A momentum exchange field applies an acceleration in a uniform direction to anything that enters it, so using the technology for anything more sophisticated than simple push/pull effects is complicated. It’s possible to create overlapping fields oriented in different directions, and the shape of the field can be manipulated fairly well. But typically you can only get sophisticated telekinesis-like effects by surrounding an enclosed space with arrays of manipulators, which isn’t practical outside of industrial applications.
A final important constraint is that the momentum exchange effect isn’t instant. Any particular field will only transfer energy at a finite rate, which has major implications in weapon design.
Applications
This one technology has so many applications that it radically changes what the setting looks like. Some of the more common applications are listed below.
Artificial Gravity
Momentum exchange fields can easily be used to simulate gravity for a ship’s crew. Normally this is only done inside the inhabited parts of a ship, while the much larger machinery spaces are left in zero gravity.
Deflectors
A repulsive momentum exchange field wrapped around a ship’s hull makes an effective defense against many forms of attack, so these deflector shields are a standard feature of all warships. A warship’s deflectors won’t necessarily stop mass driver rounds, but they greatly reduce their effectiveness by slowing down and deflecting projectiles. They also prevent more diffuse threats like plasma clouds or nanite swarms from reaching the ship at all.
Lasers are a major weakness - while a deflector can red-shift incoming light, the interaction tends to be too weak to protect against heavy weapons firing beams at x-ray or gamma ray wavelengths. The field can also be momentarily overloaded by too many impacts in a short time frame, and under sustained attack cooling the system can become a serious problem.
Fusion Reactors
Achieving plasma confinement with momentum exchange fields is far easier than with magnetic fields, making compact fusion reactors relatively easy to build. Practically all starships run on fusion power, as do stations and planetary power grids. Reactors with a volume of less than a few hundred cubic meters quickly become less efficient, but cybertanks and other large war machines often use them anyway.
Inertial Compensators
A system similar to artificial gravity, but designed to protect passengers from acceleration stress when a ship is maneuvering. A ship’s inertial compensators normally only cover the spaces where crew and passengers are expected to be, and leaving these areas during a hard burn can easily be fatal to humans. The same system can also protect against the shock of impacts as long as the ship’s computer can see them coming, so you aren’t going to see crewmen getting tossed around like the extras on a Star Trek set.
Levitation Devices
Systems designed to interact with the ground can easily support hovering vehicles in a way that looks just like classic space opera antigravity, and the strong coupling makes levitation devices efficient enough that they’ve replaced wheels or treads for many applications. These devices perform a lot like hovercraft - they can cross flat ground or water with no need for roads or bridges, and tend to be quite fast.
Once you get too high to get good coupling with the ground you need a completely different kind of device. Lightweight vehicles can use a system that pushes all the surrounding air down to generate lift, producing an effect similar to a helicopter but with a lot less noise. Heavier or faster vehicles often use a system more like a ramjet instead, sucking in air at one end of a tube and accelerating it out the back. These kinds of systems have largely replaced propellers and jets because they’re more efficient, more reliable and don’t generate as much noise pollution.
One twist that deserves special mention is the effect of field emitter scaling on levitation devices. A hovercar 4 meters long with a lift system on the underside will have a maximum altitude of maybe 4-6 meters, high enough to pass over people and avoid a lot of ground clutter. A 12-meter truck will be able to cruise at ~16 meters, flying over trees and other obstacles. The bigger the vehicle is the higher it can fly, and the less it has to worry about terrain. On densely populated worlds this leads to phenomena like 200-meter cargo ships cruising the skies, or giant resort hotels floating half a kilometer above scenic locations.
Mass Drivers
A railgun-like device that uses a momentum exchange field to accelerate a projectile to high speeds. Weapons of this type are frequently used as small arms, or as the primary armament of ground vehicles or small spacecraft. Guns designed for use in an atmosphere will have a muzzle velocity of several thousand meters per second, while those mounted on spaceships will frequently reach thousands of kilometers per second.
A much larger variety of mass driver, with a muzzle velocity in excess of 0.98C, is used as a spinal mount weapon on some large warships. At these velocities point defense systems generally can’t intercept the projectiles, making them a highly effective way to deliver energy to a target. The impact energy of these weapons is limited primarily by waste heat generation - if you want to fire shells with hundreds of megatons of kinetic energy you’re going to be generating megatons of waste heat inside the gun, so you’d better have a truly massive heatsink or cooling system.
Plasma Shields
If you’re worried about people shooting at you with lasers, using a momentum exchange field to trap a cloud of ionized gas in a bubble around your ship can be an effective defense. Of course, the cloud will also interfere with your own sensors, and if it absorbs too much laser fire it will get hot enough to leak out of the confinement field. Layering both deflectors and a plasma shield around the same ship provides an excellent defense against most weapons.
