Force Fields

The energy fields featured as a plot device on shows such as Star Trek would certainly be of considerable value to the military- the premise appears to involve some form of invisible barrier which performs the function of conventional armour, though more effectively; projectiles and energy weapons either bounce off of or are absorbed by the shield. The same principle considered in the previous 'Light Sabre' post may be used to form an energetic barrier of sorts- simply projecting a series of points where laser light is focused could form a 'wall' of intense heat sufficient to destroy incoming projectiles that attempted to pass through it.

The science fiction force field defences were also effective against energy weapons, and is unclear how this could be achieved, but in any case, attempting to simultaneously project some form of 'blocking' energy around an entire spacecraft simultaneously will inevitably require considerably more power than would generating an energy beam at a single point with power equal to or greater than the 'shield energy' at the same point. Assuming both weapon and shield are both provided by the same power plant, such a spacecraft will not be able to withstand an attack by its own guns (it would be 'unbalanced' in old naval parlance).

Point defence is much more efficient- energy can be focused and targeted rapidly by computer control, in order to intercept incoming projectiles at specific points. The previously referenced developments in 3-d laser projection illustrate the flexibility achievable by such a system.

Light Sabres

The 'light sabre' of the 'Star Wars' franchise is something of an oddity. Essentially a glowing sword blade comprising some incorporeal material that allows the user to cut or burn through opponents.

It has often been pointed out that a laser beam cannot be used to create this effect- a laser shone from the handle cannot be compelled to 'stop' at a fixed distance to create a blade of finite length. It is also frequently suggested that the path traced out by a laser beam doesn't glow in the way usually portrayed. This isn't quite true however- in a vacuum certainly, the path of a laser beam is invisible, but a sufficiently energetic laser will ionise air to create a convincingly visible beam in the atmosphere (http://www.youtube.com/watch?v=t65_JJrLFZ8&NR=1).

Recent advances in computer controlled lasers have demonstrated the ability to project images in 3-dimensional space (http://www.aist.go.jp/aist_e/latest_research/2006/20060210/20060210.html). The technique uses a lense to focus a laser beam onto a chosen point in space, creating a plasma 'flashpoint'. Since the focal point of the laser can be moved rapidly, it is possible to create a large number of such flashpoints almost simultaneously.

An effect comparable to the 'light sabre' could thus be created relatively simply by generating a line of flashpoints by rapidly cycling the focal length of a laser source up and down the intended length of the 'blade'. See figure 1:





Figure 1: Light sabre projection

Creating the nastier destructive effects of the sword is then a matter of increasing the laser's power output. It should be noted that one could not block the 'blade' with another blade- they'd pass straight through each other. Also achieving the required energy and power density in a portable device would be a tall order.

Electric Armour

High tensile strength materials are extremely useful. As well as finding applications in ropes and cables they combine with high compressive strength materials to create composites with impressive mechanical properties. (Reinforced concrete for example, combines the compressive strength of concrete with the tensile strength of steel). In principle the highest achievable tensile strength for a polymer strand would require it to comprise a single, giant macromolecule spanning its entire length, but this is a rather difficult proposition. An alternative might be to compel much shorter polymer chains to connect themselves together electrostatically.

The attractive force between two oppositely charged plates in a parallel plate capacitor is given by F(att) = (EoAV^2)/(2d^2), where 'Eo' is the electric permittivity of free space, 'A' is the area of the plate, 'V' is the potential difference between the plates and 'd' is the separation distance between plates. In principle then, the tensile strength of the two plates (in the sense of the force required to separate them), is limited only by the magnitude of the voltage that can be applied across them.

The force of attraction is also inversely proportional to the square of the distance between plates of course, but capacitors can also be arranged in series, as in figure 1:

Figure 1: Parallel plate capacitors in series

In figure 1, the total attractive force between each set of parallel plates is again given by (EoAV^2)/(2d^2), where 'A' is the area of a plate, but 'd' is the sum of the distances between all the plates in the series. If the voltage 'V' is sufficiently large however, the tensile strength of this 'string' of capacitors is limited only by the strength of the connecting wires.

Returning to the matter of the tensile strength of polymer strands, it is proposed that a 'string' of capacitors be created on the molecular scale. For connecting wires, we may substitute an unsaturated polymer chain constituting a conjugated pi-system, see figure 2 (this is capable of conducting electron density along its length).


Figure 2: Conjugated pi-system- conducting polymer.

The construction of a 'molecular capacitor' is perhaps a little more challenging. A capacitor is fundamentally an arrangement of two opposite charges separated by a dielectric, such that current may not flow between them. In principle then, a conducting molecular chain terminating in a non-conducting moiety could form the building blocks of such a device. In order to make a capacitor, at least two of these moieties must be positioned in close proximity, and unfortunately, molecules cannot generally be placed wherever we see fit.

We might compel long polymer chains to align themselves roughly parallel to one another (this is essentially how liquid crystals behave). We might also be able to persuade them to align end-to-end in the desired manner, by making the individual molecules zwitterionic.

A (relatively) simple example of such a molecule might be as shown in figure 3:

Figure 3: Zwitterionic molecular capacitor component

The innate charges on each end of the polymer (the ethylene functionality in the middle may be repeated to extend the chain) should serve to orientate the molecules end to end, and the addition of a high voltage potential difference along the length of the chain should serve to strengthen these electrostatic interactions to create a material with immense tensile strength, see figure 4:


Figure 4: Molecular capacitor series.

Assuming the molecular chain continues to behave like a capacitor series, the electrostatic interactions between the individual molecules may actually exceed the strength of the bonds within the molecules, given a sufficiently substantial applied voltage- a step towards the 'force-fields' that grace so many of the more dubious works of science fiction. (The latter typically view creating a force field as 'build a wall, then take away all the atoms'...)