Antimatter in Space

Acceleration of particles is not the only way to study antimatter. Antimatter exists somewhere in the outer space. In the late 1950s, the amount of antimatter in our galaxy was calculated to be less then one part in a hundred million. If there were an isolated system of antimatter in the universe, free from interaction with ordinary matter, no earthbound observation could distinguish its true content.

So, even if nothing was visible, the possibility of extragalactic antimatter was wide open. And in the following years, motivated by basic symmetry principles, it was belived that the universe must consist of both matter and antimatter in equal amounts. However, it is nowadays strongly believed that there is merely one universe, composed primarily of matter. One could speculate, though, that if any natural antimatter, let say antinuclei from an antimatter galaxy, would try to reach us, it would annihilate with nuclei in the earth's atmosphere, and never be detected.

Over the past twenty years, scientists have tried to take their instruments as high as possible in the atmosphere (originally with balloons, later with satellites) on the attempt to overcome this annihilation problem, but such an effort is costly and difficult. Todays, experiments are planned to be implemented on satellites.

According to the Big Bang Theory about 15 billion years ago, matter and antimatter were created in a gigantic Big Bang in equal amounts. To explain the absence of antimatter, scientists have come out with two possibilities: either antimatter completely disappeared during the history of universe, or matter and antimatter have been separated from each other to form different regions of the universe.

A team of physicists built the Alpha Magnetic Spectrometer (AMS) to try to detect particles of antimatter over Earth. During the 10 days that AMS was in space, not a single antinucleus was seen among the 3 million nuclei that traversed the experiment. In 2004, a new version of the experiment, called AMS-02, will be installed on the International Space Station. AMS-02 will again be searching for any extragalactic antimatter, but this time with more sensitivity, over a longer time period and in a wider energy range. AMS-02 will be installed on the long arm of the ISS and exposed to cosmic rays for three years.

Even though antimatter is rare in the big picture, small amounts of it are present everyday.