Would a wound from a monomolecular blade instantly heal?

Question

Or, phrased another way, how thick would the blade behind the cutting edge need to be in order to cause significant and lasting damage to a human body?

My question can be considered an expansion of this question, but dealing more with the effects of the wound. I don't question the monowire's ability to cut, only whether the cut would be meaningful.

A true monomolecular blade might be so thin that it could pass through the interstitial spaces between many cells. My guess is that this sort of damage would be repaired almost immediately by natural processes, with any actual gaps caused by cell destruction filled in by replacements. Severed molecular bonds should reattach even more quickly due to Van der Waals interactions. I doubt there would even be enough of a wound for a drop of blood to leak out.

Am I wrong? If not, how thick would the part of the weapon behind the blade need to be to create enough separation between intact body tissues that the wound would be visible and large enough to cause severe bleeding or amputation? And at that point, would there be any difference between an exotic monowire blade and a very sharp conventional sword?

Answer 1

Leaving biology entirely aside, it depends how much resistance the blade faces.

If it faces no resistance at all, which is sometimes how monomolecular weapons are portrayed, then that's because (by whatever means) it's not interacting at all with the body, so how can it do any damage? This is more of a "neutrino blade" than a monomolecular blade, so it's not very realistic, but it illustrates an extreme end of the scale.

So, let's say the blade meets some resistance. This means it's moving stuff around. We're probably assuming that it's sharp enough to "cut through anything" -- the resistance won't bounce it back or snag it -- otherwise it's a rubbish weapon because "weighs nothing" and "bounces off" are the weapon characteristics of a feather. When it cuts, it takes adjacent molecules in the proteins it meets, and makes them not-adjacent any more.

Proteins won't survive that. Yes, in principle, if both sides of a molecule were held exactly in place the chemical bonds would reform, but both sides aren't held in place, (most of) the body is not so rigid at the cellular level.

We can take the loss of a few protein molecules, there's plenty more about. So at this point we need to bring some biology in: how not-adjacent, and will the cells survive it? I'm not entirely sure but I very much suspect that they will not. An ovum of course can be punctured with a needle and survive, but a point entry is not the same as being cloven across an entire plane. Supposing that in just one smallish region of the cell, the two "sides" move relative to one another by just the thickness of the cell wall, then clearly it can't just join back up again once the blade is out of the way. IIRC cell walls are often under tension, so if it doesn't join up that means it completely comes apart.

The further these little bits of cell move, the more resistance the blade faces, but "cuts through anything" means that almost all the work it does is going into separating micro-structures, very little of it is going into moving larger-scale components that can survive being rearranged. That is to say, it could fit into inter-cellular spaces, but it won't do that, because it's so sharp it will cleave through a cell, not push it out of the way. However much oomph the wielder puts into it, that work is translated directly into micro-damage on a plane through the target's body.

As such, I think to a close approximation we can say the blade kills every cell it touches. Furthermore, anything under tension (muscle fibres, ligaments, tendons, downward-hanging appendages such as arms, blood vessel walls, the diaphragm) is cloven for the period of time it takes the blade to pass. Assuming we're talking a monomolecular blade, not a monomolecular filament, this is a substantial time in molecular terms, the width of the blade (let us say 1cm) divided by the speed it's moving (a few m/s depending on the wielder's choice). So perhaps more than a millisecond. How far do the "sides" move apart in that time under their tension, never mind any work done by the blade in moving them? The structure cannot re-form provided it moves enough to bring it out of range of the molecular forces holding it together. Which is really not very far at all to move in a whole millisecond.

For stuff under compression, and supposing the cut is not perfectly perpendicular to the direction of compression, then there's a shearing force applied by the source of compression (basically, the weight of the target) during the time the blade passes. Similar result to a lesser extent: things slide down slopes, and they don't have to slide far to get everything out of alignment.

This blade with width would also need low friction on the sides of course, otherwise there's a lot of resistance slowing it down without cutting anything, and you end up with it embarrassingly stuck. Worst case scenario, you have to twist it and pull it back out the way it went in, like some kind of medieval peasant!

So, a blade with width can be as thin as you like, the body's internal forces will do the job of ripping everything apart. A filament perhaps needs a bit more thickness: enough to move everything out of van der Waal's range would be plenty because that means every structure it meets is definitely disrupted. Of course you can kill with a less thorough job than that, and the thickness of the filament is just a lower bound on the distance it separates the things it passes through: actually it'll move molecules further than that within a random range according to the kinetics of the collision.

