麻豆淫院

Trapping and cooling a microscopic clump of gas and then suddenly releasing it would normally result in the gas rapidly expanding outward in all directions, like a spherical bubble.

But what if it doesn鈥檛? When a result doesn鈥檛 turn out as anticipated, nature may be revealing its secrets. And when the result also sheds light on Big Scientific Questions that weren鈥檛 even part of the experiment, researchers sit up and pay even closer attention.

That鈥檚 what鈥檚 been happening since Duke physicist did this experiment with lithium-6. The key was using only light to chill the gas to almost absolute zero and adding the right amount of magnetic energy, a combination pioneered in Thomas鈥檚 lab.

Instead of expanding evenly, the gas blob took the shape of a cigar standing on its tip. It then morphed asymmetrically within milliseconds into 鈥渢his funny flow that stood still in one direction but expanded rapidly in the other,鈥� recalls Thomas, an expert on the physics of ultracold temperatures and the university鈥檚 Fritz London Professor of 麻豆淫院ics.

The stand-up stogie didn鈥檛 grow any taller, as Thomas noted with the aid of a microscope and time-freezing camera. But it bulged topsy-turvily in the middle, swelling into a kind of melon shape that shifted the overall orientation from vertical to horizontal.

In a much-cited report published in the Nov. 13, 2002 issue of the journal Science, Thomas鈥檚 research group suggested this phenomena pointed to a never-before-observed form of group behavior among this kind of gas鈥檚 frigid atoms.

It鈥檚 a condition that might help explain important phenomena that have been difficult to study, such as the flow of electrons in high-temperature superconductors, or the tightly bound nuclear matter in neutron stars, they said.Subsequent reports in Science and other journals firmed up the notion that the gas could be exhibiting the coordinated flow of a special kind of superfluidity 鈥� a strange liquid state in which very cold substances seem to move so effortlessly that nothing can stop them, in some cases even climbing walls.

At about the same time, researchers at the Brookhaven National Laboratory鈥檚 (RHIC) were getting intriguing results from their attempts to recreate the dawn of creation鈥檚 first white-hot microseconds. They did so by smashing together gold atoms propelled to nearly light speed, producing temperatures 150,000 times hotter than the sun鈥檚 interior within a time interval too fleet to measure.

This big bash at RHIC was supposed to liberate quarks 鈥� the fundamental units of all matter 鈥� from the gluons that normally hold them together, creating a hyper-energized gas called a quark-gluon plasma.

Using statistics and simulations to visualize what could not be seen, scientists discovered the plasma actually acts like a superhot fluid. And it behaves a lot like Thomas鈥檚 frozen cigars and melons. Both exhibit what the scientists called an 鈥渆lliptic flow,鈥� ballooning preferentially in only one direction. Thomas calls this 鈥渁nisotropic expansion.鈥� Soon illustrations from Thomas鈥檚 journal reports on the cold temperature experiment were being displayed at quark-gluon symposia 鈥� literally bridging the gap separating the very coldest from the very hot.

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Further research suggested that although the systems exist at opposite extremes of temperature, both behave like 鈥渘early perfect鈥� fluids, flowing with practically no impeding viscosity.

Theorists involved in superstring physics have taken notice of this remarkable convergence. Some have begun using their complicated mathematical tools to bridge quantum mechanics and general relativity and explain why Thomas鈥檚 supercold world bears similarities to the superhot. Already some of their calculations have yielded insights.

鈥淩HIC鈥檚 system is at about 2 trillion degrees, while we鈥檙e typically at one-tenth of a microdegree above absolute zero 鈥� 19 orders of magnitude difference in temperature!鈥� Thomas says. In terms of density, 鈥渢here is also about 25 orders of magnitude difference between theirs and ours.鈥�

And yet, Thomas, the experts on quark-gluon plasma and string theorists came together in a single session at this year鈥檚 annual meeting of the American Association for the Advancement of Science in Chicago to describe 鈥渢he surprising confluence of such different physics fields as a sort of perfect storm,鈥� according to the magazine Science News.

To have a system that connects cold, condensed gases to high-temperature superconductors and neutron stars and then to quark-gluon matter and even string theory is pretty amazing,鈥� Thomas said.

Various researchers are still exploring what these very different phenomena might have in common. But Thomas said the special behavior of his Lithium-6 gas is related to the nature of its atoms.

Lithium-6 is among many atomic isotopes classified as 鈥渇ermions.鈥� Greta Garbos of the atomic world because they 鈥渧ant to be alone,鈥� fermions are loners compared to their chummier alter-ego counterpart atoms, the 鈥渂osons.鈥�

The key is the state of their 鈥渟pins,鈥� an electromagnetic trait that all fundamental particles possess. Fermions have an 鈥渙dd鈥� spin of 1/2, which means they cannot share the same energy states with each other. Bosons, on the other hand, actually prefer getting together. Previously only certain boson type atoms were known to exhibit the group behavior of superfluidity.

Protons, neutrons and electrons 鈥� the constituents of atoms 鈥� are fermions, too. Were it not for their mutual repulsions, 鈥渨e would collapse,鈥� says Duke theoretical physicist Berndt Mueller. 鈥淲e鈥檙e made up of positively charged nuclei and negative charged electrons, which should attract,鈥� he explains. 鈥淏ut those are also all fermions, so they try to keep away from each other.鈥�

Thomas鈥檚 experiments test the limits of this repulsion by making fermions very cold. Cooled to 50 billionths of a degree above absolute zero and influenced by the weird principles of quantum mechanics, the atoms鈥� spheres of influence balloon to an incredible large millionths of a meter. They also crowd up as closely as nature allows.

His group was the first to both chill fermions low enough with laser beams and also trick them into behaving for a short time like they鈥檙e part of one big molecule. Turning up a magnetic field to just the right level makes them want to collide and pair up into what he calls a 鈥渟trongly interacting system.鈥� It鈥檚 their exceptional interactivity that produces the exploding-cigar effect and also makes his fermions flow like a nearly perfect fluid. They enter a realm known as 鈥渦niversal behavior,鈥� where they emulate traits of other very different systems.That鈥檚 why scientists are now using strongly interactive fermions to model how high-temperature superconductors work.

鈥淵ou can test the theory,鈥� Thomas says. 鈥淚t鈥檚 easier using our gas because it鈥檚 a very controlled system.鈥漊niversally behaving fermions also let researchers model microscopic properties within the densest of nuclear matter - something not readily tested on a distant neutron star.

This article by Monte Basgall has originally appeared in . Reprinted with permission of Monte Basgall.