(From Wikipedia the free encyclopedia, by MultiMedia)
Antimatter is matter that is composed
of the antiparticles of those that constitute normal matter. An atom
of anti-hydrogen, for instance, is composed of a negatively-charged
antiproton being orbited by a positively-charged positron. If a particle/antiparticle
pair comes in contact with each other, the two annihilate in a burst
of electromagnetic radiation.
With antimatter, the entire possible energy of the
matter could be harnessed, instead of the very small chemical energies
or nuclear energies that can be extracted today. The reaction of 1 kg
of antimatter with 1 kg of matter would produce 1.8×1017
J of energy (by the equation E=mc2). In
contrast, burning a kilogram of petrol produces 4.2×107 J,
and nuclear fusion of a kilogram of hydrogen would produce 2.6×1015
Since the energy density is vastly higher than these
other forms, the thrust to weight equation used in antimatter rocketry
and spacecraft would be very different. In fact, the energy in a few
grams of antimatter is enough to transport a small ship to the moon.
It is hoped that antimatter could be used as fuel for interplanetary
travel or possibly interstellar travel, but it is also feared that if
humanity ever gets the capabilities to do so, there could be the construction
of antimatter weapons.
Scientists succeeded in 1995 to produce anti-atoms
of hydrogen, and also anti-deuteron nuclei, made out of an anti-proton
plus an anti-neutron, but not yet more complex antimatter. Also, they
exist for a very short time, they can not be stored. As far as we know
there are no antimatter atoms in existence in this universe outside
of our particle physics labs. This is a great mystery since one would
expect matter and antimatter to have been generated in equal amounts
after the Big Bang. The scarcity of antimatter has given us a stable
universe, however, without which life could not have evolved.
The scarcity of antimatter means that it is not readily
available to be used as fuel. Generating a single atom of antimatter
is immensely difficult and requires particle accelerators and vast amounts
of energy - millions of times more than is released after it is annihilated
with ordinary matter, due to inefficiencies in the process. No more
than a handful of antimatter atoms have ever been made. Therefore, unless
substantial quantities from some as-yet unimagined natural source of
antimatter are found, or ways to generate antimatter more efficiently
are determined, antimatter will remain a curiosity rather than a viable
The symbol used to denote an antiparticle is the same
symbol used to denote its normal matter counterpart, but with an overstrike.
For example, a proton is denoted with a "p", and an antiproton
is denoted by a "p" with a line over its top ().