Science / Medicine : In Nature, Differing Patterns Are Formed Purely by Chance

The pattern of stripes is as different from one zebra to the next as the sprinkling of spots is on one leopard compared to its cousin. The same holds true of snowflakes and even the circles and swirls comprising fingerprints.

These differences, it has been surmised for years, are likely due to chance. But for the first time, three physicists at the University of California have shown mathematically that this age-old observation is probably true, at least for patterns on the surface of water.

“We never touched a zebra. We’re talking water here,” David Cannell said.

“But there are many, many kinds of patterns (in nature) that are the result of processes which might be described by very similar kinds of mathematical equations.”

Cannell, along with Guenter Ahlers and Christopher Meyer, described their work in a recent issue of the Physical Review of Letters.

They speculate that it may ultimately take mathematical applications to help crack some of nature’s codes, perhaps answering how chance might figure into any number of phenomena, from snowflake patterns to individuality in the animal kingdom.

For example, no two zebras or tigers are striped exactly alike, even though all zebras and tigers have stripes. Stand a couple of leopards side by side and one certainly will have a spot where the other does not. And no two people have the same fingerprints, including identical twins, even though they are genetically the same.

“There is the fundamental question of where these patterns come from. That is how we got into this in the first place,” Cannell said. “One place to start is at the beginning.” Thus the choice of water--the source from which all life sprang.

Starting with still water in a special vessel with a solid copper bottom and sapphire top to ensure that the top and bottom temperatures were uniform, the scientists heated the water to see what would happen.

They were able to read convection patterns, miniature heat waves in the form of shadows that rose from the vessel as the temperature increased.

“When we used this very special cell,” Cannell said of the vessel, “the patterns that were formed were like splotches and they were different every time. That’s the evidence that chance, or ‘noise’ is involved.”

But not just any noise. In the early runs of the experiments, it was a disturbing thermal noise that kept throwing off results and forcing convection patterns to form concentric circles, or bull’s-eye patterns. The scientists determined that the thermal noise was caused by differences between the temperature of the water and the plastic sides of the container.

By insulating the vessel with a type of water-based gel to keep the water from touching the sides, thermal noise was dramatically reduced.

The team then ran the experiment again, “reading the shadows” of the convection patterns by observing the waves of heat emitted through the transparent, pure sapphire top.

Such heat convection waves can be seen over a toaster or on pavement on a hot day.

The result, Cannell found and demonstrated mathematically, was patterns produced by chance, each one different and each a veritable kaleidoscope’s pattern.

“The nature of the physics here is to advance further and further into the water until we physically and totally understand it, because there are so many questions that are still unresolved,” Cannell said of the studies.