Scientists Ponder Universe's Missing Antimatter

July 6, 2005

Why is the universe dominated by matter? It is among the most perplexing questions to face particle physicists, scientists who study the tiniest building blocks of the universe.

Theories of physics require that for every particle of matter created at the big bang—the cosmic explosion that marked the beginning of the universe—so too was its antiparticle equivalent, or antimatter, said Persis Drell, a particle physicist at the Stanford Linear Accelerator Center (SLAC) in Menlo Park, California.

"That's fine, but all we see now is matter. Everything on Earth, in the solar system, everything as far out as we can see is made of matter," she said. "What happened to all the antimatter?"

Elvin Harms, head of the antiproton source department at the Fermi National Accelerator Laboratory in Batavia, Illinois, said another way to phrase the question is: Where is the antimatter?

"Is it just this part of the universe that tends to be dominated by matter?" he said, raising the possibility that other parts of the universe are dominated by antimatter.

In recent years researchers have begun to formulate answers to these questions, but their best explanations fall short of accounting for the matter-antimatter imbalance in the universe today.

According to Drell, a new particle collider under construction on the border between France and Switzerland by European Organization for Nuclear Research (CERN) and a second collider proposed by the international science community may provide more answers.

"We are hoping from these particle colliders—the Large Hadron Collider and the [International] Linear Collider—to go another step deeper and make progress," she said.

Particle Annihilation

Matter and antimatter share nearly identical properties except the antiparticle has an opposite electric charge from the particle. For example, an electron has a negative charge, so its antiparticle, the positron, has a positive charge.

Since opposites attract, particles and their antiparticle counterparts are inclined to join together. But when they do, they annihilate each other in a flash of pure energy.

Star Trek fans may recognize the matter-antimatter reaction as the fuel for the spaceship Enterprise. "It's true and cool," Drell said. "If you take an electron and anti-electron they will annihilate, and you'll get pure energy."

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