In 1928, the shy, brilliant physicist Paul Dirac predicted the existence of antimatter. When it was actually discovered 7 years later, Dirac should have become a household name. But his yearning to avoid publicity — he almost turned down the Nobel Prize — discouraged media attention, and he’s known today only among science geeks.
Antimatter has the same appearance and behavior as ordinary matter. An antimatter Sun would look just like our normal one, and even spectroscopic analysis couldn’t tell them apart. But let an antimatter object touch anything made of conventional matter, and both would vanish in a violent flash.
Unlike most exotic particles and objects that live in the “weird section” of the modern cosmological zoo, antimatter is stone simple to understand. It’s merely ordinary matter with all of its electrical charges reversed. An anti-atom’s nucleus, for instance, is negative instead of positive. And the electrons orbiting it have a positive charge instead of negative, so we therefore call them positrons.
We long ago learned how to create antimatter positrons, thereby moving them from the sci-fi world to the high-tech marketplace. Positrons can create exquisite noninvasive images of the human body: They’re the “P” in a medical PET scan.
Just because antimatter is logically simple doesn’t rob it of mystery. Every version of the Big Bang theory says that equal amounts of matter and antimatter should have been created 13.7 billion years ago. Yet somehow we find ourselves in a matter-dominated universe. What happened to all the potential anti-planets, anti-oceans, and antipasto? Currently, the best explanation is that — contrary to long-held theory stating nature shows no preference for one thing over another — we’ve observed a tiny bias in particle-antiparticle events, and matter appears slightly favored.
It’s a good thing, too. A universe with a lot of antimatter would be a dangerous place. No explosion is more powerful than when matter and antimatter meet. It’s a 100 percent E=mc² conversion of the masses of both objects. If a 1-gram pencil eraser touched an equivalent anti-eraser, the resulting explosion would release two billion trillion ergs of energy — enough to light every bulb in the United States for 10 days. Ounce for ounce, antimatter is 143 times more energy-potent than the Sun’s fusion furnace or an exploding H-bomb.
Although a peek into the night sky offers no way of knowing whether a particular star is made of matter or antimatter, there are good reasons to believe that ours is a matter-based neighborhood in a matter-based galaxy. The explosive contact between matter and antimatter produces gamma rays with a distinctive energy signature of 511,000 electron volts. Thus, if any antimatter fringe material contacted ordinary particles, they’d produce unique energy halos.
