Photograph courtesy Niels Madsen, ALPHA/Swansea/CERN
Free-ranging antihydrogen atoms annihilate inside a trap at the ALPHA experiment in Switzerland. Image courtesy CERN.
Published November 18, 2010
For the first time, scientists have trapped antimatter atoms—mysterious, oppositely charged versions of ordinary atoms—a new study says.
Though the achievement is "a big deal," it doesn't mean the antimatter bombs and engines of science fiction will be igniting anytime soon, experts say. (See "Antimatter-Rocket Plan Fuels Hope for Star Trek Tech.")
But the feat, undertaken a couple of months ago at the Geneva, Switzerland-based European Organization for Nuclear Research (CERN), paves the way to the potential solution of a fundamental cosmic conundrum. (Related: "Scientists Ponder Universe's Missing Antimatter.")
Theories predict that antimatter particles and matter particles have opposite electrical charges but are otherwise nearly identical. Whenever the matter and antimatter meet, they self-annihilate in a shower of pure energy.
Yet for all the similarities, scientists think matter and antimatter must differ in some other fundamental way. That's because, even though matter and antimatter should have been created in equal amounts during the big bang, the universe we know is made almost entirely of matter.
"It's a central mystery in physics," said Joel Fajans, a physicist at the University of California, Berkeley, who co-authored the new study, published today in the journal Nature.
The unprecedented trapping of antimatter atoms for study is a key step toward understanding why nature seems to abhor antimatter. (Read about a new material that may help explain why matter and antimatter are out of balance.)
Cliff Surko, a physicist at the University of California, San Diego, called the trapping of antimatter atoms "a big deal."
"This is the next step, and it's a key next step" toward solving that central mystery, said Surko, who did not participate in the research. "It's a relief to have this step in hand."
Antimatter Bonding Activities
For the new experiments, the team used CERN's ALPHA experiment, a tangle of corrugated pipes, electromagnetic "bottles," and other equipment.
First, scientists had to create antiprotons and antielectrons, or positrons, and get them to bond. This formed atoms of antihydrogen, the simplest antimatter element—a feat first achieved in 2002 at CERN. (Related: "Proton Smaller Than Thought—May Rewrite Laws of Physics.")
To make the antiprotons, the team took some of the protons normally used to feed CERN's nearby Large Hadron Collider, smashed them into metal targets, and captured the byproducts. The positrons were captured from a radioactive sodium source.
To get the antiprotons and positrons to bond, the team used an oscillating electric field, nudging the antiprotons into the same energy level as the positrons.
Next came the hard—and unprecedented—part: getting the antimatter particles to sit still.
Aiming for Permanent Antimatter-Atom Incarceration
The major challenge of trapping antimatter is that, once created, the particles are typically too hot and energetic to be trapped.
Fajans likens the task of antihydrogen trapping to games that involve tilting a toy disk to roll a ball bearing into a dimple or hole.
"If the ball is moving too fast, it won't stick in the dimple," Fajans said. "That was our problem with antihydrogen atoms. They were moving too fast to stay stuck in the traps we were making for them."
To slow them down, the team used a series of electric and magnetic fields to cool the antimatter.
Of the millions of antihydrogen atoms the ALPHA team created, only about 38 were cold enough—and slow enough—to be held in a kind of "magnetic bowl" that prevented them from interacting with normal matter.
Because the experiments were intended only to prove that antimatter atoms could be trapped, the team let the antihydrogen atoms go after only two-tenths of a second. But they hope to drastically increase the incarceration time in future experiments.
"Two-tenths of a second is nice, but forever is even better," Fajans said.
And forever may not be so far away. Since the experiments covered in the Nature study, the researchers have created many more antihydrogen atoms and held them for much longer—fodder for a future report.
According to Fajans, "We're doing much better now."
If more antihydrogen atoms can be produced and trapped for longer periods, scientists might finally be able to study them in enough detail to explain their scarcity in our universe, he added.
No Antimatter Bombs?
John Bollinger, of the U.S. National Institute of Standards and Technology in Colorado, agreed that the new results represent a major step forward—with caveats.
"It is a big deal," said Bollinger, who didn't take part in the experiment, "but more big deals need to be achieved before precise studies can be made—for example, extending the lifetime of the trapped antihydrogen and identifying the state ... of the antihydrogen."
As for real-world antimatter applications, UC San Diego's Surko said that the harnessing of antimatter as an energy source—say, for use in weapons or a Star Trek-style propulsion system—remains a far-fetched idea.
"The problem is that ... it takes so much more energy to make than you get out that it's pretty inefficient," he said. "And you have to go to great lengths to confine it for a long time."
NIST's Bollinger was likewise skeptical. "The amount of antimatter that can be trapped is very small," he said.
"Even if the efficiency of the trapping process is increased, it is fundamentally limited by the amount of antiprotons that can be generated. Therefore I do not see applications in terms of new energy sources or weapons."
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