[nitpick]
Nanotubes aren’t carbon-60. The molecules can have arbitrary numbers of carbon atoms. Also, there isn’t just one molecular structure for nanotubes. There are straight nanotubes and spiral nanotubes, for example.
[/nitpick]
Carbon atoms are not basically a fluid. They have a valence of 4, meaning they can chemically bond with up to 4 other atoms. Maybe you’re thinking of graphite. Graphite is a lubricant because the carbon bonds in sheetlike forms, with the sheets sliding over each other, not because each individual atom remains unbonded.
As for your bullet, imagine a big sandbag. Instead of neutrons being held together by gravity, you have sand grains being held together by a sack. While the sandbag can stop a bullet, you wouldn’t want to build anything permanent out of it. Furthermore, if you take a handful of sand out of the sack the grains don’t stay together anymore. While you can put the handful in a smaller container, gravity doesn’t scale down in the same way.
I was being a smartass. A hypothetical collection of single carbon atoms would indeed be a fluid – basically a bunch of little ball bearings. You’re not likely to get that (although I don’t think there’s any reason why you theoretically couldn’t), so let’s fill up the valences with hydrogens. What do you get? Methane. A fluid. My point was that the reason for the stability of the nanotubes is as arbitrary as the stability of the neutronium. Neutronium is incredibly strong under immense gravitational fields. Carbon is immensly strong when bound to for other carbons in the form of diamond. It is even stronger when arranged in forms like C60 or nanotubes. Neutronium is not stable when there isn’t an immense gravitational field around. Nanotubes also have conditions where they become unstable. I’m not an expert, but I suppose two of those would be extremely high heat, and intense gravity like on a neutron star. These conditions would result in the breakdown of the nanotube, just as neutronium breaks down in the absence of gravity. However, the discussion is on what is stronger, not what their various states are. Ice is relatively strong. Just because steam is an amorphous, thin substance does not rob ice of its strength.
Once again, I am not talking about building bricks out of neutronium and using those to make skyscrapers. I am saying that neutronium in its stable form (i.e., in a neutron star) is inherently strong. No you wouldn’t want to build anything out of it, but it is still strong. Hit a neutron star with a giant hammer made out of nanotubes, and the hammer will break before the neutron star.
-b
I think you’re missing the point here.
Carbon atoms in nanotubes link together through the electromagnet interactions of their valence electrons. Because of these interactions, carbon atoms want to stick to each other. You have to pull them apart with some force to break the valence electron bonds. This is what makes nanotubes a solid (not a liquid), and gives them their high tensile strength.
Neutronium is made up of neutrons jam-packed into a solid mass. With no electrons and no charge to them, there’s no electromagnetic interaction to hold them together. In fact, the neutrons in neutronium very much don’t want to be held together - they’re actually pushing each other apart with a lot of force. It’s only the intense gravity in a neutron star that keeps the neutronium from violently disassociating into normal matter.
Since there’s no attractive force (and in fact, a very high repulsive force) between the component neutrons in the neutronium, it has no tensile or shear strength. If you could somehow make a beam or rod out of neutronium, it would offer no resistance to being pulled or cut into two pieces. Neutronium has no intrinsic strength whatsoever.
True, a bullet fired into a solid sphere of neutronium won’t get very far. That’s because neutronium is vastly more dense than the bullet. If you throw a wooden sphere at the ocean, it won’t penetrate far either, but it doesn’t mean that water is stronger than wood.
Neutronium has phenomenal compressive strength, and is probably the strongest possible material in that regard. However, it has zero shear strenght, and even less tensile strength, which together make it absolutely useless for building anything other than neutron stars.
Carbon nanotubes, meanwhile, have the strongest tensile strength of any known substance, a considerable shear strength (against the grain, at least), and a nonzero compressive strength, making them very attractive as a structural material.
Don’t get to excited about nanotech manufacturing, by the way. Most folks think of it as push a button, get a skyscraper, but it’s much more realistic to think of growing a tree. How long would it take to grow a two thousand foot tree? That’s about how long it would take for a two thousand foot skyscraper or ship.
What do you call gravity if not an attractive force?
[italization mine]
Now you’re adding the word tensile. I will agree that neutronium has little, if any, tensile strength. The problem with this debate is that we’re using different definitions of the word “strength,” which makes it a pretty pointless argument. My whacking-with-the-hammer argument is about the compressive strength of neutronium, which is incredibly high. Insurmountably high, most likely. I’d be willing to wager, however, that the amount of compression force that neutronium can withstand is significantly higher than the amount of tensile, shear, compression, or any other type of force that nanotubes can withstand.
But you sure as hell wouldn’t want to build a bridge out of it.
-b
Great, I suppose that means they’ll start wrapping CD’s in nanotube sheets then. 