We and every thing around us seems to be made out of matter alone. We don’t observe any anti-matter laying around, why is that? In the Big Bang there should theoreticly have been created the same amount of matter as anti-matter. and therefor this matter and anti-matter should have annihalated each other, leaving nothing but radiation behind, so clearly this was not the case. But wait a minute, aren’t we jumping to conclusions here? After all, how do we know that the anti-matter didn’t go lumpy and form entire anti-matter galaxys.
Well if they did we would see intense gamma radiation from when matter and anti-matter collides like when for example an anti-matter star explodes and throws pieces of itself out in space, that anti-matter will sooner or later collide with matter and creating huge burst of gamma rays. And allso if there were allot of anti-matter out there we would notice it in the constant rain of particles that hits earth all the time, the cosmic rays. These cosmic rays contain very few anti-particles and the anti-particles that is in it can be explained by particles hitting each other in space with high speeds and therby creating anti-particles and by forms of radioactive decay. So it has to be something else.
Anti-matter reacts to all the known forces in the exact same way as normal matter does. Exept for the weak force, which is responsible for differnet kinds of radioactive decay, therefor there seems to be a slight a asymmetry between matter and anti-matter. Anti-matter might decay easyer then normal matter thereby leaving a surplus of matter in the beginning of the universe to form our galaxies and planets.