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Lurking antimatter galaxies
Q: Are there anti-matter galaxies? (Lanney,
Albuquerque, New Mexico)
A: An antimatter intelligent cloud floats into Federation
space and threatens every planet in the galaxy! It is hungry for planets. The
U.S.S. Enterprise to the rescue! But, the creature envelops the starship and
bombards the Enterprise with antimatter! Her shield
leaks badly...
Star Trek: "One of our Planets is Missing",
1973
Could
antimatter galaxies with antimatter worlds and perhaps antimatter creatures like
Star Trek’s cloud exist? Conceivably, but unlikely. Science supports the notion
but Big-Bang history argues against it. Certainly, antimatter exists.
 The jet is a stream of matter and antimatter propelled to
half-light speed by the Crab pulsar, a rapidly rotating neutron star the size of
Manhattan. (NASA, the Chandra X-ray Observatory , and TRW, Inc.)
The science. First, we theorized antimatter’s
existence. In 1928, British physicist Paul A.M. Dirac described the motion of
electrons in electric and magnetic fields and incorporated the effects of
Einstein’s Special Theory of Relativity in his description.
His new theory predicted a strange new particle — an
anti-electron or "positron" as it came to be known. Dirac theorized these
bizarre specks exist with the same mass as electrons but with positive
electric charges. Indeed, his theory indicates that all fundamental particles
have corresponding antiparticles. (And we have found many.)
A short four years later, we discovered the positron — the
first antimatter particle. While studying cosmic rays, American physicist Carl
Anderson noticed oddly deviating tracks in a cloud chamber. The tracks bent in
the opposite direction from electrons as the particles passed through a magnetic
field. Eureka! They could only be positrons.
Soon, we produced antiprotons (1955) in accelerators and
finally, in 1995, we combined a positron with an antiproton to produce an
antimatter atom. We used the CERN accelerator in Switzerland to make 9
antimatter hydrogen atoms.
Antimatter also occurs in nature as Anderson learned and,
sometimes, in fairly large amounts. In July 2002, a solar flare erupted and
created about a pound (half a kilogram) of antimatter. The antimatter
immediately annihilated when it collided with matter from the Sun.
That’s the problem — antimatter and matter annihilate when
they meet. So, for an antimatter galaxy to exist, it would have to be isolated
far from matter galaxies — and be a relic from the Big Bang when the Universe
began.
We think the Universe is practically all matter now — but not
because of Dirac’s equations. Those equations and present particle physics say
that matter and antimatter are equivalent. Thus, science indicates that
antimatter galaxies could exist just as well as matter galaxies.
Big Bang history. The Big Bang probably created almost
equal numbers of antiparticles and particles as the Universe cooled ten
billionths of a second later.
The numbers weren’t, however, exactly equal. Matter had
a small edge. For every billion antimatter particles, there were a billion and
one matter particles. The particles and antiparticles squared off — one on one
annihilation until only a relatively tiny amount of matter was left over. It all
happened fast. Poof! In a second, antimatter essentially vanished and matter
almost did — converted violently into radiation energy. (That radiation is
called the Cosmic Background Radiation.)
In that one second, as the Universe continued to expand, the
temperature dropped too low to create new particle-antiparticle pairs. Then the
Universe was stuck with almost all matter — fortunately enough to make us and
the cosmos as we know it.
Some antimatter may still exist. An antimatter star or galaxy
somewhere, perhaps. Our data argue against it, though, because the antimatter
would surely encounter matter eventually. The annihilation would generate huge
energies in the form of enormous numbers of gamma rays. Even with extremely
sensitive instruments, we have not detected these gamma rays in sufficient
quantities.
But, who knows? Maybe an antimatter cloud drifts somewhere far
out between galaxies. She is lonely — and hungry for planets.
Further Reading:
HyperPhysics by Rod Nave: the antimatter problem
CERN: Antimatter academy by Rolf Landua
CERN: Antimatter: mirror of the Universe
NASA: What’s the matter with antimatter
Space.com: The Reality of Antimatter
Yale University: Observational tests of antimatter cosmologies by Gary Steigman
(Answered Dec. 24, 2004)
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