From: "Damian"
Date: 23 July 2005

Q Is there such a thing as anti-dark matter?

A The short answer is that we're not sure - scientists have not yet discovered what dark matter really is, and so we can't yet be sure if it has an antimatter counterpart. People have done a lot of thinking about this, however.

In the most popular theories, the dark matter is composed of some new kind of elementary particle, usually just called a Weakly Interacting Massive Particle ("WIMP"). This particle would have been created in large numbers in the Big Bang, along with everything else we see in the universe around us. In many of these theories (including most models derived from supersymmetry), the dark matter particle is its own antiparticle. This means that if two WIMPs were to come unto contact with one another, they could annihilate to produce energy in just the same was as a proton and antiproton. There is no separate "anti-WIMP".

It's also possible that the WIMP is not its own antiparticle, in which case the universe could be filled with both WIMPs and anti-WIMPs. Most theorists think that the Big Bang should have produced matter and antimatter in equal quantities, so there would be roughly equal amounts of both WIMPs and anti-WIMPs. Of course, we can see that there is a lot more ordinary matter than antimatter in the world around us, so it's possible that there might also be an imbalance between WIMPs and anti-WIMPs.

Even though WIMPs should annihilate one another when they collide, WIMPs interact with one another so weakly that these collisions should be very rare. They should happen fairly often in places where lots of WIMPs clump together, such as the center of the galaxy. Many astronomers are trying to detect dark matter indirectly by looking for radiation from such annihilations coming from the galactic center.

Jeff Filippini
UC Berkeley Cosmology Group