Thursday, April 21, 2011

Our Shields Are Down!

One of the earliest and most common future technologies that is featured in sci-fi literature is the force field. It is easy to conceive of future weapons that involve beams or bursts of energy, so naturally, the good guys of the future must have a way to defend themselves against such attacks. If physical arrows are blocked by physical shields, it seems reasonable to block energy weapons with a "shield" of energy. But that is as far as reason gets us, because the mechanism to "generate" such a defense has never been satisfactorily explained to general audiences. This entry is dedicated to the near impossible ubiquity of force fields.

A force field must produce a repulsive force. As far as we know today, there are only four types of fundamental forces. Gravity is attractive only, so it is out of the running. The weak and strong nuclear forces both act over such tiny distances (like atoms), that there does not seem to be any conceivable way to harness them on a macro scale. We are left with electromagnetism (EM). In fact, the whole idea of "shielding" was probably born from analogy with EM shielding. It is possible to deflect charged particles with an electric or magnetic field. Is that how they do it?

I doubt that sci-fi authors are envisioning such a mundane mechanism for creating force fields. In most fictional stories, the fields repel any type of matter, not just charged or magnetic stuff. Certainly space ships and people would not be stopped by an EM field. You could not keep a prisoner behind bars with such a field, nor could you stop projectiles like bullets. What about those beams of energy? Could they be stopped? Possibly, but you must still then explain how such a field would be generated. The strongest EM fields require something on both sides of it (cathode/anode, etc.). If you are trying to create a field that surrounds you, as is usually portrayed, then you are left with generating a complete EM field in all directions. Instead of blocking the incoming energy, you would in fact be deflecting it around you. This is how the earth uses its magnetic field to deflect the charged particles of the solar wind. Of course, a field that strong would probably end up bending your space ship out of shape (magnetic) or short circuiting all the controls (electric). There's no way to get around immersing yourself in it, and that's not really the way force fields are portrayed in film and books anyway.

There are current theories that postulate a fifth force which is causing the universe to expand more rapidly than expected. But this can only be felt over galactic sized distances so you can rule that one out too even if it exists. How about plasma? That's what the original Star Trek always attributed such things to. But for a shield, the plasma must still be held in place by an EM field, and then you're back to square one again. What about momentum? You can stop matter if you shoot something at it in the opposing direction, but that is not a static shield. It requires a constant flux of matter or energy in the outward direction. For example, meeting an energy beam with an opposing energy beam would be enough to stop it, so why do our protagonists always need impossible energy shields? All they really need is computerized targeting technology and they are quite nicely protected while using a heck of lot less energy.

One final word on a related topic. If you reverse the direction of the force you get another ubiquitous future technology usually referred to as a tractor beam. Although one could use electromagnetism to reach out and grab a metallic object, it would not be possible to control the object's trajectory as is usually portrayed, and it would be more of a wide field (a net) than a beam. Again, no one actually attempts to explain how such a thing would actually work.

So the next time you encounter a story that features the use of force fields, just remember that although there is some wiggle room to work with, the existence of such a thing is extremely improbable even in the distant future. I have yet to encounter an author that has even attempted to come up with a merely plausible explanation. If anyone out there finds one, please leave a link for me.


  1. Space really is a dangerous place! Thankfully our blue planet is protected by an amazing armor.

  2. if you ask me, electromagnetism is the only way.

    If you look at the earth's field, it's generated by the flow of plasma from the planet's core, going towards the surface, and going back into the core again.

    However, even though shows like star trek feature plasma, which is a common element, designing a technology based on that is certainly out of our reach for the near future.

    But in the meantime, for something far more simple like deflecting bullets, grenades or even rockets, your best bet would be to use a small version of the "star wars misile defense system", which uses high-intensity lasers to change the course of a projectile.

  3. Yes, your conclusions are similar to my own. In fact, I meant to implicate a Reagan-esque missile defense system when I referred to a "targeting system". I think I like your phrase-ology better though so I'll edit it in.

  4. Hmmm... What if one day they create a particle accelerating "magnet" (using nuclear generating heat probably) where the particles between the two sides of this horseshoe magnet move up and down so fast that nothing can pass through them?

    1. Or a simple magnet that changes its poles extremely fast and you have iron filings going up and down so fast that nothing can pass through them?

    2. Most shields in cinema are shown as transparent for obvious reasons (so the audience can see what is going on). Any large particle shield would probably block visibility. But the main problem with particles traveling along the shield surface is they have no way to provide a repulsive force, and that's no matter how fast they are moving. But your idea led me to think - what if instead of a repulsive field, you create a destructive field. A power laser beam could incinerate anything that passed through it, for example. Only problem would be needing to put the generators adjacent to the shield rather than behind it, which would make them easy to take out in a conflict.
      Thanks for the good food for thought!