One of the biggest areas of speculation in interstellar science is whether there may be Dyson Spheres somewhere out there in the cosmos. A Dyson Sphere is a giant construct around a star, designed by its creators to capture as much of the star’s energy as possible in order to optimize that civilization’s development and longevity.
But if you think about it, a Dyson Sphere is illogical, because it assumes a star is a stable, predictable source of energy—when it really isn’t. And if you want to lengthen the lifespan of your race, building a permanent construct around an essentially unstable star is just about the last thing you want to do.
A star like our sun is a beast of chemicals caught in a constant state of fusion burning. But there is nothing constant about its output, despite the fact that it may seem pretty constant over a few light years away and a few thousand years of observation. In fact, our own observations of the Sun in just the last few decades has revealed irregular and unpredictable outputs, producing more and less energy, radiation and energetic particles all the time. We have found correlations between these irregular outputs and changes to our atmosphere and temperature, impacting ice ages and regional habitability. Studies suggest that we could see even larger irregularities in the future, which could strain our existing planet’s viability significantly.
Besides this irregular output, we know that a star has a limited shelf life. In approximately 5 billion years, the sun will begin the helium-burning process, turning into a red giant star. When it expands, its outer layers will consume Mercury and Venus, and reach Earth. Every other star will similarly burn out at some point, either going nova in the process, or collapsing upon itself, perhaps turning into a black hole.
So, imagine you’re an alien race that wants its species to live forever: Would you commit mind-boggling resources and time to creating a giant habitat around a star that’s only going to die eventually and leave you with a mind-bogglingly huge lifeless shell?
I don’t think so. It would make more sense (and consume a lot less in time and resources) for that alien race to shoot for full mobility, in order to move from star to star as needed. They would become a space-faring race, building either groups-small or populations-large spacecraft and living off space like nomadic tribesmen, transiting to solar systems whose star could provide them energy, and perhaps planets that they could mine for needed resources; and when the star no longer suited them (about to nova or collapse, or simply putting out too many unpredictable flares of energy and particles), they would gather enough energy and resources to sustain them as they head out to the next system.
Stephen Hawking once said about alien travelers: “I imagine they might exist in massive ships, having used up all the resources from their home planet. Such advanced aliens would perhaps become nomads, looking to conquer and colonize whatever planets they can reach.” Blatant name-dropping aside, I agree with his idea of interstellar nomads, though not with his impression that they would be star-faring marauders: Because they would surely need to conserve their energy and resources as a matter of survival, and as war is an energy- and resource-intensive business, they would surely avoid any efforts, like wars, that unnecessarily waste valuable resources. It’s unlikely that our wild, dangerous, oxygen-rich planet would be anything but an incredible curiosity to them; but scattered throughout our system are greater resources, mostly easier to get, than those on Earth (including water, you sci-fi movie hacks). They might arrive in our solar system and safely plunder the asteroids and a few of Saturn and Jupiter’s moons, but they’d probably just monitor Earth from orbit or ground-based outposts, likely to add alien life knowledge (and wildlife footage) to their libraries. Maybe, if we’re lucky, they’d leave an outpost behind when they move on, and we might learn something about them.
This point is so important that it should be added as a variable to the Drake Equation (the formula used to predict the possibility of other intelligent life in the cosmos). One element in the Drake Equation is the state of a world’s habitability. But if you take into account that a race may have evolved and departed a planet or system before it became uninhabitable, then the habitability variable must be expanded to include planets that may at one time have been habitable enough for long enough to spawn a race, even if it is no longer habitable. So habitability becomes a limited span, long enough for a race to develop far enough to be able to leave for a new star system… but that also expands the possible number of habitable planets.
This also suggests that, if a race became star-faring, that they no longer need a single habitable planet… but they will periodically need to replenish some supplies from resources they can potentially find on multiple planets at different times. So a new variable needs to be added: That of a star system with enough accumulated resources to help sustain a transitory race as it moved from system to system. And its resources don’t need to be comprehensive: If a space-faring race can accumulate resources A, B and C in one system, and wait until they transit to another system to replenish resources D, E and F… again, you’ve expanded the number of planets that may support the survival of a civilization.
Such alterations to the Drake Equation would suggest a higher possibility of neighbors out there, perhaps in places we may not have looked before, since they may be able to harvest resources from a wider array of systems than we have previously assumed. Or possibly in transit from one system to another, and not likely to be wasting valuable resources on beaming signals about looking for other races; at least, not until they reach an oasis that will sustain them for long enough to do some local exploring for the next system to transit to.
This last point could be potentially interesting, too: For a space-faring race that moves from system to system, harvesting resources as needed, they may someday see the Solar System as a valuable oasis to visit. But for those who are worried that they may feel the need to—I dunno—attack the Earth, subjugate or kill us, and steal our resources… be assured that most of this system’s most valuable resources can be more easily obtained from the many outer planets, moons and asteroids of the solar system, and those resources would not be contaminated with the pesky and unpredictable organic life infesting this planet at present. Because we already know the aliens wouldn’t be big on unpredictability… it makes it much harder and more energy-intensive to survive.
So, I think we can stop looking for Dyson Spheres out there; I doubt there will be many races, capable of building them, who would not be smart enough to know how wasteful they would be. Instead, we should be looking for potential space-oasis systems, and the nomadic ships transiting between them.
They could even turn up in our system, respectfully keeping their distance as they harvest resources from the outer planets and trying to avoid the locals.