Ya gotta love humanity. Although we can be cruel and wasteful, this doesn’t outweigh the beauty and innovation we’ve achieved. Consider all of the languages and literary traditions of the past and present, the art and architecture, philosophies and religions, music and performance, the triumphs of science and technology. These are all perhaps the natural consequence of having so many people living in so many places across our planet. And while the proliferation of Homo sapiens has made such cultural richness possible, it is also a cause for anxiety. Even those that doubt that overpopulation is yet a problem must admit that we are on a worrying trajectory.
The planet can only support so many human beings. Indeed, the strain we are putting on Earth’s resources has already begun to limit our population growth. By zooming in on this graph we can see that our rate of population growth peaked in the late 1960s. This is an underappreciated fact. It means we are beginning to outgrow Earth. The United Nations predicts that the world’s population will level off at about 10.9 billion by the year 2100.
Whether we put the brakes on our own growth or let nature continue to do it for us, it is bound to be a difficult and unpleasant process. However, there may be an alternative. Population projections like these hinge on the assumption that we are confined to Earth. In the near future this is definitely true. Even the eventual establishment of off-Earth settlements, although technically providing more space to grow, will not help, at least not right away. If anything such expansion will at first dampen growth, since these new habitations will be more dangerous and still heavily dependent on resources from the mother planet. But in the long term, well, it’s interesting to consider the possibilities.
It has now been over sixty years since humans first ventured beyond Earth and stepped onto the Moon. As remarkable as this was, no one has returned to the Moon since 1972. In recent years a lot of attention has been given to proposals to send humans back to the Moon or even as far as Mars, with the idea of building permanent bases there. But progress on this front has been slow. Our current efforts at crewed missions lack the urgency of the Cold War era space race. However this masks the important--albeit less glamorous--achievements more recently made in robotic space missions. Robots have already managed to land safely on the Moon, Venus, Mars, Titan, various asteroids, and even a comet. In fact, if we are to ever see large populations of humans in space, sending robots in our place may paradoxically be a critical first step. Robotic missions not only reduce the dangers, loneliness and tedium of space travel, they have the potential to rapidly accelerate the construction of space infrastructure.
Perhaps the most important way that robots could pave the way for human space settlement is with mining missions to the Moon and to some of the larger asteroids between Mars and Jupiter. One such venture, called Planetary Resources, began in 2012. While it ultimately folded in 2020, it did have serious investors behind it, including executives at Google and the billionaire Ross Perot Jr., as well as a stable of engineers, some of whom worked on space missions with NASA. Such projects are obviously major undertakings, and while none yet have succeeded there’s good reason to assume they eventually will. After all, we already go to extraordinary lengths to harvest resources here on Earth. Interestingly, much of the Earth’s most valuable metals were drawn into its core after the planet’s formation, making them inaccessible. It is estimated that a single asteroid with a diameter of less than 500 meters could yield more nickel, palladium and platinum than has been mined on Earth in all of history. This may not be surprising given that much of Earth’s accessible supply was deposited by asteroids soon after its formation. The biggest challenges facing asteroid miners is getting there and back. Once an asteroid is reached its minerals are relatively easily harvested using techniques like magnetic raking.
Progress in asteroid mining could be greatly accelerated by using a type of robot theorized by the famous mathematician and philosopher John von Neumann. These hypothetical robots, often referred to as von Neumann probes, would be capable of traveling to new locations in space and using the material found there to build more robots. Such robots could self replicate exponentially. This may sound scary, but there’s no reason to suppose that they would get out of control. Each individual robot’s role could be fairly narrow in scope, and would not need to possess superhuman intelligence. A detailed 1980 study conducted by NASA looked into the possibility of using such replicators to build a permanent settlement on the Moon. Ultimately it was determined that the Moon lacked sufficient chlorine to make this feasible (we'd need our lunar swimming pools disinfected, after all!), but would this be the case elsewhere?
Besides mining and “seeding” other planets and moons with human-ready habitations, von Neumann style robots could also be tasked with constructing more large-scale infrastructure. One example are spacecraft known as a Dyson swarm, named after the physicist Freeman Dyson. A Dyson swarm is essentially a fleet of solar-paneled satellites that would orbit the Sun or other star and beam large amounts of energy to nearby planets or space stations. The virtually limitless amount of energy that could be harnessed from such a formation is considered essential for any civilization wishing to branch out into space. As such there have been several attempts to detect them in other parts of the galaxy, as this would be evidence of extraterrestrial intelligence.
Another important role for von Neumann self-replicators would be in terraforming other worlds, making them more suitable for human life. Terraforming involves warming a planet enough for volatile substances to evaporate and create a thicker atmosphere. This in turn would create a greenhouse effect and further warm the planet. The atmosphere would then need to be altered to contain breathable oxygen. Several suggestions have been offered as to how such terraforming could be achieved, and the details depend greatly on the location and composition of the target world. As you might guess, terraforming an entire planet or moon would be a massive and technically challenging project, and not something that will happen in the near future. By the time we reach such a capability we may find, given the abundance of matter available from space mining, that it may be easier to build our own megastructures to live on. One example would be an O’Neill cylinder, a vast space habitat consisting of two nested tubes many miles in diameter. These would rotate in opposite directions for stability and to create artificial gravity. But given the scale any of these plans we would almost certainly require some version of von Neumann style robots to carry out the bulk of the labor.
If we humans eventually do manage to make the leap to off-Earth settlements we would of course begin with our own solar system. Besides Mars and our own moon, Jupiter’s moons of Ganymede and Callisto, as well as Saturn’s moon Titan have all been suggested as suitable locations for permanent bases. But why stop there? Space travel at ten percent the speed of light is considered “non-exotic”, meaning it is feasible with current technology. Achieving this kind of speed safely with human beings on board, however, is another matter. But if we can figure out a way to pull it off, we could in theory reach the next nearest star system in less than fifty years.
The idea of expanding into other star systems is very speculative, but also very fascinating. What would it look like if in the far future humanity has spread throughout the galaxy? For one thing our current population of 7.9 billion would be a mere rounding error compared to what it could become. But this unfathomable multitude would be quite fragmented. One-way communication between one star system and its nearest neighbor would take about five years, and the time needed to contact even farther systems (to say nothing of actually traveling there) would be prohibitive. This means that, barring some Star Trek-like warp drive technology, each star system would be physically and culturally isolated from the others, free to diverge in all sorts of interesting ways. Think for a moment of what to you is the most exotic place on Earth. Such a place, being at most a day’s journey, would seem like your back yard compared to a civilization light years away. Given enough time the people in different systems could even diverge into different species. With enough of these human star colonies spread across the galaxy it would be likely that some of them, whether due to a civilizational collapse or some other reason, would “forget” the existence of the others. In this case the rediscovery of their distant relatives would be as startling as encountering aliens. Who knows, maybe something like this has already occurred.
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