Antimatter

Antimatter

Dec. 1, 2005

Antimatter is a large subject which is covered through all the science fields. Antimatter or antiparticles is often called the "mirror image" of ordinary matter. For every type of ordinary matter particle, an antimatter particle can be created that is identical in characteristics except for an opposite electric charge and some other properties like magnetic moment. While staying with the topic of astronomy, this paper will describe the discovery of antimatter, the origins of antimatter, and antimatter as energy.

To describe antimatter we must first look at the history in its discovery. The history of discovering antimatter begins in 1929 by the proposal of an English Physicist named Paul Dirac. In attempting to combine quantum mechanics with special relativity to describe the behavior of an electron, he found that the solutions of the equation which showed that if matter is created from energy then an equal amount of antimatter is also created. For example, the equation, X squared equals four can have two possible solutions (X equals two) or (X equals negative two.) Dirac's equation proves two possible solutions, one for an electron with positive energy, and one for an electron with negative energy. This showed that for every proton in the universe there should be an antiproton or a proton with a negative charge, for every electron there’s a anti-electron or an electron identical in everyway but with a positive charge, and every neutron there’s a antiparticle called an antineutron. The combined theory was called the Quantum field theory. From 1930, the hunt for the mysterious antiparticles began. A scientist named Victor Hess had discovered a natural source of high energy particles called cosmic rays. Cosmic rays are very high energy particles that come from outer space and as they hit the Earth's atmosphere they produce huge showers of lower energy particles that have proved very useful to physicists. In 1932 Carl Anderson, a professor at the California Institute of Technology, was studying showers of cosmic particles in a cloud chamber and saw a track left by a positively charged particle with the same mass as an electron. He concluded that the tracks were actually anti-electrons each produced alongside an electron from the impact of cosmic rays in the cloud chamber. He called the anti-electron a "positron", for its positive charge. This proved the existence of antiparticles as predicted by Dirac. Since an antiproton (or proton) is almost 2000 times heavier than an anti-electron (or electron), it takes a lot more energy to create them. Twenty-three years later technology advanced enough to create enough energy to produce an antiproton. In 1954, a particle accelerator called the Bevatron was built at Lawrence Berkeley Laboratory which possessed sufficient energy to create its own antimatter. The Bevatron could collide two protons together at a energy of 6.2 GeV. This was expected to be the optimum for producing antiprotons. Meanwhile a team of physicists designed and built a special detector to see the antiprotons. In October 1955 the big news hit the front page of the New York Times with the discovery of the antiproton. A year later the Bevatron created the antineutron. So if particles bound together in atoms are the basic units of matter, it is natural to think that antiparticles bound together in anti-atoms are the basic units of antimatter. In 1965 two teams of physicists observed the making of an anti-deuteron, a nucleus of antimatter made out of an antiproton plus an antineutron. In 1995 an anti-electron was combined with an anti-deuteron to create an anti-atom. And finally the Anti-hydrogen atom was created.

Acceleration and deceleration of particles are not the only way to study antimatter. Antimatter could exist somewhere in outer-space. Dirac was the first to consider the existence of antimatter in an astronomical scale. It was only after the confirmation of his theory, with the discovery of the positron, antiproton and an antineutron, that led use to believe that antimatter is a mirror energy of matter and can be a solid, liquid, gas, or plasma. This led to the possible existence of anti-planets, anti-stars, anti-galaxies and even an anti-universe. According to our current knowledge there aren’t any great deposits of antimatter in our universe. That will most likely be true because when matter and antimatter meet they annihilate each other. We also do not see the signatures of electron-positron annihilation, or proton-proton annihilation coming from the edges of galaxies, or from places where two galaxies are near each other. As a result, we believe that essentially all of the objects we see in the universe are made of matter not antimatter. When antimatter and matter annihilate each other they convert into radiation, which is a form of energy. Cosmic radiation and solar winds can create some antiparticles in upper parts of our atmosphere but those are usually annihilated almost instantly. If there were an isolated system of antimatter in the universe free from interaction with ordinary matter, no earth based observation could distinguish its true content. The possibility of extragalactic antimatter was more practical. It is believed that the universe must consist of both matter and antimatter in equal amounts. According to the big bang theory, antimatter and matter were created in the gigantic Big Bang about 15 billion years ago. It is therefore surprising that our Earth, the solar system, and our galaxy (the Milky Way) do not contain any antimatter. To explain this absence, scientists have thought of two different 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. In the late 1950s, the amount of antimatter in our galaxy was calculated to be less then one part in a hundred million. To search for this extragalactic antimatter, the best way is to place a particle detector in space. In 1998 a high-energy particle detector called the Alpha Magnetic Spectrometer (AMS), was flown on the Space Shuttle Discovery for a ten-day mission. One of its goals is to measure the fluxes of charged antiparticles and anti-nuclei to search for any form of cosmic antimatter. During the 10 days that AMS was in space, not a single anti-nucleus was seen among the 3 million nuclei that traversed the experiment. In 2004, a new version of the experiment, called AMS-02, was installed on the International Space Station. AMS-02 will again be searching for any extragalactic antimatter, but this time with more sensitivity, over a three year period, and in a wider energy range.

Matter