5 ms·

Isn't it more remarkable if something grew in a straight line? A spiral shell is just: progress forward as you grow in diameter, maintaining contact with yours

• jameshart 5y ago
  Right - straight lines require iterated translation without rotation; spirals are just the result of iterated translation + rotation. Generally to make something grow straight you need a feedback mechanism to correct for rotation, or spirals will result. Like driving a car in a straight line requires steering inputs; if you just hit the gas and hold the steering wheel steady, the car will go into a spiral. Similarly spirals show up when phenomena emerge in a vector field (like water running down a plug hole or a tornado) because the one field configuration with radial flow around a point (with curl of zero) tends to be unstable, and without correction, curl tends to arise. In effect, the absence of spirals is exactly the evidence of design and intent that the author was looking for. That the ancient pyramids don’t twist as they grow taller is what tells you they were constructed with intent, rather than by a natural process.
  • jameshart 5y ago
    It occurs to me that while today we have the idiom ‘spiraling out of control’, that probably dates from a post-aviation world.
  • gfjvkbff 5y ago
    Really skeptical about the pyramids comment. It's definitely the regularity of the pyramids that identifies them as human made, BUT, at another scale, that regularity occurs in the forms of crystals: flat surfaces, straight edges, exact angles. https://en.m.wikipedia.org/wiki/Ren%C3%A9_Just_Ha%C3%BCy#/media/File%3ACrystallography_Ha%C3%BCy_integrant_molecules_form_pentagonal_dodecahedron_of_pyrite_1801.jpg https://en.m.wikipedia.org/wiki/Ren%C3%A9_Just_Ha%C3%BCy#/me... The idea that, as a general rule, only humans make things that don't twist doesn't hold water.
    • jameshart 5y ago
      Fair. Crystals are exceptionally good at creating straight lines in spite of how hard it is to do so. And you can mimic it macroscopically with scenarios like piles of uniform spheres, which will form very long straight lines. So yes, not universally true that you need active control to maintain a straight line - some systems passively produce them (another example is folding - when you crease paper the crease wants to continue straight, not curve).
  • CobaltFire 5y ago
    Pedantic point: a vehicle with its wheels locked straight will go straight. It may veer a little depending on the torque distribution, but that’s due to frictional imbalances. The only mechanism I can think of that supports your example of a vehicle “spiraling” is torque steer, which is a unique issue to a certain subset of vehicles and requires an imbalance to generate in the first place.
    • jameshart 5y ago
      I’m not talking about an ideal car on an infinite smooth plane - I mean a real car.
      • CobaltFire 5y ago
        Nor am I. I’m not entirely sure what variety of mechanism you think will cause it to spiral, but I’m not aware of one.
        • jameshart 5y ago
          How straight do you think you can line up the wheels, really? If they’re off by even a fraction of a degree you are not going in a straight line.
          • CobaltFire 5y ago
            True, but you also aren’t spiraling in any meaningful sense of the word as used here. That’s what I’m curious about.