The U.S. Air Force is quietly spending millions of dollars investigating ways to use a radical power source -- antimatter, the eerie "mirror" of ordinary matter -- in future weapons.

The most powerful potential energy source presently thought to be available to humanity, antimatter is a term normally heard in science-fiction films and TV shows, whose heroes fly "antimatter-powered spaceships" and do battle with "antimatter guns."

But antimatter itself isn't fiction; it actually exists and has been intensively studied by physicists since the 1930s. In a sense, matter and antimatter are the yin and yang of reality: Every type of subatomic particle has its antimatter counterpart. But when matter and antimatter collide, they annihilate each other in an immense burst of energy.

During the Cold War, the Air Force funded numerous scientific studies of the basic physics of antimatter. With the knowledge gained, some Air Force insiders are beginning to think seriously about potential military uses -- for example, antimatter bombs small enough to hold in one's hand, and antimatter engines for 24/7 surveillance aircraft.

More cataclysmic possible uses include a new generation of super weapons -- either pure antimatter bombs or antimatter-triggered nuclear weapons; the former wouldn't emit radioactive fallout. Another possibility is antimatter- powered "electromagnetic pulse" weapons that could fry an enemy's electric power grid and communications networks, leaving him literally in the dark and unable to operate his society and armed forces.

Following an initial inquiry from The Chronicle this summer, the Air Force forbade its employees from publicly discussing the antimatter research program. Still, details on the program appear in numerous Air Force documents distributed over the Internet prior to the ban.

These include an outline of a March 2004 speech by an Air Force official who, in effect, spilled the beans about the Air Force's high hopes for antimatter weapons. On March 24, Kenneth Edwards, director of the "revolutionary munitions" team at the Munitions Directorate at Eglin Air Force Base in Florida was keynote speaker at the NASA Institute for Advanced Concepts (NIAC) conference in Arlington, Va.

In that talk, Edwards discussed the potential uses of a type of antimatter called positrons.

Physicists have known about positrons or "antielectrons" since the early 1930s, when Caltech scientist Carl Anderson discovered a positron flying through a detector in his laboratory. That discovery, and the later discovery of "antiprotons" by Berkeley scientists in the 1950s, upheld a 1920s theory of antimatter proposed by physicist Paul Dirac.

In 1929, Dirac suggested that the building blocks of atoms -- electrons (negatively charged particles) and protons (positively charged particles) -- have antimatter counterparts: antielectrons and antiprotons. One fundamental difference between matter and antimatter is that their subatomic building blocks carry opposite electric charges. Thus, while an ordinary electron is negatively charged, an antielectron is positively charged (hence the term positrons, which means "positive electrons"); and while an ordinary proton is positively charged, an antiproton is negative.

The real excitement, though, is this: If electrons or protons collide with their antimatter counterparts, they annihilate each other. In so doing, they unleash more energy than any other known energy source, even thermonuclear bombs.

The energy from colliding positrons and antielectrons "is 10 billion times ... that of high explosive," Edwards explained in his March speech. Moreover, 1 gram of antimatter, about 1/25th of an ounce, would equal "23 space shuttle fuel tanks of energy." Thus "positron energy conversion," as he called it, would be a "revolutionary energy source" of interest to those who wage war.

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