During my worldbuilding process I said to myself “no force fields”. Instead, I’m forced to get a little more creative and down to earth with my (ironically) sci-fi concepts. Enter the monomolecular wire, which will be the basis for this analog force field.

The devices are assorted with thousands of monomolecular wires, which are at the press of a button rotated at high speeds forming a protective bubble around the wearer. The mono-wires are attached to both ends of the device. Because they could cut a person feet off if they formed a full circle around the wearer, the device has a ring which is connected to the other end of the mono-wires. Both the top and bottom of the device spin to create a spherical or elliptical field, depending on the relative distance of the handle and ring from each other. Think of it as a jumping rope with one handle and the string attached to a hoop.

The device is usually a wearable one you’d keep on your arm. You hold the handle while the ring is attached to your forearm. The spinning mono-wires would form a shield of sorts. A full body version would have the handle on top of your head and the ring around your legs. The same system can be scaled up to ships and buildings.

The advantages of the device compared to an ordinary shield are: very light and made with next to no materials. It’s basically a handheld motor with a bunch of one atom thick strings. Talk about efficient! The material used for the mono-wires is graphene.

How protective is this device really?

  • $\begingroup$ Wouldn't the air viscosity at the scale you're thinking make the drag overpower the centrifugal force (vastly), turning the wearer into a pile of steaks as soon as it's turned on? A solution might be to create an electrostatic repulsion between the wearer's flesh and the filament.... just a thought. $\endgroup$ Dec 25, 2021 at 1:41
  • $\begingroup$ I'd fire a bullet wrapped with the same monomolecular wire or something else harder into the "shield" to cause the spinning monowires to deform and tangle up, shredding the person within it. $\endgroup$ Dec 25, 2021 at 2:13
  • $\begingroup$ So far all this criticism has proven to be very helpful. It means it won't be so easy to go for a concept like this after all. Back to the drawing board! $\endgroup$ Dec 25, 2021 at 12:00
  • $\begingroup$ Thanks! It’s a great question. I had never looked at monofilament in any detail. Essentially, if I understand it right, the protected person is at the center of a human sized weed eater. It works, actually. Good luck! $\endgroup$ Dec 25, 2021 at 23:10
  • $\begingroup$ Protect against what? Can I Jump Rope Fast Enough To Stop The Rain? $\endgroup$ Dec 26, 2021 at 2:15

3 Answers 3


The equations you are looking for are :

  • Centripedal Force -- ${m v^2}\over{r}$

    Where $m$ is the mass of the line, equal to ($\rho_{line} \pi r_{line}^2 l$), and $r$ is the radius of the rotation, from the center of rotation (which is not necessarily the same thing as the line length, $l$.

    For the sake of an example, let's assume the line is tungsten ($\rho$ = 19,300 ${kg}\over{m^3}$ ), and this is true monoatomic line with a radius (for tungsten) of $193 \times 10^{-12} m$

  • Air Resistance -- ${1\over2}\rho A C_d v^2$,

    where $\rho$ is the density of air (1.225 ${kg} \over {m^3}$ ), $A$ is the area of the line relative to the wind ($d_{line} \times l$), $C_d$ is the drag coefficient of the line (let's assume its designed to have a low drag profile; I see drag coefficients as low as 0.22 for some cars)

For the line to ever be taught, the derivative of Centripedal Force (CF) with respect to velocity ($v$) must be greater than the derivative of Air Resistance (AR) with respect to $v$.

  • ${{\delta CF} \over {\delta v}} = {{2mv} \over r} $
  • ${{\delta AR} \over {\delta v}} = {\rho A C_d v}$

Plugging in the values we know --

  • ${{\delta CF} \over {\delta v}} = {{2 \times 19,300 \times \pi \times (193E^{-12})^2 \times 1 v} \over 1} = 1.44 \times 10^{-15} v$

    (using an arbitrary 1 meter radius and line for this example)

  • ${{\delta AR} \over {\delta v}} = {1.225 \times 193E^{-12} \times 1 \times 0.22 \times v} = 5.2 \times 10^{-11}$

So, no. Not exactly as written.

The monomolecular line doesn't have enough mass to overcome air resistance. However, you might have a weight built-in on the far end to give the line tension and overcome air resistance.

In that case, the next trouble will be the strength of the line. I'm having trouble finding good strengths for tungsten, but see enough references to 500 MPa, to use that.

