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Recently, there have been some great questions pertaining to monomolecular blades and filaments, so I wanted to ask two very essential questions. If we can't definitively answer these, we can never make such a tool.

  1. Could you see it with the naked eye, assuming 1 molecule by 1 meter by 2 cm, made of a typically visible solid element or compound?

  2. What could you make it from, assuming our current non-theoretical knowledge of elements and alloys, in order to last the longest?

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This question asks for hard science. All answers to this question should be backed up by equations, empirical evidence, scientific papers, other citations, etc. Answers that do not satisfy this requirement might be removed. See the tag description for more information.

  • $\begingroup$ Great question. Yet it might not be necessary to see the actual blade, as long as something (handle) alerts to its presence. Compare existing lasers in the infrared. The opponents inability to guess its extent, might be used! $\endgroup$ – Ludi Sep 2 '16 at 17:21
  • $\begingroup$ However, if you are interested in visibility, you may easily design something visible to give it away, like a light beam. For the beam to be visible, just use some vapour. $\endgroup$ – Ludi Sep 2 '16 at 17:27
  • $\begingroup$ The visibility depends on the material I think. Some materials would be opaque in a single layer and would be visible unless you viewed the blade perfectly edge-on. Others could be transparent but not necessarily fully invisible. In regard to the material... I would investigate carbon nanotubes (may need to be woven together somehow) or maybe graphene. I suspect that neither of these are quite strong enough to function as a single molecule blade, but you could probably use a very small number of molecules of these to make a very thin and durable weapon. $\endgroup$ – trevorKirkby Sep 3 '16 at 3:25
  • $\begingroup$ @someone-or-other Feel free to add an answer, then! $\endgroup$ – Caleb Woodman Sep 3 '16 at 3:59
  • $\begingroup$ in two words: um-possible ;-) $\endgroup$ – Karl Sep 23 '16 at 20:30
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You probably could actually see it. Obviously we can't see something that's 1 molecule wide on edge, but we have stereoscopic eyes, so the blade should be visible to at least one eye unless its held perfectly horizontal. The more interesting question is whether you can see it from the side. That question really depends on the composition of your blade, which is not included in the question, but we do have some prior art. A common mirror coating used in astronomy is an evaporated layer of aluminum, deposited in a vacuum. Prior art suggests that a thickness of 812nm is a reasonable number to make a mirror that is highly reflective in the visible spectrum. In metallic bonding aluminum has an atomic radius of 0.145nm, suggesting that 5600 atoms thick is sufficient to not only be visible, but to be as reflective as a mirror!

As far as materials, there is no hard-science answer. The structural integrity of a monomolecular blade is the subject of science fiction. As such, the best material to make the blade from to last the longest is not going to be based on the strength of the atomic bonds. Instead, it will be dominated by the question of which material interacts best with the science function stabilization devices.

The same caveat applies to the visibility. If you stabilized a blade that was actually one atom thick, my visibility estimates based on 5600 aluminum atoms thick are dominated by whatever visibility effects that science fiction stabilizer might do.

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This question asks for hard science. All answers to this question should be backed up by equations, empirical evidence, scientific papers, other citations, etc. Answers that do not satisfy this requirement might be removed. See the tag description for more information.

  • $\begingroup$ You do mean "science fiction stabilization device", not "..function ..", right? ;-) Also: Yes, it is not possible without science fiction, or a rigid 3D frame around it. Which makes a "blade" kind of useless, i'm afraid. $\endgroup$ – Karl Sep 23 '16 at 13:00
  • $\begingroup$ What about bending the surface? If the material has good tenile strength, this would make it stand as a blade, not flop as a ribbon. $\endgroup$ – Daerdemandt Sep 23 '16 at 13:25
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Cort Ammon mentions the thickness of metal needed to act as a mirror, which seems to be the right value for the penetration depth of the electric field of visible light frequencies.

But graphene is completely different. A single atom-thin layer will block πα ≈ 2.3% of light.

Now a blade, to be useful, will not be some ordinary molecule. We expect it will have extaordinary properties and graphine is a good example of what we might expect. It might be unusually opaque, reflective, or invisible compared to what you expect of normal material that thin; and the details can vary with the frequency of light, producing complex color effects.

Note that unusually opaque is still only 2.3%, and unusually reflective would be the same order of magnitude. Most light that passes by simply does not interact with the electrons at all.

Now is the blade thin in one dimension or two? If it’s a nano-wire, say a superconductive carbon nanotube given rigidity via magnetic fields, light will simply refract around the wire that’s smaller than a wavelength of light.

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An extended, regular 2D structure is necessarily unstable (Landau-Peierls instability and friends) and will always make an irregular wave pattern, and then if there is no external 3D frame structure that forces it, crumble into a ball.

So, question two : Not possible. At temperatures ever closer to absolute zero, the allowed size of the blade will rise, but that is rather impractical. ;-)

Question one: It will definitely be quite translucent, and have a different colour than the bulk material, because the 2D structure has a quite different electronic structure.

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This question asks for hard science. All answers to this question should be backed up by equations, empirical evidence, scientific papers, other citations, etc. Answers that do not satisfy this requirement might be removed. See the tag description for more information.

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