Plausible Technologies from Science Fiction

A commonly seen element of science fiction stories, force fields are invisible walls of force that protect the user from harm.

Their real life cousins, actual force fields, are calculating tools to help determine the force that one object will apply to another under certain conditions. Although this may seem less exciting, a strong field may be useful under many self-defense scenarios. Here we will discuss three types of force fields – gravitational, electric, and magnetic fields.

The gravitational force is the least applicable to self-defense. The reason for this is because a gravitational field affects anything that has mass, whereas electric and magnetic fields only affect things that are magnetized or have charge. This may be more useful – for example, if you need to stop a bullet of neutral charge and no magnetic poles, this couldn't be done simply using electric or magnetic fields. The problem is that it's impossible to select what would be affected by the field – everything with mass, including you, would feel the force.

Furthermore, gravity is a strictly attractive force, meaning to stop a bullet coming at you, the source of the field would need to be behind the bullet. Also, to attract the bullet to any appreciable degree, the source of the field would have to be incredibly massive (more so, in fact, than the planet). Finally, since the gravitational force is proportionate to the masses that are attracted, the force that the field applies to you will be greater than the force applied to the bullet exactly enough (assuming distance is negligible) such that you and the bullet will both accelerate toward the mass at the same rate. So, although you are both accelerating toward the source of the field, the bullet is still getting closer to you.

Another drawback of the gravitational field is that there is no easy way to activate or deactivate it, since mass cannot be simply “removed”.

An electric or magnetic field could be much more practical – the problem is that few projectiles used by modern weapons are charged or magnetic.

An electric field comes from charges. For example, an insulated capacitor provides a huge voltage drop across a room, causing an electric field pointing from the north to the south side. A positively charged bullet is fired from the south side to the north, but the immense amount of electric force pushes it back to the south side.

There are many reasons this would be difficult. First of all, an electric field appreciable enough to repel a bullet (depending on the charge of the bullet) would have to come from very large charges, which are naturally unstable. The same force that repels the bullet compels the large charge to neutralize with a negative charge – meaning the capacitor would have to be well-insulated to prevent the charge moving from positive to negative and frying everyone inside the room.

A second problem is that capacitors leak charge when they're not exposed to external voltage, so the user would have to be careful to charge his shield before being fired upon, meaning he either keeps it charged regularly or he knows ahead of time when someone's going to try to kill him.

These problem could be solved using a magnetic field instead of an electric field. Magnetic fields are easy to generate artificially using currents in wires, particularly coiled wires. For example, Holtzman coils are placed above and below a room, hooked up to current sources that can be activated remotely. Therefore, a magnetic field could be activated or deactivated quickly with little difficulty. This means someone attacked in his own home could activate his force field with a remote control hidden on his person.

Furthermore, magnetic fields are relatively harmless for a person to stand inside, so the chances of being burnt to a crisp by your own force field are substantially reduced.

The problem with a magnetic field is that, to an electric charge, it must apply a force orthogonally to both the field and the motion of the charge. In the case of a charge being fired to the north, in a magnetic field pointed downwards, then the force would push the bullet to the west. This means the field would not be able to stop the bullet or push it backwards, but it could deflect the bullet to the side, spin it around and shoot it backwards, or trap in in circular motion until gravity pulls it to the ground.

A magnetic field for self-defense seems very plausible, but there is one problem remaining: most bullets used today are charge-neutral. If you can charge a charge-neutral bullet between the time it's fired and the time it enters the magnetic field, then the field would be able to affect it. The reality is, a flying bullet is charged to some extent just by friction against the gun barrel and against the air, according to Dr. David Newman, professor of Physics at the University of Alaska Fairbanks, but it could be charged much more thoroughly by exposing it to ionizing radiation, such as X-rays or Gamma-rays. These waves have high enough energy to remove an electron from an object, leaving it with a positive charge.

The final result is this: an armed assassin breaks into your living room and aims his pistol at you. You push a button on your watch, activating X-rays firing across the room and Holtzhelm coils above and below. The assassin fires, the bullet passes through the X-ray stream and leaves positively charged. It then enters the magnetic field and turns in a circle, leaving the magnetic field at almost the same speed at which it entered, passes through the X-rays again and finally hits the assassin in the chest, both wounding him and discharging on him. You are almost entirely unharmed, save for some limited and brief exposure to X-rays.