Finally, "monomolecular" covers a range. In some sense a flawless diamond is a monomolecular bludgeon. It's plenty monomolecular, it just isn't sharp. Your monomolecular blade isn't necessarily the thickness of, say a molecule of polythene consisting of a carbon chain with hydrogen hanging off it. It might of comparable thickness to the cutting edge of an extremely sharp metal blade, and still "act sharper" if it's stronger and harder than steel, and if the whole blade is that thin, not just the cutting edge. This is more than big enough to totally separate any cells or other biological structures it encounters, beyond any hope of them chemically re-bonding even at van der Waals range, at any speed.

So a monomolecular blade is extremely destructive, but the work to do that destruction does still have to be put in by the wielder because it manifests as resistance to the blade's motion through the target. It might not be quite the simple matter of slicing someone's torso in half with a flick of the wrist, that we sometimes see in fiction. Depending on the characteristics of the blade you may still have to put your back, or at least your arm, into the swing. Absolute minimum, put in enough energy to overcome the chemical bonding energy of the damage you do, otherwise the blade comes to a halt in the target.

Answer 2

Severed molecular bonds should reattach even more quickly due to Van der Waals interactions. I doubt there would even be enough of a wound for a drop of blood to leak out. Am I wrong?

I think you may be partly wrong. Your scenario holds if there is no transversal force in the area being cut, for very slow cuts and specific parts of the body.

In general, I fear it wouldn't work.

Where I live, we sometimes cut either butter using a very thin metal wire, or we cut polenta using a string. In both cases, if the substance is soft enough^*, and the wire goes slow enough, you'll see that the "wound" closes immediately after the wire has gone by.

At that point, what you do (for butter, e.g.) is to exert a torsion on the butter bar, so that the cut opens wider the farther the wire goes through.

In the human body, most cells are subjected to a smaller or greater pressure, so that cutting e.g. through a vein or, even more, an artery would result in the wound opening. Same goes for the bones.

Some kind of wounds could perhaps self-heal where the force is only compressive, re-binding the tissues together, but I feel this to be unlikely, because cells are held together by specialized structures and cutting through at random will not allow those to un-bind and re-bind quickly enough.

(*) there are small religious wars on the proper softness of polenta

Answer 3

There's a reason that monomolecular blades are the stuff of science fiction: we know of no way to forge a molecule strong enough to function as a blade. The strongest molecules we could make, or even imagine how to make, would bend or break upon impact with a macroscopic body. In Ringworld, by Larry Niven, the monomelucular blades are surrounded by a stasis field to give them the strength they need. I'm assuming you mean something like this.

Such a blade would be lethal, for several reasons.

1. If you have a tissue under tension, even the tiniest cut will cause the tissue to separate. If you cut through any muscles under tension, they would separate and not reform. The blood vessels in the muscles would not reconnect and internal bleeding would be a serious problem.

2. A human cell is about 10,000 times smaller in diameter than a human torso, and coincidentally also about 10,000 times larger than the width of a molecule (Wikipedia). The tiny molecule would slice right through each of the 100 million cells it would encounter. Even if you posited that the cell walls could recover from such injury (which I highly doubt), about 1/3 of those cells would have their nuclei ruptured.

3. Blood clotting is triggered based on chemicals normally only found inside cells. When a cell is ruptured, its contents spill out and clotting starts. Dumping that much cell detrius into the blood stream would lead to massive clotting.

4. As others have pointed out, severed nerve dendrites do not heal.

Slicing through someone with a monomolecular blade might not leave a visible wound, but it would create a layer of dead cells that would likely prove fatal (or cause a limb to fall off, at least).

Answer 4

For the purposes of this question I'm going to assume the monomolecular blade is about 1-2 water molecules across. Much smaller than that and quantum forces start to dominate and I'm not a quantum physicist, I'm a biologist.

Anyway. Such a blade behaves very strangely, and how much damage it does depends a lot on the kinetics of what you're doing with the target. A leg holding a person up, for instance, will be nearly completely unaffected. It might hurt, but not much and not for long. Cell membranes are, on the microscale, self-healing. They're built of phospholipids that self-assemble into two-sided layers, and if disrupted they reassemble very quickly.

Nerves are essentially long tubes made of cell membrane, and the opening in the membrane created by the blade's passage is not wide enough or long-lasting enough to damage the neuron.

The membranes will therefore mostly be fine, and any damage is small enough to be repaired by the body.

DNA deserves a quick look, but essentially any nucleus that the blade passes through will have its DNA shredded into hundreds or thousands of pieces, and even organisms capable of reassembling double-stranded breaks are bound to get it wrong at least once. Catastrophic DNA damage, and cell death follows. However, the slice of cells this actually happens to is pretty small, and cell death from DNA damage takes a few minutes minimum, so this isn't fatal or even particularly wounding.

