When it comes to building big things, megascale engineering is where "there's no way you could build that" loses out to our knowledge of mathematics.
Megascale engineering projects are more than just fantastical objects out of science fiction, they are already being actively planned in some parts of the world and they are not new — humans have been building megascale structures for thousands of years.
In fact, the drive to build bigger and more complex contraptions, machinery, and structures is as old as construction, and its history goes back farther than you might realize.
What is megascale engineering?
Megascale engineering is generally considered the kind of exercise where one sits down with a pencil and paper, and designs a project without feasibility towards the technology involved, the material needs, or the labor and time investment, and at an enormous scale.
We say "generally considered" because the more precise definition leaves us with an interesting debate that we'll get to in a bit.
Typically, megascale is defined to include any structure greater than 1,000 kilometers (about 620 miles) in any dimension, making it one megameter long. These are obviously the kinds of structures that can be found in the worlds and minds of science fiction writers, but not exclusively.
Many leading scientists have worked up megascale engineering ideas as well, including some of the most famous examples of megastructures.
What are some early megascale engineering projects?
The famous mathematician of ancient Greece, Archimedes, is said to have claimed: "Give me a place to stand, and a lever long enough, and I can move the Earth!" Archimedes had a deep understanding of levers and torque, knowing that with a long enough lever with a precisely positioned pivot, one person could exert many multiples of force beyond what their body alone could produce.
Though, the lever he would have needed would have been long indeed, far longer than anyone in ancient Greece (or even today) would be able to produce. But that's kind of the point of megascale engineering: Take the things we know about engineering and mechanics and blow them up to scales far beyond our present reach.
Another notable case of this from history was Christoph Grienberger's "Golden Earth" mover. Born in 1561, Grienberger was a Jesuit priest who became essentially the academic peer reviewer of scientific work put out by Jesuit authors at that time. He also had a fundamental grasp of the uses of torque to amplify human power.
Working from the basis that a 1:10 gear ration could allow a dock worker to lift cargo ten times heavier than he could have done with his hands alone, Grienberger sat down with ink and paper and devised a contraption of gears and ropes that would be able to lift the entire planet.
There have been several proposed engineering projects that might not have produced a single 620-mile-long (1,000 kilometers) structure to show for it, but would without question have that kind of outsized impact had they been attempted.
One such project, Altantropa, was the brainchild of the German architect and engineer Herman Sörgel who proposed in 1927 that Europe should erect a dam across the straits of Gibraltar and other key locations in and around the Mediterranean Sea.
This, he predicted, would lower the sea level of the Mediterranean by up to 660 feet to provide more than 148,263,229 acres (600,000 square kilometers) of arable land for European colonization.
There was much more to Sörgel's plan, much of it full of outright racist and colonial attitudes that were endemic at the time, but even though vast amounts of land reclamation isn't quite the same thing as a towering space elevator, the scale and the imagination of the project are more in line with what we think of when we talk about megascale engineering.
By the time we reach more modern times, science fiction writers picked up the ball from day-dreaming engineers and scientists and gave us many of the megastructures we think of today.
The Dyson Sphere
Speculating about the search for extraterrestrial life in 1960, Dyson wrote a paper in which he argued it wasn't enough to look for radio transmissions, because that required an alien race to send them out in the first place, which isn't a guarantee.
But, he figured, because of the exponential growth in population on a habitable terrestrial world, any sufficiently advanced species would have to find places to colonize other than their home planet, and pickings in their local solar system might be slim.
One possibility would be for the alien civilization to cannibalize any of its system's gas giants for materials to construct immense, connected platforms, 6 to 10-feet-thick (1.82 to 3.08 m), in a kind of shell around their host star. The platforms would be located at a distance from the star to allow them to experience the same temperature as they would on their home world.
Such an alien race could then live on the platforms in an artificial biosphere, and this is something Dyson thought we would be able to detect without them having to actively broadcast any signals.
The presence of these large platforms would block out a substantial percentage of visible light from their host star, but the heat from the star hitting the platforms would still have to radiate out into space somehow, or else the platforms would melt.
