Published October 3, 2013
Imagine standing in a jam-packed room and shouting “fire!” The commotion you caused would reverberate outward, with those closest to you repeating your warning and entering a state of alert, while people standing further away might not respond at all.
Our actions influence those around us, and similar principles hold true in the world of physics.
But how far can an action spread?
Over the past several years, UB physicists studying liquid helium have discovered that tiny packets of this fluid can influence one another from surprisingly large distances—an observation that now has inspired a new study by Michael E. Fisher, one of America’s pre-eminent scientists.
In two papers that appear in Physical Review this week, Helen Au-Yang at Oklahoma State University and Fisher at the University of Maryland cite the work of SUNY Distinguished Professor Francis Gasparini, writing in one that the results of their new theoretical research reflect “quite directly many of the novel proximity and coupling features uncovered in the striking experiments of Gasparini and co-workers for liquid helium.”
Gasparini is a member of UB’s physics department. Since 2010, he and his students, including Justin Perron, now a scientist at the National Institute of Standards and Technology, have published a series of studies detailing interesting phenomena that occur when liquid helium is confined to very small spaces.
In experiments, Gasparini and his colleagues created silicon wafers pocked with millions of miniscule, box-like cavities. The team then filled these chambers with liquid helium and capped them with another wafer, leaving each packet of helium connected with the others only by a thin film of the same substance.
The researchers used this setup to study how the microscopic boxes of liquid influenced each other near the temperature at which helium undergoes a phase transition from a normal fluid to a superfluid with zero viscosity.
The experiments yielded a big surprise.
They found that a fluctuation in the properties of helium in one pocket could induce the same fluctuation to occur in a pocket 10,000 atomic lengths away—a surprisingly large distance. When helium in one cavity experienced a phase transition from normal fluid to superfluid, it could act from afar to influence other helium samples to do the same.
The experiments shed light on two effects in physics:
“What we saw was remarkable,” Gasparini says. “What we found is that the effects are much stronger than expected and extend to much-larger spatial distances than one would predict.”
The new theoretical articles in Physical Review by Yang and Fisher explore coupling and proximity in a very different physical system: the Ising model, which describes how the magnetic moments of an infinite array of atoms align during a phase transition that leads to the onset of magnetism.
Despite many differences between the Ising model and Gasparini’s helium-filled wafers, Yang and Fisher found that the effects the UB team described were “alive and well” in the Ising model, Gasparini says.
Gasparini and student Stephen Thomson are continuing to work on new designs for helium confinement to probe these effects further. The research is funded by the National Science Foundation.
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