Bones are a bit weird, but on that scale ossified cartilage(bone) is more like a sponge than a continuous material. See here for pictures. The space between the pores is filled with cartilage and other goopy things, but if the bone is under compression the spiky bits of sponge will jam into the holes on the other side and hold together enough to heal properly. If the bone was under tension it depends on the forces involved.

Proteins are a different question entirely. Muscles are essentially extremely long proteins overlapping in a staggered configuration, and are nearly always under some amount of tension. The blade would cut these protein assemblages and they'd recoil, leaving a gap between muscle proteins. Laminins and the proteins that give structural strength to skin and connective tissue would also be cut neatly.

In terms of the bigger picture, the two bits of flesh would be structurally very weakly connected for the first . Two perfectly smooth surfaces stuck together with a sticky semifluid adhere fairly tightly, so even though the proteins are cut there's still some strength to the join. In a short period of time(seconds? less? The kinetics are complicated) the protein matrices that give strength to the tissue will recombine. Shortly after that blood clotting factors released by ruptured cells will glue together other damaged pieces of tissue. Note: the cells won't be ruptured by the blade, but more likely by the spring-loaded protein networks inside them suddenly moving.

Recovery of full strength may take days in the case of cartilage but there are few structures in the human body that aren't under constant remodeling.

If the body part is under strong forces at the time of the cut the two halves might peel apart before they can be knit back together, but the strength required is a question of strike speed, temperature, body viscosity, and some other unknowns.

NB: 'strong forces' are experienced by the heart every time it beats, so whether you live or die may be a question of whether your heart was beating when you got slashed with the monofilament or not.

Answer 5

Monomolecular needle is a fact. it is used in Atomic Force Microscopy.

Let's read what scientist who uses it has to say:

"You solve a couple of problems," says NIST physicist Thomas Perkins. "You solve the problem of finding the object you want to study, which is sort of a needle in a haystack problem. You solve the problem of not contaminating your tip. And, you solve the problem of not crashing your tip into what you were looking for. This prevents damaging your tip and, for soft biological targets, not damaging your sample."

Emphasis mine. This means, or at least strongly suggests, that monomolecular blade would rather be destroyed by crashing on a cell, than the other way around.

Answer 6

Let there be an infinitely thin cutting edge, that is, basically a line segment in 3d space. Let this edge consist of an electric field centered on the line and which diminishes rapidly with growing distance from the line, so that at distance r from the line it's essentially 0, with r->0.

Well, atoms are mostly free space, so the edge would mostly pass through free space and do nothing. Sometimes it would pass through an electron and mess up it's impulse (jolt it in another direction, accelerate or decelerate it). Sometimes it would pass through a nucleus and either also apply a force on it, or cause it to disintegrate.

The former would mess stuff up chemically (and no, this wouldn't just "reattach" or whatever you thought of your "bonds"), the latter would produce radiation.

The weapon would glide through the body with very little resistance and would not directly influence biological structures at all.

To approximate the extent of those effects (with the goal of then finding out what this would do to the macro structure) I need to know how often the cutting edge meets electrons and nuclei. Let the human body consist of water (close enough). Water is H_2O so there are three nuclei per molecule and 18 electrons. Water weighs 18g/mol so 1/18 Mmol per cubic meter. Taking the third root squared of this gets us a surface density. Hmmm. But I'm not quite sure if it's the kind of surface density I want.

Anyway, no, the wound likely would never look anything like a cut. It would be a zone of radioactive decay and damaged molecules. The molecules wouldn't be damaged in the sense of "cut in half" (although that may indirectly happen sometimes), but more like a (mostly interior) sunburn.

If you added any kind of blade behind the edge (so far I was only looking at an edge with nothing behind it) then the chemical effect becomes a lot worse because now you aren't just bouncing against electrons, but the electrons also bounce against the side of your blade which is in the way of their paths (they did that before, but it was negligible, I think). This would increase the amount of affected electrons tremendously. Even a tiny blade (not any wider than the edge, but extending a tiny bit backwards behind it, say 1mm) would have that effect. This would mess up a whole layer of atoms at the very least. Probably it still wouldn't cut, but could create poison, make bones brittle at that point and stuff under tension much more likely to break. This goes to much into chemistry/biology for me to say.

And if you add a decent amount of blade behind the edge, say 10cm, then it would start to become exactly like a traditional bladed weapon (just cutting through everything with hardly any resistance) and you get the biological effects some others already described. The other effects would still happen, but if you are already dead I guess they don't matter as much anymore.

