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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