Is antimatter science fact or science fiction?

It sounds far out, but antimatter is firmly grounded in science. Antimatter is the weird mirror of ordinary matter. The proton and every subatomic particle has a corresponding antiparticle with equal mass but opposite properties. The antiproton, for example, has a negative charge. The antielectron, called a positron, has a positive charge.

This is an example of theory coming before observation. Physicist Paul Dirac predicted the existence of antimatter from calculations he did with pencil and paper in the 1920s. Scientists at University of California, Berkeley, discovered the positron in the 1930s. The discovery of the antiproton came in the 1950s.

The lore of antimatter developed because of the terrific power that matter-antimatter collisions unleash. When matter collides with its antimatter twin, the two particles annihilate -- that is, they transform into pure energy. This is 100% efficient; no "ash" remains. Burn a piece of paper, and you will get energy (fire) plus ash. Even nuclear fusion in the sun -- combining hydrogen atoms to create energy -- creates helium ashes. Matter and antimatter transform into pure energy, or light, a perfect conversion described by Einstein's famous E=mc2.

Just a gram of antimatter can provide the same energy as over 20 space shuttle tanks of fuel. So from way back in the Buck Rogers days of science fiction, antimatter was the fuel of the future. Today antimatter is less of a mystery but still a fascination. The Universe, we have learned, is filled with matter-antimatter annihilations.

There are many space experiments studying antimatter. One satellite, called INTEGRAL, made a big discovery in 2004. INTEGRAL is operated by the European Space Agency. NASA's colleagues in Europe discovered that the center of our Milky Way galaxy is sizzling with matter-antimatter collisions. The collisions produce gamma-ray light, which INTEGRAL detects. This form of light is millions of times more energetic than the visible light our eyes detect. Gamma rays are even more energetic than X rays.

The exciting thing about the INTEGRAL discovery is that no one knows where the antimatter is coming from. There are ideas. To make antimatter, you need a powerful generator. Black holes come to mind. Scientists think that black holes create particle jets that create positrons and accelerate them to nearly light speed. Another idea is that star explosions called supernovae in the galaxy's core are making all the antimatter. But there doesn't seem to be enough supernovae or black holes to account for all the antimatter detected. One speculative idea is that that antimatter is created in the decay of dark matter. This has many people excited because dark matter -- a mysterious substance that outnumbers regular atoms 9 to 1 -- has never been detected directly. This could be a first. Scientists are watching INTEGRAL results closely.

Another experiment, called BESS-Polar, will fly around the South Pole on a balloon above most of the atmosphere. BESS is largely a Japanese experiment with scientists at NASA Goddard and elsewhere. The flight is planned for December and January. BESS-Polar will collect antiparticles. The experiment is steeped in Big Bang theory. According to theory, the Big Bang should have produced equal amounts of matter and antimatter. So, in theory, entire anti-galaxies could exist filled with antimatter. This would be bizarre, and most scientists doubt it. Something (and no one knows what) likely caused an imbalance of matter over antimatter during the Big Bang. Matter and antimatter annihilated, and they leftover matter formed all the stars we see today.

The antiproton is a mirror image of the hydrogen atom without an electron. Antiprotons, as mentioned earlier, are created in violent "modern-day" events in space. BESS is searching for anti-helium, which only could have been created in the Big Bang. If BESS detects just one little anti-helium particle, then strange anti-galaxies might exist. This would be a major discovery. However, BESS, with its near yearly balloon flights, is showing how there is no anti-helium in the millions of antiparticles collected so far. BESS provides the information scientists need to understand why matter dominates over antimatter today.

Unfortunately, the antiparticles that BESS collects can't be used for fuel. Even millions of particles don't add up to much fuel. For example, there are about a billion billion atoms in a grain of salt. So we have much more collecting to do before we can think of powering any spaceships.

This week's question comes from Christopher Wanjek. Mr. Wanjek is a science writer supporting the Beyond Einstein initiative, a roadmap to understand the forces of nature beyond General Relativity and Quantum Mechanics through the study of the Universe from the Big Bang to black holes.