[HN Gopher] The Spiralist: the gyre of James Bell Pettigrew's De...
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       The Spiralist: the gyre of James Bell Pettigrew's Design in Nature
        
       Author : Hooke
       Score  : 18 points
       Date   : 2021-08-13 04:43 UTC (1 days ago)
        
 (HTM) web link (publicdomainreview.org)
 (TXT) w3m dump (publicdomainreview.org)
        
       | Grakel wrote:
       | 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 yourself on one side.
        
         | jameshart wrote:
         | 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.
        
           | CobaltFire wrote:
           | 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 wrote:
             | I'm not talking about an ideal car on an infinite smooth
             | plane - I mean a real car.
        
           | gfjvkbff wrote:
           | 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#/me.
           | ..
           | 
           | The idea that, as a general rule, only humans make things
           | that don't twist doesn't hold water.
        
             | jameshart wrote:
             | 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).
        
           | jameshart wrote:
           | It occurs to me that while today we have the idiom 'spiraling
           | out of control', that probably dates from a post-aviation
           | world.
        
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