Thrusters
A thruster is just a mass driver optimized to handle a large flow of liquid reaction mass instead of a few projectiles. This kind of engine is often used on aircraft, shuttles and other vehicles that need to operate in close proximity to ground or space installations. Since the exhaust velocity can be dialed up or down at will thrusters can be used for delicate maneuvers like docking with another ship, without any fear of damaging something with the exhaust.
In theory a high-velocity thruster could be used as the main drive for a starship, but this approach generally isn’t competitive with fusion torch drives. The thrusters can achieve even higher exhaust velocity, but they produce massive amounts of waste heat inside the ship where cooling can be problematic. So the acceleration of a thruster-based ship would be sharply limited by the size of its radiators, and for anything over a million tons square-cube law issues would quickly degrade performance. Since ships larger than that are commonplace, the usual approach is to use a fusion torch as the main drive and confine thrusters to attitude jets and small craft.
Appendix III – Artificial Intelligence
Probably the single most difficult technical issue facing anyone who wants to write far-future SF today is the question of what to do about AI. At this point it’s obvious to anyone with an IQ above room temperature that some kind of artificial intelligence is coming, and it’s hard to justify putting it off for more than a few decades. So any far-future setting needs to deal with the issue somehow, but neither of the standard approaches works very well.
The writers of space opera and military SF have largely adopted a convention of ignoring the whole topic, and pretending that space navies a thousand years in the future are still going to rely on human beings to manually pilot their ships and aim their weapons. This often leads to the comical spectacle of spaceships that have less automation than real modern-day warships, with fatal results for the reader’s suspension of disbelief. I’m not interested in writing that kind of story, so that approach is out.
The other major camp is the guys who write Singularity stories, where the first real success with AI rapidly evolves into a godlike superintelligence and takes over the universe. Unfortunately this deprives the h
umans in the story of any agency. If we take the ‘godlike’ part seriously it means the important actors are all going to be vast AIs whose thoughts are too complex for any reader (or author, for that matter) to understand. If you want to write a brief morality play about the dangers of AI that’s fine, but it’s a serious problem if the goal is a setting where you can tell stories about human beings.
So for this setting I’ve had to create a middle ground, where AI has enough visible effects to feel realistic but doesn’t render humans completely irrelevant. The key to making this possible is a single limiting assumption about the nature of intelligence.
AI Limits
There’s been an argument raging for decades now about the nature of intelligence, and how easily it can be improved in an AI. There are several different camps, but the differences in their predictions mostly hinge on disagreements about how feasible it is to solve what I call the General Planning Problem. That is, given a goal and some imperfect information about a complex world, how difficult is it in the general case to formulate a plan of action to achieve your goal?
Proponents of strong AI tend to implicitly assume that this problem has some simple, efficient solution that applies to all cases. In order to prevent the creation of AI superintelligences, my assumption in this setting is that no one has discovered such perfect solution. Instead there is only a collection of special case solutions that work for various narrow classes of problems, and most of them require an exponential increase in computing power to handle a linear increase in problem complexity.
In other words, solving problems in any particular domain requires specialized expertise, and most domains are far too complex to allow perfect solutions. The universe is full of chaotic systems like weather, culture and politics that are intrinsically impossible to predict outside of very narrow constraints. Even in well-understood areas like mechanical engineering the behavior of any complex system is governed by laws that are computationally intractable (i.e. quantum mechanics), and simplified models always contain significant errors. So now matter how smart you are, you can’t just run a simulation to find some perfect plan that will infallibly work. Instead you have to do things the way humans do, with lots of guesswork and assumptions and a constant need to deal with unexpected problems.
This means that there’s no point where an AI with superhuman computing power suddenly takes off and starts performing godlike feats of deduction and manipulation. Instead each advance in AI design yields only a modest improvement in intelligence, at the cost of a dramatic rise in complexity and design cost. A system with a hundred times the computing power of a human brain might be a bit smarter than any human, but it isn’t going to have an IQ of 10,000 the way a naive extrapolation would suggest. It will be able to crack a few unsolved scientific problems, or perhaps design a slightly better hyperspace converter, but it isn’t going to predict next year’s election results any better than the average pundit.
Of course, in the long run the field of AI design will gradually advance, and the AIs will eventually become smart enough to be inscrutable to humans. But this lets us have AIs without immediately getting superintelligences, and depending on the risks and rewards of further R&D ordinary humans can feasibly remain relevant for several centuries.
So what would non-super AIs be used for?
