Hello,

We noticed you're browsing in private or incognito mode.

To continue reading this article, please exit incognito mode or log in.

Not an Insider? Subscribe now for unlimited access to online articles.

Emerging Technology from the arXiv

A View from Emerging Technology from the arXiv

Pearls and the Puzzle of How They Form Perfect Spheres

Physicists have finally solved the problem of how pearls form almost-perfect spheres: they rotate as they grow.

  • April 18, 2013

“Pearls, the most flawless and highly prized of them, are perhaps the most perfectly spherical macroscopic bodies in the biological world. How are they so round?”

So begin Julyan Cartwright at the University of Granada in Spain and a few pals in a paper that gives an interesting answer to this question. Such a mechanism must not only explain the near spherical perfection but also drop-shaped pearls, which have rotational symmetry but are not spherical, and so-called baroque pearls that have no symmetry.

The answer turns out to be based on a relatively simple effect. Cartwright and co say the surface of a pearl has a ratchet-like texture. This generates a force that tends to turn the pearl as it grows in the presence of random jostling from the environment. “Pearl rotation is a self-organized phenomenon caused and sustained by physical forces from the growth fronts,” they say. “Rotating pearls are a—perhaps unique—example of a natural ratchet.”

In the absence of other forces, this rotational process causes the pearl to become spherical. However, small defects in the shape of the pearl can easily distort the process so that certain rotational symmetries end up being preferred. The result in that case is that the pearl becomes nonspherical but maintains a rotational symmetry to form a drop shap, for example.

Baroque pearls form when the defects in the pearl’s shape prevent the rotation from occurring at all. However the growth continues, leading to a shape that has no rotational symmetry.

That’s a interesting insight which Cartwright and co say could be useful for nanotechnology. “The understanding of the pearl as a natural ratchet should have interest for technological applications,” they say.

Cartwright and co aren’t clear about what they have in mind but that has never stopped readers of the Physics arXiv Blog from suggesting creative uses for new technologies. So if you have any ideas for pearl-inspired ratchets could be used, post them in the comments section, please.

Ref: arxiv.org/abs/1304.3704: Pearls Are Self-Organized Natural Ratchets

Become an MIT Technology Review Insider for in-depth analysis and unparalleled perspective.

Subscribe today

Uh oh–you've read all of your free articles for this month.

Insider Premium
$179.95/yr US PRICE

Want more award-winning journalism? Subscribe to Insider Plus.
  • Insider Plus {! insider.prices.plus !}*

    {! insider.display.menuOptionsLabel !}

    Everything included in Insider Basic, plus the digital magazine, extensive archive, ad-free web experience, and discounts to partner offerings and MIT Technology Review events.

    See details+

    What's Included

    Unlimited 24/7 access to MIT Technology Review’s website

    The Download: our daily newsletter of what's important in technology and innovation

    Bimonthly print magazine (6 issues per year)

    Bimonthly digital/PDF edition

    Access to the magazine PDF archive—thousands of articles going back to 1899 at your fingertips

    Special interest publications

    Discount to MIT Technology Review events

    Special discounts to select partner offerings

    Ad-free web experience

/
You've read all of your free articles this month. This is your last free article this month. You've read of free articles this month. or  for unlimited online access.