Johns Hopkins Gazette: October 9, 1995

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

     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

     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

     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

     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

     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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