, tentative exploration of space as we seek to stretch our civilization beyond the confines of the planet that gave us birth. Though we are newly on the scene, we are already thinking of how to create and inhabit large structures in space. The International Space Station (ISS), currently circling the globe every ninety minutes, is the size of a football field—and we built it using technology from the 1970s (Figure 1).

Figure 1. The International Space Station, our first step toward space megastructures? (Image courtesy of NASA.)

In the next several decades, we will have the technology to build space sails with deployed areas the size of city blocks, space solar power stations that make the ISS look like a toy, and space elevators thousands of kilometers long to carry people and cargo to and from the surface of the Moon, Earth, or Mars. If we can do this, then what might an alien civilization that is thousands or tens of thousands of years older than ours be capable of constructing? With the resources of a complete solar system at their disposal, these hypothetical stellar engineers might be capable of disassembling asteroids and small planets to make structures many times their size—literally making new worlds for themselves among the stars.

These ideas have been explored in both speculative science and science fiction. From Clarke’s space elevator to Dyson spheres and ringworlds, intriguing possibilities abound. And, thanks to recent data from the Kepler Space Telescope, from which thousands of possible extrasolar planets have already been discovered, it is possible that reality is catching up with the fiction.

Analysis of data from one of the stars in the Kepler data set has led to intriguing speculation regarding "Tabby's Star." Named after one of the astronomers in the Kepler data analysis teams, Tabetha Boyajian, Tabby’s Star shows intriguing periodic dips in its luminosity that cannot be neatly explained as a naturally occurring phenomenon. One interpretation is that Kepler detected a Dyson sphere. Granted, a natural explanation is far more likely to emerge than one requiring intelligent aliens, but it is nonetheless an intriguing possibility.

Are space megastructures possible? Can humans eventually build them? And are we now detecting the first megastructures built by aliens? Let’s explore the possibilities in more detail.


The International Space Station (ISS) is our first very large structure in space. A stunning 356 feet in length and weighing 450 tons, the ISS was designed, developed, built and launched into space by a consortium of nations including the USA, Russia, Japan, Canada, and member states of the European Space Agency (ESA). It required more than forty launches over thirteen years and has been continuously inhabited since 2000. The ISS is a child’s toy when compared with what today’s generation of spacecraft systems designers think is possible.

Since the ISS’s initial conception in the mid-to-late 1980s, space technologies have continued to advance—getting lighter weight, more robust, and more compact. Combine these innovations with cell phones (which are really full-blown computers masquerading as telephones), 3D printing, and advanced, lightweight materials, and you have a recipe for building structures in space that are many times larger than the ISS and of comparable or lighter weight. That last part is significant because the key cost of flying anything in space is the launch cost from Earth. Since launch costs are largely based on weight, if you reduce the weight of a payload, then you may reduce the cost of getting it into space.

Add another innovation into the mix—lightweight, thin-film solar cells—and you can now consider building, packaging and launching into space large area solar panels for collecting sunlight, converting into electricity, and beaming to the Earth by either a laser or microwave transmitter (Figure 2). A network of such space solar power stations could conceivably replace much of the terrestrial power generation facilities (coal, natural gas, or nuclear) and reduce greenhouse gas emissions. China and Japan have plans to build and test such systems in the next few years and their commercialization will likely soon follow.

Figure 2. Space solar power stations may be built and launched into space within the next decade, providing abundant power for Earth and, perhaps, a growing near-Earth space infrastructure. (Image courtesy of NASA.)

Now that we have relatively inexpensive space launch, thanks to companies like SpaceX and Blue Origin, and the ability to generate abundant electrical power in space using space solar power stations, we have all the ingredients we need to begin industrializing near-Earth space.

What’s next? Thanks to advances in materials science and the discovery of strong, lightweight materials like graphene, we can now take the next logical step toward building space elevators and kilometer-scale solar sails or sail-derived structures. (For more information about graphene, see the Baen essay, “Graphene: Not Just Another Miracle Material.”)

