As opposed to stasis fields, which obviously don’t exist (more’s the pity). For those unfamiliar, a variable blade in the works of Larry Niven is basically your standard, garden-variety monomolecular razor-wire held inside a stasis field to make it stiff like an invisible blade. But is some sort of magic, time-stopping forcefield really necessary? Couldn’t you make such a blade-like weapon out of a thin spool of razor wire simply by employing a powerful magnetic field? Or would this be impractical in a handheld weapon?

This is basically an exercise in developing a concealed blade/cutting tool with absurd cutting power for a near-future sci-fi setting. I was contemplating using this same method only employing flux-pinning to keep the wire rigid, but I realized that’d require room temperature superconductors to work and I’d rather avoid that if possible.

  • 2
    $\begingroup$ So you are basically asking for a hack to turn an ink jet printer stream into a knife blade, right? $\endgroup$
    – steverino
    Oct 30, 2017 at 3:43

2 Answers 2


Try an electret:

This is a substance with a surplus or shortage of electrons. It's a non-conductor so the charge has no real way of dissipating, but is trapped in the material.

These are real: You can make one yourself if you have access to a very high voltage DC generator. A Van de Graff generator or Whimhurst machine works well.

  • Take a largish surface of smooth non-conducting material.
  • Tape a square of aluminum foil to the surface, and run anc electrical lead out.
  • Spray with a non-stick agent (Pam, fiberglass mold release wax, diesel fuel...)
  • Prepare an aluminum pie pan by attaching a lead to it and spraying the bottom with release agent.
  • Melt a bunch of polystyrene plastic until moderately runny.
  • Attach the lead from the pie-plate and the lead from the foil to the output terminals of the high voltage generator.

The next steps need to happen as fast as possible:

  • Pour the molten plastic on the aluminum foil.
  • Push the pie pan down firmly squishing out the plastic. Put a lead brick or small steel ingot on it to keep the pressure.
  • Turn on the generator.

Relax. Have a beer. You didn't short 50 kV to ground.

  • wait for the plastic to cool.
  • peel off the pie plate.
  • peal the plastic off the surface. Remove the foil if it came too.

You now have an electret. This is the electrical equivalent of a magnet, with a permanent + charge on one face and a - charge on the opposite. You can test it by all the cute things you did with temporary static things. Separate pepper from salt. Play with pith balls.

Ok Get to the point. Where's my variable sword.

Extend this idea: You have seen how the big insulators on power lines have nested glass cones. Do this, writ small:

At the core is a strand of your equivalent of Sinclair Monofilament, or shadow square wire. Very high tensile strength. Suppose this material is 100 nm in diameter.

On it you string 10 micron disks 100 nm in thickness. Each disk is an electret. They are oriented with like faces two disks facing each other. Except that instead of making them with a measly 100 kV van de Graff, you but real charge on them. The charges repel, so each disk tries to keep the wire straight.

Another way would be to do the same thing with disks of room temperature super conductors. Induce a monster current in each one. Adjacent disks have opposing magnetic fields. (Yes, each type of super conductor has a magnetic quench value where it stops being an SC. I don't know the limits of this.)

While it would spring out with ease, eclair and savoir-faire, retracting it into the hilt would require bending it would would take work. Much like a switchblade or stiletto.

Downsides: Electrons leak off of electrets. Room temp super conductors are still magic. I suspect that there would be interesting side effects from having this intensity of magnetic field or electric field in a small space. E.g. Waving the superconductor version near any metal object would set up eddy currents in the object that would slow the swing. I bet the current computer chips would be seriously unhappy about someone waving this around them.

  • $\begingroup$ You are limited in what charge you can put on the electret as to mush charge and it arcs to the ground. $\endgroup$ Oct 30, 2017 at 14:25
  • $\begingroup$ It's not clear to me what that limit is. Electrets that are oriented dipoles hold their charge indefinitely. Materials that have a surplus of charge gradually leak away in times spans depending on the charge and resistivity of the material. $\endgroup$ Oct 31, 2017 at 13:15

first you have to have a monofiliment that reacts to some kind of electromagnetic effect. Not too likely as it has next to no mass and is so thin that it will not react to anything except radio waves, which can create a current flow, but transfer no mechanical energy.

I think the need to hold the "blade” rigid is operator safety .. the premise of the cutting effect is that you have a "wire” so thin that it severs atomic bonds .. or perhaps just molecular bonds? I don’t recall if Niven said anything about the physical effect of the vario sword .. so the cutting action will not deform the blade and the operator will not feel any resistance. But the operator needs to know that the blade extends out from its handle so he does not slice himeself, or anything else that he wants to keep safe.

To hold it rigid one could use tension from the far end and for the end to be held in its place relative to the handle. I do not see how you do that without something along the length of the blade .. certainly there is no force that can be built into a handle that with push on something a meter or so away hard enough to keep it in place.

OR perhaps a sideways force along the length of the wire .. but i cannot see how you could do that .. i suspect the force applied using electrets would be insufficent and arranging a bunch of them along the length of the wire would rather ruin the desired cutting effect. I cannot think of any configuration of magnets that would do the job, not at the distances needed.

SO .. unless one could make a rigid monofiliment that would stay straight I do not need it happening ..

And there is the need to attach a handle to a wire that is so thin that it does not interact with anything that it touches because it is so thin that it cuts right through .. so how were you going to make that handle anyway?

I don’t see this on happening without the stasis field.


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