I should still do those quantitative calculations I begun in the middle, maybe later.

Answer 7

(First problem: How do you expect your muscles and tendons to stay in place during the passage of the blade? But let's forget about that.)

You can cut a piece of metal in two parts, polish the planes really good, bring them together again, and they will fuse perfectly, at room temperature.

Won't work with tissue and your special knife, because you will cut all kinds of covalent bonds and hydrogen bonds, which will momentarily interact with each other on each side of the blade, and not be the same when the other side comes into view again. It would take some hours for your body to repair all that local damage, in the meantime, you bleed to death.

Same problem with the metal pieces above: If you don't use gold, or go in an inert atmosphere, the metal surface will oxidise momentarily, and it doesn't work.

Answer 8

I don't think so. I'm not sure that the notion of the wound rejoining instantly makes much sense, insofar as the idea seems to rely on the cut being under no significant physical stress, but what part of the body isn't under some stress? There's gravity of course, but also internal pressure and forces. Would blood pressure be enough to force the wound open wherever it intersects a blood vessel? Then you have internal bleeding, even if the rest of the wound closes rapidly. Would the blood pooling internally be enough to hold more of the wound open? Then there are the muscles, many of which are constantly moving without our conscious control. Cutting through any of these or anything connected to them, the force of the muscle contractions may be enough to hold the wound open. Some muscles are going to be contracted even when we're at rest to maintain our posture. Would those simply pull apart under their own tension?

Another thing to consider is that many molecular structures in the body are very complex, and rely on having a very specific form to function properly. Even if these structures rejoin quickly, will they be rejoined in the proper form so that they continue to function? I'd also guess that you'd be left with a thin layer of damaged and dead cells - of course, cells die all the time, but generally not so many at once in such a high concentration. The body may have some trouble dealing with that, especially if there are other traumas resulting from the cut. I think the entire cut would be badly damaged, even if it did hold together.

Answer 9

No, it would pass through cells, not feel around for the boundry and deform the blade on a cell-sized length scale to only pass between them.

Imagine a regular sized cord and a pile of bricks made of jelly. Would the strong cord be deflected by the soft objects? And if so, why would it make the cord reshape to go around the bump rather than pushing the unyeilding cell out of the way, opening up a large tear in the tissue?

Answer 10

Well, the most wide spread scenario in fiction excludes most of those scenarios mentioned here, an erratic path of the monomolecular blade and some force applied, far less than for a super sharp conventional blade but still easily enough to penetrate someone's body. And there is inevitably a lot of motion because it is not some kind of science experiment where sci fi methods are used to ensure the body does not move at all but rather some kind of combat situation/ trap so near instantly the cells are out of alignment and no longer touching. Also, of course the blade has the thickness of one molecule, not one atom and would not simply slide through the empty space between the electrons and nuclei of the atoms making up the person as it is obviously far too big for that and of course does not have remotely enough energy to split molecules apart, just to cut but between individual molecules while encountering far less resistance than super sharp conventional blades due to the sharpness of one molecule instead of the far greater number of the edge of a conventional blade.

As material carbon seems likely (although I do not know how big carbon atoms are compared to e.g. the atoms making up Obsidian) because carbon nanotubes are quite strong and even if some kind of energy would be required to stabilize the blade it ought to be a good deal less than other atoms like e.g. Hydrogen (which is a gas anyway, kinda doubt that would cut anything).

So basically, a monomolecura blade would leave very clean cuts that can heal faster than cuts from any conventional blade and re-attaching a lost limb, especially since this requires a sci fi setting where medical science is likely to be roughly equally advanced as material science would need to be for monomolecuar blades to exist, should be feasible with proper medical attention and happen fairly compared to current medical standards of e.g. re-attaching a lost finger.

However, the damage is done and it cannot heal on its own and would behave largely the same as a wound from a very sharp conventional blade.

PS: while details about the exact kinetic energy involved are of course nonexistent and unknowable since it's all speculative fiction anyway, it does make perfect sense that fairly little effort is required to cut through a person with a monomolecular blade because it encounters far less resistance than a regular blade, for regular blades the resistance encountered and thus the effort required when cutting through a person depends largely on the sharpness of the blade, hence the common joke of cutting someone up with a blunt spoon.

Answer 11

John Brunner used this in one of his back in the 70's or so, a monomolecular wire strung across a road. The vehicles were fine, because glass and metal welds itself back together, but muscles and tendons under strain sprung apart, with fatal consequences for the passengers involved.