That radiation, in the infrared spectrum, would be visible to us no matter how quiet an alien species might have wanted to remain, and that was what Dyson proposed we start looking for.
Dyson suspected that people at the time mistook the word "biosphere" for an actual sphere, and went to town with the idea, and he might be right. But other physicists and engineers say that some sort of ball or structure surrounding a star that converts 100% of its energy to practical use isn't as far-fetched as even Dyson believed it to be.
Obviously, our material science is not nearly advanced enough for this sort of project, but as we move humanity out into space, constructing something like a Dyson sphere is more a matter of resources, time, and labor than it is an impossibility.
In fact, back in 2015, scientists reported that the light from the star KIC 8462852, about 1,480 light-years away from us, was behaving in an unexplainable fashion. There were many theories put out there, including one that this could be an actual alien megastructure.
The fact that it wasn't completely laughed out of the room by actual scientists is telling, and the researchers who discovered the dimming were given precious time on the Allen Telescope Array to take another look at the star and test their hypothesis.
As it turned out, there was too much blue light coming from the star for the dimming to have been from a Dyson Sphere, but the mystery remains open, and something like a so-called Dyson Swarm (where, rather than a sphere around a star, you have a cloud of millions of solar energy collectors to achieve the same thing) could still be a possibility.
Probably the second most-famous megastructure after the Dyson Sphere is the space elevator, and if humanity ever builds a megastructure first described in a science fiction novel, this may be the one we build.
The basic idea is to run a cable anchored to the ground up into space past geostationary orbit. Beyond that point, a counterweight of sufficient mass anchors the cable in space so that the tension of the cable is always taut, much like a plum line here on Earth.
From there, you would only need a climber vehicle to run up the cable and into orbit, and since this could be done using a solar-powered vehicle, you would not have to expend fuel in the process, making trips into space essentially an investment where nearly all the costs are paid upfront, rather than the ongoing expense of launching rockets at a cost of tens of thousands of dollars for every kilogram of weight in your rocket.
The challenge for space elevators is that the force of rotation around the Earth's axis every day is far too great for even the most advanced materials we have developed. There is talk about carbon nanotubes being a possible solution, but there are those who believe that an Earth-based space elevator is simply out of the question from a materials standpoint.
However, that's just for Earth. On the Moon and Mars, where gravity is significantly less than that of Earth's, a space elevator could be constructed using materials we already have, like Kevlar. For future space missions, space elevators might be critical for resource extraction, human transportation, and more, and would have the benefit of being practical as well, once we leave Earth's gravity that is.
Have we ever built a megastructure?
While most megascale engineering projects are purely speculative, there is an honest debate about whether it has always been so. The Great Wall of China, for instance, is more than 13,000 miles long (~21,000 km), which puts it well past the megameter threshold for being considered a megastructure.
But whenever anyone mentions the Great Wall, people who are most interested in these kinds of things invariably say, "Yeah, but that doesn't count because..."
Maybe it's because it's old and low tech, a structure of stone, wood, and mortar, it's somehow not what any of these people meant by the term "megastructure".
Maybe it took too long to build, starting as far back as the seventh century BCE with the most well-preserved parts being completed in the 17th century CE, so roughly two millennia from start to finish.
But the Great Wall was not originally conceived of as a single structure. In the third century, Emperor Qin Shi Huang, who united China, connected a number of existing defensive walls into a single system. The wall was added to over time, including with branches and other secondary sections. At times, the wall would fall into disrepair and be rebuilt by later emperors. This was the kind of project that was more of an aspiration than a concrete plan — until it wasn't, and most of the Great Wall that stands today is the result of work done during the reign of the Hongzhi Emperor (1487–1505).
How long, exactly, do people believe it'll take to build a Dyson Sphere around a star? Even with an army of nanomachines working non-stop, you are still looking at the work of centuries or more.
Part of what makes the Great Wall of China seem like it doesn't quite fit with these other megascale engineering projects is that it's something that we've actually done, and that seems to betray the spirit of a megascale engineering project in some way.
Megascale engineering projects and structures are meant to be ideas more than blueprints, but the same could be said of the Great Wall — right up until the moment someone started laying down stones to build it.