Many science fiction readers are familiar with the concept of a space elevator thanks to the pioneering novels that contain them such as The Fountains of Paradise by Arthur C. Clarke and Ian Douglas’ Star Carrier series. The basic idea is simple: build a cable from the surface of the Earth, anchored somewhere along the Earth’s equator, and extend it upward into space to beyond geosynchronous Earth orbit, GEO (~22,000 miles), where it is counterbalanced by a large mass object like a small asteroid, and voila! You have an elevator (Figure 3) that can take you and your spacecraft from the surface of the Earth to just beyond GEO where the additional energy required to send you to nearly anywhere in the solar system is negligible (when compared to the energy required to use a rocket to get from the surface of the Earth to the same point in space). The marginal cost of getting from the surface of the Earth to space would be roughly the cost of the electricity to run the elevator. Dirt cheap access to space.

Until recently, the biggest stumbling block to building a space elevator on Earth was the material needed. Engineers simply didn’t have the recipe for building long cables that were strong enough to do the job. Then along came graphene—a 2D form of carbon that is one of the strongest materials yet discovered. In other words, the material we need to build a space elevator now exists. (Though to be accurate, the engineering does not yet exist. For one, we can only now make graphene sheets that are millimeters to centimeters in length; we need kilometer length cables. And then there’s the problem of constructing it—for instance, do you build up from the ground, or top down from space?)

Figure 3. Artist concept of an elevator to space. Building a structure >22,000 miles long would be a true megastructure. (Image courtesy of NASA.)

The Japanese flew a 2000 square foot solar sail to Venus in 2010. (A solar sail is a lightweight, thin gossamer structure that reflects solar photons, light, to achieve thrust for a spacecraft just like an earthly wind-powered sail reflects air to propel a boat.) Within the next two years, NASA will fly the Near-Earth Asteroid Scout which uses a sail four times larger than the Japanese sail. Thanks to these pioneering missions, it is now possible to build sails that have areas larger than two football fields. Within the next few decades, and using materials readily available today, it is conceivable we will be able to build and launch solar sails larger than a city block, propelling spacecraft across the solar system quickly and efficiently.

And these sails may be useful for more than just propulsion. A flotilla of such sails could be placed between the Earth and the Sun to reduce the amount of incident energy reaching the Earth and mitigate the effects of climate change. The idea has been explored in detail by many research teams. One such concept, called Dyson Dots, calls for no less than 270,000 square miles of sail area to offset the effects of the carbon dioxide trapping heat in our atmosphere. (Dyson Dots are named in honor of the scientist, Freeman Dyson, whose name is now inextricably tied to a concept he created that will be discussed later in this article—Dyson Spheres.)

Space elevators. Giant space stations and solar power generation systems. Fleets of solar sail propelled cargo ships crisscrossing the solar system. Dyson Dots protecting the planet until we become a carbon neutral civilization. All these things are now within our technological grasp.

But what about the future? Or the present for some hypothetical alien civilization that has been around longer than we? What large structures might we one day create or observe that someone else has already accomplished?

To answer this question, it would be useful to consider a metric for a civilization’s capability to manipulate its environment. Fortunately, just such metrics were devised by Soviet astronomer Nikolai Kardashev and they are broken into three categories or types:

• Civilizations that use and/or store all the energy available on their planet. We would achieve this status if we can readily collect and use all the Earth-incident solar energy, totally approximately 1017 Watts (100,000,000,000,000,000 Watts). For comparison, the current estimated global energy use is about 1012 Watts. We are 100,000 times short of being a Type I civilization. (Drat!)

• Civilizations that use the total energy output of their star. Previously in this article was discussed a swarm of Dyson Dots measuring 270,000 square miles. These dots would be capable of capturing approximately 1015 Watts. If you can imagine expanding the size of the “dots” until they form a complete spherical shell around the sun, capturing all its radiated power (approximately 1026 Watts), you would have a Dyson Sphere. (This was original conceptual idea attributed to Freeman Dyson: Dyson Dots were derivatively named.)

