The Year in Science: Physics

Sunday, January 08, 2006

Big Bang Reenacted In the Laboratory

Physicists at Brookhaven National Laboratory on Long Island in New York announced in April that they had re-created the searing-hot mix of exotic particles that filled the universe during the first few microseconds after the Big Bang. Their experiment implies that the cosmos started out not as a hot, dense cloud of gas but as a strangely sublime, friction-free liquid.

This dramatic result marks the culmination of three years of data collection by hundreds of scientists at Brookhaven's colossal atom smasher, the Relativistic Heavy Ion Collider (RHIC). To mimic the conditions of the early universe, researchers sent electrically charged gold atoms racing along the collider's 2.4-mile-long tunnel at near light speed, producing a fireball 150,000 times as hot as the center of the sun. At this temperature, the constituents of ordinary matter melt down into a soup of particles known as quarks and gluons. With this achievement, physicists can finally stop speculating about what matter was like right after the Big Bang and start studying it.

Cosmologists previously thought that this primordial matter would have been chaotic, with quarks and gluons flying freely in all directions. Instead, the particles appeared to flow together in coordinated streams—like a perfect fluid. The results may help explain the behavior of subatomic particles and the evolution of the early universe. But for now, the findings mostly have physicists puzzled. "Many of the people working at RHIC were surprised by this striking finding," says Sam Aronson, associate lab director for high-energy and nuclear physics at Brookhaven.  —Alex Stone

Mystery Particle Shakes Up Physics 

A new particle, announced by an international team of researchers in June, calls into question what we know about the composition of matter. Dubbed Y(4260), the mysterious particle has appeared about 100 times after billions of collisions of electrons and positrons recorded by the BaBar detector at the Stanford Linear Accelerator Center. That the particle exists seems certain; what exactly it may be is anybody's guess.

Y(4260) is thought to be a union of quarks, which come in six varieties and which are considered part of nature's set of fundamental particles. From there, things get confusing. The properties of Y(4260) imply that it contains one particular combination of two quarks, known as a charm quark and an anticharm quark. But its mass and the manner in which it decays run counter to theoretical expectations for a particle composed of those two quarks.

"We thought we understood how you can combine quarks and antiquarks into matter, but this doesn't fit that pattern," says David MacFarlane, a spokesman for the BaBar experiment. "It suggests that there may be a whole new spectrum of matter due to more exotic combinations of quarks." Other perplexing particles observed in BaBar and additional accelerator experiments in recent years drive home the message that physicists still have much to learn about the most basic building blocks of the universe.  —Susan Kruglinski

Tabletop Machine Triggers Telltale Nuclear Fusion

Extraordinary claims require extraordinary evidence, as Carl Sagan liked to say. So when Seth Putterman and his colleagues at UCLA announced in April that they had achieved nuclear fusion using a simple device that fits on a lab bench, they knew their work would come under close scrutiny. In addition to outlining their findings in the journal Nature, they also released graphs, photos, videos, and their complete raw data showing the telltale production of neutrons, a signature of a fusion reaction. "We published probably the largest dose of supplementary material ever to accompany a paper," Putterman says.

The UCLA team was determined to avoid a repeat of the 1989 "cold fusion" fiasco that promised unlimited energy but delivered little besides unrepeatable results. This time, the researchers were completely open about what they have done. Their experiment relies on a small piece of lithium tantalate, a material that generates a voltage when it is heated or cooled. "Just a 30 degree Celsius [54 degree Fahrenheit] increase in the crystal temperature is enough to build up 80,000 volts," says Brian Naranjo, the paper's lead author. When surrounded by deuterium atoms (heavy hydrogen), that voltage gives the atoms an electric charge and then accelerates them into a nearby solid target containing additional deuterium. When the deuterium atoms smash together, some of them fuse, producing a helium nucleus and a neutron.

Putterman notes that this process is too inefficient to provide any worthwhile amount of energy, but it could have significant practical impact all the same. For example, tabletop fusion may find a use as a cheap, compact way to produce neutrons and to replace the bulky accelerators now used for neutron scanning in oil exploration and baggage screening. Putterman also hopes his work will help restore a semblance of credibility to fusion research. "I think what we've done is get a gorilla off everyone's back," he says. "Maybe this will encourage people to think differently about fusion and, building on what we've done, come up with still better ideas."  —Alex Hutchinson

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