In real life, we’re accustomed to astronauts floating in zero-G, probes receiving a gravity assist from planets as they journey to their destination, and the effects of weightlessness on human physiology. Science fiction writers, like myself, portray these phenomena in our stories to further immerse readers in the narrative. They have become typical set dressing, much like castles and knights are clichés of epic fantasy. There’s nothing wrong with that, but what about the real, long-term effects of gravity?
This invisible force has had immeasurable effects on not only our planet and the surrounding universe, but our very species. Everything from bone structure, the colors we can see, our shape—and possibly, even how we age. Could gravity be the deciding factor in our future among the stars?
We already have some sort of destiny beyond the Earth. Our space probes, such as Voyager I & II, are proof of that, for they will likely outlast our species by billions of years. But gravity will play a larger role in that future, other than being a slight obstacle in escaping Earth orbit. It will determine where we can live. Where we can survive.
But science fiction has touched on that. Here are some areas it doesn’t typically address:
Sentient intelligence: Does gravity have a long-term, evolutionary effect on our brains? Does it inhibit or encourage the complex arrangement of neurons and chemicals that grant us the processing power to think? Or to feel? If humans had evolved on a planet with a different gravity—say, three times that of Earth—would we think differently? Or can intelligence, as we know it, even evolve under different conditions? I’m sure it can, but until we know for certain, it does pose a fascinating question: could we interact with, or even understand, a species that evolved in a vastly different gravity? I’m talking about aliens that evolved under, say, six times our normal gravity. How would that change possible communication, beyond the physiological constraints?
Childbirth: Since no child has been carried to term and birthed in a zero gravity environment (or any other alternate gravity, for that matter), what effects will it have when that happens? I’m guessing less bones mass, perhaps weaker muscles. Maybe not in a crippling way, but I doubt that such an environment would have no effect on the fetus. Will these children be a link between our past and our future? Birthed by a lifeform from a certain gravity, with its genetic makeup, but influenced by a gravity at odds with how those very genes evolved? Would there be birth defects if the child were born on a high-G world, with such powerful forces tugging on every second of its development in the fetus? Over time, could another species evolve from us, one that could survive alternate gravities? This isn’t referring to just zero-G, I’m also including Mars’s gravity. Though about one third of Earth’s, would its gravity reshape future colonists over several generations?
Sensory limits: Our own gravity, and our sun, influence our eyesight. Right now, we can only see a small fraction of the electromagnetic spectrum. We can only hear within a certain aural range. Would this be the same for a human born and reared on another planet? A world with different gravity than Earth’s, and one with a hotter, brighter star? Or even a dimmer, colder star? If a colony survived on such a world for, say, a thousand years, how different would their offspring be from those born on Earth? I’d imagine there’d be some differences. And I mean beyond the assumed ones (generations birthed on a low-G world would be slighter, etc.). I’m referring to how they’d interact with their environment. Would their eyes discern different colors than ours, for example? What about their other senses?
Technology: This is something, off the top of my head, that I haven’t seen in science fiction—a disparity in technologies due to different native gravities. And I don’t mean that one civilization has a super-duper ray gun and one doesn’t. I mean, could we even utilize another species’ tech if they developed it for use in another gravity? Imagine trying to wield a gun fabricated by a high-G species. Or piloting a starship, where its process for creating artificial gravity during flight aggravates or even kills another species that wasn’t that vessel’s intended occupants. I think more than just physiology and philosophy would be at work here, in making an object alien to human understanding. I’d imagine that everything would be different. Gravity could have a hand in that.
Economics: Gravity, as we currently understand it, is a universal, irrevocable force. One that we manipulate, and even escape at times, but we still cannot control it. In most interstellar science fiction, FTL travel is common, and artificial gravity aboard starships and space stations is the norm. But gravitational forces would still make such endeavors expensive. What if there were extra tariffs placed on goods from a low-G world, because they’re likelier to break? What if there were taxes incurred whenever one traveled to a high-G planet, due to the extra fuel and danger that such a landing/takeoff would involve? In very advanced civilizations, gravity could become a commodity, where the rich reside in comfortable living spaces attuned to their native gravity, while the poor dwell in gravity that is harmful to them. Think of the health costs in an intergalactic society. Is it really worth it to colonize a high gravity world? Would space travelers have to pay more for medical services, because their extra needs (bone reinforcement, reversing muscular atrophy, accelerated pulmonary conditions) puts a strain on society?
If a science fiction writer has already touched on these issues, then I still have a lot of reading to do. Though I tried to inject the side-effects of gravity into my novel INHERIT THE STARS, I didn’t touch on all of these issues. The story didn’t call for them, and that’s true for many other authors. It’s not always a sign of lazy writing—my novel isn’t Hard SF, after all. But I would like to see more of these concerns expressed in science fiction. I have some ideas gestating on this, since I’m fascinated by gravity’s effects on us. Through my fiction, I intend to explore more of those effects.