The distance between stars may seem impossible for us; barring the discovery of the warp drive which would allow us to travel faster than the universe’s absolute speed limit–the speed of light–travel to the nearest star would take years or decades. And that star doesn’t even have anything of clear interest to us; the only potentially habitable planet currently known to man is centuries away at best. It may seem that, barring the long-shot which is the warp drive (current physics doesn’t look great for this technology’s feasibility in the near future), humans will never spread beyond the tiny patch of space ruled by our own parent star.
But this line of thinking rests on a single major assumption: that humans need planets. It’s pretty easy to see why we assume this: presently, we do. Even our best space environments are far from self-sustaining, and require frequent shipments of essentials like food, water, oxygen, and spare parts from the surface of the Earth. But must that always be the case? Several sci-fi authors have made convincing arguments to the contrary.
The ideal for any off-of-Earth settlement is a completely closed, self-sustaining ecosystem. The ideal space station in orbit around Earth would produce all of its own food, water, oxygen, and energy. The same holds for an ideal settlement on Mars or the Moon. And for any starship that hopes to ferry humans between habitable worlds at sublight speeds.
There is no reason any of this is theoretically impossible. Water is found in asteroids, in comets, on pretty much every rocky body and in every gas giant atmosphere. It’s even found in deep space. So, too, are the building blocks of life–the carbon and nitrogen that make up the proteins and sugars our bodies use for food. All we would need would be to find a way to harvest these carbon and nitrogen compounds and convert them into forms we could use–a feat which his arguably possible with advancing biotechnology–we’re already making our own bacterial species from scratch. Who knows what a century or two of experimentation in harvesting organics from alien atmospheres could bring?
Even energy is free; near stars, the potential for solar power is theoretically limitless. Between stars, a properly managed nuclear fission reactor can produce energy for centuries.
Now, if the humans of the future manage to build these self-sustaining space environments, they’ll be faced with a new question. If we can become self-sustaining in orbit–then why on Earth do we need planets at all?
Why travel 600 light years for an Earth analogue when the Sun’s nearest neighbor, Proxima Centauri, is likely to host water, organic molecules, metal, and solar power just like our own solar system? Humans could spread to Proxima Centauri–and every star–without need for anything so kushy as a habitable planet like the one that birthed our species.
It is entirely possible that in the future, humanity may exist spread across dozens or hundreds of star systems. These humans may look back on a distant era in which we relied on our parent planet in the same way that we view our own ancestors who hadn’t figured out how to use fire yet.
The changes such a lifestyle would bring about to human form and culture may be unimaginable. But a few writers have tried. In Hyperion, Dan Simmons’ “Ousters” are star-faring nomads who see no necessity for clothes (except pressure suits for spacewalks). Their rituals, cultures, and art forms developed in zero-gravity. Isaac Asimov’s Nemesis deals with the first self-sustaining orbital “settlement” of humans who decide to strike out for a nearby star, realizing they have no further need of Earth or worlds like her.
Others have speculated that, freed from the demands of planetbound life, humans may take on almost unrecognizable forms; becoming human brains with machine bodies, merging minds like computer programs into collective consciousness, adapting or discarding whole new body parts through cybernetics, bioengineering, and nanotechnology as a given “human” society’s environment requires.
These last speculations are far-off thoughts, of course. But it’s a very interesting question, and well worth considering. In the grand scheme of things, is sticking around habitable worlds our best survival strategy? And what forms may humanity take when we have the power to gather the resources we need from any star system, as well as the computing power and biotech we’re now beginning to glimpse in our current age?