Wednesday, February 21, 2001
 
A Knotty Problem
 
By Jennifer McKee
Journal Staff Writer
 
LOS ALAMOS - On its face, this sounds like a real yawner: Scientists
discover how simple knots work.  But go a little deeper, said Eli
Ben-Naim, a physicist at Los Alamos National Laboratory who has, in
fact, unraveled the secrets of simple knots, and you're talking about
a model for the behavior of DNA strands, the structure of rubber, the
insides of proteins. In short, he said, you're talking about a whole
chapter of math, physics and biology interested in how long strings of
things - anything from genetic material to the strings of molecules in
plastics - tie themselves up and straighten themselves out again.
 
   Ben-Naim, fellow lab researcher Robert Ecke, and collaborator Zahir
Daya, also at the lab, spent much of last summer watching knots
unravel.  In the process, they discovered several basic truths about
knots - most notably, that infused with enough energy, every knot
eventually unravels itself. They can predict how long such unraveling
will take and have mapped several steps every unraveling knot
eventually goes through, despite the fact that the unraveling itself
is completely random.
 
   "There's some very generic behavior," Ben-Naim said.
 
   For these researchers, the discovery was science for science's
sake, and not necessarily tied to any practical applications. But you
never know what happens to knowledge, Ben-Naim said.  "You put it out
there," he said. "You don't know what people will do with it."
 
   Their findings were published in the American Physical Society's
Physical Review Letters on Monday, although about 30 other researchers
have already heard about their work and visited Los Alamos to watch
the scientists duplicate it.
 
   Their data sprang from experiments amazingly simple and
serendipitous. Ben-Naim's forte is the random movement of particles.
Ecke had been talking to another scientist who spent decades studying
proteins - which are long strings of molecules often tangling and
detangling themselves.
                                                                                
"I asked (Ecke) one day, 'Why don't we do this?' '' Ben-Naim said.
 
   Ben-Naim went to Metzger True Value Hardware in a Los Alamos strip
mall and bought a spool of metal bead cord - the light metal chain
that attaches pens to the bank counter. He picked up a Wal-Mart
stopwatch and the two rigged up a simple vibrating board. They knotted
the chain, placed it on the vibrating board and watched as the cords
jiggled, jumped and wormed their way to knotlessness. They repeated
the experiment hundreds of times, making sure their findings weren't a
fluke.
 
   "That was the fun part," Ben-Naim said.
 
   The three are hardly the first to study knots and polymers. But the
beauty of their experiment was how big and "watchable" it was. Most
polymers, or strands of particles, are way too tiny to see with the
naked eye and even too small to watch their behavior under a
microscope, Ecke said. But this experiment was very obvious. You just
watch the chain and time it as it unravels. No guesswork.
 
   The vibration is nothing more than energy, Ben-Naim said. And the
metal chain is very much like the polymers and macromolecules the
three were trying to understand, Ecke said.
    
    Macromolecules, like proteins or plastic, are strands of smaller
molecules strung together like beads. Although they may look like
strings under a microscope, they don't behave like a knotted
shoestring. That's because the particles don't have any friction
holding them together, Ecke said, just like the metal chains in their
experiments.
 
   Believe it or not, Ben-Naim said, scientists have been trying to
figure out knots for years. Their discovery comes as fresh insight for
lots of scientists around the world.
 
   "Everybody who comes in has been fascinated with it," Ben-Naim
said.  Turns out, the three weren't the first to discover vibration's
powerful effect on knots. Since news of their findings has spread, the
lab researchers have learned that fishermen around the world
traditionally throw their knotted ropes overboard. The vibration of
the waves eventually works the knots out, Ben-Naim said.  "So, we're
not so smart."