The equation in charge here is :

  • $F_{yield} = T_{yield} \times A$

    Where $A$ in this case is $\pi (193E^{-12})^2 = 1.17 \times 10^{-19}$ , meaning $F_{yield} = 5.85 \times 10^{-11}$

Compared to the force of air resistance partially calculated above, a tungsten line is barely strong enough to take the load.

You can have a hypothetical material ten times the strength of tungsten (5 GPa). That would allow a velocity of around 3 ${m} \over {s}$


In order to proceed, we need to figure out the counterweight : if the monoline is stable at 1 ${m} \over {s}$

Since we’ve chosen a velocity and radius of 1, the mass of our counterweight in kilograms is conveniently equal to the air resistance $2.6 \times 10^{-11}$ kilograms. Or, about 30 nanograms. Or about the mass of 30 thousand bacteria stacked together. The weight of the line is orders of magnitude lighter than the counterweight. I’m ignoring the line weight for what comes next.

The energy in the line is $E = {{1} \over {2}} m v^2$. Which is equal to $1.3 \times 10^{-10}$ joules.

For low speeds (and 3 meters per second qualifies) you can very roughly estimate cutting power as $E = F_{yield, target} d$, where d is the depth of the cut and $F_{yield, target} = T_{yield, target} \times 2 \times r_{line} \times 1$

Plugging in values for human bone (50 MPa) : 0.0193 joules of energy are required per meter of cut.

This isn’t going to do much injury.

Alternatively, it might not be "true" monomolecular line.

If you want to imagine that "monomolecular" is just sales puffery from whoever is manufacturing these things, we have some more options :

If the line is 193 micrometers ($10^{-6}$) in radius, the max tension our “sci-fi ten times tungsten” line can handle is 585 Newtons.

Air resistance has gone up with the thicker line to $2.54 \times 10^{-5} \times v^2$ Newtons.

The top speed of the whole assembly, then, can be up to 4,800 meters per second.

The flyweight might need to be recalculated, but this post is getting long. At 4,800 meters per second, the faux monofilament line has 0.000299 joules behind it. Each cutting hit with the line will cut away 0.015 meters, or 1.5 centimeters of bone-equivalent material.

Like a weed eater, as long as the line is not broken, it can loop back around again (4,800 times per second) biting away more material. Expressed as a cutting rate (provided a motor could keep up) you could cut about 74 meters per second.


The last category is solidness. This is expressed by the formula ${{rpm} \times {{l_1 + l_2} \over {v}}}$. L1 is the length of the incoming object. L2 is the length of the line (negligible unless the incoming object is also very small). And v is the velocity of the incoming object. What you end up with is a number that, if greater than 1, indicates the number of times the line will strike the incoming object (the integer part). If the number is less than one, the value represents the percentage chance that the line will hit the incoming object at all.

  • $\begingroup$ A shame I can't upvote this more than once. $\endgroup$ Dec 25, 2021 at 13:21
  • $\begingroup$ Yeah great answer +1 "The monomolecular line doesn't have enough mass to overcome air resistance" remarkable conclusion.. a standalone monomolecular wire can't rotate properly. $\endgroup$
    – Goodies
    Dec 26, 2021 at 12:26

If it works, it's appallingly dangerous to the wearer. It won't be visible, so accidents are far too easy.

  • The whole-body version means you lose a hand if you try to raise it above your head.
  • The shield-on-an-arm version eviscerates you if you lower your arm without turning the device off and readily amputates your other arm if it strays near the shield.

Fortunately, it won't work, because of air drag and easy countermeasures.


Not very tough.

Graphene isn't especially tough, and shatters easily. If someone throws a rock at you then it will shatter the monomolecular barrier easily, and hit you.

Also, if someone throws a rock at you, then you now have super fast bits of monomolecular blades slicing at your skin when they break.

Same issue if someone stabs you with a sword or shoots you.

  • $\begingroup$ The question is about a mono-molecular wire, not a 2D surface. A grapheme surface would never be able to withstand the centrifugal force of the rotation, it would be ripped apart. Would a hypothetical mono-molecular wire of carbon be able to do it ? Hand-waiving for now, how to produce that wire ? $\endgroup$
    – Goodies
    Dec 25, 2021 at 3:39
  • $\begingroup$ A wire is less tough than a 2d surface. $\endgroup$
    – Nepene Nep
    Dec 25, 2021 at 12:10
  • $\begingroup$ Depends what you do with it.. anyway James has put the answer. It's not going to work, 1D or 2D whatever.. it won't be able to overcome air resistance ! $\endgroup$
    – Goodies
    Dec 26, 2021 at 12:34

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .