Would a knife blade that was one atom thick slice things truly effortlessly?

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Ayla97 · Answer

I once made such a knife; I electrochemically etched the edge of a very thin piece of tungsten and it made a very sharp edge. A colleague of mine was often relaxing by sharpening his pocket knife, and I challenged him to a test. His best knife vs my etched tungsten. We didn’t try it on fruit, but rather on the edge of a thin piece of paper. He conceded; my etched edge was sharper than his best knife.
Of course, only the edge was sharp, and it was supported by a wedge of metal behind it. And that very thin edge didn’t wear well. I took some scanning-electron microscope photos of it, and it appeared to be several atoms thick, not just one. But it was marvelously sharp.
I recall the first time I got a paper cut. I was shocked that gentle, flexible, soft paper could make such a painful cut! (I think I was probably 7 years old.)
Aluminum foil is about 1/10 the thickness of paper—and yet you don’t get aluminum foil cuts. The reason is that as the material gets thinner, even if it is made out of metal (aluminum is much stiffer than paper!), it tends to bend when it enters, and so the force from behind is not conveyed to the sharp edge.
The problem is that the atoms on the end of the knife will stick to the fruit atoms almost as strongly as they stick to the knife atoms. At best, they will deflect; at worst, they will break off. It will be impossible to convey a force to them from the one-dimensional support of the knife atoms behind them.

Amara129 · Answer

In short - and with the exception of purely microscopic material manipulations in nanoscale dimensions: No!  Cutting is not a static problem but actually a fairly complex and very dynamic process. I myself had to undergo hours and hours of lectures and exercises in a production technology class to learn how to calculate optimum metal cutting tool geometries and machining parameters - at times it was quite a pain. (A very brief introduction here on Wikipedia:  Speeds and feeds - Wikipedia )  One major and very critical aspect aside from material abrasion on the edge of the tool (or knife) is the necessity for heat dissipation from the cutting edge due to the nature of the cutting (material separation) process always incorporating friction and (much more importantly) due to the fact that a lot of deformation energy is necessary to separate materials and to create new surfaces and a cut.  Any tool with a cutting edge (including those with just a single atomic layer at the tip) will heat up at the tip and sides while performing the work during the cutting process. And the smaller the tools edge and the sharper the angle, the less material is there to support the tip of the cutting edge and the less material to transfer and dissipate the heat away from the tip.  This is why a cutting edge no matter how sharp it may be at the start will instantly start to be rounded off when put to use and will instantly develop some sort of radius at the tip.  When forcing the cutting edge into the material being cut the tip will instantly be (plastically) deformed by the forces required and it will also instantly begin to wear off from abrasion and it will instantly begin to heat up.  A wedge with a single atomic layer at the front will immediately be subject to this compression, abrasion and increased heat. This will cause the atoms at the very tip to separate. The tip of the tool will simply “melt away” until a dynamic equilibrium is established where the tip is finally rounded off so that heat dissipation away from the tip of the tool is sufficiently possible for the tip not to heat up any further during the continuing cutting process. From then on abrasion additionally keep wearing the tip off and will (slowly) round the edge off further and further.  The dimensions of the radius and the state of the equilibrium rounding off the tip will be determined by all sorts of parameters such as the materials involved the tools geometry and the wedge angles, the cutting parameters such as speed and feed, temperature, use of coolant…(and so on and on and on….).  So any extremely sharp edge, especially one with single atoms at the tip will so to speak just be “destroyed” at the front and the atoms at the tip will immediately be dislocated and removed from the tool very quickly (practically speaking almost instantly) and the tip will round off due to the thermodynamic nature of the cutting process. And the longer the tool is in use, the more it will additionally round off due to abrasion.  A little further information from scientific experts at the famous MIT on that matter here:  Introduction to the Physics of Machining

Jade · Answer

One atom thick would not work. It would bend. It would break. However, one atom thick is not necessary to make something that cuts very well.
In Arthur C Clarke’s The Fountains of Paradise he describes a monofilament diamond tool that was spooled onto a little belt mounted unit. Basically a long narrow single crystal. I assume he had checked out the physics. It was strong enough to support the weight of a man but basically invisible. And very good at cutting stuff. Invisible and very good at cutting stuff equals dangerous. The guy had cut off his own finger with it by accident, waving it into the stretched filament when demoing it.
Carbon nanotubes have a theoretical strength around 300 GPa. Manufacturing imperfections mean about 20% of the theoretical strength has been achieved so far. This is still like 60 times the strength of high tensile materials like nylon or spider web. This is heading for the scifi finger remover.

Parker · Answer

The only metal that is maleable enough to be “smushed” (actual scientific term!) down to one atom thick is gold. Ever seen a 24 karat sheet of gold leaf? You can buy sheets of 24 k gold for use in foods and drinks, as well as for use in some religious rites, and in gilding things such as picture frames. It’s VERY flexible, and it is much more than 1 atom thick! I don’t know of any other natural metals or elements that can be formed into 1-atom-thick sheets that would be uniform in thickness. Diamonds have a lattice structure that one would think would lend itself to that dimension, but it really would not. It has to be at least 2 layers of atoms thick to actually be part of a diamond’s lattice structure.
If you want something that slices food stuffs (and possibly everything else) really well, a one-atom-thick knife of any material wouldn’t be very useful. Food, when sliced, would stick to it, and be very difficult to pry loose because a “perfectly flat surface” cuts a perfectly flat surface, and requires channels of air from the inner touching surfaces (the knife and whatever it is cutting) to the outside edge or those surfaces to break the tension and allow the sliced food to come away from the “knife” with ease. Some cooking knives are intentionally manufactured with “dimples” along the blade for just that purpose.

Genesis · Answer

Your question challenges a lot of ideas.
First of all it’s not possibly to build a knife of that width sturdy enough to remain intact under normal conditions. There is absolutely no way the metallic bond between a group of atoms from end to end could withstand the friction of our atmosphere.
So let’s overlook this problem and assume the you are able to build a knife one atom wide sturdy enough to maintain its shape.
The second problem is with the concept of how you cut things. By things I mean real world objects, like you said, fruits and vegetables.
The equation for pressure is, P = F/A.
Which means if the area is really small, the force will be really big. We can use a simple example to explain this. If you take a small pin and squeeze in the pointy end on a foam board, it’ll effortlessly go in. But if you were to try and press the wider end against the foam board trying to push the pointy end with the finger, it’ll pierce your finger.
The cone shape of the pin, allows it to do what it’s meant to do, apply a massive pressure at a tiny point, move the few atoms around the contact point of the board and slowly go through the board.
It’s pretty much the same with knives. So in general the thinner the sharp end of the knife is, the less force you will need to apply with the handle to cut something.
But knives, especially ones used to cut harder things, like rope or people, need sharpening often. Can you guess why?
Yes. Because the sharper the sharp end is, the more susceptible it is take damage and flatten out.
So now we have two opposite phenomena working against one another.
The thinner the knife is, the less for you need to cut things with it.
But at the same time the thinner it is the weaker and more vulnerable to damage it gets.
So, your blade, even though is the sharpest thing possible, is completely impractical for use. If you can however create a knife with its sharp end slowly sharpening down from thick steel to the width of about a molecule, what you get is a very regular replica of your average vegetable knife.
Now, yet another idea is about friction. You know diamond cuts glass right? It’s because diamond is like one big molecule, and its pointy end can be extremely thin. It’s pretty much the thinnest it gets before becoming too fragile to put to use. Diamond can work like that because it’s one big molecule its not vulnerable to damage either.
Why does diamond cut glass but not people? Because with the oil and irregular pattern molecules on our skin, it barely has any scope for friction. And without friction it’s hard to cut.
So how well will your regular knife perform? It’s hard to say. The physics of the very small does not follow conventional rules. Neither do nanoparticles. If I were to take a guess, I would say it would be very sharp but it can never be like a lazer sword. Put a group of theoretical physicists in a room with some doughnuts arguing over this, I’m sure you’ll get to hear some pretty bizarre ideas but sadly this is as far as my patience with thoughts takes me over one question on quora.

Eden · Answer

Of course not - if you don’t apply force, how would the knife move? The amount of force might be infinitesimal, but it would have to be > zero.

Reagan · Answer

Let’s assume that the blade is infinitely sharp, infinitely strong, and frictionless. Guess what, it still won’t cut through anything solid without effort!
As Robert Stewart pointed out, breaking the chemical bonds requires some energy. For liquids it can be calculated from the surface tension and the increase of liquid surface caused by the cut. I think for solids, surface tension is hardly given, but the logic is the same.
The total energy needed to cut something must be roughly the same as the energy needed to shatter it into two halves. For a hard material it’s not negligible. An effortlessly cutting blade would violate the conservation of energy!

Adalyn · Answer

I find this interesting, yet pointless. Why not keep questions of knives and sharpening to a more practical level? We’re questioning atomic blades. What’s next? Subatomic? This stuff simply doesn’t exist in the pocket or sheaf of any common man. So, I find it pointless.

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Amara · Answer

The most important thing to consider here is not the width of the blade but the quantifiable and fixed minimum amount of energy needed to disrupt the bonds between two molecules within a lattice multiplied by the number of molecule pairs that sit across the cross sectional plain. This minimum effort (i.e work) can be expressed in joules, ergs, foot-bounds, heat, etc. But, regardless of the unit, it is the minimum needed to do the job (all else constant of course) and it is not zero.
Now, I have a different question. Will a blade one atom thick cut through or pass through the lattice? If the lattice is loose enough would pulling a 1 atom thick blade through it have the same result as cutting water?

Bella · Answer

It's very sharp. If you applied pressure or a slicing movement you'd cut yourself.  There's nothing particularly special about a blade of this sharpness, except that it cuts better and wears out quicker. The old science-fiction rubric of monomolecular blades notwithstanding, an edge that sharp isn't going to slice through steel like butter or lop off your fingers at the slightest touch. It's just a very sharp knife which cuts precisely the same way as other sharp knives.

Alexandra98 · Answer

A wedge that tapers to a single atomic line can be easily made by breaking monocrystalline materials, for example by cleaving silicon wafers. Such wedges would be indeed sharp, but not much sharper than a high-quality shaving blade, which is typically sharpened to about 100 nm.
Now, if we are talking about a wire or plane with single-atom thickness, there are obvious issues with practicality and durability that others have pointed out: as you try to force this blade through a material, the resistance of the atomic bonds in the material would likely generate a force that exceeds the deformation or breaking limit of the blade. And any chemical interaction could further rupture the blade’s atoms.
However, I would argue that if such a blade was made of a reasonably hard and inert material, it can be in fact used for cutting through macroscopic layers of materials with almost no force applied. But you would have to cut extremely slowly to ensure that the resistance forces do not exceed the limits of your blade. You would be breaking a single atomic bond in the material at a time, so to speak. You might have to go at a rate of 1 micron per hour, for example. So yes, you would be able to cut with almost no force applied, but you would need a lot of patience. It would not be a samurai sword action.

Rose · Answer

Width of one atom... Length would mean you're trying to cut fruit with the handle. Anyway, you would still have to apply some force- just not much- and the factor slowing you down would for the most part be friction between the blade and the object. Remember, there are such things as monofilament shoe laces and we don't see kids lopping their fingers off with them.

Aaliyah · Answer

I know nothing about the science involved, but for the SF/Gamer crowds, here are some entertaining entries on the topic of  Monofilament Blades  .  Larry Niven   uses  monomolecular wire  to devastating effects in his  Known Space   stories (the    Ringworld  saga are among my favorites).

Jade · Answer

You still have to break the covalent and ionic bonds that make up the vegetable or fruit. Or the stronger molecular bonds, if you are slicing atoms from one another. So there is still force involved in causing this change of state for the solid materials you are cutting through.

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Sophia · Answer

This answer is somewhat off topic, for which I apologise, but there are many excellent on topic answers in this thread already!
The author Philip Pullman considered this in his book “The Subtle Knife” – the second volume of the Dark Materials trilogy. The knife in question has a blade so fine that it can cut at a quantum level, and if used correctly can cut an opening between parallel universes.

Piper · Answer

“An obsidian blade is the sharpest in existence, with a cutting edge of one molecule. The American Medical Association has reported that that is five hundred times sharper than the best steel scalpel. Obsidian scalpels are being used in surgery today.”
Not sure if the one atom claim is correct, but they are extremely sharp.
BACK TO THE STONE AGE
How obsidian Stone-Age knives still cut it in surgery
Diamond knife
Obsidian

Elliana97 · Answer

Consider there is a blade having thickness as much as one atom and we hypothetically consider that we can hold it in straight line while applying force(it doesn’t bend)(it’s not possible as stated by Richard Muller ).
But still we assume we have such a knife and we have means to apply such pressure without bending the knife.
Then what I think happens is that since the knife is one atom thick, as you bring it to surface to cut through and you try to pierce, it’ll not cut through the material but it’ll bond with the material, because consider a atom coming in between two atoms(of material).
What do you think happens?
I think what happens it that there will not be a considerable decrease in interatomic forces between two atoms of material due to the inclusion of a third atom in between them because it’s not much distance, besides there also can be attraction between atoms of material and atom of knife, in which case it’ll hold the knife between cut.
So to conclude I think knife will be a part of the material if it’s of single atom thickness and will not cut through but pass through.
Please correct me if my theory is wrong, because this is just what I think as I can’t have any conclusive proof of what I say.

Mackenzie · Answer

Two things that I didn’t see mentioned here:
Hacksaw blades.
Monolayer graphene.
If you’ve ever compared the sawing efficacy of a hacksaw blade unmounted and mounted, you’ll have noticed that in the unmounted case the blade is too flimsy to cut, while in the mounted case with the blade under great tension it cuts very well.
So take a hacksaw blade made of monolayer graphene, under tension somewhat below its breaking point. This material has two terrific properties: tremendous strength, and a dense crystalline structure that even hydrogen atoms can’t pass through, let alone steel, etc.
As it passes through what it is cutting into two halves, those halves won’t be able to rejoin until the whole blade has passed through because of the second property. By then you’ll be able to pull the halves far enough apart to prevent any rejoining.
As to wear, the carbon bonds are so much stronger than the bonds of the material being cut that they should experience no wear at all.
Of course this needs to be quality monolayer graphene. But if someone makes a hacksaw blade out of it, and it doesn’t behave as I’ve described above, then I’d like to take a very close look at it to make sure the experiment has been done right

Beatrix · Answer

The physical chemists here have answered your question quite well. So permit me to offer a logical extension of your question.
Makers of razor blades keep offering ever-sharper blades, and more of them. We may now be up to five or six packs, with no end in sight.
SO… do we have a limiting case here? What is an infinite number of infinitesimally sharp blades – just a block of steel?!

Myna · Answer

It it is 'one atom thick' it is not obsidian. And it will collapse immediately from even the slightest shear stress.

Ama12a · Answer

You can think of a beam of fast atoms sent one by one. Energetic atoms (ions) would stop at certain depth in your fruit and deposit there most of their energy. This will be rather sharp drill than knife. But good physicist should be able to cut with drill and drill with knife 🙂

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Josie · Answer

Yes, it would cut through everything, even flesh! However I don’t recommend making one. It can be dangerous

Charlie · Answer

Cutting or shearing depends on pressure. Pressure is inversely proportional to the area of contact, so if the area of contact would be so small, cutting a diamond would be easier than slicing through butter.
But in today’s technology, its not possible to make a stable knife, that can be seen, of that width. But, maybe sometime its possible.

Ava · Answer

Truely an opaque question,dependant upon what the blade was made of and what you are cutting as well as the seraded edge of the knife and its sharpness-with a blade 1/1000 of an inch thick this would be the most impractable as well as serading of the blade.
Diamond used to be the hardest substacne known to man-maybe naturally but now scintists have developed a process of carbine and carbide compressed to which mimick crystal structure of a idiamond but are actually 100x or more harder.
These bits are very expensive and are usually alloyed with other metals to add durability an dthe prevention of unwanrted chipping from friction and heat -natural physical degradation from use and not from storage.

Ama12a · Answer

The best it could do would be to make a 1-molecule deep scratch on the surface, then the blade would start to push the material apart – that would take more effort than cutting the next 1-molecule thick layer.
While the cutting takes effort (molecules have to be separated from each other), most of the effort is pushing the material out of the way so the cutting can continue.
If the entire knife blade were one-atom thick, the slightest air current would cause it to tear and crumple becoming useless.

Eden97 · Answer

An Aluminum foil is around 200000 atoms thick. Look how easy it its to rip it apart.
One atom thickness or even 100 atom thickness will be too weak. It won’t have the structure to cut through anything solid with a crystal/metallic lattice.

Xime97 · Answer

There are definitely some more interesting answers here but here’s my take: The thinner the knife, the sharper the knife. The thicker the knife, the more durable it will be. And extremely thin blades are extremely weak, even though they’re extremely effective while they last. Think of a box cutter, for example: you need to replace the blade all the time because it’s so thin that sometimes it’ll even chip! You wouldn’t ever want to use a box cutter to carve a wooden statue, because you might end up with metal shrapnel in your eye when the blade breaks.
And likewise, if you’ve ever owned a hunting knife or a sword and tried to open a box with it, you’ll probably find it’s not too effective. Even though a box cutter would fail miserably at the kinds of things your hunting knife can do, it still tears through cardboard like nothing else!
So while a super thin “blade” like that would be super sharp, it would be limited severely by it’s durability. When considering how the thickness of a blade impacts the performance of a knife, it would be a incorrect to say that a thinner blade will always cut things more easily than a thicker blade – there’s a reason why so many knives exist and it’s because they all serve particular functions.

Peyton · Answer

I’ve heard and cannot substantiate this: Some chipped obsidian blades can have an edge that is only one atom thick. They are said to be very sharp.

Iris · Answer

Not only does my one atom knife slice thru things effortlessly, but I can cut your head off and you will never know it. It will not disturb a single molecule in your neck.

Lana · Answer

It would be plausible for a knife to cut effortlessly if the knife had no resistance coming from the side.

Eva · Answer

no. You say “effortlessly”, but this defies physics, as every action has an equal and opposite reaction. You would need to expend energy to force the blade through whatever you’re slicing, therefore it can never be ‘effortless’.

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Elliana · Answer

I'm having difficulty visualizing this “blade”, if it was even possible to be created, and how, exactly?  The answer to your question must be yes, surely it should be absurdly sharp, far surpassing merely dangerous? However, what strength would the body (& cutting edge) possess? Would such a body posses sufficient rigidity to faithfully continue directing it's edge) straight ahead, severing that which is intended? I've no experience with such attractive or binding forces, so am unable to predict the physical responsiveness of a blade one atom thick? What other conceivable force(s) would be present to maintain the body of the blade at a thickness of one atom? Would it In fact even be visible? This is intriguing!

Daisy · Answer

I found a flint “hide scaper” at Chico Texas knapping site. It had a curious half circular open “hole” near the top on the back edge and at the time I thought it was a mistake in flaking. When I got home and started seeing how good it was, I realized there was a small pointed hook at the edge of the hole. It sliced cowhide better than ANY of my leather working tools that I’ve ever had. I used it for years and never did it get dull.

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Athena · Answer

I'm guessing nothing. You are a few orders of magnitude away from any damage. For example many,many solar neutrinos are passing through your body right now. While atoms are way bigger, no damage would likely be done.

Charlie · Answer

If you could somehow make a blade that thin and yet make it as strong/tough as a conventional knife blade, it’d cut Scary easily. Not effortlessly, but SCARY easily. Case in point:
You have two identical knives of conventional design. One is sharpened to the Nth degree, and the other is dull… You’re trying to slice up a cheap, tough piece of meat. Which blade cuts easier? The sharp one, of course, because the sharper the edge, the THINNER the blade is at the point of contact! Now, I’m not a scientist, but I’m pretty sure that the sharpest knives available, probably have blades a dang-sight thicker at the edge than a single atom… There you have it, except for the fact that no such blade exists… Yet!(Something for you to work on.) 😉

Would a knife blade that was one atom thick slice things truly effortlessly?

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