Skip to Content
Uncategorized

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.

“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

Keep Reading

Most Popular

Large language models can do jaw-dropping things. But nobody knows exactly why.

And that's a problem. Figuring it out is one of the biggest scientific puzzles of our time and a crucial step towards controlling more powerful future models.

OpenAI teases an amazing new generative video model called Sora

The firm is sharing Sora with a small group of safety testers but the rest of us will have to wait to learn more.

Google’s Gemini is now in everything. Here’s how you can try it out.

Gmail, Docs, and more will now come with Gemini baked in. But Europeans will have to wait before they can download the app.

This baby with a head camera helped teach an AI how kids learn language

A neural network trained on the experiences of a single young child managed to learn one of the core components of language: how to match words to the objects they represent.

Stay connected

Illustration by Rose Wong

Get the latest updates from
MIT Technology Review

Discover special offers, top stories, upcoming events, and more.

Thank you for submitting your email!

Explore more newsletters

It looks like something went wrong.

We’re having trouble saving your preferences. Try refreshing this page and updating them one more time. If you continue to get this message, reach out to us at customer-service@technologyreview.com with a list of newsletters you’d like to receive.