Experimentalists have reported strong evidence that the bizarre state of the theory threes that was reported over 40 years ago is in-fact real.
While most forces act in pairs, Vitaly Efimov identified the effect that requires three components to spring into action. The so-called Efimov “trimer” could consist of a trio of protons, a triatomic molecule or any other set of three particles, as long as their properties were tuned to the right values.
“It’s a pretty wild idea,” said Randy Hulet, a physics professor at Rice University in Houston. “You get this infinite series of molecules.”
“It’s like layers of an onion,” Hulet said. “You see molecules at one layer. Peel the layer away, and you see that there’s a molecule there 22.7 times smaller. Every time you peel away a layer, you find another molecule.”
“For the classic Efimov scenario, the story is now basically completed,” Grimm said. But as a paradigm for looking at few-body phenomena in cold atoms, he said, “it’s like the tip of the iceberg.”
For some, the results mark the end of an era, as well as a starting point.[SOURCE](http://www.simonsfoundation.org/quanta/20140527-physicists-prove-surprising-rule-of-threes/)