• Civilizations that control all the energy on the scale of the galaxy, approximately 1037 Watts.

Type I and II civilizations are no strangers to readers of science fiction. Consider Larry Niven’s Ringworld in which he envisioned a partial Dyson Sphere consisting of giant ring (like a wedding ring) surrounding a star at approximately the same distance as the Earth's orbit around the Sun. Niven’s ringworld is slowly spinning to provide simulated gravity and approximately one million miles wide—making it a positively huge habitat for its inhabitants with a surface area far larger than available on Earth. Yes, there may be reasons Niven’s ringworld as originally conceived is unstable, but any civilization capable of building such a structure will undoubtedly have the ability to build in a to-be-developed technology to stabilize it. We can’t invoke Type I status in one technology area and not assume comparable capabilities in others.

More recently, Niven collaborated with Gregory Benford on a series of books describing a civilization somewhere beyond Type I and on its way to Type II wherein the aliens create a giant bowl around a portion of their star (giant in this case means a surface area >1 million Earths!) and use it to propel themselves, and their star, through space. The authors describe how their solar system sized propulsion system works in the afterword of Bowl of Heaven:

“Our bowl is a shell more than a hundred million miles across, held to a star by gravity and some electrodynamic forces. The star produces a long jet of hot gas, which is magnetically confined so well it spears through a hole at the crown of the cup-shaped shell. This jet propels the entire system forward . . .”

Full up Dyson Spheres have also appeared in science fiction literature and film, including Tim Zahn’s Spinneret and Federation World by James White.

But do Type I civilizations exist and, if so, can we find them? The good news is that a civilization capable of building a Dyson Sphere should be readily detectable by our telescopes. Nearby Dyson spheres should be readily seen by looking at the universe in infrared light. Such a structure would capture and use most of the energy from its star, but that doesn’t mean that nothing would radiate from the outside of the sphere since we cannot assume that even an advanced civilization can cheat on the laws of nature, including the laws of thermodynamics. Simply put, no matter how efficient the machine, there will always be energy lost in the conversion and use of it, producing waste heat. The waste heat coming from a Dyson sphere would be seen as something called a “black body,” radiating in the far infrared (Figure 4). Such a black body in the nearby region of our galaxy should be readily observable by some of the space telescopes launched in the last few years and . . . none have been observed. Does this mean none are out there? It does not. It just means that if they are out there, then they are not in our region of the galaxy.

Figure 4. Even a civilization capable of encapsulating its home star in a Dyson Sphere and capturing and all its radiant energy cannot escape the laws of thermodynamics. There will always be energy lost in the power conversion process, producing waste heat that should be detectable across light years. (Image is in the Public Domain.)

Telescopes have observed something possibly related to a Dyson sphere that is worth mentioning. The star KIC 8462852 is a fairly typical star located about 1400 light years from Earth. It’s typical in that the star itself is normal and like many other stars in the galaxy. What is around it is not so typical. Before explaining why it is atypical, some background information is warranted.

The discovery of thousands of exoplanets these last few years resulted from the flight of the Kepler Space Telescope in 2009. Kepler (the telescope) used a technique called the transit method to detect regular, small variations in the light output of stars to find and characterize planets circling them in the line of sight between us and the star in question. The average dimming caused by a planet passing between the star and the Earth is on the order of a fraction of a percent. So, when a team of citizen scientists were looking at the data and found a star that was dimming a whopping 22 percent, people took notice. The star, KIC 8462852, is now referred to as Tabby’s Star. Since its discovery and the media interest it generated, another star exhibiting similar behavior was found in 2018: star VVV-WIT-07. The light from this old, red star dimmed slightly for a few days and then plummeted by seventy-five percent for over a month before returning to its “normal” brightness. Various explanations have been put forward, most of them involving purely “natural” phenomena, and there is not yet a consensus as to what is causing the stars’ dimming. There is one “unnatural” explanation that has been offered: The decrease in light escaping the stellar system in question is due to a partial Dyson sphere surrounding the star. While this explanation is appealing to many, given the lack of evidence that intelligent life exists beyond Earth, it is considered a very low likelihood explanation—but “low likelihood” does not equal zero.