Bots
Robots controlled by non-sentient AI programs are generally referred to as bots, to distinguish them from the more intelligent androids. A bot’s AI has the general intelligence of a dog or cat - enough to handle the basic problems of perception, locomotion, navigation and object manipulation that current robots struggle with, but not enough to be a serious candidate for personhood. Most bots also have one or more skill packs, which are specialized programs similar to modern expert systems that allow the bot to perform tasks within a limited area of expertise. Voice recognition and speech synthesis are also common features, to allow the bot to be given verbal commands.
Bots can do most types of simple, repetitive work with minimal supervision. Unlike modern robots they can work in unstructured environments like a home or outdoor area almost as easily as a factory floor. They’re also adaptable enough to be given new tasks using verbal instruction and perhaps an example (i.e. “dig a trench two meters deep, starting here and going to that stake in the ground over there”).
Unfortunately bots are easily confused by unexpected problems, which tend to crop up a lot in the field. They are also completely lacking in creativity or initiative, at least by human standards, and don’t deal with ambiguity or aesthetic issues very well. So they need a certain amount of sentient supervision, and the more chaotic an environment is the higher the necessary ratio of supervisors to bots. Of course, in a controlled environment like a factory floor the number of supervisors can be reduced almost indefinitely, which makes large-scale manufacturing extremely cheap.
Due to their low cost and high general utility bots are everywhere in a modern colony. They do virtually all manual labor, as well as a large proportion of service jobs (maid service, yard work, deliveries, taxi service, and so on). They also make up the majority of military ground troops, since a warbot is much tougher and far more expendable than a human soldier. Practically all small vehicles are technically robots, since they have the ability to drive themselves wherever their owner wants to go. Most colonies have several dozen bots for every person, leading to a huge increase in per capita wealth compared to the 21st century.
Androids
The term ‘android’ is used to refer to robots controlled by AIs that have a roughly human level of intelligence. Android AIs are normally designed to have emotions, social instincts, body language and other behaviors similar to those of humans, and have bodies that look organic to all but the most detailed inspection. In theory an android can do pretty much anything a human could.
Of course, an android that thinks exactly like a human would make a poor servant, since it would want to be paid for its work. There doesn’t seem to be any way to make an AI that has human levels of intelligence and initiative without also giving it self-awareness and the ability to have its own motivations. There are, however, numerous ways that an android AI can be tweaked to make it think in nonhuman ways. After all, an AI has only the emotions and instincts that are intentionally programmed into it.
Unfortunately it can be quite difficult to predict how something as intelligent as a human will behave years after leaving the factory, especially if it has nonhuman emotions or social behaviors. Early methods of designing loyal android servants proved quite unreliable, leading to numerous instances of insanity, android crime and even occasional revolts. More stringent control mechanisms were fairly successful at preventing these incidents, but they required crippling the AIs in ways that dramatically reduced their usefulness.
Thus began an ethical debate that has raged for three centuries now, with no end in sight. Some colonies ban the creation of androids, or else treat them as legally equal to humans. Others treat androids as slaves, and have developed sophisticated methods of keeping them obedient. Most colonies take a middle road, allowing the creation of android servants but limiting their numbers and requiring that they be treated decently.
At present AI engineering has advanced to the point where it’s possible to design androids that are quite happy being servants for an individual, family or organization, so long as they’re being treated in a way that fits their programming. So, for example, a mining company might rely on android miners who have a natural fascination with their work, are highly loyal to their tribe (i.e. the company), are content to work for modest pay, and have no interest in being promoted. Androids of this sort are more common than humans on many colonies, which tends to result in a society where all humans are part of a wealthy upper class.
Companion Androids
One phenomenon that deserves special mention is the ubiquity of androids that are designed to serve as personal romantic companions for humans. A good synthetic body can
easily be realistic enough to fool human senses, and for the true purist it’s possible to create organic bodies that are controlled by an android AI core instead of a human brain.
Contrary to what modern-day romantics might expect, designing an AI that can genuinely fall in love with its owner has not proved any harder than implementing other human emotions. Androids can also be designed with instincts, interests and emotional responses that make them very pleasant companions. Over the last two centuries manufacturers have carefully refined a variety of designs to appeal to common human personality types, and of course they can be given virtually any physical appearance.
The result is a society where anyone can buy a playful, affectionate catgirl companion who will love them forever for the price of a new car. Or you could go for a brooding but powerful vampire, or a timid and fearful elf, or anything else one might want. A companion android can be perfectly devoted, or just challenging enough to be interesting, or stern and dominating, all to the exact degree the buyer prefers.
Needless to say, this has had a profound effect on the shape of human society. Some colonies have banned companion androids out of fear of the results. Others see the easy availability of artificial romance as a boon, and encourage the practice. A few groups have even decided that one gender or another is now superfluous, and founded colonies where all humans share the same gender. Marriage rates have declined precipitously in every society that allows companion androids, with various forms of polyamory gradually replacing traditional relationships.
Perilous Waif (Alice Long Book 1) Page 51