Force fields want to be two different kinds of thing at the same time. They want the physical presence, fixed location and barrier qualities of matter but somehow at the same time be energy. The nearest natural example is Earth’s own magnetic field which does not operate as a barrier per se but does effectively deflect the impact of the solar wind. Deflecting/diverting energy around an object makes more sense and interestingly that idea also points towards invisibility devices and cloaking devices.
However, the classic force field acts more as a barrier than a system of energy diversion. Not unlike a physical barrier, for dramatic purposes the more a force field is hit by weapons the weaker it gets. Other qualities of fictional force fields include:
- Transparent but usually partly visible (either glows or glows when touched).
- Requires power to be maintained.
- Selectively permeable. Some energy can pass through (e.g. light) and sometimes physical objects can pass through. Sometimes it lets air through but prevents solid objects and sometimes vice-veras. Personal shields in Dune let slow things through for example, whereas shields on hanger-bays in Star Wars let space ships in but stop the air evacuating.
- Centrally controlled.
- Has a distinct shape and location. Unlike Earth’s magnetic field (which is everywhere on Earth and dissipates gradually) a force field occupies very defined space.
Arguably, any society that is advanced enough to control gravity has a sufficient understanding and control over fundamental forces that maybe anything is possible. I think I can break down the fictional science of force fields into two basic options.
- The force field is built using principles of forces and energy beyond our understanding. Of course that raises all sorts of other questions about how the rest of the future technology is more limited.
- For spherical force fields maybe it is some fundamental force that we aren’t familiar with currently. The force acts at very, very specific distances.
- The force field is more physical than it looks.
For example, maybe the force field is actually a cloud of many tiny objects. Imagine many microscopic drones that are also computer controlled and fly about along specific routes. Quite how, I don’t know, but tiny computer controlled objects give some of the physicality and selectivity of how force fields appear in science fiction.
Come to think of it, tiny energy emitting drones flying around in fixed positions would also help explain how light sabres work. Light sabres themselves have many of the same issues as force fields to the extent that they would appear to be the same technology.
Skipping back to Star Trek, force fields also (sometimes) stop teleportation. I think that makes sense for any kind of teleportation where essentially the transportation occurs by beaming a person as energy from one place to another.
Finally, maybe the terms ‘force’ and ‘field’ are just misdirection — at least for the space ship style deflector shield style. Maybe your spaceship is just covered with tiny emitters that can fire lasers, particle beams and/or tiny bullets at any incoming objects or beams. The appearance of a distinct layer is an illusion. The force field appears that way because that is the optimal distance at which an incoming beam etc can be intercepted after detection.