The bottom line is that we have yet to see any evidence that Type I or II civilizations exist. But what about Type III?

If there were aliens capable of using the energy of their entire galaxy, how would we know? Remember that our home galaxy, the Milky Way, is typical as galaxies go. It is about 100,000 light years across and contains billions of stars. And it’s among billions of galaxies that make up the known universe. If aliens were capturing and using the energy of entire galaxies, we might expect to see evidence of their existence by looking for changes in galaxies, mostly likely by their shape changing or, like a galaxy-wide Dyson Sphere would create, by them vanishing entirely. Have we found anything like this in our observations of the universe? Perhaps!

Consider the Bootes Void.

When our telescopes have looked deep into the universe, we see galaxies almost everywhere. In fact, with one notable exception, we do see galaxies everywhere. The exception is the Bootes Void. Located in the constellation Bootes, the void is an almost spherical region of space devoid of galaxies. Located over 330 million light years from Earth and comprising approximately 0.27 percent of the observable universe (which is a lot), sits a great emptiness containing only about 60 galaxies. There should be more than 2000. The scale of the void is mind boggling: it is 250 million light years in diameter. It is growing. And it is not alone—there are other, though much smaller voids in the universe that are equally unexplained.

What if . . .

A Type III civilization arose in a galaxy within the void and began using the energy of their galaxy, encasing it in the galactic equivalent of a Dyson Sphere. They then migrated to the neighboring galaxies and repeated the process, causing an expanding shell of darkened galaxies that would have once lit up the sky. This would explain the nearly spherical shape of the Bootes Void and account for why it is growing. Unfortunately, the Bootes Void is too far away for our infrared telescopes to detect galaxy-scale black body radiation so we can’t use this to verify or disprove their existence.

Coming full circle, we’re building our first large structures in space and today can conceive of building Dyson Dots capable of intercepting enough of the sun’s energy to affect the energy balance on our home planet. From there, it will be a logical step to consider how to take the material left over from the formation of the planets, the asteroids and comets, and use it to build our own Ringworld or partial Dyson Sphere. Next would be a complete Dyson sphere and the expansion of the human species to other stars in the galaxy.

Is this possible? Physics says, “yes!”

To quote Freeman Dyson from his essay, “The Search for Extraterrestrial Technology” Perspectives in Modern Physics (1966), “When we look into the universe for signs of artificial activities, it is technology and not intelligence that we must search for. It would be much more rewarding to search directly for intelligence, but technology is the only thing we have any chance of seeing."

The universe awaits—and let’s hope we reach Type III status before the Bootes Void reaches us.

Further Reading

Greg Matloff and C. Bangs recently published book, Stellar Engineering (Curtis Press, 2019), provides an excellent summary of megastructures in space. I highly recommend it.

For more information about Dyson Dots and using sunshades to mitigate climate change, please refer to Kennedy III, Robert G., Kenneth I. Roy, and David E. Fields paper, "Dyson Dots: Changing the solar constant to a variable with photovoltaic lightsails." Acta Astronautica 82.2 (2013): 225-237.

To learn more about graphene and its uses, please refer to the book I recently co-authored on the subject with Dr. Joe Meany, Graphene: The Superstrong, Superthin, and Superversatile Material That Will Revolutionize the World.

Copyright © 2019 Les Johnson

Les Johnson is a Baen science fiction author, popular science writer, and NASA technologist. He is the author of Mission to Methone, and co-author of On to the Asteroid and Back to the Moon with Travis S. Taylor, Rescue Mode with Ben Bova, and numerous general science publications. Stellaris: People of the Stars (Baen, September 2019), an anthology Les co-edited with Robert E. Hampson, is a collection of original fiction and non-fiction essays about what may become of humans as we become an interstellar species. To learn more about Les, please visit his website at www.lesjohnsonauthor.com.