Overcoming the Challenge: Artificial Gravity

In my previous Overcoming the Challenge post, we examined how sci-fi authors can tackle the challenge of faster-than-light travel. In this post, we examine another difficult and often overlooked difficulty: artificial gravity. The idea that advanced starships have gravity almost identical to Earth’s is another seemingly automatic trope used in just about every science fiction book, movie, and show you can imagine. A very notable exception is The Expanse, which probably gives us one of the best depictions of how the effects of gravity and acceleration would work in space in real life. But the technology level of humanity in The Expanse is relatively low compared to say Star Trek, so as technology increases there is the expectation that “true” artificial gravity will come onto the scene.

But creating gravity, something that we take for granted every day on Earth, isn’t as easy at it might appear. I think it’s the very fact we take it for granted in our everyday lives that results in it making its way so easily into our fiction. Good science fiction, however, will consider gravity, or the lack thereof, to be a very important part of any space setting.

Realistic Forms of Gravity

The first and easiest way to create artificial gravity is through acceleration. Just like when you really step on the gas in your car, you feel pushed back against the seat. The same physics is at work on a spacecraft firing its rockets or thrusters. When a ship is designed with the back of the ship being the floor of each deck, back becomes down. When the ship accelerates, everyone will be pressed into the floor, and it will create the sensation of gravity. A ship can control the amount of gravity by controlling the acceleration. To reach high speeds by conventional means, a ship would be accelerating and decelerating constantly, so it wouldn’t be too hard to have this kind of gravity most of the time. The difficulty of this comes from inertia. If the ship must turn or make any kind of fast maneuver, people will be thrown around the inside of the ship like balls in a tumbler, likely being injured or killed. Again, The Expanse gives us many scenes depicting this very well. In a combat situation, the crew would need to be strapped into chairs for their own protection, and extreme acceleration or sudden deceleration could be fatal.

The next best way is to use rotation to create gravity. Currently, this is most likely how we as humans today will create gravity in space. In rotational gravity, out becomes down, so the ship is built like a ring with all the floors facing outward. A gravity similar to Earth’s can be generated with a certain speed of rotation. As long as you don’t look out any windows, it would be impossible to tell that you are spinning, and it would feel like normal gravity. The limitations here are obviously ones of design, as ships would require rotating sections and any loss of rotation would equal a loss of gravity. This form of AG (artificial gravity) would also conflict with acceleration gravity, and the crew would need to be strapped in during any significant acceleration, greatly limiting the speed of the craft. A rotating ship would accelerate for a short time and then coast the rest of the way. This would save fuel, very important for current spacecraft, but you won’t go very far or very fast. Rotational gravity is much more likely to be used on stationary structures like space stations or orbital shipyards.

Ultra Sci-Fi Gravity

Now things get fun! The following forms of gravity are currently impossible for humans, but they may be possible with significant advances in technology.

First, the graviton. This is a current scientific consideration, although there has been some debate. Many theorists wonder that since we have discovered a particle for basically every other force, there must reasonably be a particle for the force of gravity, yet it remains undiscovered. A possible reason for this is that gravity is an extraordinarily weak force compared to most other forces in the universe. This means it will be proportionally hard to discover the graviton and may simply be outside our current level of technology. While the graviton isn't strictly necessary for our current models of how the universe works, many physicists still assume it exists and acts on us and everything else in the universe constantly. Fiction-wise, the graviton is an easy way out. Particles can be manipulated and controlled. Therefore, if gravity is a particle it can also be manipulated and controlled. If AG is described at all in a book that does not use the more realistic forms of gravity, you can assume it involves something with the graviton or similar.

Second, the use of a singularity. Yes, I’m talking about that kind of singularity, a black hole, a very small one, of course. A very, very tiny black hole, would create a powerful gravitational field anywhere. This is real science. The problem, of course, is how we would create, stabilize, and control a black hole so that it did what we wanted it to do. This is currently entirely beyond our understanding, and we don’t even have a really solid idea of what a black hole is or what happens around it. We have theories based on math rather than direct experimentation. It would require a giant leap in technology to control black holes and gravity. A ship based around a black hole would be odd since it would result in everything being pulled to the middle. Ships would likely all have to be spherical in construction, and this was a limitation I didn’t want in my book.

My Holy Grail of Artificial Gravity

Third and final, is something I stumbled across in my research while working on the later drafts of Darksea. At that point, AG in my book was basically not described at all. I took it for granted, requiring readers to suspend disbelief, just like almost everybody else, and it bothered me. I was understandably delighted when I found some articles (real science articles, in fact) related to the idea of negative mass matter. Matter with a negative mass reacts to force and gravity in a way opposite to that of regular matter. Perversely, if you were to push on a ball of negative mass matter, it would move toward you rather than away. In a regular gravity field like that one Earth, an object with negative mass would move up, away from the source of gravity, instead of down.

We know with certainty that negative mass matter exists because we have created it in laboratory conditions, so it is not entirely in the realm of fiction. The challenge would be to produce enough of the material for practical use, and we are still quite a way from being able to do that.

How would negative mass matter help with AG? The material can be used to create a gravity field simply by opposing it with regular matter. Therefore, a ship constructed with ceilings of negative mass panels and floors of equal positive mass panels would create a push-pull effect similar if not identical to that of normal gravity. Negative mass in the outer hull of the ship could also act as an inertial dampener. This would be vital to any ship likely to engage in high-energy maneuvers or combat to prevent the crew from being thrown around like our previously mentioned tumbler balls. The solution of negative mass for the production of AG was the perfect discovery. It is plausibly scientific, the physics are sound, and there is every reason to believe that an advanced civilization could produce sufficient negative mass matter for use in industry. It may even be the case that in our own future spaceflight, negative mass AG will become the standard for our own real-life starships.

UPDATE: In the original posting of this blog, I was a bit too harsh on the poor graviton. Further research softened my view, and I now consider it a reasonable option for generating AG. I updated the post accordingly.