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What is Antimatter? - Page 6

An intriguing puzzle arises when we consider that the laws of physics treat matter and antimatter almost symmetrically. Why then don't we have encounters with anti-people made of anti-atoms? Why is it that the stars, dust and everything else we observe is made of matter? If the cosmos began with equal amounts of matter and antimatter, where is the antimatter?

Experimentally, the absence of annihilation radiation from the Virgo cluster shows that little antimatter can be found within ~20 Megaparsecs (Mpc), the typical size of galactic clusters. Even so, a rich program of searches for antimatter in cosmic radiation exists. Among others, results form the High-Energy Antimatter Telescope, a balloon cosmic ray experiment, as well as those from 100 hours worth of data from the Alpha Magnetic Spectrometer aboard NASA's Space Shuttle, support the matter dominance in our Universe. Results from NASA's orbiting Compton Gamma Ray Observatory , however, are uncovering what might be clouds and fountains of antimatter in the Galactic Center.

We stated that there is an approximate symmetry between matter and antimatter. The small asymmetry is thought to be at least partly responsible for the fact that matter outlives antimatter in our universe. Recently both the NA48 experiment at CERN and the KTeV experiment at Fermilab have directly measured this asymmetry with enough precision to establish it. And a number of experiments, including the BaBar experiment at the Stanford Linear Accelerator Center and Belle at KEK in Japan, will confront the same question in different particle systems.

Antimatter at lower energies is used in Positron Emission Tomography (see this PET image of the brain). But antimatter has captured public interest mainly as fuel for the fictional starship Enterprise on Star Trek. In fact, NASA is paying attention to antimatter as a possible fuel for interstellar propulsion. At Penn State University, the Antimatter Space Propulsion group is addressing the challenge of using antimatter annihilation as source of energy for propulsion. See you on Mars?


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