Cosmic Antimatter Becoming a Part of the Real World Emil Venere --------------------------------- Homewood News and Information It sounds like science fiction--physicists will put an instrument on the international space station to search for stars and galaxies made of antimatter. They will use a super-strong magnet to look for the telltale trajectory of atoms from this seemingly bizarre, inverse realm. "If it's there we will probably find it," said Aihud Pevsner, a high-energy particle physicist in the Bloomberg Center for Physics and Astronomy. Pevsner and research scientist Andre Gougas were among physicists who, in a published scientific paper, officially proposed the idea in 1994. The mission was given final approval on Sept. 20 by NASA and the Department of Energy, the agencies paying for the Alpha Magnetic Spectrometer (AMS) project, which involves scientists from 37 universities and laboratories around the world. Nobel Prize-winning physicist Samuel Ting, from the Massachusetts Institute of Technology, is leading the effort. The AMS will get a test flight on a space shuttle in 1998 and is scheduled to be installed on the space station in 2001. Once considered strictly theoretical, antimatter has been steadily emerging into the world of reality. Since 1932, when a Caltech physicist discovered the antimatter equivalent of an electron--a positron--scientists have found "antiparticles" for just about every subatomic particle in existence. Antiparticles look and behave the same as ordinary subatomic particles. But although they have the same mass as their matter counterparts, they have the opposite electrical charge. If particles and antiparticles meet, they instantly annihilate each other, releasing a large amount of energy in the process. Physicists use particle accelerators to produce antiparticles, but some are made naturally. Cosmic rays are constantly streaming into Earth's upper atmosphere, bombarding atoms of ordinary matter and causing a spray of assorted subatomic particles, including antiprotons. The best way to prove the existence of antimatter stars and galaxies would be to find a heavy antimatter particle, perhaps a carbon atom. Only the lightest elements, hydrogen and helium, were copiously produced at the birth of the universe. The heavier elements, including those making up the planets, are produced inside stars and distributed in space by gigantic stellar explosions called supernovas. "One bonafide anticarbon undoubtedly would have had its source in an antigalaxy where a supernova was formed," Pevsner said. The AMS project represents an attempt to find further evidence for the role of a substance that lies at the heart of modern physics. Antimatter is the essential glue needed to merge two major schools of thought explaining atomic structure and function: quantum mechanics, which reveals that subatomic particles behave as both particles and waves, and Einstein's theory of relativity. Both views are needed to explain the behavior of atoms, but they are incompatible without antimatter. Antimatter also is a key piece of the puzzle of how the universe was born. All versions of the Big Bang theory require that, at some point after the initial explosive birth, there had to be equal parts of matter and antimatter. "One of the most important current problems of Big Bang theories is explaining where the antimatter has gone," Pevsner said. There are two theoretical possibilities. One theory states that the antimatter decayed into lighter particles by processes not yet fully confirmed. The second theory is that the antimatter is still present in today's cosmos, existing in pockets of space populated by antimatter galaxies. To astronomers using conventional telescopes, antimatter galaxies would appear exactly like their ordinary-matter counterparts. However, scientists armed with a magnetic spectrometer would be able to identify antiparticles from space. A particle passing through AMS's powerful magnetic field would give away its identity by the curvature of its path, the key to its vital characteristics. Physicists have tried this approach in past experiments, using magnetic spectro-meters hoisted into the upper atmosphere on balloons. But balloons are limited--they cannot stay aloft for more than a few hours or days, and the instruments have been 100 times too insensitive to detect heavy antimatter particles, Pevsner noted. The space station, however, will allow scientists to make major strides beyond past experiments. AMS's magnet will be much more powerful than those used in previous work and putting it on the space station will boost its sensitivity 10,000 times. One reason for the increased sensitivity is that the instrument's exposure time can be extended far longer than the balloon experiments; the initial duration is planned to last three years. But the effort still could fail to produce positive results if intergalactic space is not entirely devoid of matter. Even a minuscule amount of matter in space could be sufficient to interact with antimatter and cause its annihilation. It was for that very reason that Pevsner and Gougas proposed that the AMS instrument package be enhanced with an additional spectrometer. The supplemental spectrometer will provide redundancy for the mission's major objective, the quest for antimatter galaxies. But it also will enable researchers to probe details about our own solar system and galaxy and to search for dark matter, the mysterious yet undiscovered material that some scientists believe makes up 90 percent or more of the universe. "Once you place a powerful analyzing detector in space, with literally hundreds to a thousand times more sensitivity than in previous experiments, you can look anew at a whole range of phenomena," Pevsner said.
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