One of the biggest mysteries in physics is why there's matter in the universe at all. This week, a group of physicists at the world's largest atom smasher, the Large Hadron Collider, might be closer to an answer: They found that particles in the same family as the protons and neutrons that make up familiar objects behave in a slightly different way from their antimatter counterparts.
While matter and antimatter have all of the same properties, antimatter particles carry charges that are the opposite of those in matter. In a block of iron, for example, the protons are positively charged and the electrons are negatively charged. A block of antimatter iron would have negatively charged antiprotons and positively charged antielectrons (known as positrons). If matter and antimatter come in contact, they annihilate each other and turn into photons (or occasionally, a few lightweight particles such as neutrinos). Other than that, a piece of matter and antimatter should behave in the same way, and even look the same—a phenomenon called charge-parity (CP) symmetry. [The 18 Biggest Unsolved Mysteries in Physics]
Besides the identical behavior, CP symmetry also implies that the amount of matter and antimatter that was formed at the Big Bang, some 13.7 billion years ago, should have been equal. Clearly it was not, because if that were the case, then all the matter and antimatter in the universe would have been annihilated at the start, and even humans wouldn't be here.
But if there were a violation to this symmetry—meaning some bit of antimatter were to behave in a way that was different from its matter counterpart—perhaps that difference could explain why matter exists today.
To read more, click here.