Each antiparticle of antimatter carries the opposite electric charge that the corresponding particle would in normal matter. If matter and antimatter meet, they annihilate each other spectacularly, releasing 100% of the energy stored within their structures. By comparison, atomic bombs release less than 1% of the energy stored in their atoms. The energy released in a matter-antimatter reaction comes in the form of gamma rays.
If you could convert just 1 kilogram of matter (or a half-kilogram each of matter and anti-matter) into pure energy with no energy lost, it would power your car for 100,000 years of constant non-stop driving. However, we can't currently achieve anything like that. To build a matter-antimatter engine or battery, you'd first have to create the antimatter. With current technology, a great deal of energy is needed to create antimatter. So much energy is needed to make the antimatter in the first place, that currently any attempt to power an engine or machine with antimatter is actually millions of times less efficient than powering it with a steam engine. Even at CERN the huge particle accellerators only create enough antimatter every year to power a lightbulb for a few seconds.
Whenever a new particle of matter is produced, the same reaction also produces a new antiparticle, and they travel away from each other in opposite directions at equal speed. You can't make one without the other - or at least we've never observed that happen in the lab or in nature. However, it's believed that somehow this didn't happen exactly as expected during the Big Bang, since our current universe is composed almost entirely of (normal) matter (and hardly any antimatter at all). Instead, during the very earliest era of our universe there was an imbalance, a slight asymmetry, with just a tiny percentage more matter being made than antimatter. Eventually, the temperature of the firey new universe dropped low enough to stop making more pairs of particles and antiparticles. The antiparticles and most of the particles annhilated each other, but the extra particles remained to form normal matter. These annhilations also created the Cosmic Background Radiation.
The most common (and best-known) particle of antimatter is the Positron, also known as the anti-electron. Other forms of antimatter include the antiproton and antineutron particles, and even larger and more organized "anti-atom" collections of antiparticles such as antihydrogen and antihelium. It's also possible for positrons and electrons to briefly form a faux atom called Positronium before breaking down and destroying each other.
Positrons are created in nature in supernova reactions as stars collapse. They are then flung great distances at great speeds, often traveling thousands of light years before they slow down enough to meld with an electron and wipe both out of existence. They are also produced by a class of stars known as hard low mass X-ray binaries (LMXB's). There is also a large cloud of antimatter near the center of our Milky Way Galaxy. Various more mundane particle impacts and radioactive decay can result in small amounts of positron creation.
Once produced in quantity, there's also the dangers of storing and transporting your antimatter. If it touches normal matter, there'll be a huge explosion, so you have to use some method to contain it without physical contact. For positrons and antiprotons, the obvious choice is to use a magnetic field or bubble to contain them, but for larger forms of antimatter that don't carry a strong electric charge, things may get trickier.
Tiny amounts of positrons are created by medical scanning machines specifically designed to scan these. The PET scan, or Positron Emission Tomography scanner uses radioactive decay and the release (and immediate annihilation) of trace amounts of antimatter to scan brain activity. Seriously, I'm not making this up. Cool, huh?
Game and Story Use
- Antimatter is a fun applied phlebotinum that provides immense power along with huge downsides. Yes, you've got a source of limitless power, but it's also prone to earth-shattering explosions, and requires elaborate protective measures. It can really spice up your game.
- In many sci-fi settings, the FTL stardrive or other major spaceship technology is powered by or based upon matter-antimatter reactions.
- A robot or android with a positronic brain springs a leak or malfunctions, ejecting antimatter.
- Which could mean critical hits on robots are really impressive.
- Or it could be used as a clue or plot device. In a mystery scenario, perhaps the murderer is an android, and there's signs of very small-scale antimatter reactions at the crime scene.
- A damaged robot leaking positrons might stress the hull integrity aboard a spaceship.
- Antimatter weaponry is a possibility. The U.S. government has even done some research into it. Currently, the cost is prohibitive, since it's so hard to make antimatter in quantity.
- If you could get around that cost, though, antimatter would detonate with enormous blasts coming from very small payloads. Terrorists and Spies would find that very attractive.
- Antimatter explosions leave no fall-out (and relatively little radiation) so some nations or planets might decide it's a safer alternative to nuclear war.
- Artificial antimatter production is costly, but antimatter does occur in nature.
- A deep-space mining operation might gather up antimatter from the cloud near the center of our galaxy, or from an a low mass X-ray binary star.
- This would be hazardous work, possibly automated. If any people are involved at the site, light years from the nearest habitable world, you can be they get paid very well.
- It's possible (though probably unlikely) that entire planets, stars or even galaxies could be made of antimatter. They would react to light and gravitation just like normal matter, and a spacecraft might get dangerously close before realizing the difference. Don't try to land on the anti-planet!